Multilayer exchange spring recording media

Abstract

A multilayer exchange spring recording media consist of a magnetically hard magnetic storage layer strongly exchange coupled to a softer nucleation host. The strong exchange coupling can be through a coupling layer or direct. The hard magnetic storage layer has a strong perpendicular anisotropy. The nucleation host consists of one or more ferromagnetic coupled layers. For a multilayer nucleation host the anisotropy increases from layer to layer. The anisotropy in the softest layer of the nucleation host can be two times smaller than that of the hard magnetic storage layer. The lateral exchange between the grains is small. The nucleation host decreases the coercive field significantly while keeping the energy barrier of the hard layer almost unchanged. The coercive field of the total structure depends on one over number of layers in the nucleation host. The invention proposes a recording media that overcomes the writeability problem of perpendicular recording media.

Claims

1. A magnetic recording system, comprising: a writing head; and a disk, including a magnetic recording medium, comprising an essentially non-magnetic substrate an underlayer formed on the non-magnetic substrate; and an exchange coupled magnetic multilayer structure, including a hard magnetic storage layer, having a first coercive field H.sub.s>0.5 T, formed on the underlayer; and a nucleation host, having a second coercive field H.sub.n without the hard magnetic storage layer, lower than the first coercive field, H.sub.n<H.sub.s, wherein said nucleation host is formed on the hard magnetic storage layer such that the hard magnetic storage layer is between the nucleation host and the non-magnetic substrate, is exchange coupled to the hard magnetic storage layer, and comprises ferromagnetic layers with increasing anisotropy constant K from layer to layer.

2. The magnetic recording system of claim 1, wherein: the nucleation host and the hard magnetic storage layer are in direct contact.

3. The magnetic recording system of claim 1, wherein: H.sub.c(α=20°)<H.sub.c(α=45°), wherein H.sub.c(α) is a coercive field of the magnetic recording medium if an angle between an external field and a normal of the magnetic recording medium is α.

4. The magnetic recording system of claim 1, wherein: the nucleation host comprises grains with an average diameter greater than 2 nm and less than 10 nm.

5. The magnetic recording system of claim 1, wherein: a coupling layer is disposed between the nucleation host and the hard magnetic storage layer.

6. The magnetic recording system of claim 1, wherein: the nucleation host is separated from the hard magnetic storage layer by a layer of thickness less than 5 nm.

7. A magnetic recording medium, comprising: an essentially non-magnetic substrate; an underlayer formed on the non-magnetic substrate; and an exchange coupled magnetic multilayer structure, including a hard magnetic storage layer, having a first coercive field H.sub.s>0.5 T, formed on the underlayer; and a nucleation host, having a second coercive field H.sub.n without the hard magnetic storage layer, lower than the first coercive field, H.sub.n<H.sub.s, wherein said nucleation host is formed on the hard magnetic storage layer such that the hard magnetic storage layer is between the nucleation host and the non-magnetic substrate, is exchange coupled to the hard magnetic storage layer, and comprises ferromagnetic layers with increasing anisotropy constant K from layer to layer, wherein at least two of the ferromagnetic layers are coupled with a thin exchange coupling layer.

8. The magnetic recording medium of claim 7, wherein: H.sub.c(α=20°)<H.sub.c(α=45°), wherein H.sub.c(α) is a coercive field of the recording medium if an angle between an external field and a normal of the recording medium is α.

9. The magnetic recording medium of claim 7, wherein: the nucleation host comprises grains with an average diameter greater than 2 nm and less than 10 nm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic sectional view of a magnetic recording disk with a multilayer exchange spring recording media.

(2) FIG. 2 shows a hysteresis loop in some embodiments. For comparison, the hysteresis loop of a conventional single phase grain is shown.

(3) FIG. 3 shows the coercive field as a function of the angle between the easy axis and external field for bilayars with different values of the anisotropy in the softest layer in the nucleation host.

(4) FIG. 4 shows the hysteresis loop of different exchange spring films comprising of 14×14 grains.

(5) FIG. 5 illustrates the reduction of the coercive field for a nucleation host with a continuously increasing anisotropy.

(6) FIG. 6 shows the energy barrier as a function of the hard layer thickness.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates the cross sectional view of the layer structure of an existing disk of recording medium. The disk includes a substrate 5, a soft magnetic underlayer 7, an interlayer 9, an optional seed layer 11a and underlayer 11b, a hard magnetic storage layer 24, strongly exchange coupled to a nucleation layer 21, an optional coupling layer 22, a protective layer 28a, and a lubricant layer 28b. Although the hard magnetic storage layer is shown on top of the nucleation layer, the order of the layers can also the reversed.

(8) Substrate 5 may be made of any suitable material such as ceramic glass, amorphous glass, or NiP plated AlMg or an AlMg alloy base with a NiP surface coating.

(9) Soft magnetic underlayer 7 is deposited on substrate 5, soft magnetic underlayer 7 may be made of any suitable material such as NiFe, CoNbB, FeAlSi, CoFeB, FeTaN, FeTaC, FeCoB, FeSiO, FeAlSi, FeTaN, FeN, CoFe, CoZr, CoFeB, CoZrNb, NiFeNb or equivalents. Soft magnetic underlayer 7 may have a thickness in the range of about 50 nm to about 500 nm.

(10) Interlayer 9 maybe important for the grain structure of the hard magnetic recording media. Interlayer 9 maybe any suitable material such as Pt, Ge, Si, CoCr, SiO.sub.2, Au, Al, CoZr, Ta, Ti, TiCr, Ru, RuCrCo, TiZr, or equivalents.

(11) Optional seed layer 11a maybe used in order to improve the growth of underlayer 11b. Optional seed layer 11a may be formed of a suitable material of hep, fee, bee or even amorphous structure. It provides a smooth wetted surface for the subsequent growth of underlayer 11b.

(12) Underlayer 11b is deposited onto optional seed layer 11a, if present, or otherwise directly onto substrate 5. Underlayer 11b may be formed of a suitable hep material with a lattice parameter close to the alloys of the first layer in the magnetic layer. These alloys may be, for example, Ru-based alloys, Re-based alloys or Pd based alloys. Underlayer 11b may have a thickness in the range of about 1 nm to about 20 nm. Other thicknesses can also be used.

(13) The recording media includes hard magnetic storage layer 24 and softer nucleation host 21. Hard magnetic storage layer 24 can be a ferromagnet, ferrimagnet, antiferromagnet, or any other synthetic antiferromagnetic structure. The coupling between the nucleation host and the hard magnetic storage layer may be ferromagnetic or antiferromagnetic. Hard magnetic storage layer 24 maybe formed from any material that has large perpendicular anisotropy. These materials include tetragonal Llo-ordered phase materials, CoPt and FePt based alloys, CoPtCr alloys, including CoPtCrB, CoPtCrTa, CoCr based granular media, pseudo-binary alloys based on the FePt and CoPt L1.sub.0 phase, i.e., FePt—X and CoPt—X, where the element X may be Ni, Au, Cu, Pd or Ag, as well as granular composite materials such as FePt—C, FePt—ZrO, FePt—MgO, FePt—B.sub.2O.sub.3, materials containing at least one of B, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Pd, Sm, Nd, Dy, Hf, Mn, Ni and other similar composites.

(14) In some embodiments the thickness of hard magnetic storage layer 24 is between 3 nm and 30 nm. In other architectures it can be outside these ranges. In embodiments where the anisotropy of nucleation host 21 is continuously increased, hard magnetic storage layer 24 is optional.

(15) In some embodiments nucleation host 21 can be formed on hard magnetic storage layer 24. In other embodiments the order is changed so that hard magnetic storage layer 24 is deposited on nucleation host 24. Nucleation host can be formed as a granular or a continuous film. The exchange coupling between hard magnetic storage layer 24 and nucleation host 21 can be sufficiently strong to enable the formation of a domain wall across the interface of these layers during reversal.

(16) Any of the materials, listed for hard magnetic storage layer 24 can be also used for forming nucleation host 21. In some embodiments a magnetic material is referred to as “hard” if its coercive field Hc>0.5 T, and “soft” is its coercive field is Hc<0.5 T. In some embodiments these terms are defined in a relative sense: the coercive field of (soft) nucleation host 21 can be half of the coercive field of hard magnetic storage layer 24. In other embodiments this ratio can be different. In some embodiments a layer is referred to as “hard”, if Δk.sub.max/k.sub.min<0.5. The definition of the terms in this inequality will be given below.

(17) In some embodiments the grains of nucleation host 21 are aligned with the grains of hard magnetic storage layer 24, as shown in FIG. 1. In some embodiments this alignment is only approximate. These embodiments are sometimes called columnar media.

(18) In some embodiments nucleation host 21 and hard magnetic storage layer 24 are in direct contact. In other embodiments, they are separated by optional coupling layer 22. Optional coupling layer 22, disposed between hard magnetic storage layer 24 and nucleation host 21, can provide a strong “exchange coupling”. Optional coupling layer 22 may enhance the granular growth between hard magnetic storage layer 24 and nucleation host 21. Optional coupling layer 22 may have a thickness between 0.1 nm and 3 nm. Optional coupling layer 22 may provide an exchange constant A in excess of A=10.sup.−14J/m. In conventional perpendicular recording the exchange constant between grains is small. In exchange spring media both large and small values of the lateral exchange can be useful. For a large value of the lateral exchange in hard magnetic storage layer 24 the transitions of the bits are not necessarily located at the grain boundaries. Instead, domain wails are formed that separate the bits. A large value of the anisotropy of hard magnetic storage layer 24 decreases the domain wall width, so that the transition parameter of the bits may not be significantly larger than 2 nm to 3 nm that can be equal to about the grain diameter. In the case of large lateral exchange the domain walls are not pinned at the grain boundary in the hard magnetic storage layer but the domain walls are pinned due to the granular laterally weakly exchange coupled nucleation host. A weak exchange in the hard magnetic storage layer may require a large exchange in the nucleation layer.

(19) In the following the plane of nucleation host 21 will be identified as the x-y plane. For example, in a magnetic storage disk, the plane of the disk is essentially parallel to the x-y plane of nucleation host 21. The z coordinate then parameterizes the direction of the thickness of nucleation host 21.

(20) In some embodiments nucleation host 21 contains more than one layer which have different anisotropy K. In other embodiments nucleation host 21 is characterized by a spatially varying anisotropy K(z). In these embodiments, the anisotropy assumes more than one value in a substantial magnetic portion of nucleation host 21. In this sense the embodiments differ from single layer nucleation hosts, whose anisotropy assumes varying values only in an insubstantial portion. This may occur e.g. because of surface effects, in a very thin layer at the surface. Also, the variation is occurring in the magnetic nucleation host 21 itself. In this sense, embodiments differ from disks which have a single layer nucleation host 21 and a spacer layer.

(21) In some embodiments, the softest, or smallest value of the anisotropy K is half of the anisotropy of hard magnetic storage layer 24. In other embodiments this ratio can be closer to one. This softest value of if is the anisotropy of the softest layer in multilayer embodiments, or the softest value in the spatially varying embodiments.

(22) In some embodiments the lateral, or nearest neighbor, exchange between the grains of nucleation host 21 is small.

(23) Protective layer 28a, sometimes called overcoat, is typically diamond-like amorphous carbon or nitrogenated carbon, but may be any conventional disk overcoat. Overcoat 28a is typically less than 15 nm thick.

(24) All of the layers described above from seed layer 11 to overcoat 28a can be sputtered in a continuous process in either an in-line sputtering system or a single disk system, such as commercially available single disk systems with multiple sputtering target capacity. The sputter deposition of each of the layers can be accomplished rising standard targets and techniques known to those in the field with the modifications described above.

(25) In the following, some considerations will be provided, which may be relevant for understanding features of the embodiments. Some embodiments combine benefits of softer magnetic layer with that of harder magnetic layers.

(26) In some embodiments nucleation host 21 includes only one layer. In these embodiments the recording media is referred to as a bilayer, which includes nucleation host 21 and hard magnetic storage layer 24. Under the assumption that both layers remain completely homogeneous, the bilayer structure does not provide any improvements for the writeability compared to a single, layer system. This conclusion is different from that of Y, Inaba et al. in the paper “Preliminary Study on (CoPtCr/NiFe)—SiO2 Hard/Soft-Stacked Perpendicular Recording Media”, IEEE Transactions on Magnetics, Vol. 41, No. 10, October 2005, pp. 3136.

(27) A hard/soft layer structure where the magnetization in the hard and soft layer is parallel and uniform can be described with one average magnetization M.sub.eff=(M.sub.hard×I.sub.hard+M.sub.soft×I.sub.soft)/(I.sub.soft+I.sub.hard) and one average anisotropy constant K.sub.eff=(K.sub.hard×I.sub.hard+K.sub.soft+I.sub.soft)/(I.sub.soft+I.sub.hard). In a simple model the energy barrier can be estimated by ΔE=F×K.sub.eff×(I.sub.soft+I.sub.hard), where F is the area of the basal plane of one grain of the media. The coercive field is H.sub.c=2K.sub.eff/M.sub.eff. The ratio of the energy barrier to the coercive field, the “ratio barrier” ΔE/H.sub.c only depends on the value of the average magnetization and the grain volume. Therefore, this bilayer structure leads to the same thermal stability as the single layer structure of the same thickness for the same value of the coercive field and for the same value of the average magnetization.

(28) In embodiments of the invention, the design of the recording media is capable of supporting the formation of a domain wall during reversal. This magnetic domain wall becomes pinned at hard/soft interfaces. Compared to single phase media with the magnetic properties of the hard layer, the coercive field in a bilayer structure can be significantly reduced. In embodiment this reduction reaches a factor of four, as described by Loxley et al. in the paper: “Theory of Domain Wall Nucleation in a Two Section Magnetic Wire”, IEEE Transactions on Magnetics, Vol. 37, July 2001, pp. 1998-2100). However, Loxley et al considered an idealized magnetic wire instead of a magnetic recording medium. A factor of five decrease was shown by Hagedorn in the paper: “Analysis of Exchange-Coupled Magnetic Thin Films,” Journal of Applied Physics, Vol. 41, 1970, pp. 2491-2502, when a finite anisotropy in the soft layer was assumed.

(29) A feature of embodiments of the invention is that the coercive field and the thermal energy barrier can be separately adjusted. In contrast, the above works considered these quantities closely connected and thus not adjustable separately. The thermal energy barrier is primarily determined by the material parameters of hard magnetic storage layer 24, substantially independently from the material parameters of nucleation host 21. Thus, in embodiments the ratio

(30) $r=\frac{\Delta E_{\mathrm{thermal}}}{\Delta E_{\mathrm{hyst}}}$
can be selected in the range of 0.5 to 10. In others the range can be even broader. Here the thermal energy barrier ΔE.sub.thermal is the energy barrier separating the two magnetic states, which has to be overcome by the thermal fluctuations. The hysteretic energy loss ΔE.sub.hyst=J.sub.sH.sub.cV is the product of grain volume V, the coercive field H.sub.c and the average magnetization J.sub.s which characterizes the energy to be overcome during a write process. For single domain particles these energy scales are closely connected with a fixed ratio r of 0.5.

(31) The field, required to overcome the pinning field to push a domain wall from the softer layer to the hard layer depends on the difference between the anisotropy constants of these layers as described by a formula by Hagedorn et al. If the number of layers is increased, this difference can be decreased leading to a reduction of the pinning and coercive field. For example, if the anisotropy of the m-th layer assumes the value K.sup.m=(m−1)K.sub.hard/(N−1), the difference between the anisotropy constants of adjacent layers is K.sub.hard/(N−1). Such an architecture leads to a coercive field of the whole structure of H.sub.c=1/(4N−4)×2 K.sub.hardJ.sub.s. Here, K.sub.hard is the anisotropy constant of the hardest layer (the hard magnetic storage layer), J.sub.s the magnetic polarization of the structure and N is the number of layers. For sufficiently thick hard magnetic storage layer the thermal stability is given by the domain wall energy in the hard magnetic storage layer. Importantly, therefore, at zero field the nucleation host does not lower the thermal stability.

(32) FIG. 2 illustrates the micromagnetic simulations, which were performed to demonstrate the benefit of multilayer exchange spring media. FIG. 2 compares the hysteresis loop of different multilayer exchange spring media with a conventional recording media. Only one grain of the media was modeled. The parameters are for illustrative purposes only and can widely vary in different embodiments. The external field is applied at an angle of 0.5°. Nucleation host 21 is assumed to have a granular structure. The thickness of the entire grain structure is 25 nm. The grain diameter is 5 nm. The magnetization is M.sub.s=0.5 T/μ.sub.0. The grains are formed from a magnetic hard material with K.sub.1=2 MJ/m.sup.3.

(33) The trace “single phase” illustrates an embodiment in which the grains have a single anisotropy value. The trace “bilayer soft K.sub.soft=0” illustrates an embodiment, where 7 nm of the grain are magnetically extremely hard with K.sub.hard=2 MJ/m.sup.3, the other 18 nm are perfectly soft K.sub.soft=0. The trace “bilayer soft K.sub.soft=0.2 MJ/m.sup.3” illustrates an embodiment where again 7 nm of the grain is extremely hard K.sub.hard=2 MJ/m.sup.3. The softer region has still a relative high anisotropy of K.sub.soft=0.2 MJ/m.sup.3. The “trilayer” trace illustrates the embodiment where 7 nm again has K.sup.1=K.sub.hard=2 MJ/m.sup.3, 5.6 nm of the grain has K.sup.2=1.11 MJ/m.sup.3 and 12.4 nm of the grain has K.sup.3=0.22 MJ/m.sup.3.

(34) Visibly, the coercive field of the bilayer structures is severely reduced from that of the single phase media by a factor of about 4-4.5. The trilayer structure has its coercive field further reduced, by about a factor of 7 compared to the single phase media. The discrepancy to the theoretical limit of 9 can be attributed to the finite layer thickness. The effect of reversible magnetization processes can be observed by the non-rectangular shape of the hysteresis loop.

(35) Some embodiments have a gradually varying anisotropy K(z) in nucleation host 21. Such embodiments will be referred to as “G-layer”. In FIG. 2 the hysteresis loop of G-layers are shown. The trace “continuous strayfield” illustrates the embodiment in which the anisotropy increases quadratically as a function of the z coordinate, the distance from the bottom of the grain: K(z)˜z.sup.2. The demagnetizing field of the grain is taken into account. The trace “continuous” illustrates the embodiment in which the demagnetizing field was omitted. FIG. 2 shows that the coercive field is just 1/10 of the coercive field of the single layer structure for a thickness of 25 nm. It is also interesting to note that the hysteresis loop is almost perfectly rectangular. If the strayfield is taken into account, the coercive field increases by about 3%, which can be attributed to the additional uniaxial anisotropy caused by the shape anisotropy.

(36) The variation of K(z) can take many different form. The rise can be linear, or follow any polynomial or other rising function. It can have plateaus or steps, connected by rising segments. It can also have decreasing segments. In some embodiments, the functional form of K(z) is chosen to optimize the switching properties of the recording media, e.g. by increasing the thermal energy barrier while keeping the writing field, or coercive field, essentially unchanged, or even decreasing it.

(37) FIG. 3 illustrates the angular dependence of the coercive field H.sub.c(α) as a function of the angle α that is measured between the easy axis and the external field. So the coercive field is measured for different angles α. The solid line shows the angular dependence of the trilayer of FIG. 2. The dotted line shows the angular dependence of the coercive field if the anisotropy in the softest layer of the nucleation host is set to zero. In contrast to single phase media, the coercive field does not have a minimum for a field angle of 45°. The pinning force to depin the domain wall at the hard/soft interfaces depends inversely from the cosine of the angle between the easy axis and the external field. It can be seers that the coercive field H.sub.c(α=20°) is smaller than H.sub.c(α=45°). A similar dependence can be found if instead of the coercive field the field H.sub.m(α) is introduced, where H.sub.m is the field that is requited to decrease the magnetization of the saturated film (M.sub.r/M.sub.s=1) to M.sub.r/M.sub.s=0.5. Differences of the field H.sub.m and H.sub.c occur if the media comprises of a thick soft layer with high magnetization.

(38) FIG. 4 shows the hysteresis loop of an exchange spring perpendicular recording film consisting of 14×14 grains. The parameters of this embodiment are for illustrative purposes only. The average grain diameter is 5 nm. The film thickness is 23 nm. The exchange field between the grains is about 0.25T. The thickness of the nucleation layer is equal to the thickness of the hard magnetic storage layer which is 10.5 nm. The two layers are separated by a 2 nm thick optional coupling layer 22. The exchange constant in the coupling layer is varied from A=1×10.sup.−12 J/m to the bulk value of the exchange in the nucleation layer and the storage layer which is A=1×10.sup.−11 J/m. The hysteresis loops show that with increasing coupling the coercive field decreases. Furthermore the hysteresis curves for A=1×10.sup.−12 J/m and A=2×10.sup.−12 J/m show that the slope of the hysteresis loop

(39) $k=\frac{\mathrm{dM}}{\mathrm{dH}}\frac{H_c}{M_s}$
changes in the interval −0.7< M/M.sub.s<00.7, significantly. For A=2×10.sup.−12 J/m the slope k changes in the interval −0.7< M/M.sub.s<0.7 by about a factor of 2.5. In embodiments the anisotropy of hard magnetic storage layer 24 and the exchange coupling between nucleation host 21 and hard magnetic storage layer 24 is chosen to keep the change of the slope k smaller than 3. A ratio k.sub.max/k.sub.min<3 indicates a strong coupling between nucleation host 21 and hard magnetic storage layer 24.

(40) Furthermore the squareness S of the hysteresis loops was calculated.

(41) $S=1-\frac{\mathrm{dM}}{\mathrm{dH}}\frac{H_c}{M_s}{|}_{H_c}.$
For the fully coupled case (A=1×10.sup.−11 J/m) the squareness is 0.8. It is important to note that for all calculations the hysteresis loops are not desheared.

(42) FIG. 5 illustrates the reduction of the coercive field for nucleation host 21 with thickness t.sub.G and a continuously increasing anisotropy, fully exchange coupled to the hard magnetic storage layer. The value of the anisotropy constant of the hard magnetic storage layer is changed from 1 MJ/m.sup.3 to 4 MJ/m.sup.3. FIG. 4 shows the reduction of the coercive field of hard magnetic storage layer 24 with a thickness of 20 nm and a value of the anisotropy constant of K.sub.hard that is coupled to a G-layer. The anisotropy constant depends quadratically on the depth z in the layer, K(z)=z.sup.2K.sub.hard/t.sub.G.sup.2. The grain has the maximum anisotropy (K.sub.hard) at the surface of nucleation host 21. The thickness of nucleation host 21 is t.sub.G. This embodiment does not have hard magnetic storage layer 24.

(43) FIG. 6 illustrates the influence of the thickness of hard magnetic storage layer 24 on the energy barrier of the bilayer structure. The particular parameters are for illustrative purposes only—other embodiments have different parameters. The thickness of nucleation host is 20 nm (limit of infinite thick soft layer). The anisotropy in hard magnetic storage layer 24 is K.sub.hard=1×10.sup.6J/m.sup.3. The grain diameter is 6 nm. The energy barrier levels out for thicknesses larger than 20 nm. It is important to stress that at zero field the energy barrier does not depend on nucleation host 21. Due to thermal fluctuations a domain wall is formed in the nucleation host. The energy of the domain wall successively y increases as it is driven by thermal fluctuations in the harder layers. The domain wall has largest energy when it is located in the hardest layer. The difference this highest energy state minus the energy of the homogenous state when the spins in the grain point up (down) denotes the energy barrier. For all structures the highest energy state is given by the domain wall energy in the hard magnetic storage layer which is independent if a nucleation host 21 is present. The demagnetizing field of the structure may slightly decrease the energy barrier. The decrease of the energy barrier may be larger if a nucleation host is present as without nucleation host 21. In embodiments the energy barrier of a typical grain of hard magnetic storage layer 24 is smaller by 25% of the energy barrier of a typical grain of hard magnetic storage layer 24 without the nucleation host at most.

(44) We note feat parameters of an unknown magnetic recording media can be characterized by different methods. For example, an energy barrier of a hard magnetic storage layer can be determined: (i) by depositing only the hard magnetic storage layer on a non-magnetic substrate, or (ii) by removing a nucleation host from a multilayer structure; or (iii) by performing a micromagnetic calculation with parameters appropriate for the multilayer.

(45) Some embodiments, described throughout this specification, can include a magnetic recording medium, comprising: an essentially non-magnetic substrate; and a magnetic bilayer, comprising: a granular hard magnetic storage layer having a coercive field of H.sub.s without another magnetic layer; and a granular nucleation host, disposed on the hard magnetic storage layer in a columnar manner, having a coercive field H.sub.n without the hard magnetic storage layer, wherein 0.7 T<H.sub.n<H.sub.s; and the nucleation host is having a magnetic polarization J.sub.s=μ0M.sub.s between 0.3 T and 1.0 T, wherein the nucleation host and the hard magnetic storage layer are arranged either in direct contact or separated by a coupling layer of less than 5 nm thickness.

(46) In some embodiments of the magnetic recording medium, the nucleation host and the hard magnetic storage layer are in direct contact.

(47) In some embodiments of the magnetic recording medium, an exchange coupling between the nucleation host and the hard magnetic storage layer is sufficiently strong and the nucleation host is sufficiently hard so that the derivative k of the normalized magnetization with respect to the external field normalized to the coercive field does not change by more than a factor of 3 in a magnetization interval −0.7<M.sub.z/M.sub.s<0.7, wherein:

(48) $k=\frac{\mathrm{dM}}{\mathrm{dH}}\frac{H_C}{M_S}$

(49) M being a magnetization of the recording medium, M.sub.z being a component of the magnetization perpendicular to a plane of the recording medium, H being an external magnetic field parallel to a normal of the layers, dM/dH being the derivative of the magnetization with respect to the external magnetic field, H.sub.c being a coercive field, M.sub.s being a saturation magnetization.

(50) In some embodiments of the magnetic recording medium, a squareness S of a hysteresis loop is less than 10% different from the squareness of the hysteresis loop of the hard magnetic storage layer without the nucleation host.

(51) In some embodiments of the magnetic recording medium, the hard magnetic storage layer comprises of at least one of Cr, Pt, Ta, B, Fe, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn and Ni.

(52) In some embodiments of the magnetic recording medium, H.sub.c(α=20°)<H.sub.c (α=45°), wherein H.sub.c(α) is the coercive field if the angle between the external field and the film normal is α.

(53) In some embodiments of the magnetic recording medium, H.sub.m (α=20°)<H.sub.m(α=45°) wherein H.sub.m(α) is the required field to reduce the normalized magnetization from the saturation to −0.5 if the angle between the external field and the film normal is α.

(54) In some embodiments of the magnetic recording medium, the nucleation host comprises at least one of Fe, Ni, Al, Si, B, Co. Cr, Pt, Ta, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn, Ni and O.

(55) In some embodiments of the magnetic recording medium, the nucleation host, comprises grains with an average diameter greater than 2 nm and less than 10 nm.

(56) In some embodiments of the magnetic recording medium, the thickness of the nucleation host is larger than 7 nm.

(57) In some embodiments of the magnetic recording medium, the nucleation host is in direct contact with the hard magnetic storage layer.

(58) In some embodiments of the magnetic recording medium, the nucleation host is coupled to the hard magnetic storage layer by a strong exchange coupling layer.

(59) In some embodiments of the magnetic recording medium, the nucleation host is coupled to the hard magnetic storage layer by an antiferromagnetic coupling.

(60) In some embodiments of the magnetic recording medium, parameters of the media structure comprise: a anisotropy constant in the nucleation host K.sup.n.sub.1; a hard magnetic storage layer anisotropy constant K.sup.th.sub.1; a nucleation host grain diameter; a hard magnetic storage layer grain diameter; an exchange constant between grains in the nucleation host; an exchange constant between grains of the hard magnetic storage layer; a saturation polarization in the nucleation host as a function of the layer depth; a saturation polarization of the hard magnetic storage layer; a layer thickness of the nucleation host; a layer thickness of the magnetic storage layer and an exchange constant between the nucleation host and the hard magnetic storage layer.

(61) In some embodiments of the magnetic recording medium, the coercive field of the hard magnetic storage layer is determined by at least one of: depositing only the hard magnetic storage on the non-magnetic substrate; removing the nucleation host from a multilayer structure; and performing a micromagnetic calculation with parameters appropriate for the multilayer.

(62) In some embodiments of the magnetic recording medium, an energy barrier of the hard magnetic storage layer is determined by at least one of: depositing only the hard magnetic storage layer on the non-magnetic substrate; removing the nucleation host from the multilayer structure; and performing a micromagnetic calculation with parameters appropriate for the multilayer.

(63) In some embodiments of the magnetic recording medium, a parameter of the magnetic bilayer has a value such that a coercive magnetic field of the hard magnetic storage layer is less than ½ of the coercive magnetic field of the hard magnetic storage layer without the nucleation host.

(64) In some embodiments of the magnetic recording medium, a parameter of the magnetic recording medium has a value such that a coercive field of the magnetic recording medium increases when grains of the recording media are misaligned relative to a normal of the non-magnetic substrate.

(65) In some embodiments of the magnetic recording medium, the recording medium is usable for perpendicular recording or for recording on patterned elements.

(66) In some embodiments, a magnetic recording medium is comprising: an, essentially non-magnetic substrate; and an exchange coupled magnetic multilayer structure, comprising: a nucleation host with an anisotropy varying in the film normal direction, and a hard magnetic storage layer; wherein a ratio

(67) $r=\frac{\Delta E_{\mathrm{thermal}}}{\Delta E_{hyst}}$

(68) is in the range of 0.5 to 10 wherein a thermal energy barrier ΔE.sub.thermal separates two magnetic states, and a hysteretic energy loss ΔE.sub.hyst=J.sub.sH.sub.cV is the product of a grain volume V, the coercive field He and an average magnetization J.sub.s.

(69) In some embodiments, as described throughout this specification, a magnetic recording medium is comprising: an essentially non-magnetic substrate; and an exchange coupled magnetic multilayer structure, comprising: a nucleation host with an anisotropy varying in the film normal direction; and a hard magnetic storage layer; wherein the anisotropy assumes more than one value in substantial magnetic portions of the nucleation host.

(70) In some embodiments of the magnetic recording medium, an exchange coupling between the nucleation host and the hard magnetic storage layer is sufficiently strong and the nucleation host is sufficiently hard so that the derivative k of the normalized magnetization with respect to the external field normalized to the coercive field does not change by more than a factor of 3 in a magnetization interval −0.7<M.sub.z/M.sub.s<0.7, wherein:

(71) $k=\frac{\mathrm{dM}}{\mathrm{dH}}\frac{H_C}{M_S}$

(72) M being a magnetization of the recording medium, M.sub.z being a component of the magnetization perpendicular to a plane of the recording medium, H being an external magnetic field parallel to a normal of the layers, dM/dH being the derivative of the magnetization with respect to the external magnetic field, H.sub.c being a coercive field, M.sub.s being a saturation magnetization.

(73) In some embodiments of the magnetic recording medium, the nucleation host and the hard magnetic storage layer are in direct contact.

(74) In some embodiments of the magnetic recording medium, the nucleation host, comprises of ferromagnetic layers with increasing anisotropy from layer to layer.

(75) In some embodiments of the magnetic recording medium, the nucleation host, comprises a ferromagnetic layer with a continuous change of anisotropy in the film normal direction.

(76) In some embodiments of the magnetic recording medium, the nucleation host and the hard magnetic storage layers comprise ferromagnetic layers with increasing anisotropy values.

(77) In some embodiments of the magnetic recording medium, the hard magnetic storage layer comprises at least one of Cr, Pt, Ta, B, Fe, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn and Ni.

(78) In some embodiments of the magnetic recording medium, a coercive field of the nucleation host is less than ½ of a coercive field of the hard magnetic storage layer.

(79) In some embodiments of the magnetic recording medium, a H.sub.c(α=20°)<H.sub.c(α=45°), wherein H.sub.c(α) is the coercive field if the angle between the external field and the film normal is α.

(80) In some embodiments of the magnetic recording medium, a H.sub.m(α=20°)<H.sub.c(α=45°), wherein H.sub.m(α) is the required field to reduce the normalized magnetization from the saturation to −0.5 if the angle between the external field and the film normal is α.

(81) In some embodiments of the magnetic recording medium, the nucleation host comprises at least one of Fe, Ni, Al, Si, B, Co, Cr, Pt, Ta, Cu, Ag, W, Mo, Ru, Si, Ge, Nb, Co, Pd, Sm, Nd, Dy, Hf, Mn, Ni and O.

(82) In some embodiments of the magnetic recording medium, the nucleation host has a thickness smaller than 30 nm.

(83) In some embodiments of the magnetic recording medium, the nucleation host comprises grains with an average diameter greater than 2 nm and less than 10 nm.

(84) In some embodiments of the magnetic recording medium, a height of a plurality of grains is greater than a diameter of the grains.

(85) In some embodiments of the magnetic recording medium, the nucleation host is in direct contact with the hard magnetic storage layer.

(86) In some embodiments of the magnetic recording medium, the nucleation host is separated from the hard magnetic storage layer by a layer of thickness less than 5 nm.

(87) In some embodiments of the magnetic recording medium, the nucleation host is coupled to the hard magnetic storage layer by a strong exchange coupling layer.

(88) In some embodiments of the magnetic recording medium, the nucleation host is coupled to the hard magnetic layer by antiferromagnetic coupling.

(89) In some embodiments of the magnetic recording medium, parameters of the medium comprise: a anisotropy constant in the nucleation host K.sup.n.sub.1 as a function of the layer depth a hard magnetic storage layer anisotropy constant K.sup.h.sub.1; a nucleation host grain diameter; a hard magnetic storage layer grain diameter; an exchange constant between grains in the nucleation host; an exchange constant between grains of the hard magnetic storage layer; a saturation polarization in the nucleation host as a function of the layer depth; a saturation polarization of the hard magnetic storage layer; a layer thickness of the nucleation host; a layer thickness of the magnetic storage layer and an exchange constant between the nucleation host and the hard magnetic layer.

(90) In some embodiments of the magnetic recording medium, a parameter of the magnetic multilayer has a value such that a coercive magnetic field of the hard magnetic storage layer is less than ½ of the coercive magnetic field of the hard magnetic storage layer without the nucleation host.

(91) In some embodiments of the magnetic recording medium, a parameter of the magnetic multilayer has a value such that an energy barrier of a typical grain of the hard magnetic storage layer is smaller at most by 25% of the energy barrier of a typical grain of the hard magnetic storage layer without the nucleation host.

(92) In some embodiments of the magnetic recording medium, an energy barrier of the hard magnetic storage layer is determined by at least one of: depositing only the hard magnetic storage layer on the non-magnetic substrate; removing the nucleation host from the multilayer structure; and performing a micromagnetic calculation with parameters appropriate for the multilayer.

(93) In some embodiments of the magnetic recording medium, a parameter of the magnetic multilayer has a value such that a coercive field of the magnetic multilayer increases when grains of the recording media are misaligned relative to a normal of the non-magnetic substrate.

(94) In some embodiments of the magnetic recording medium, the thickness of the nucleation host has a value such that the in plane component of a magnetization of a remanent state is less than 20% of a total magnetization.

(95) In some embodiments of the magnetic recording medium, the recording medium is usable for at least one of perpendicular recording or recording on patterned elements.”

(96) Further, to accommodate the insertion of new paragraphs [0077]-[401011] please renumber presently numbered paragraph [0077] to [0102], without any modification to its text, as follows:

(97) While the present invention has been particularly shown and described with reference to certain embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention. Accordingly, the disclosure was intended merely as illustrative and the scope of the invention is limited only as specified in the appended claims.