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A hybrid soft underlayer, consisting of a thin crystalline soft underlayer stacked above a non-magnetic seed layer and a conventional amorphous soft underlayer, provides an alternative approach for reducing the effective head-to-keeper spacing in perpendicular recording. Micromagnetic simulations indicate that the media using a hybrid soft underlayer helps enhance the effective field and the field gradient in comparison with conventional media that uses only an amorphous soft underlayer. The hybrid soft underlayer can support a thicker non-magnetic seed layer yet achieve an equivalent or better effective field and field gradient. In principle, both writability and growth texture can be simultaneously improved. Index Terms--Micromagnetic simulation, perpendicular magnetic recording.

Exchange coupled composite media has a lower switching field compared to conventional perpendicular media at the same level of thermal stability, making it promising for high areal density recording. In this paper, we propose head and media specifications, calculated micromagnetically at a density of 1 Tb/in (2), using a composite media with a synthetic antiferromagnet hard layer. We assume realistic constraints such as jitter to bit length ratio, skew, seed layer, and grain boundaries. [T.sub.50] of the read back pulse is estimated using a current perpendicular to plane (CPP) giant magnetoresistive (GMR) reader and the magnetization noise is calculated. The signal to dc noise ratio is also estimated for the media used. Index Terms--Exchange coupled composite media, terabit per square inch recording.

Exchange coupled composite (ECC) media exhibits a lower switching field than conventional perpendicular media at the same level of thermal stability, and thus is able to achieve higher areal density. The inhomogeneity of ECC media is predicted to enhance the thermal attempt frequency: this increases both writability and adjacent track erasure (ATE). The adverse change in ATE is, however, countered by the angular dependence of the ECC media switching field. This angular dependence is further exploited with a head design featuring a larger pole width than track width and the introduction of notches in the down track direction. This reduces the effect of head skew and increases the write field. An optimized head is found to be consistent with terabit/[in.sup.2] recording. Index Terms--Exchange coupled composite (ECC) media, pole head, thermal fluctuation.

Exchange coupled composite (ECC) media has been shown to possess several major advantages relative to conventional perpendicular media, including a reduction in the switching field of approximately a factor two for the same thermal stability and greater insensitivity to easy axis distribution. In this paper, full magnetostatic interactions are included: this allows comparison between the behavior of multi-grain thin films and that of isolated grains as presented earlier. Significant results include hysteresis loops for thin films under various conditions including inadequate and excessive intra granular exchange between the hard and soft materials. An important distinction is made between the coercivity and remnant coercivity as a function of angle between applied field and easy axis. A perpendicular magnetic recording head is used to compare the shape of effective fields for ECC and conventional perpendicular media. Written transitions in the ECC media appear to be similar to those written in perpendicular media at comparable densities. Index Terms--Exchange coupled composite media, perpendicular magnetic recording, thermal fluctuations.

Co/Pd-based multilayers have been Si doped in order to enhance their potential for extremely high-density perpendicular magnetic recording (PMR) media. Co/Pd multilayers have high interface-induced perpendicular anisotropy, high coercivity, and high remnant squareness, all of which make them excellent candidates for PMR. Dopants can be utilized to reduce grain size as well as to reduce magnetic coupling between grains via compositional segregation to the grain boundaries. Here, Si was chosen for a dopant because the phase diagrams indicated that Si may migrate to form silicides at the grain boundaries. An additional benefit of Si as a dopant is that it ran be detected chemically, unlike the more common dopant B, which is a much lighter element. A significant difference between the current doping and all other doping in PMR media is that Si was added into the Pd layers rather than the Co layers, which keeps the magnetic layer pure and improves the magnetic properties. This media was also made at room temperature, which yields smaller grains and reduces interfacial diffusion. The static magnetic properties of the Si-doped multilayers were very promising as measured by vibrating sample magnetometry: Hc = 5400 Oe, Ms = 160 emu/[cm.sup.3], and [alpha] = 4[phi]dM/dH [approximately equal to] 1. The fact that the latter term was unity suggests that the grains are magnetically decoupled which promises low transition noise. The samples were measured by atomic force and magnetic force microscopy (AFM/MFM) and by X-ray scattering. They were found to have 12-nm grains. In addition, Si-doped multilayer media that were spin-stand tested showed an increase in signal-to-noise ratio of 5 dB compared to high-performing B-doped media. Index Terms--Co/Pd multilayers, ITO seed layers, perpendicular magnetic recording (PMR), Si doping.

The intrinsic damping mechanism arising from the magnon-magnon scattering in three-dimensional and two-dimensional ferromagents is examined. The magnetization aligns with the field direction transferring energy from initially excited uniform (k=0) precession mode to the non-uniform (k is unequal to 0) magnons.

Grain boundaries play a crucial role in determining the macroscopic properties of magnetic recording media. The authors employ electronic structure theory, based on the local spin density approximation, to calculate the exchange energy, anisotropy energy, and magnetization at two types of grain boundaries. They incorporate these values into a micromagnetic simulation, thus correlating hysteresis loops and switching properties to atomic features. The authors show that small intergranular spacings (less than 0.2 nm) effectively break exchange, while a larger Cr thickness is required to achieve the same effect. Index Terms--Electronic structure, grain boundaries, intergranular exchange, micromagnetic simulation.

A strategy for high-density perpendicular magnetic recording with a soft underlayer is introduced. The approach is based on three concepts: 1) the nonzero magnetic susceptibility of the recording layer; 2) the use of intergranular exchange to partially cancel magnetostatic effects; and 3) a novel head architecture. Micromagnetic simulations involving recording head, soft underlayer, and recording layer are employed to specify a particularly advantageous design. It is shown that the expected density approaches 1 Tbit/[in.sup.2]. Index Terms--High-density perpendicular recording, intergranular exchange, micromagnetics, permeability.

A system including a perpendicular recording head, a soft underlayer, and a recording layer has been studied using a micromagnetic simulation. The model uses Voronoi cells to represent the recording layer and cubic cells for the soft underlayer and head. The total field consists of the magnetostatic interaction field, the demagnetization field, the exchange field, the anisotropy field, and the field generated by the nontip region of the head. The geometrical configuration of the pole tips and soft underlayer was optimized for performance at 100 Gb/[in.sup.2]. It is demonstrated that high anisotropy fields in the soft underlayer have only small effects on peak fields and gradients. This suggests that low permeability underlayers are an effective way of combating stray field effects. Simulations of the recording layer show the effects of increasing anisotropy on reducing trackwidth. We find a large increase in the perpendicular recording field caused by the permeability of the recording layer exceeding that of free space. This should greatly aid the achievement of adequate recording fields at high density. Index Terms--Micromagnetics, perpendicular recording, soft underlayer.

Developing a predictive understanding of the exchange biasing of a ferromagnet (FM) by its interaction with an antiferromagnet (AF) is a long-standing problem of great technological and scientific interest. Several competing theories to explain the FM/AF coupling have been proposed in the literature but a quantitative application of these theories to a particular FM/AF pair with industrial relevance has been lacking. In this work, we investigate the specific system of NiFe and polycrystalline NiMn using a micromagnetics approach. The NiFe is represented by an array of uniformly magnetized cubes with two-dimensional periodic boundary conditions, i.e., an infinite slab. We incorporate appropriate treatments of the magnetostatic interaction, the exchange interaction within the FM, and the external applied field. We include the presence of the polycrystalline NiMn by an additional term that represents the energy of direct coupling to a NiMn grain. We consider that some NiMn grains are hysteretic as the applied field is rotated. We calculate a hysteresis loop that shows an exchange bias of 272 Oe and an enhanced coercivity of 121 Oe. These results compare favorably to the relevant experiments. We believe that this is the first demonstration of such agreement. Index Terms--Exchange bias, ferromagnet-antiferromagnet bi-layers, micromagnetics, unidirectional anisotropy.

Use of the layer Korringa-Kohn-Rostoker electronic structure method helps derive the first-principles values of the magnetocrystalline anisotropy energy of superlattices having imperfect interfaces. A symmetry model enables the simulation of interdiffusion in two specific ways. The model also includes the anisotropy estimates for imperfect and perfect interfaces, indicating that these defects reduce the magnetic anisotropy of the lattices.

Electronic structure calculations have been used to predict the magnetic anisotropy of Co/Pd, Co/Pt, Co/Cu, Fe/Pt and Fe/Ag superlattices. In the case of Co/Pd and Co/Pt, the magnetic anisotropy has been analyzed as a deconvolution of volume and interface contributions. The surprising experimental result of an orientation independent interface anisotropy of 0.63 + or - 0.05 ergs/cm squared for Co/Pd superlattices is also predicted by theory. The theoretical interface anisotropy was found to be 0.62 + or - 0.06 ergs/cm squared, in close agreement with experiment. This result is not universally observed, and based upon calculations for strained and unstrained superlattices appears to be a consequence of the degree of strain found in the Co/Pd system. A symmetry derived model based upon summing L(M.R) squared pair interactions accurately reproduces the observed anisotropy, and the dependence upon atomic constituents, strain and growth direction.

Exchange-coupled composite (ECC) media consisting of hard and soft coupled regions has been predicted to exhibit attempt frequencies that are much larger than conventional perpendicular media due to the presence of two degrees of freedom. As a result, adjacent track erasure (ATE) and archivability are adversely affected, whereas writability is significantly enhanced due to thermal fluctuation assisted recording. Recording heads for ECC and perpendicular media, designed dimensionally for recording at 250 Gbits/[In.sup.2], are evaluated within this context. In comparison, recording on ECC media is shown to yield about a factor 2 advantage in areal density. Index Terms--Attempt frequency, exchange-coupled composite (ECC) media, perpendicular recording, thermal fluctuations.

A writer is designed for 10-nm-thick exchange coupled composite (ECC) media. At the air bearing surface (ABS), the writer is 60 nm x 60 nm. Down track notches, cross track flares, and side shields are employed. A recording density of 1.18 Tb/[in.sup.2] is achieved based on the write field profile. The bit aspect ratio (BAR) is estimated to be 8.9. Index Terms--Exchange coupled composite (ECC) media, perpendicular recording, perpendicular writer.

An analytic formula to predict the bit transition shift due to the magnetostatic field generated by neighboring written tracks is derived. In order to test this theory, we have employed a micromagnetic simulation including recording head, soft underlayer and Voronoi ceil-based recording layer. This neighbor-induced transition shift scales worse than linearly with the density of the recording medium, reaching ~70% at 1 terabit/[in.sup.2] in worst case scenarios such as de-erased media. Index Terms--Micromagnetics, neighbor-induced transition shift (NITS), perpendicular recording.

Two of the most publicized methods for anisotropy field dispersion characterization, the M-H loop method and the complex transverse susceptibility (TS) method, are evaluated with micromagnetic simulation. For the M-H loop method, the measured parameter is found to be dependent on grain saturation magnetization and easy axis dispersion, but only weakly dependent on intergranular exchange. It also depends on the dispersion of the anisotropy field as originally proposed. For the complex TS method, the technique is calculated to be most dependent on the intergranular exchange and exhibit little dependence on microstructure. Index Terms--Anisotropy field dispersion, micromagnetics, perpendicular recording, perpendicular recording media.

The life time of stored data depends on the storage density as well as the physical properties and microstructure of the media. Perpendicular media for ultra-high density recording needs to have high anisotropy to withstand thermal instabilities over long time. In this study, we used a micromagnetic model based on a scaling method to numerically calculate the percentage of magnetic decay caused by thermal fluctuations after ten years. Realistic grain configurations for 1 Tbit/[in.sup.2] and 125 Ghit/[in.sup.12] recording were used to seek the critical grain magnetization and anisotropy field of magnetic media that are thermally stable, for ten years. For less than 10% decay, an [H.sub.K] of 20 kOe and [M.sup.grain.sub.S] of 600 emu/[cm.sup.3] is required. Alternatively, [H.sub.K] can be reduced to 16 kOe if [M.sup.grain.sub.S] is 800 emu/[cm.sup.3]. Index Terms--Micromagnetics, perpendicular recording, perpendicular recording media, thermal decay.

The fabrication of CoB/Pd multilayers for reducing the intergranular exchange and for inhibiting the grain growth at elevated temperature is discussed. An areal recording density of 10.92 Gb/in(super 2) at bit-error-rate (BER) of 10(super -6) with a potential of 30 Gb/in(super 2) is observed in the CoB/Pd multilayer perpendicular media.

The characteristics of perpendicular recording media with a soft underlayer are examined with the help of a readback model. The media signal to noise ratio (SNR) declines by about 4.7 dB due to cluster formation with areas equal to about three times the grain size.

A new scaling technique has been used to forecast bit decay over long time scales. A comparison of a longitudinal film with a perpendicular film with an identical grain configuration indicates that the perpendicular film is more thermally stable at high recording densities.

Two magneto-optic media configurations, which used a traditional bias magnet for light intensity modulated-direct overwrite, were proposed. The first media configuration comprised an intermediate layer and a memory layer, while the second contained two magnetic layers that utilized an intermediate soft magnetic layer for exchange coupling.

Theoretical expressions characterizing magnetic anisotropy in strained, fcc, bcc and simple cubic superlattices were presented. The expressions were based on summing pair interactions using the potential (MxR)squared, where M is the magnetization and R represents the vector connecting the two atoms. The theory was able to predict the orientation independence of the interface anisotropy in Co/Pd superlattices.

The article presents a new approach, which employs the numerical micromagnetics for the optimization of the magnetic anisotropy and applied fields for hyperthermia applications.

A hybrid soft underlayer (H-SUL) structure to obtain optimized topographic, microstructural, magnetic, and recording properties of perpendicular recording media is presented. The results demonstrated that the H-SUL scheme could be used to improve writing field effectiveness and increase field gradient along down-track and cross-track directions.

Micromodeling is used for examining the remnant field of a single pole type (SPT) writer with both cross and down track flares. The studies have shown that this design has reduced the remnant field considerably and has produced both a high write field and a square shaped footprint.

The effect of the intragranular exchange parameter, A, on the switching of exchange-coupled composite (ECC) media is studied using a magnetic approach. The results reveal that the coercivity of ECC media increases less rapidly with sweep rate than it does with perpendicular media.

The composite perpendicular magnetic recording (PMR) media is fabricated by combining a nanogranular FeSiO soft layer and a [Co/PdSi]n hard layer. The PdSi spacing layer (0-4 nm) is used to study the exchange coupling effects between the FeSiO(5 nm) and the [Co(0.26 nm)/Pd(1 nm)]14 layers in the composite films.

An energy minimization and balancing approach is adopted to predict the occurrence of spike noise by obtaining estimates of the magnetostatic and total wall energy of a soft underlayer (SUL) for a given configuration of domain walls. The findings indicate that single-layer SULs are usually sources of spike noise unless their saturation magnetization is below 70-100 emu/cc.

A perpendicular recording head for an areal density of 1 Tbit per square using a self-consistent three-dimensional (3D) micromagnetic model is discussed. Finally simulations show that a high perpendicular H(sub k) reduces the flux spreading from the narrow tip, therefore it enhances the recording field.