Magnetization dynamics and its scattering mechanism in thin CoFeB films with interfacial anisotropy

Abstract

Studies of magnetization dynamics have incessantly facilitated the discovery of fundamentally novel physical phenomena, making steady headway in the development of magnetic and spintronics devices. The dynamics can be induced and detected electrically, offering new functionalities in advanced electronics at the nanoscale. However, its scattering mechanism is still disputed. Understanding the mechanism in thin films is especially important, because most spintronics devices are made from stacks of multilayers with nanometer thickness. The stacks are known to possess interfacial magnetic anisotropy, a central property for applications, whose influence on the dynamics remains unknown. Here, we investigate the impact of interfacial anisotropy by adopting CoFeB/MgO as a model system. Through systematic and complementary measurements of ferromagnetic resonance (FMR) on a series of thin films, we identify narrower FMR linewidths at higher temperatures. We explicitly rule out the temperature dependence of intrinsic damping as a possible cause, and it is also not expected from existing extrinsic scattering mechanisms for ferromagnets. We ascribe this observation to motional narrowing, an old concept so far neglected in the analyses of FMR spectra. The effect is confirmed to originate from interfacial anisotropy, impacting the practical technology of spin-based nanodevices up to room temperature.

Femtosecond laser-heating effect on the magnetization dynamics in perpendicularly magnetized Ta/CoFeB/MgO film

“…ratio a Considering the proportional correlation between the SOC and damping parameter, it is reasonable to define a damping term inter a that arises from the interfacial SOC. As also recently demonstrated by Okada et al [35], the interfacial PMA is found to be correlated with the Gilbert damping manifested by monitoring the ferromagnetic resonance linewidths with varying temperatures and sample thickness. According to the…”

Enhanced magneto-optical Kerr effect at Fe/insulator interfaces

“…The Kerr angle θ Kerr is proportional to the ratio σ xy /σ xx by definition, and a large θ Kerr develops at Fe/insulator interfaces with decreasing σ xx and large σ xy . Our results show an efficient way to design novel devices, such as ultrathin ferromagnetic films 65 and ferromagnetic nanogranular films 66,67 by manipulating the substantial spin-orbit coupling effect at metal/insulator interfaces without using heavy elements.…”

Tunable magnetization relaxation of Fe2Cr1−xCoxSi half-metallic Heusler alloys by band structure engineering

“…Using out-of-plane FMR measurements, we determined the intrinsic damping by purposely suppressing the extrinsic contributions causing non-linear frequency dependence [16,17,44]. In practical applications, the relaxation mechanism for magnetization in the film-plane is of primary importance.…”

“…Still, reducing and tuning magnetic damping in metallic materials can be difficult due to magnon scattering by high density conduction electrons [10]. Notably, the lowest reported damping for CoFeB, the material employed by industry for MRAM development, is approximately 0.004 [16,17].…”