Novel phase change magnetic material

Detailed description of the invention

[001] The present invention relates to a novel material (specifically, a novel phase-changing magnetic material) and a method for producing the same. The present invention also includes optical media, phase-change random access memory (PCRAM) devices, magnetic random access memory (MRAM) devices, solid-state memory devices, sensor devices, logical devices, cognitive devices, artificial neuron networks, and three level devices. device), control devices, SOC (system on chip) devices and related to the use of such materials in semiconductors.

[Background of invention] [002] Over the last three decades, materials for rewritable media have received increasing attention in the scientific community and industry. Since the discovery of chalcogenide thin film materials in 1968, a variety of materials have been found in many important applications, including non-volatile memory devices where electrical writing and erasing are performed, cognitive semiconductors and rewritable optical discs. It has developed into a complex technology.

[003] Recent research efforts have focused on the development of non-volatile phase-change random access memory, as well as rewritable discs with large storage capacities and fast read / write speeds. Such rewritable media currently in widespread use include rewritable compact discs (CD-RW), rewritable digital video discs (DVD-RAM, DVD-RW, DVD + RW), and rewritable blue laser optical discs. (Blu-ray, HD-DVD) is included.

[004] In the phase change medium, the phase change material is used as a recording medium. This medium is thermally written and optically read. Data is written and erased by inducing a phase change in the material between the crystalline and amorphous phases. A laser beam is typically used to heat the medium to cause a phase change. Each phase is accompanied by different levels of light reflectivity, i.e., the crystalline phase is highly reflective and the amorphous phase is less reflective, so both low-reflectivity traces and high-reflectivity backgrounds. Can be formed on the material to represent computer-readable data bits.

[005] The use of rewritable materials for optical discs was first reported in 1971, in which case the recording medium contained a phase-changing composite material of chalcogenide (Feinleib et al., Appl. Phys. Lett., Vol. 18 (1971). ), P. 254). Since then, many attempts have been made to provide new materials for rewritable media in response to increasing computer data sizes and correspondingly increasing demands for larger storage capacities and faster read / write speeds. It has been done.

[006] For example, U.S. Pat. No. 5,709,978 describes a phase-changing optical disc that contains a phase-changing component (eg, Sb-Te-Ge, etc.), at least one lanthanide element, and a transition metal in a recording material. The recording thin film is disclosed. The melting point component is precipitated on the recording thin film so as to coexist with the phase change component so that the recording thin film does not flow and separate during recording and erasing.

[007] Another type of rewritable medium that is widely used is a magneto-optical (MO) medium, which is used, for example, in minidiscs. The MO medium operates on the principle of both magnetic storage devices and optical storage devices, the writing is performed magnetically after the heat treatment, and the reading is performed optically. Typically, a focused laser beam is applied to one side of the medium to heat the MO material to its Curie point or compensation temperature, thus making the MO medium sensitive to a magnetic field. The digital data is then recorded on the disc by activating a magnetic head located on the opposite side of the disc to change the magneto-optical polarity of the heated region.

[008] U.S. Pat. No. 6,132,524 discloses an example of a semiconductor magneto-optical medium. This material includes semiconductors in which fine magnetic particles are dispersed (eg, MsAs: GaAs). This material exhibits a magneto-optical effect at room temperature and can be used for signal processing and for manufacturing optical isolators and integrated circuits.

[009] Its use in composites containing two or more material components and recording media is disclosed in US Pat. No. 5,709,978. In carrying out the synthesis of such composites, the material components of the composite are combined and prepared from one mixture, or one material component is deposited on the other material component. Such composites individually exhibit either magnetic or phase-changing properties, but cannot exhibit both magnetic and phase-changing properties at the same time.

[010] Several studies have been conducted on materials for optical discs. In the study of the erasing process on optically rewritable discs, Shi et al.₂Sb₂Te₅), And the dynamic crystallization behavior associated with erasing data on such discs (Jpn.J.Appl.Phys., Vol. 42, Part 1, No. 2B, p. 841 ~ 847, 2003).

[011] In another study, Sato et al. Disclose GaN-based ferromagnetic dilute magnetic semiconductors for semiconductor devices (Jpn.J.Appl.Phys., Vol. 40, Part 2, No. 5B, L485 to L487, 2001). In yet another study, Sun et al. (Appl. Phys. Lett., Vol. 82, No. 12, pp. 1902-1904, 2003) disclose the use of Cu-sputtered FePt magnetic thin films.

[012] Despite these developments that have been undertaken, various limitations in current materials still exist. For example, the capacity and recording rate of rewritable optical media are currently limited by the laser diffraction limit and crystallization rate of the recording material. Therefore, continued efforts are needed to provide new materials with new characteristics.

[013] Therefore, it is one of the objects of the present invention to provide new materials, for example, new materials that provide improved performance.

[Outline of Invention] [014] According to the first aspect of the present invention, a phase change magnetic composite material containing a phase change material component and a ferromagnetic material component is provided. This material has a crystalline phase with a first magnetic property and a first phase change material property. In addition, this material has an amorphous phase with a second magnetic property and a second phase change material property. The materials of the present invention have unique electrical, magnetic, thermal, crystallization and optical properties in different phases (eg, fully crystalline, amorphous and partially crystalline phases). The materials of the present invention exhibit both magnetic and phase change effects and can be used in a wide variety of applications. Examples of applications in which the materials of the invention may be used include optical media, phase-change random access memory (PCRAM) devices, magnetic random access memory (MRAM) devices, solid-state memory devices, sensor devices, logical devices, cognitive devices, and man-made devices. Includes, but is not limited to, neuronal networks, three-level devices, control devices, SOC devices and semiconductors.

[015] According to another aspect of the present invention, there is provided an optical recording medium for recording information, which comprises the phase change magnetic material of the present invention. The materials according to the invention have different electrical, magnetic and optical properties in different phase states (eg, crystalline, amorphous and partially crystalline states). The present invention further relates to the use of phase change magnetic materials in various devices such as solid state memory devices, semiconductors, logic devices, magnetic random access memory devices, artificial neuron networks and phase change random access memory devices.

[016] These and other aspects of the invention will be more fully understood in light of the following description, drawings and non-limiting examples.

[Detailed description] [028] The present invention is based on the discovery that phase change materials and magnetic materials can be used to form uniform composite materials that exhibit both phase change and magnetic effects. In the context of the present invention, a material is said to exhibit a phase change effect if the material exhibits a change in its physical properties when it undergoes a phase change. Examples of such physical properties include resistivity, absorption at different wavelengths, optical constants, dispersion relations, permittivity, density, thermal conductivity, thermal diffusion coefficient, specific heat, active energy, lattice constants, crystallization temperature. , Includes glass transition. Similarly, when a material is exposed to a magnetic field, it is said to exhibit a magnetic effect.

[029] Although not bound by theory, we now combine phase-changing and magnetic components such that the crystal structure of the resulting phase-changing magnetic material changes under suitable growth conditions. It is believed that some of the atoms of the phase change material are replaced by the atoms of the magnetic material in the crystal structure, resulting in the formation of a new unit cell with a unique crystal structure. That is, the atoms of the magnetic material are made to replace the positions of some atoms of the phase change material without disturbing the crystal structure of the phase change material. In this way, the phase-changing magnetic composite material can exhibit both a phase-changing effect due to a similar crystal structure with respect to the phase-changing material and a magnetic effect due to the magnetic atoms present in the crystal structure.

[030] One of the advantages provided by the materials of the present invention is that each phase of the material is associated with a unique set of phase change and magnetic properties. This means, for example, that when a material undergoes a phase change from a crystalline phase to an amorphous phase, the material undergoes its phase change characteristics (eg, optical reflectance, optical constants) and its magnetic properties (eg, magnetic field strength). ) Means to show the corresponding changes in both. The benefits of dual characteristic changes are available for a wide variety of applications, such as sensing applications, data storage applications, logical applications, cognitive applications, control applications, SOC (system on chip) applications and semiconductor applications. Can be used for. For example, for recording applications, this property makes it possible to detect read signals from contributions of both optical reflectance changes, polarization, frequency and magnetic changes at the same time and at the same point. The recording density and data transfer rate in a recording medium using the material of the present invention can be increased. In sensing applications, this property can make sensing measurements very accurate for electrical, thermal, optical, magnetic, magneto-optical, thermoelectric, electro-optical and combinations thereof.

[031] The phase change characteristics exhibited by the phase change magnetic material of the present invention (hereinafter referred to as "PCM material") include high electrical resistivity, low thermal conductivity and low light reflectivity in the amorphous phase, and It includes the properties of low electrical resistivity, high thermal conductivity and high light reflectivity in the crystalline phase. Various physical parameters (eg, resistance, reflectivity, absorption, optical constants, refractive index and absorption coefficient, dielectric constant, density, thermal conductivity, thermal diffusion coefficient, specific heat and active energy, etc.) are in an amorphous state. It depends on the partial crystalline state in the range from the physical parameters in the above to the physical parameters in the crystalline state. These properties are similar to those exhibited by known phase change materials and are therefore now known as phase change effects.

[032] The magnetic properties exhibited by the material (which will be used interchangeably with the term "magnetic effect") include paramagnetic properties in the amorphous (disordered) phase and magnetic properties in the crystalline (ordered) phase. Includes having. Magnetic effects also include magnetic properties (eg, saturated magnetic field Ms, holding magnetic field Hc, anisotropic magnetic field Hk, uniaxial anisotropic constant Ku, squareness, residual magnetization Mr, saturation magnetic flux density (saturation induction) Bs. , Curie temperature Tc and compensation temperature, etc.) are included. These properties are similar to those exhibited by magnetic materials and are therefore now known as magnetic effects.

[033] The phase-changing magnetic composite material of the present invention contains two main components, namely a phase-changing component and a magnetic component.

[034] The phase change component includes any type of phase change material. The phase change material exhibits a phase change at a temperature above standard room temperature (ie, 25 ° C), or more preferably at a high temperature above 100 ° C, or at a high temperature above several hundred ° C (ie). That is, the material can be melted at such a temperature) is preferred in some embodiments. Such high temperatures can be provided by any suitable focused laser beam or any current or heating device. For recording purposes, the phase change material preferably changes from a crystalline phase to an amorphous phase and does not regain its crystalline form when heated and subsequently cooled. In this way, amorphous traces in combination with crystalline regions can be used to represent the data. Phase change materials that undergo a phase change at temperatures higher than those that can be provided by standard laser equipment can also be used. When such materials are used, they require greater operating power to induce a phase change. On the other hand, phase change materials such as paraffin wax and polyimide (eg, polymeric organics) used for thermal isolation of buildings, for example, have relatively low phase change temperatures and are therefore not suitable for use in the present invention. Considered unsuitable.

[036]<u style="single">phase</u>change<u style="single">material</u>Ingredients include chalcogenide alloy<u style="single">.. two</u>Former chalcogenide alloy system, ternary chalcogenide alloy system and quaternary chalcogenide alloy<u style="single">To the system</u>Is<u style="single">, G</u>e₂Sb₂Te₅, GeSb₂Te₄, GeSb₃Te₄, GeSb₄Te₇, In₃SbTe₂, Ag₅In₅Sb₆₀Te₃₀, Sb₂Te₃, Sb₇₀Te₃₀, GeTe, GeSb, Sb₂Se₃<u style="single">as well as</u>Sb₂Te₃-GeTe<u style="single">One system with an equation selected from the group consisting of</u>Is included<u style="single">To.</u>

[037] The second component present in the phase-changing magnetic material of the present invention is a ferromagnetic component. The term "ferromagnetic component" refers to a material that has a large positive magnetic susceptibility with respect to an external magnetic field. Typically, such materials have unpaired electrons, and their spins generate a net magnetic moment at each atom of the ferromagnetic material. The electron spins of an atom are aligned in a microscopic region known as a domain. Very large numbers of atoms in these domains (typically about 10)¹²~ 10¹⁵The pieces) are aligned in parallel, and as a result, the magnetic force inside the domain is strong. When the ferromagnetic material is in a non-magnetized state, the domains are organized almost randomly and the net magnetic field for that part is zero overall. When a ferromagnetic material is placed under the influence of a magnetic field, the domains are aligned by the magnetic field, thereby bringing a strong magnetic field inside that part of the material.

[038] In one embodiment, the ferromagnetic component used in the present invention is selected from, but is not limited to, elements of iron, nickel and cobalt. Further examples include ferromagnetic alloys containing at least one ferromagnetic component, such as iron, nickel and cobalt. Examples of ferromagnetic alloys containing at least one ferromagnetic component include FePt, CoPt, PdCo, TbFeCo, GdFeCo, CoCrPtB and CoCrPtTa, to name just a few.

[039] When the material of the present invention is used in a conventional recording medium (for example, a compact disc, a digital video disk, a magnetic medium system, etc.), the material obtained by obtaining the respective proportions of the phase change component and the magnetic component is conventionally used. Phase change media, conventional magnetic media, and similarly in conventional photomagnetic media, or in conventional phase change media, conventional magnetic media, and also in conventional photomagnetic media. Selected to exhibit the desired properties, as a result, the medium can function according to the requirements of standard equipment for reading and recording. To this end, the components of the phase change magnetic material are selected such that the composite material exhibits at least one physical state selected from crystalline, amorphous and partially crystalline states. can do. The components of the phase-changing magnetic material can also be selected such that the composite material exhibits different electrical, magnetic, thermal, crystallization and optical properties in each of the at least one physical state.

[040] Desirable features in the phase change optical medium are different refractive coefficients for crystalline and amorphous phases (due to optical contrast), low melting point (due to low laser power), high crystallization rate and good non-existence. Includes crystal stability. Desirable features in magnetic media include perpendicular magnetic anisotropy (to facilitate perpendicular magnetic recording), small grain size, large vertical coercive force, large vertical anisotropy, large squareness, and proper saturation magnetization. included. Desirable features in magneto-optical media include amorphous structures (for flat surfaces and domain boundaries to reduce system noise), suitable Curie temperatures (for medium stability and low laser power), Rapid decrease in coercive force near Curie temperature (due to sharp recording threshold), perpendicular magnetic anisotropy, chemical stability (due to constant material properties under repeated heating and cooling) , And a large coercive force at room temperature (for medium stability, prevention of accidental data loss). Therefore, in one embodiment, the components of the material are selected to achieve at least one of the above properties.

[041] In one embodiment, the phase change component and the ferromagnetic component are such that the obtained phase change material is a crystalline phase having a first magnetic property and a first phase change property, and a second magnetic property and a second magnetic property. It exists in a proportion such that it has an amorphous phase with a phase change characteristic. The proportion of each component present in the material allows the magnetic and phase change properties of the second set to be recognizable and different from the properties of the first set, thereby allowing these properties to be present. , Must be able to be used to represent the recorded information on the material.

[042] In some embodiments, the resistivity ρ of the material is generally 1 × 10 in the amorphous state.^-3Ωcm &lt;ρ &lt;1 × 10³The range is Ωcm, or 0.1Ωcm &lt;ρ &lt;10Ωcm, and in the crystalline state, 1 × 10^-4Ωcm &lt;ρ &lt;1 × 10^-1Range of Ωcm, or 1 × 10^-7Ωcm &lt;ρ &lt;1 × 10^-2It is in the range of Ωcm. The difference in resistivity of the material between the amorphous phase and the crystalline phase is at least about 2-10.⁶Is the size of. In another preferred embodiment, the coercive force of the material in the crystalline phase is at least about 1 oersted, or optionally at least about 40 oersted.

[043] In a further embodiment, the phase-changing magnetic material has a crystal structure that is at least substantially similar to the phase-changing material component. In this embodiment, the atoms of the magnetic material replace the positions of some of the atoms in the phase-changing material without disturbing the crystal structure of the phase-changing material. Atoms of a magnetic element or magnetic material replace and replace some of the atoms in the phase-changing material in order to form a new unit cell with a unique crystal structure under appropriate growth conditions. Since is a specific range of substitutions, these materials exhibit both phase change and magnetic effects.

[044] In a further embodiment, the phase change magnetic material has the composition of formula (I) below: A_xB_y(During the ceremony, A indicates a ferromagnetic component; B indicates the phase change component; x represents the total atomic percentage of A, 1% x 50%, y represents the total atomic percentage of B, 50% y 99%).

[045] In one currently preferred embodiment, the phase-changing magnetic material as defined by formula (I) is a ferromagnetic component A and Sb, selected from any of the elements Co, Fe, Ni and the alloy FePt. Te, GeTe, Sb₂Te₃, GeSb, Sb₇₀Te₃₀, InSbTe, Ag-In-Sb-Te and Ge-Sb-Te with phase change component B. The chemical formula of the composite material having formula (I) can be selected from one of the following simplified chemical formulas: Fe (Sb)₂Te₃), Co (Sb₂Te₃), Ni (Sb)₂Te₃), FeGeSb, CoGeSb, NiGeSb, Fe (Sb)₇₀Te₃₀), Co (Sb₇₀Te₃₀), Ni (Sb)₇₀Te₃₀), FeInSbTe, CoInSbTe and NiInSbTe. An exemplary example is Co_6.3Ge_31.1Sb_27.1Te_35.5, Co_3.6Ge_20.8Sb_30.5Te_44.9, Co_2.8Ge_17.9Sb_31.9Te_47.1, Co_6.1Ge_14.3Sb₃₃Te_46.5, Co_3.0Ge_18.5Sb_30.1Te_48.2, Co_5.0Ge_16.9Sb_31.6Te_46.5, Co_1.5Ge_17.3Sb_32.9Te_48.3, Co_5.4Ge_17.2Sb_30.5Te_46.9, Co_2.0Ge_17.7Sb_32.5Te_47.8, Co_5.8Ge_17.1Sb_32.3Te_44.8, Co_4.6Ge_14.9Sb_33.4Te_47.1, Co_10.1Ge_14.4Sb_34.6Te_40.9, Co_26.1Ge_17.2Sb_22.1Te_34.6, Co_5.6Ge_15.8Sb_33.6Te₄₅, Fe_20.2Ge_21.5Sb_16.9Te_41.4, Fe_9.2Ge_16.3Sb_27.4Te_47.2, Fe_4.7Ge_18.5Sb_28.1Te_48.6, Fe_4.4Ge_14.8Sb_34.2Te_46.6, Fe_11.1Ge₁₆Sb_25.9Te_47.1, Fe_1.0Ge_15.7Sb_35.2Te_48.2, Fe_7.2Ge_14.7Sb_32.9Te_45.2, Fe_28.2Pt_32.4Ge_30.0Te_9.3, Fe_4.1Pt_4.2Ge_64.5Te_27.1, Fe_2.1Pt_5.5Ge_63.9Te_28.4, Fe_1.1Pt_2.7Ge_64.3Te_31.9, Fe_4.6Pt_7.3Ge_59.5Te_28.6, Fe_5.0Pt_6.8Ge_59.6Te_28.6, Fe_1.1Pt_1.1Ge_50.4Te_31.1, Fe_4.8Pt_4.6Ge_58.2Te_32.4, And Fe_1.2Pt_2.5Ge_54.2Te_41.9, Fe_1.0Pt_2.0Ge_62.1Te_34.9Includes, but is not limited to.

[046] In a further embodiment, the phase change magnetic material has the composition of formula (II) below: A_xB_yC_z(During the ceremony, A indicates a ferromagnetic component; B indicates the phase change component; C indicates manganese compound component; x represents the total atomic percentage of A, 1% x 40%, y indicates the total atomic percentage of B, 40% y 98%, z indicates the total atomic percentage of C, 1% y 20%).

[047] In one currently preferred embodiment, the phase-changing magnetic material as defined by formula (II) is a ferromagnetic component A and Sb, selected from any of the elements Co, Fe, Ni and the alloy FePt. Te, GeTe, Sb₂Te₃, GeSb, Sb₇₀Te₃₀, InSbTe, Ag-In-Sb-Te and Ge-Sb-Te with phase change component B. The third component C is selected from MnAs, MnGa, MnSb and MnAl. Component A and component B of the currently preferred composite material having formula (II) are currently preferably combined to form one of the following compounds: Fe (Sb).₂Te₃), Co (Sb₂Te₃), Ni (Sb)₂Te₃), FeGeSb, CoGeSb, NiGeSb, Fe (Sb)₇₀Te₃₀), Co (Sb₇₀Te₃₀), Ni (Sb)₇₀Te₃₀), FeInSbTe, CoInSbTe and NiInSbTe. An exemplary example is Co_6.3Ge_31.1Sb_27.1Te_35.5, Co_3.6Ge_20.8Sb_30.5Te_44.9, Co_2.8Ge_17.9Sb_31.9Te_47.1, Co_6.1Ge_14.3Sb₃₃Te_46.5, CO_3.0Ge_18.5Sb_30.1Te_48.2, Co_5.0Ge_16.9Sb_31.6Te_46.5, Co_1.5Ge_17.3Sb_32.9Te_48.3, Co_5.4Ge_17.2Sb_30.5Te_46.9, Co_2.0Ge_17.7Sb_32.5Te_47.8, Co_5.8Ge_17.1Sb_32.3Te_44.8, Co_4.6Ge_14.9Sb_33.4Te_47.1, Co_10.1Ge_14.4Sb_34.6Te_40.9, Co_26.1Ge_17.2Sb_22.1Te_34.6, Co_5.6Ge_15.8Sb_33.6Te₄₅, Fe_20.2Ge_21.5Sb_16.9Te_41.4, Fe_9.2Ge_16.3Sb_27.4Te_47.2, Fe_4.7Ge_18.5Sb_28.1Te_48.6, Fe_4.4Ge_14.8Sb_34.2Te_46.6, Fe_11.1Ge₁₆Sb_25.9Te_47.1, Fe_1.0Ge_15.7Sb_35.2Te_48.2, Fe_7.2Ge_14.7Sb_32.9Te_45.2, Fe_28.2Pt_32.4Ge_30.0Te_9.3, Fe_4.1Pt_4.2Ge_64.5Te_27.1, Fe_2.1Pt_5.5Ge_63.9Te_28.4, Fe_1.1Pt_2.7Ge_64.3Te_31.9, Fe_4.6Pt_7.3Ge_59.5Te_28.6, Fe_5.0Pt_6.8Ge_59.6Te_28.6, Fe_1.1Pt_1.1Ge_50.4Te_31.1, Fe_4.8Pt_4.6Ge_58.2Te_32.4, Fe_1.2Pt_2.5Ge_54.2Te_41.9, And Fe_1.0Pt_2.0Ge_62.1Te_34.9Includes, but is not limited to.

[048] The phase change magnetic material of the present invention includes an optical medium of the material of the present invention, a phase change random access memory (PCRAM) device, a magnetic random access memory (MRAM) device, a solid-state memory device, a sensor device, a logical device, a cognitive device, and an artificial structure. It is understood by those skilled in the art that it can be used in combination with any suitable type of secondary material known in the art that aids in neuron networks and semiconductors. Secondary materials include, for example, dyes to improve reflectivity and sacrificial coatings to prevent decomposition by moisture.

[049] Since both the phase change effect and the magnetic effect are exhibited in the material, the phase change component and the ferromagnetic component are phased without the atoms of the magnetic material causing any substantial change in the crystal structure of the phase change material. It may be present in the material according to a suitable ratio that allows it to replace the atoms of the changing material. Many methods are suitable for synthesizing the phase change magnetic material of the present invention. Examples of methods that allow uniform composite material to be formed and can therefore be used herein include laser ablation, sputtering, ion plating, chemical vapor deposition (CVD), plasma. Includes chemical vapor deposition, organic metal vapor deposition, spin coating, molecular beam epitaxy (MBE), top-seeded solution growth, thermal pressurization, vacuum melting and conventional crystal growth.

[050] In one embodiment, the materials of the invention are synthesized by laser ablation or laser synthesis. Preferably, the materials of the invention are synthesized by laser synthesis. In the context of the present invention, the term "laser synthesis" includes a synthesis method involving dual beam laser ablation of different targets for synthesizing new materials within overlapping plasma regions. Laser synthesis is performed by laser pulses from excimer lasers used to heat the precursor component material mounted on the rotating gantry. By arranging the gantry so that the plumes released from the precursor overlap at least partially, the substrate can be placed inside this overlapping region, resulting in the formation of a uniform thin film on the substrate. Can be made to. This technique is described, for example, by Song et al. (Appl. Phys. A., Vol. 79, pp. 1349-1352, 2004).

[051] In another aspect, the invention relates to an optical recording medium for recording information, comprising a phase-changing and ferromagnetic component and comprising a phase-changing magnetic material exhibiting both a magnetic effect and a phase-changing effect. The design of optical discs as such, and methods of manufacturing optical discs, are known to those of skill in the art and are described, for example, in US Pat. No. 6,469,977. Actual execution of such optical discs includes CD-RW, DVD-RAM, DVD-RW, DVD + RW, Blu-ray, HD-DVD. Next-generation products of various optical discs, including discs with holographic recording, near-field optical recording, multi-layer optical recording and multi-level recording, have been the subject of intensive research in recent years. Other uses of phase-change magnetic materials according to the invention include phase-change random access memory (PCRAM) devices, magnetic random access memory (MRAM) devices, solid-state memory devices, sensor devices, logical devices, cognitive devices, three-level devices, Includes use in control devices and semiconductors.

[052] In practical use, the information recording medium having a recording layer containing the material of the present invention is provided with a phase-changing magnetic material in either a crystalline phase or an amorphous phase. During the recording process, the laser selectively heats the region of the recording track present on the optical disc beyond the melting point or crystallization temperature of the phase-changing magnetic material. The material is thawed and subsequently "frozen" or crystallized by quenching the layer. The reflectance of the amorphous region is very different from the reflectance of the crystalline region, which produces a signal similar to the signal generated from the pits and lands of a ROM type disc during the read period. Changes in optical reflectance can be used to represent the stored data on the recording medium. A new overwrite signal can be used by adjusting the laser output of the recording laser beam and recorded by erasing the existing recorded signal. At the time of overwriting, some amorphous regions along the track are returned to the crystalline phase by slowly cooling below the melting point by using a convergent laser beam, and the material is specific for recrystallization. Over the retention time, it is roughly heated locally to a temperature between the melting point and the crystallization temperature. Similarly, some crystalline regions are converted to an amorphous phase by heating above the melting point and then quenching, as described above. This process can be repeated thousands of times for a single disc. For rewritable optical media, the background is, in some cases, preferably crystalline. The medium using the phase change magnetic material of the present invention can also be made for writing only once. The background of the disc can be either crystalline or amorphous in order to write the medium or so-called "recordable medium" once.

[053] At the same time, when the material is reversibly changed between the amorphous and crystalline states, the magnetic properties of the materials of the present invention change correspondingly due to structural changes. Therefore, this structural change can be detected by measuring the read signal with the change in magnetic properties. Finally, read signals from both optical reflectance and magnetic change contributions are detected at the same time and at the same point. Recording density and data transfer rate increase. For conventional phase change media, only changes in optical reflectance from the material can be detected. For the materials of the present invention, both optical reflectance changes and magnetic changes can be detected at the same time and at the same point (location). Recording density and data transfer rate increase.

[054] In utilizing the magnetic properties of the material, conventional methods used for reading and writing on magneto-optical discs can be practiced. For example, at the time of reading, the laser projects a beam onto an optical disc, and changes in the polarization of the reflected light are interpreted as binary data. The reflected light changes according to the magnetic data stored on the disc. The change in the polarization of light is caused by the presence of a magnetic field on the surface of the disk (Kerr effect). When a beam of polarized light illuminates a surface, the light polarization of the reflected beam changes slightly (typically less than 1 °) when the reflected beam is reflected from a magnetized surface. When the magnetization is reversed, the change in polarization (Kerr effect) is also reversed. Magnetized regions (pits) cannot be seen with normal light, but only with polarized light. Changes in the direction of magnetization can be associated with a number of 0s or 1s, thus allowing storage of binary data. At the time of recording, the light becomes more intense, so the light can heat the material to the Curie point or compensation temperature at only one spot. This allows an electromagnet located on the opposite side of the disc to change the local magnetic polarization, which is retained as the temperature drops. This fact that the coercive force of the material decreases at higher temperatures allows thermal-assisted magnetic recording to occur with relatively weak magnetic fields.

[055] At the same time, when the light polarization of the material changes due to the reversal of magnetization, the structure of the material according to the invention changes reversibly between the amorphous and crystalline states, and this change is detected. Also, changes in reflectance can be seen from the readout signal due to structural changes. Finally, combined readout signals from the contributions of both changes in light polarization and changes in optical reflectance are detected at the same time and at the same point / location. Recording density and data transfer rate increase as a result. For conventional magneto-optical media, only changes in light polarization due to magnetic reversal can be detected. For the materials of the present invention, both changes in light polarization and changes in optical reflectance are detected at the same time and at the same point. Recording density and data transfer rate increase as a result.

[Example 1: Laser synthesis] (Synthesis procedure) [056] A schematic diagram of the laser synthesis system of the present inventors is shown in FIG. 7 (a) below. Synthesis was performed in chamber 8. The KrF excimer laser beam from laser 10 is split into two beams by a splitter 12 and converged by two focal lenses (16, 18) and by two reflectors 30 onto two rotating targets 14. It was. Two overlapping plumes were made on the substrate 20, respectively. Laser fluence at each target is 0.5 J / cm²~ 6J / cm²Between. The target was mounted at 45 ° to the laser beam. The substrates 20 were attached to the 2-inch stainless steel holder 22 with silver paste, with the targets facing each other at a distance of 2 cm to 8 cm. The two mirrors are for reflecting the separated lasers on the focusing lens. 2 × 10^-6Torr background pressure was achieved with a turbo molecular pump (not shown). The growth temperature was between room temperature and 900 ° C. The composite was typically grown at a repetition rate of 10 Hz for 12000 pulses. After laser synthesis, the material was cooled to room temperature.

[057] In the context of the present invention, a synthesis method involving dual beam laser ablation of different targets for synthesizing new materials within overlapping plasma regions is referred to as the term "laser synthesis". In this method, the components containing various atoms, molecules, electrons, ions and clusters for material synthesis are high energy evaporators produced by laser ablation. The use of short laser pulses for ablation is more likely to achieve consistent ablation to keep stoichiometry during mass transfer from the target to the substrate, which facilitates control of the composition of the new material. To. Laser interactions with gas-phase species are relatively weak, allowing many types of reactive gases to be introduced for material synthesis. This method is flexible in adjusting the synthesized elements and compositions by varying the substrate position within the target, laser fluence and input gas, and overlapping plasma regions. A preferred single crystal substrate can be selected to result in crystal growth of the new material. This method can also heat the substrate to a high temperature to provide a suitable environment for new material synthesis. This method is inexpensive, convenient, and allows new materials to be synthesized quickly.

[058] According to the above experimental conditions, one target is selected from Fe, Co, FePt, and another target is Ge.₂Sb₂Te₅And GeTe. Three groups of phase-changing magnetic materials were synthesized. They included Co-Ge-Sb-Te series, Fe-Ge-Sb-Te series and Fe-Pt-Ge-Te series. The composition of the manufactured material was analyzed by X-ray electron spectroscopy (XPS). The crystal structure was analyzed by XRD. All magnetic, electrical and optical properties were investigated.

[059] As shown in FIGS. 2a-2d, conventional phase change materials (eg Ge)₂Sb₂Te₅And GeTe, etc.) exhibit diamagnetic properties, while the phase-changing magnetic material of the present invention exhibits magnetic properties. In comparison, as shown in FIGS. 3a and 3b, the phase-changing magnetic material in the crystalline state exhibits stronger magnetic properties than the phase-changing magnetic material in the amorphous state. This indicates that the magnetic properties of the phase-changing magnetic material change with the state change of the phase-changing magnetic material.

[060] FIG. 4 is a photomicrograph showing the contrast change between the amorphous phase and the crystalline phase induced by a pulse laser for the phase change magnetic material according to one embodiment of the present invention. It has been shown that phase-changing magnetic materials have different optical properties between the amorphous phase and the crystalline phase, which are similar for phase-changing materials.

[061] FIG. 5 shows a table of data comparing the electrical resistivity of conventional phase-changing materials and phase-changing magnetic materials according to one embodiment of the invention in amorphous and crystalline states. It is shown that both phase-changing and phase-changing magnetic materials show relatively large differences in electrical properties between the amorphous and crystalline states. This means that the phase-changing magnetic material has similar electrical properties with respect to conventional phase-changing materials.

[062] In summary, the phase-changing magnetic material of the present invention not only exhibits the characteristics of the conventional phase-changing material, but also the magnetic properties and characteristics of the magnetic semiconductor material.

[063] Figure 6a shows sample Fe_4.4Ge_14.8Sb_34.2Te_46.6The XRD profile that characterizes the crystal structure of is shown. As can be seen from the figure, this material showed a crystallinity peak, thus confirming the presence of a crystalline phase for the Fe-Ge-Sb-Te system synthesized at 300 ° C. Fe synthesized from the analysis of peak position_4.4Ge_14.8Sb_34.2Te_46.6Crystal structure is Ge₂Sb₂Te₅It was found that it resembled the crystal structure of.

[064] The second sample contained the Fe-Pt-Ge-Te system synthesized according to the synthesis procedure described above. In XPS analysis, the composition of the compound is Fe_4.6Pt_7.3Ge_59.5Te_28.6It was clarified that. Figure 6b shows the XRD profile that characterizes the crystal structure of this sample. As can be seen from this XRD profile, this material shows a crystallinity peak, thus confirming the presence of a crystalline phase for the Fe-Pt-Ge-Te system synthesized at 300 ° C. It was. Fe synthesized from the analysis of peak position_4.6Pt_7.3Ge_59.5Te_28.6It was found that the crystal structure of GeTe was similar to that of GeTe.

[065] Based on the experimental results shown in FIGS. 6a-6b, the phase-changing magnetic material has a crystal structure similar to that of the phase-changing material, or a crystal structure similar to the phase-changing material component used to synthesize the phase-changing material. Can be concluded to have. One possible explanation for this property is that the atoms of the magnetic material replace the atoms of the phase-changing material in the unit cell of the phase-changing material without disturbing / breaking its crystal structure. is there. Therefore, this new material exhibits not only the phase change effect due to its similar crystal structure with the phase change material, but also the magnetic effect caused by the presence of magnetic atoms in the crystal structure.

[Example 2: Synthesis by sputtering] (Synthesis procedure) [066] Sputtering methods can be used to synthesize the materials according to the invention. Leybold In our sputtering system supplied by Vacuum and schematically illustrated in FIG. 7 (b), two DC sputtering cathodes and two RF sputtering cathodes were installed and four targets (two of them) were installed. Is labeled DC01 and DC02, and the rest are labeled RF02 and RF01) are physically separated from each other. The position of the cathode is below the target in FIG. 7 (b). The rotating board was placed on a water-cooled turntable, and the board holder was placed 50 mm above the target. A pre-shutter 48 (which can control opening and closing) is located between the target and the board holder. Place the substrate, target and shutter in the vacuum chamber. Argon gas 50 is introduced into the chamber at low pressure and used as a sputtering gas. A gas plasma is applied using a power source to ionize the gas. The ions are accelerated toward the target surface, collide with the target surface, and the target atom is separated from the target and deposited on the substrate surface. A thin film of material according to the invention is produced on a substrate by placing the substrate under a target target for some time and opening the shutter for a period of programmed time controlled by computer 60.

<figref num="1">[017] It is a schematic diagram which shows the synthesis of the phase change magnetic material by one Embodiment of this invention.</figref><figref num="2a">[018] Conventional phase change material (Ge₂Sb₂Te₅) Shows the graph data that characterizes the magnetic properties. As can be seen from the figure, this material exhibits anti-magnetic properties.</figref><figref num="2b">[019] Phase change material, ie Fe according to one embodiment of the invention._4.4Ge_14.8Sb_34.2Te_46.6The graph data that characterizes the magnetic characteristics of is shown. 38 Oersted coercive force value H_{o o}Is recognized with zero magnetization.</figref><figref num="2c">[020] Shown are graph data that characterize the magnetic properties of GeTe phase change materials.</figref><figref num="2d">[021] Fe according to the present invention_4.6Pt_7.3Ge_59.5Te_28.6Shows the magnetic properties of the phase-changing magnetic material. [022] As shown in FIGS. 2 (a-d), the conventional phase-changing magnetic material exhibits anti-magnetic properties, while the phase-changing magnetic material according to the present invention exhibits magnetic properties.</figref><figref num="3a">[023] Co in amorphous state_6.3Ge_31.1Sb_27.1Te_35.5The graph data that characterizes the magnetic characteristics of is shown.</figref><figref num="3b">Co in crystalline state_6.3Ge_31.1Sb_27.1Te_35.5The graph data that characterizes the magnetic characteristics of is shown.</figref><figref num="4">[024] FIG. 6 is a photomicrograph of a material according to the invention in an amorphous phase and a crystalline phase when induced by a laser pulse. This photograph shows that this phase-changing magnetic material has different optical properties in the amorphous and crystalline phases, similar to the phase-changing material. Experiments have also shown that there is a partial crystalline state between the crystal and the amorphous, which means that the crystallinity ratio x is in the range 0 &lt;x &lt;1.</figref><figref num="5">[025] It is a table of data comparing the electrical resistivity of the conventional phase change material and the phase change magnetic material of the present invention in the amorphous state and the crystalline state. The data show that the phase-changing magnetic material according to the invention has electrical properties similar to those of the phase-changing material.</figref><figref num="6a">[026] Fe, a phase-changing magnetic material_4.4Ge_14.8Sb_34.2Te_46.6The XRD profile that characterizes the crystal structure of is shown.</figref><figref num="6b">Fe, a phase-changing magnetic material_4.6Pt_7.3Ge_59.5Te_28.6The XRD profile that characterizes the crystal structure of is shown.</figref><figref num="7a">[027] A schematic diagram of a laser ablation system that can be used to synthesize the phase change magnetic material of the present invention is shown.</figref><figref num="7b">The schematic diagram of the sputtering system which can be used for synthesizing the phase change magnetic material of this invention is shown.</figref>