Interplay of large two-magnon ferromagnetic resonance linewidths and low Gilbert damping in Heusler thin films

Abstract

We report on broadband ferromagnetic resonance linewidth measurements performed on epitaxial Heusler thin films. A large and anisotropic two-magnon scattering linewidth broadening is observed for measurements with the magnetization lying in the film plane, while linewidth measurements with the magnetization saturated perpendicular to the sample plane reveal low Gilbert damping constants of (1.5 ± 0.1) × 10 −3 , (1.8 ± 0.2) × 10 −3 , and < 8 × 10 −4 for Co2MnSi/MgO, Co2MnAl/MgO, and Co2FeAl/MgO, respectively. The in-plane measurements are fit to a model combining Gilbert and two-magnon scattering contributions to the linewidth, revealing a characteristic disorder lengthscale of 10-100 nm. arXiv:1909.02738v1 [cond-mat.mtrl-sci]

Magnetoelastic interactions and magnetic damping in Co2Fe0.4Mn0.6Si and Co2FeGa0.5Ge0.5 Heusler alloys thin films for spintronic applications

“…6 . It can be seen that the ΔH TMS contribution to the total ∆H is relatively strong, which is typical for in-plane broad band FMR experiments if the effective magnetic damping parameter is relatively small 97 .

Figure 6 Resonance line full width at half maximum for the 30 nm CFMS sample without additional silver buffer layer as a function of frequency at room temperature.

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“…However there are many mechanisms that may be responsible for the dissipation of magnetic energy in thin magnetic films, thus the full width at half maximum in registered FMR spectra can include the following contributions 85 : ΔH = ΔH 0 + ΔH TMS + ΔH G+sp , where ΔH 0 denotes the frequency-independent sample inhomogeneity contribution, ΔH TMS denotes the two-magnon scattering contribution (TMS), while the last term ΔH G+sp contains the spin pumping (SP) and Gilbert damping contributions and is proportional to α eff × f , where α eff is an effective magnetic damping parameter and f is the FMR frequency 85 . Considering the TMS mechanism is especially important for the samples characterized by low Gilbert damping when the external magnetic field is parallel to the film 97 .…”

Dependence of Nonlinear Response and Magnon Scattering on Damping

“…For the intrinsic contribution, doping elements with large atomic number induces large damping through an enhanced spin-orbit interaction [18]- [20]. For the extrinsic contribution, the impurity introduces two magnon scattering [14], [28]. Since the two magnon scattering has a trivial dependence on power, the damping constant α is proportional to the linewidth in the linear regime.…”

“…However, this general picture leaves many ambiguities, particularly with respect to engineering successful device designs. The model uses experimentally inaccessible factors, for example, a relaxation rate with implicit dependence on the wavevectors, while a wavevector independent constant, damping constant α, is commonly measured [14]- [17] and well-understood [18]- [20]. Also, the models present the critical amplitude, an indirect approach to the nonlinear response, while the characteristics commonly used in microwave applications are the power threshold and the nonlinear susceptibility.…”

Nonlinear Magnon Scattering Mechanism for Microwave Pumping in Magnetic Films

“…A ∼ mm 2 cleaved piece of the sample was placed face-down over the center line of the coplanar waveguide with ground (similar to that used in Ref. [30]). The center line width of the CPW is 1.2 mm and the length is 25.4 mm.…”