Laminated magnetic recording media with antiferromagnetically coupled layers as the individual magnetic layers in the laminate

Laminated magnetic recording medium with antiferromagnetic coupling layer as individual magnetic layer in laminated board

Related application

This patent application is a partial continuation of the patent application serial number 09/416,364 filed on October 8, 1999.

The present invention is generally related to magnetic recording media, and in particular, the present invention is related to thermally stable high-density media.

Background of the invention

Well-known magnetic recording media, such as magnetic recording discs in hard disk devices, generally use a granular ferromagnetic layer, such as a sputter-deposited cobalt platinum (CoPt) alloy, as the recording medium. Each magnetized region in the magnetic layer includes many tiny magnetic particles. The transition between magnetized regions represents the "bit" of the recorded data. IBM's US Patent Nos. 4,789,598 and 5,523,173 illustrate such well-known hard disks.

As the storage density of magnetic recording discs increases, the residual magnetization Mr (magnetic torque per unit volume of ferromagnetic material) and the thickness t of the magnetic layer relatively decrease. Similarly, the coercive magnetic field or coercive force (H_c) Has also increased. This leads to Mrt/H_cDecrease in ratio. To achieve the reduction of Mrt, the thickness t of the magnetic layer can be reduced, but only to a certain limit, because the layer will show increasing magnetic decay, which is attributed to the thermal activation of tiny magnetic particles Effect (superparamagnetic effect; superparamagnetic effect). The thermal stability of a certain magnetic particle is mostly due to its K_uDetermined by V, where K_uIs the magnetic anisotropy constant of the layer, and V is the volume of the magnetic particle. When the film thickness decreases, V also decreases. If the film thickness is too thin, the The stored information will no longer be stable.

One way to solve this problem is to switch to materials with higher anisotropy constants (higher K_uvalue). However, K_uThe increase of is limited to a point, at which point, the coercive force H_c(Approximately equal to K_u/Mr) has become too large to be written with a traditional recording head. A similar method is to reduce the Mr of the magnetic layer under a certain film thickness, but this method is also limited by the coercive force that can be written. Another solution is to enhance the exchange between the particles to increase the effective magnetic volume V of the magnetic particles. However, this method has proved to cause damage to the signal-to-noise ratio (SNR) of the magnetic layer itself.

Magnetic recording media with high inherent SNR (low inherent media noise) are highly anticipated because, as is well known, the inherent media noise of mixed-metal media (such as CoPt alloys) increases with linear recording density (linear recording density). ) Increases. Media noise is caused by irregular magnetic transitions, which will result in irregular changes in the peak value of the readback signal. Such irregular changes are generally called "peak instability" or "time instability". Therefore, the higher the media noise, the higher the bit error rate. Therefore, it is best to develop a thin-film mixed-metal magnetic medium that can generate noise below the maximum tolerable value to record data at the highest linear density. As we know, two (or more) laminated magnetic layers, separated by a non-magnetic spacer layer in the middle, instead of a single magnetic layer, will obtain substantially better SNR. This discovery was proposed by SE Lambert et al., published in September 1990, "Reduction of Media Noise in Thin-Film Metal Media with Laminates" in IEEE Journal of Magnetics, Vol. 26, Issue 5, Pages 2706 to 2709. In one article. And then IBM obtained its patent in US Patent No. 5,051,288. Borrow Laminates can reduce media noise, which is believed to be due to the decoupling of magnetic interaction or exchange coupling between the magnetic layers of the laminate. The use of laminates to reduce noise has caused extensive research to find suitable gasket layer materials, including Cr, CrV, Mo and Ru, and found that from 5 to 400<img file="TW584841B_D0001.tif" />The thickness of the spacer layer can lead to the best decoupling between the magnetic layers, thereby obtaining the lowest media noise. This result has been reported in the following document: "Noise Characteristics of Multilayer Co Alloy Magnetic Recording Media" proposed by ES Murdock et al., published in September 1990, IEEE Magnetics Society Journal, Volume 26, Issue 5, Pages 2700 to 2705 Proposed by A. Murayama et al., published in November 1991, IEEE Journal of Magnetics, Vol. 27, Issue 6, pp. 5064 to pp. 5066, "Spin-wave Brillouin Scattering Study of Co/Cr/Co Double-Layer Recording Films Interlayer Exchange Coupling"; and SE Lambert et al., published in January 1993, IEEE Magnetics Society Journal, Volume 29, Issue 1, Pages 223 to 229, "Overlapping Media Noise in High Density Recording" . U.S. Patent No. 5,462,796 and related documents proposed by E. Teng et al., published in the IEEE Magnetics Society Journal, Volume 29, Issue 6, Pages 3679 to 3681, "Excellent Noise and Coercive Force Orthogonal Ultra-thin chromium interlayer for high-performance magnetic disks" describes a laminated low-noise magnetic disk using intermittent Cr film. The thickness of the Cr film is sufficient to reduce the exchange coupling between the two magnetic layers in the laminate, but it is so thin It is not enough to substantially separate the two magnetic layers.

What is needed now is a magnetic recording medium that can support extremely high recording density while maintaining good thermal stability and SNR.

Summary of the invention

The present invention is a magnetic recording medium, the magnetic recording layer of which consists of at least two layers The ferromagnetic film anti-ferromagnetic (AF) are coupled together with a non-ferromagnetic spacer film in the middle. Since the magnetic moments of the two films that are antiferromagnetically coupled together are antiparallel, the net residual magnetization-thickness product (Mrt) of the recording layer is the difference between the Mrt values of the two ferromagnetic films. Achieving this reduction in Mrt did not reduce the thermal stability of the recording medium, because the particle volume of the two films that are antiferromagnetically coupled together constructively increase. At the same time, this kind of media can achieve a more pronounced magnetic transition through the reduced demagnetization field, resulting in a higher linear bit density of the media. In a specific embodiment, the magnetic recording medium includes two ferromagnetic films, each of which is a sputter deposited CoPtCrB alloy granular film, separated by a Ru spacer film, the spacer film has a thickness such that the two layers The antiferromagnetic exchange coupling of the CoPtCrB film is maximized. One of the ferromagnetic films is made thicker than the other, but the thickness of the two is selected so that the net moment of zero applied magnetic field is low, but not zero.

The AF-coupled magnetic recording layer of the present invention, that is, at least two anti-ferromagnetically coupled ferromagnetic films separated by a non-ferromagnetic spacer film, can be described in the above-cited '288 patent as the result. The described laminated media of the respective magnetic layers can produce a media with the advantages of thermal stability and low inherent media noise.

For a better understanding of the essence and advantages of the present invention, please refer to the following detailed description and accompanying drawings.

Fig. 1 is a cross-sectional view of an antiferromagnetic (AF) coupled magnetic recording layer in a recording medium according to the present invention.

Figure 2A is a diagram of the AF coupling layer, illustrating that when recording the magnetic transition, The direction of the magnetic moment in the ferromagnetic film.

Fig. 2B shows the calculated magnetic field above the AF coupling layer media and the single-layer (SL) media based on the function of the downward line position of the magnetic transition point.

Figure 3 is a cross-sectional view of the magnetic disk structure of the present invention, showing the substrate, the base layer, the film contained in the AF coupling layer, and the protective cover.

Fig. 4 shows the hysteresis loop of the AF coupling layer structure shown in Fig. 3.

FIG. 5 is a cross-sectional view of a laminated disk structure in which a conventional individual single layer is used as the magnetic layer in the laminated board in the prior art.

FIG. 6 is a cross-sectional view of a laminated magnetic disk structure with an AF coupling layer as the individual magnetic layers in the laminated board.

<u style="single">Detailed description of the invention</u>

The magnetic recording medium of the present invention has a recording layer, and the recording layer is formed by exchange coupling of two or more layers of ferromagnetic film with the adjacent ferromagnetic film antiferromagnetic (AF) through more than one layer of non-ferromagnetic spacer film of. As shown in FIG. 1, a recording layer 10 includes two ferromagnetic films 12 and 14 separated by a non-ferromagnetic spacer film 16. The thickness and composition of the non-ferromagnetic spacer film 16 are selected so that the adjacent films 12, 14 can transmit their magnetic moments 22, 24 through the non-ferromagnetic spacer film 16 to achieve AF coupling, and the magnetic moment is zero plus The magnetic field is anti-parallel.

The ferromagnetic film AF can be coupled through a non-ferromagnetic transition metal gasket film, which has been extensively studied and described in the literature. Generally speaking, as the thickness of the spacer film increases, the exchange coupling will oscillate between ferromagnetic and antiferromagnetic. The coupling relationship of this kind of oscillation variation of some selected material combinations was published in the Physics Review Correspondence Volume 64 in 1990 by Parkin et al. It is described in the article "Exchange coupling and magnetoresistance oscillation changes in Co/Ru, Co/Cr, Fe/Cr and other metal superlattice structures" on page 2034. Its material combination includes ferromagnetic films made of Co, Fe, Ni and their alloys such as Ni-Fe, Ni-Co and Fe-Co, as well as ferromagnetic films such as ruthenium (Ru), chromium (Cr), rhodium (Rh), Non-ferromagnetic gasket film made of iridium (Ir), copper (Cu) and their alloys. For each such material combination, the exchange coupling relationship (if not known) of its oscillation variation must be individually determined in order to select the thickness of the non-ferromagnetic spacer film to ensure the anti-ferromagnetic coupling between the two ferromagnetic films. The period of the oscillation fluctuation is determined by the non-ferromagnetic gasket material, but the strength and phase of the oscillation fluctuation coupling are also determined by the quality of the ferromagnetic material and interface. The oscillation variation of the ferromagnetic film antiferromagnetic coupling is applied to the rotary valve type strong magnetoresistance (GMR) recording head to design a continuously magnetized antiferromagnetic coupling film whose magnetic torque is firmly reversed in the operation of the head Coupled together in parallel. This type of rotary valve structure has been described in, for example, IBM Patent Nos. 5,408,377 and 5,465,185. The '185 patent describes a structure used in many commercially available rotary valve GMR heads, which is a laminated anti-parallel ferromagnetic layer, with the ferromagnetic thin film tightly coupled together. , During the operation of the magnetic head and can maintain stability.

The magnetic moments of films 12 and 14 are Mr.₁t₁And Mr₂t₂. (Since the residual magnetization Mr is expressed in terms of the magnetic moment per unit volume of the ferromagnetic material, the product Mrt is the magnetic moment per unit area of a ferromagnetic layer with a thickness of t.) This AF coupling structure and In other words, the directions of the magnetic moments 22 and 24 of the adjacent films 12 and 14 are arranged in anti-parallel, so that the magnetic moments of the composite layer 10 are reduced more destructively. Arrows 22 and 24 represent directly located The direction of the force pitch of the individual magnetic regions above and below the AF coupling film 16. In the absence of an external magnetic field, when the ferromagnetic film 14 is deposited on the media substrate, it will have a granular structure in which many adjacent particles will couple with each other to form individual magnetic regions. In the absence of an external magnetic field, the moment of force in such regions in the film 14 will be randomly oriented. Next, the spacer film, or AF coupling film 16, is directly deposited on the ferromagnetic film 14 with the correct thickness. Next, the second layer of ferromagnetic film 12 is directly deposited on the AF coupling film 16. When the particles of the ferromagnetic film 12 grow, they will form a magnetic region, and the direction of the force pitch is anti-parallel to the direction of the force pitch of the ferromagnetic film 14 opposite to it via the AF coupling film 16.

Types of ferromagnetic materials and thickness values of ferromagnetic films 12 and 14₁, T₂It is selected so that the net moment of zero applied magnetic field is low, but non-zero. In the situation shown in Figure 1, the Mrt of its structure is created by Mr.₁t₁-Mr₂t₂Calculated. In a preferred embodiment, Mr₁t₁Should be greater than Mr₂t₂. This can be achieved by using the same ferromagnetic material in the two films 12 and 14, but making t₁More t₂Or, by using different ferromagnetic materials for the two films, the magnetization (the magnetic moment per unit volume of the material) of the two films can be made different. Although FIG. 1 shows a double film structure with a single shim film 16, the present invention can still be extended to the structure of multiple shim films and multi-ferromagnetic films.

Compared with a magnetic layer composed of a single ferromagnetic material layer, the present invention has many advantages. There is no need to use ultra-thin magnetic layer or low magnetization alloy, that is, low net residual magnetization can be obtained. This eliminates thermal instability and the difficulties discussed above. If the magnetic layer in FIG. 1 is compared with a single layer containing only (for example) the thin film 12, the addition of the AF-coupled ferromagnetic thin film 14 makes the composite structure The net magnetic moment in the film is reduced, but the thickness and magnetization of the film 12 are not reduced at all.

Compared with a single magnetic layer, the composite structure has better thermal stability. That is because the anisotropy of the particles in the films 12 and 14 is essentially uniaxial, so it can constructively increase the stability, even if the film The magnetic moments of 12 and 14 are anti-parallel. The stability parameter K of the coupled system obtained as a result_uV is Ku₁V₁&lt;KuV&lt;(Ku₁V₁+Ku₂V₂), where Ku₁V₁Ku₂V₂These are the anisotropic energy of typical particles in films 12 and 14, respectively. Reach the upper limit of the synthetic stability parameter KuV=Ku₁V₁+Ku₂V₂The timing is when the magnetic particles in the film 12 and 14 are strongly coupled and share the same anisotropic axis. The magnetic volume V of the composite structure (layer 10) that determines the thermal stability will be approximately the sum of the volumes of the exchange-coupled particles in the films 12 and 14, while the magnetic moment of the layer 10 is the difference between the individual moments of the films 12 and 14. The antiferromagnetic coupling between the two ferromagnetic films provides a mechanism to increase the effective film thickness while reducing the net Mrt value of the composite structure. Therefore, such ferromagnetic films can contain particles with extremely small diameters and maintain thermal stability.

2A shows a schematic diagram of the AF coupling medium according to the present invention, in which the magnetic transition of recording or writing is in progress. The plus sign (+) and minus sign (-) represent the magnetic poles produced by the magnetic transition. The meridian direction magnetic field (H_x) Is calculated as shown in Figure 2B, which is a function of the X coordinate direction or the downline position of the transition point. The moment and thickness values of the two films 12 and 14 and the Mrt calculated by the AF coupling layer are all listed in FIG. 2B. For comparison, Fig. 2B also shows the typical estimated value of the meridian direction magnetic field of a single-layer (SL) medium similar to Mrt during the transition. Thickness value (t₁And t₂) Is selected to make The AF coupling medium and the SL medium have the same peak meridian direction magnetic field. The total thickness of the ferromagnetic material in the AF coupling medium is 2.7 times thicker. Therefore, AF coupling media should be more thermally stable than SL media. The magnetic field curve in the meridian direction of the AF coupling medium at the downstream position decays faster, causing a more obvious change. This symbolic transition can be closer to each other than in SL media, giving this type of media a higher linear bit density. Another point does not appear in Figure 2B. The calculated results show that the transformed demagnetizing field in the AF coupling medium also decays faster than in the SL medium. In addition, the strength and sign of the demagnetizing field are determined by the Y coordinate position in the media (see Figure 2A). Therefore, at certain Y-coordinate positions in the media, the demagnetizing field strength will drop to zero. Small demagnetization fields are needed because they can affect other transitions and cause the transitions to demagnetize themselves.

The present invention uses the traditional CoPtCrB warp direction recording medium alloy as the ferromagnetic film to demonstrate. Figure 3 shows an example structure. The structure is manufactured using traditional sputtering deposition equipment and manufacturing process. The film forming the structure is grown on a Cr base layer, which is deposited on an AlMg dish-shaped embryo substrate with a nickel-phosphorus (NiP) surface coating. The temperature of the machine material when growing the film is about 200 °C. These ferromagnetic films are all CoPtCrB, and the upper film (equivalent to film 12 in FIG. 1) is thicker (12nm vs. 7nm) than the lower ferromagnetic film (equivalent to film 14 in FIG. 1). The non-ferromagnetic spacer film is a 0.6nm Ru film. Like single-layer media, it is convenient to use granular ferromagnetic materials with isolated magnetic particles to reduce media noise. The thickness of the Ru film selects the first antiferromagnetic peak in the coupling relationship of the oscillation variation. In this example, each CoPtCrB ferromagnetic film includes an interface film, which is basically composed of 0.5 nm of Co at the interface with the Ru film. These extremely thin Co films can increase Adding the interfacial distance between the ferromagnetic film and the Ru film results in an enhanced anti-ferromagnetic coupling. However, it was previously demonstrated that antiferromagnetic exchange coupling was not added to the CoPtCrB ferromagnetic film by adding a Co interface film.

Figure 4 shows the main hysteresis loop (solid line) and residual hysteresis loop (dashed line) measured at a temperature of T=350°K for the structure of Figure 3. Lets talk about the residual hysteresis loop first. It is obtained by immersing the AF coupling layer in a positive magnetic field, and then applying a negative magnetic field that gradually increases in reverse. After applying a negative magnetic field, the residual force distance in the layer is measured. . The residual hysteresis loop is a plot of the residual torque versus the reverse magnetic field strength. In this example, the residual hysteresis loop shows Mrt=0.21, and the residual coercive field H_c_r=3.2k Erst, and S'=0.92 at room temperature, this S'is in H_c_rThe slope of the measured residual hysteresis loop. For comparison, a 15nm single layer grown in a similar way is also a CoPtCrB alloy. The relevant data is: Mrt=0.38, H_c_r=2.4k Erst, and S'=0.76 at room temperature. Therefore, the AF coupling medium can achieve a significantly lower Mrt with a larger total magnetic layer thickness.

Turning to the main hysteresis loop in Figure 4, the pair of horizontal arrows represent the direction of the AF coupling layer ferromagnetic film at different points in the hysteresis loop. The applied magnetic field increases in the positive direction (arrows 30, 32). If the applied magnetic field is very large (more than 3000 Oersted), the antiferromagnetic coupling will be overwhelmed, and the moment of the two ferromagnetic films will be parallel to the applied magnetic field (arrows 42, 44). When the applied magnetic field is reduced (arrow 34), the force of the thinner lower ferromagnetic film will be reversed and become antiparallel to the force of the thicker upper ferromagnetic film (arrows 52, 54), and also the applied magnetic field Anti-parallel, so that the net torque is reduced. This conversion occurs approximately when the lower film feels the exchange magnetic field (H_e_x₂=2000 Ers Special). H_e_x₂=J_e_x/M₂t₂, Where J_e_xTo exchange energy density across the antiferromagnetic interface of the Ru pad layer, and M₂And t₂They are the magnetization and thickness of the lower ferromagnetic film. In order to realize the anti-parallel combination of ferromagnetic films, it is necessary to make H_e_x₂Exceeds the coercive field (H_c₂). Hc₂It is the coercive magnetic field of the lower film assuming no exchange interaction with the upper ferromagnetic film. Therefore, the magnetic properties and thickness of the lower film and the AF coupling film must be designed to maintain H_e_x₂&gt;H_c₂。

The residual torque state after immersion in the positive magnetic field is that the upper ferromagnetic film has a torque parallel to the direction of the magnetic field, while the lower ferromagnetic film has an antiparallel force to the forward magnetic field (arrows 52, 54). In the reverse applied magnetic field (arrow 36), the magnetic field is in a stable state until the force of the upper ferromagnetic film is reversed, and the force of the upper and lower films is aligned in parallel in the negative electrode impregnated state (arrows 62, 64). The conversion of the upper ferromagnetic film's torque determines the coercive field of the AF coupling layer, and is H_c=H_e_x₁+H_c₁, Where H_e_x₁Is the exchange magnetic field (H_e_x₁=J_e_x/M₁t₁), while H_c₁It is the coercive magnetic field of the upper ferromagnetic film, assuming that there is no exchange interaction with the lower ferromagnetic film. Therefore, the design of the characteristics of the upper ferromagnetic film and the AF coupling film must maintain the H of the composite structure_cLower than the expected write magnetic field of the magnetic head. In this example, the path from one residual magnetic field state (arrows 52, 54) to the next residual magnetic field state (arrows 72, 74) will pass through an intermediate state where the moments of the two films are parallel (arrow 62). , 64). Therefore, in contrast to the AF coupling structure used in the rotary valve GMR recording head, the force of the ferromagnetic film in the media according to the present invention is not tightly coupled across the AF coupling film, because the coupling must be overwhelming to write To the media. The hysteresis loop in Figure 4 shows how the AF coupling layer The required characteristic is a residual magnetization that is lower than the intensity of the impregnated magnetism.

The recording performance test of the AF coupling layer uses a traditional warp-type recording head. The signal-to-noise ratio measurement determines its medium S₀NR is 31.9dB at 9500 magnetic flux change per millimeter (fc/mm), where S₀Is the isolated pulse amplitude, and N is the combined media noise at a recording density of 9500 fc/mm. These results demonstrate the feasibility of the AF-coupled magnetic layer in data storage.

The AF coupling medium according to the present invention has also been exhibited in a structure with or without one or two Co interface films, with or without one or two CoCr interface layers, and with a CoCrPtTa ferromagnetic film.

<u style="single">Laminated media with AF coupling layer</u>

According to the invention described in the previously cited '288 Patent, the laminated magnetic recording medium has also been manufactured using the aforementioned AF coupling (AFC) layer as the individual magnetic layer in the laminated board. Figure 5 shows a conventional laminated magnetic recording medium, in which the magnetic recording medium 30 includes at least two individual magnetic layers 32, 34, each with Mrt₁The two adjacent layers are separated by a non-ferromagnetic spacer layer 36. The synthesized double-layer laminated structure has a total Mrt=2Mrt₁. (For the convenience of explanation, it is assumed that all ferromagnetic layers have the same composition so that Mr is the same. However, the scope of the present invention still includes the use of different magnetic materials. At this time, the total magnetic moment of the structure in Figure 5 can be expressed as Mr.₁t₁+Mr₂t₂)。

A new type of laminated media using AFC layers is shown in Figure 6. Its structure has two sets of AFC layers and a non-magnetic spacer layer. In the laminated AFC magnetic medium of FIG. 6, the magnetic recording layer 30' includes AFC layers 32' and 34' separated by a non-ferromagnetic spacer layer 36'. Individual AFC layers 32', 34' replace the corresponding magnetic layer 32 , 34 (Figure 5). Each AFC layer 32', 34' includes two thin films (respectively 42, 46 and 52, 56) antiferromagnetically coupled by antiferromagnetic coupling thin films (respectively 44, 46), and the net Mrt of each AFC layer Namely Mrt₁-Mrt₂. This makes Mrt's control unaffected by Mr or t. As explained in the above non-laminated AFC media, we can obtain thermally stable and low Mrt magnetic media. In the new laminated structure, as shown in Figure 6, the synthetic Mrt is 2*(Mrt₁-Mrt₂). Change Mrt₁And Mrt₂The relative strength of the composite laminate structure can be adjusted without the pain of thermal instability. Therefore, a thermally stable, low Mrt laminated media can be obtained. Of course, although only two AFC layers are shown in FIG. 6, the laminated AFC media of the present invention may have three or more AFC layers, sandwiched between adjacent AFC layers with non-ferromagnetic spacer layers.

A series of traditional single-layer media, non-laminated AFC media, and laminated AFC media structures were installed on two commercially available disk substrates (glass and NiP/AlMg metal) to compare their inherent media signal-to-noise ratio. The structure on the glass substrate is a NiAl/Cr/Co₆₃Cr₃₇It grows on the base layer structure. The structure on the NiP/AlMg substrate is a Cr/Co₆₃Cr₃₇It grows on the base layer structure.

In these tests, the composition of the magnetic layer of all magnetic films is Co₆₂Pt₁₀Cr₂₂B₆. The non-ferromagnetic coupling films 46 and 56 used in the AFC layers 32' and 34' are both 6<img file="TW584841B_D0002.tif" />Thick Ru layer. The non-ferromagnetic spacer layer 36' is also Ru material, but its thickness is 12 to 48<img file="TW584841B_D0003.tif" />Range. In the laminated AFC media, the composition and thickness of the non-ferromagnetic spacer layer 36' between the two AFC layers 32' and 34' are selected so that there is no gap between the two adjacent ferromagnetic films 44 and 52. Significant ferromagnetic or antiferromagnetic coupling occurs. No significant ferromagnetic or anti-ferromagnetic coupling occurs between them. For known materials, the thickness of the gasket layer 36' can be immediately The decision, because it can be known from the oscillation coupling curve, how the exchange coupling varies from ferromagnetic oscillation to antiferromagnetic with increasing shim layer thickness. In the cited '288 patent, the Cr gasket film formed between two layers of Co alloy film has 40<img file="TW584841B_D0004.tif" />Or greater thickness, which is far beyond any detectable ferromagnetic or antiferromagnetic exchange coupling peak in the oscillatory coupling curve. To Co₆₂Pt₁₀Cr₂₂B₆For ferromagnetic films of alloys and Ru, the thickness of Ru is greater than about 10<img file="TW584841B_D0005.tif" />(The first antiferromagnetic peak in the oscillation coupling curve has been exceeded) is enough to ensure that no significant ferromagnetic or antiferromagnetic coupling occurs. This specification for the ferromagnetic layer is directly compared to the specification for the antiferromagnetic coupling films 46 and 56. Both of these have been selected to match the thickness and thickness of the first antiferromagnetic peak in the oscillating coupling curve. Ingredients.

The AFC layer in the laminated and non-laminated AFC media structure is designed to have a Mrt=Mrt₁-Mrt₂=0.20 memu/cm²of. A laminated AFC media with two individual AFC layers (see Figure 6) therefore has a total Mrt=0.40 memu/cm². Traditional media with a single CoPtCrB layer, with Mrt=0.38 memu/cm². The signal-to-noise ratios measured by these structural measurements are shown in Table 1 (glass substrate) and Table 2 (metal substrate):

<tables><img file="TW584841B_D0006.tif" /></tables>

<tables><img file="TW584841B_D0007.tif" /></tables>

In the two sets of disks, the signal-to-noise ratio can be improved by 1 to 2dB compared with the laminated media and the non-laminated AFC media and the traditional single-layer media.

Although the present invention is described with reference to its preferred specific embodiments, those skilled in the art should know the forms and details of various modifications without departing from the spirit, scope and doctrine of the present invention. Therefore, the previous description of the present invention should only be regarded as illustrative in nature, and the scope of the present invention should only be defined in the scope of the appended patent application.