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Magnon scattering studies can play a crucial role in revealing fundamental aspects of magnon physics. Due to the nonlinear nature of scattering, such studies are also important for applications ranging from traditional microwave signal processing to novel magnon-based computation. In this work, simulations employing realistic material parameters are used to demonstrate the tunable nature of magnon-based nonlinear properties. The changes are affected through modification of the dispersion relation of the magnetic system. It is demonstrated that the magnon nonlinear response is very sensitive to the sample film thickness while showing a relatively weaker dependence on saturation magnetization. Aside from the contributions to the fundamental understanding of magnons, the results presented are useful for establishing design rules for magnon-based applications. [ABSTRACT FROM AUTHOR]

The thermal distribution of granular media for heat assisted magnetic recording has been explored by the heat Fourier equation; particularly, the effect of the thermal conductivities in the grain boundary has been extensively investigated. When the thermal conductivity is sufficiently small, the grain boundary provides a natural constraint to heat dissipation: the effective in-plane thermal conductivity can be ten times smaller than that of FePt with the decrease limited only by the heat dissipation through the interlayer MgO. For low thermal conductivities in the grain boundary, the out of plane thermal gradient increases sharply owing to the inability of the heat to spread. Therefore, a compromise between power consumption and uniformity of the temperature distribution within grains should be taken into account when optimizing the media design. [ABSTRACT FROM AUTHOR]

Anisotropic exchange has been incorporated in a description of magnetic recording media near the Curie temperature, as would be found during heat assisted magnetic recording. The new parameters were found using a cost function that minimized the difference between atomistic properties and those of renormalized spin blocks. Interestingly, the anisotropic exchange description at 1.5 nm discretization yields very similar switching and magnetization behavior to that found at 1.2 nm (and below) discretization for the previous isotropic exchange. This suggests that the increased accuracy of anisotropic exchange may also reduce the computational cost during simulation. [ABSTRACT FROM AUTHOR]

We have investigated the feasibility of BPM for HAMR via Finite Difference Time Domain and atomistic simulation and we have substantiated the feasibility of 5 Tb/in2 with two filling factors 25% and 56% even when the maximum on-track bit temperature is below the Curie temperature. The success of this underheated switching is attributed to sufficiently low anisotropy instead of reduction of Curie temperature. The temperature gradient in the cross-track direction is almost doubled if the optical head width is reduced by half, indicating the possibility of higher areal densities. Moreover, contrary to continuous media, we also found that the power absorption peaks at the bottom of the bit patterned FePt when the media is illuminated from above, which is probably due to stronger coupling there between FePt and the surrounding materials. [ABSTRACT FROM AUTHOR]

Writing closely spaced tracks in the cross-track direction helps increase the storage density but leads to erasure of the adjacent tracks. This phenomenon is called adjacent track erasure (ATE). This article aims to establish the presence and numerical extent of ATE in different heat-assisted magnetic recording (HAMR) media. We find that thermal exchange coupled composite (ECC) media can be more susceptible to ATE compared with single layer FePt media of equivalent thickness. We implement optimization techniques to reduce the ATE in different media and increase the recording signal to noise ratio (SNR) in this process. While the ATE in single layer FePt media seems to be relatively impervious to changes in the applied field angle, small field angles appear to reduce the ATE for the high $T_{c}$ thermal ECC media. However, small angle also reduces the SNR, leading to the conclusion that 30° actually yields the best SNR even in the presence of overwrite. Introducing a finite intergranular exchange coupling improves the writing performance of the single layer FePt and reduces the ATE. We rigorously calculate the thermal decay constant and use it to evaluate the performance of pulsed laser recording. Finally, we establish a hypothesis that helps explain the presence of ATE in different HAMR media. We believe the ATE is proportional to the thermal stability factor at a temperature just below the write temperature. The proposed hypothesis correctly predicts the ATE in the single layer FePt media assuming coherent rotation. Our results can help increase the HAMR storage density and make HAMR media resistant to the ATE. [ABSTRACT FROM AUTHOR]

Writability of magnetic recording media with high anisotropy constant (Ku) is one of the major challenges encountered in extremely high density recording. A possible avenue to improve writability in perpendicular magnetic recording is to reduce the spacing between the writing head and the soft magnetic underlayer (SUL) or head-to-keeper spacing (HKS). A hybrid layer structure for reducing the HKS between the SUL and the writing head is investigated. The proposed structure makes use of a crystalline SUL with in-plane anisotropy together with an amorphous SUL to form a hybrid SUL (H-SUL). The H-SUL design helps to achieve better surface smoothness, thinner HKS, and good c-axis dispersion for the recording layer while still maintaining small and exchange-decoupled grains. Micromagnetic simulation demonstrates that the H-SUL scheme helps in improving writing field effectiveness and increasing field gradient along down-track and cross-track directions. [ABSTRACT FROM AUTHOR]

It is common to model recording media as interacting coherently rotating magnetic moments, but real materials frequently exhibit perpendicular switching fields less than the anisotropy field and a different angular dependence than theoretically expected. Micromagnetic simulations were performed, which included multiple elements per grain and magnetostatic interactions between elements. Two likely explanations have emerged from this analysis: the existence of low anisotropy regions within the first few atomic layers of the sputtered film or anisotropy gradation throughout the grain thickness. Both explanations offer appropriate coercivity reductions; however, grains including anisotropy gradation display this effect at more realistic values of intragranular exchange. A simplified two element model was fit to the multidomain angle-dependent results in order to find a computationally simple description that can be easily included in a recording simulation. [ABSTRACT FROM AUTHOR]

We have constructed a micromagnetic model to study the exchange coupling between Co (a ferromagnet) and γ-Fe50Mn50 (an antiferromagnet) in a thin film bilayer with (111) texturing. The intention is to compare experimental results with a micromagnetic calculation that is sufficiently sophisticated to realistically model this polycrystalline ferromagnet/antiferromagnet system. The antiferromagnet thickness dependences of exchange bias and enhanced coercivity were simulated at 10 and 300 K and comparison to experiments revealed reasonable agreement. We also examined the antiferromagnet grain size dependence of exchange bias, owing to its relation to the key issue of uncompensated spin density. Simulation finds a linear relationship between exchange bias and inverse grain size for both thermally stable and thermally fluctuating antiferromagnetic grains, but with different intercepts. Experiment also finds a linear dependence, but the extrapolation to infinite diameter reveals an unexpected negative exchange bias. Our results demonstrate the applicability of this form of micromagnetic modeling for multiple phenomena associated with the exchange bias effect. [ABSTRACT FROM AUTHOR]

The intrinsic damping mechanism arising from the magnon–magnon scattering is theoretically studied in three dimensional and two dimensional ferromagnets. We develop an analytic theory, which identifies the three-magnon (in bulk) and four-magnon (in thin films) scattering processes, responsible for rapid relaxation. Micromagnetic simulations are used to confirm the analytic theory predictions, and to investigate the damping in different realistic technologically important systems. For the large angle rotation of magnetization, this intrinsic mechanism can dominate competing linear mechanisms even for rapidly relaxing metals. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]