Spin wave excitations in exchange biased IrMn/CoFe bilayers

Using an atomistic spin model, we have simulated spin wave injection and propagation into antiferromagnetic IrMn from an exchange coupled CoFe layer. The spectral characteristics of the exited spin waves have a complex beating behavior arising from the non-collinear nature of the antiferromagnetic order. We find that the frequency response of the system depends strongly on the strength and frequency of oscillating field excitations. We also find that the strength of excited spin waves strongly decays away from the interfacial layer with a frequency dependent attenuation. Our findings suggest that spin waves generated by coupled ferromagnets are too weak to reverse IrMn in their entirety even with resonant excitation of a coupled ferromagnet. However, efficient spin wave injection into the antiferromagnet is possible due to the non-collinear nature of the IrMn spin ordering

A multiscale model of the effect of Ir thickness on the static and dynamic properties of Fe/Ir/Fe films

The complex magnetic properties of Fe/Ir/Fe sandwiches are studied using a hierarchical multi-scale model. The approach uses first principles calculations and thermodynamic models to reveal the equilibrium spinwave, magnetization and dynamic demagnetisation properties. Finite temperature calculations show a complex spinwave dispersion and an initially counter-intuitive, increasing exchange stiffness with temperature (a key quantity for device applications) due to the effects of frustration at the interface, which then decreases due to magnon softening. Finally, the demagnetisation process in these structures is shown to be much slower at the interface as compared with the bulk, a key insight to interpret ultrafast laser-induced demagnetization processes in layered or interface materials

Micromagnetic modeling of the heat-assisted switching process in high anisotropy FePt granular thin films

The dynamic process of assisted magnetic switchings has been simulated to investigate the associated physics. The model uses a Voronoi construction to determine the physical structure of the nanogranular thin film recording media, the Landau-Lifshitz-Bloch equation is solved to evolve the magnetic system in time. The reduction of the magnetization is determined over a range of peak system temperatures and for a number of anisotropy values. The results show that the heat-assisted magnetic recording process is not simply magnetization reversal over a thermally reduced energy barrier. To achieve full magnetization reversal (for all anisotropies investigated), an applied field strength of at least 6 kOe is required and the peak system temperature must reach at least the Curie point (T c). When heated to T c, the magnetization associated with each grain is destroyed, which invokes the non-precessional linear reversal mode. Reversing the magnetization through this linear reversal mode is favorable, as the reversal time is two orders of magnitude smaller than that associated with precession. Under these conditions, as the temperature decreases to ambient, the magnetization recovers in the direction of the applied field, completing the reversal process. Also, the model produces results that are consistent with the concept of thermal writability; when heating the media to T c, the smaller grains require a larger field strength to reverse the magnetization

Model of Magnetic Damping and Anisotropy at Elevated Temperatures : Application to Granular FePt Films

An understanding of the damping mechanism in finite-size systems and its dependence on temperature is a critical step in the development of magnetic nanotechnologies. In this work, nanosized materials are modeled via atomistic spin dynamics, the damping parameter being extracted from ferromagnetic resonance (FMR) simulations applied for FePt systems, generally used for heat-assisted magnetic recording media (HAMR). We find that the damping increases rapidly close to TC and the effect is enhanced with decreasing system size, which is ascribed to scattering at the grain boundaries. Additionally, FMR methods provide the temperature dependence of both damping and the anisotropy, which are important for the development of HAMR. Semianalytical calculations show that, in the presence of a grain-size distribution, the FMR line width can decrease close to the Curie temperature due to a loss of inhomogeneous line broadening. Although FePt has been used in this study, the results presented in the current work are general and valid for any ferromagnetic material

Magnetic Switching in BPM, TEAMR, and Modified TEAMR Using Dielectric Underlayer Media

In this paper, we study the coercivity of bit-patterned media, trapping electron-assisted magnetic recording (TEAMR), and modified TEAMR (M-TEAMR) media using a dielectric underlayer. The VAMPIRE magnetic simulator is used to model three structures of recording bits and to study the M - H loops using an atomistic spin model. The results show that the magnetic switching reduction in M-TEAMR and TEAMR depends on the bit size. The percentage of magnetic switching reduction in M-TEAMR is also larger than TEAMR for all bit sizes. For a bit size of 1.6× 1.6 × 3.2 nm3, the percentage of magnetic switching reduction in M-TEAMR is approximately four times higher than that in TEAMR