Near- T_c Ferromagnetic Resonance and Damping in FePt -Based Heat-Assisted Magnetic Recording Media

Abstract

High-temperature ferromagnetic resonance (FMR) in FePt-based media materials was studied for the first time. The FMR linewidth (ΔH) as a function of temperature (T), field angle (θ H), and the volume fraction (x) of carbon in the material were determined, and the effective Gilbert damping constant and the Bloch-Bloembergen relaxation time were estimated. The data suggest that at temperatures 10-45 K below the Curie temperature, two-magnon scattering and spin-flip magnon-electron scattering make comparable contributions to ΔH. With a decrease in T, ΔH increases due to enhancement of the two-magnon scattering. ΔH can be tuned via varying x and shows a maximum at θ H ≈45° when varying θ H .

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

“…Clearly, the magnon contributions to the damping give rise to an increase of the damping with increasing temperature, which is inconsistent with the results of Richardson et al [15]. However, the experiments described in ref [15] give the temperature dependence of the linewidth which likely has contributions from inhomogeneous line broadening arising from dispersion of magnetic properties. In the following we develop a model accounting for the inhomogenous line broadening which gives good qualitative agreement with the experiments.…”

“…It is important to note that these values include both intrinsic and extrinsic contributions, the purely intrinsic damping being even smaller than the reported values [13,14]. Recently, Richardson et al [15] reported experimental measurements of damping at elevated temperatures showing an unexpected decrease of damping with temperature. A decrease in the effective damping can be crucial in HAMR, as this can increase the switching time, affect the signal to noise ratio and negatively impact the performance of HAMR.…”

“…Richardson et al [15] have shown that, in the case of a granular system of FePt, close to T C a decrease in damping/linewidth is observed. This effect was attributed to the competition between two-magnon scattering and spin-flip magnon electron scattering.…”

Interlayer Exchange Coupling in Magnetic Hard-Soft Bilayered Structures

“…The FMR measurements included (1) frequencydependent FMR measurements using a co-planar waveguide (CPW) and a vector network analyzer (VNA) at room temperature 16 , 17 and (2) temperaturedependent FMR measurements using a microwave cavity. 18 Figure 2 shows the experimental configuration and representative data for frequencydependent FMR measurements. Figure 2(a) sketches the experimental setup, which consists mainly of a CPW device and a VNA.…”

“…More details about this approach are provided in Ref. [18]. Figure 4(b) presents the FMR data (blue dots) measured at T=373 °C on a sample where the soft layer was made of a 5.0-nm-thick Co film.…”