Increased ferromagnetic resonance linewidth and exchange anisotropy in NiFe/FeMn bilayers

Abstract

In the past investigations, the exchange-biased bilayers show much larger ferromagnetic resonance ͑FMR͒ linewidth than that of single ferromagnetic layer films. However, the mechanism of the large linewidth remains controversial. In this paper, the FMR linewidths of NiFe/FeMn bilayers prepared by dc magnetron sputtering system are systematically studied. Besides the intrinsic damping and magnetic inhomogeneity, the extrinsic relaxation based on two-magnon scattering process should be also considered to explain the strong in-plane angular dependence of the linewidths. The fitting of the out-of-plane angular dependence of the linewidths shows that the intrinsic Gilbert damping effect plays a major role in the increased linewidth in the bilayers. The value of the g factor increases due to the effect of the exchange coupling at the NiFe/FeMn interface, resulting in an enhancement in the Gilbert damping factor G. The fitting results indicate that the line broadening of the exchange-biased films is related to the exchange anisotropy. The effects of FeMn layer thickness, growth sequence of FeMn layer, and temperature on the linewidths further approve this interpretation.

Electrical manipulation of ferromagnetic NiFe by antiferromagnetic IrMn

“…7(c), we show that the enhancement of the spin-angular momentum transfer through the interface is indeed due to the interfacial exchange coupling, as α is proportional to the square of the exchange bias. This dependence also suggest that one of the main damping mechanisms in our samples is the two-magnon scattering at the FM/AFM interface, in agreement with the previous studies [19,41,42]. The exact mechanism of the enhancement of h z is of complex origin due to the strong spin-orbit coupling in the system and the interface magnetic coupling.…”

Micrometer thick soft magnetic films with magnetic moments restricted strictly in plane by negative magnetocrystalline anisotropy

“…thickness. The weak discrepancy of the experimental and calculated data may result from the revised Kittel's equation derived from the LLG equation by neglecting the damping effect [26].…”

“…To quantify this effect and to get the value of the intrinsic magnetocrystalline anisotropy is smallest when the applied magnetic field is parallel to the easy axis and the largest when perpendicular. From published works [13,20], the relationship between the resonance field and the angle H  can be expressed as:…”

Influence of the thickness of an antiferromagnetic IrMn layer on the static and dynamic magnetization of weakly coupled CoFeB/IrMn/CoFeB trilayers

“…For various other applications a fast relaxation is favored, e.g., in magnetoresistive heads [ 24 – 25 ]. The FM/AF exchange coupling is one of the approaches to tune the magnetization relaxation by enhancing the field linewidth Δ H and displacing the resonance field H r [ 26 – 29 ].…”