Magnetic anisotropy, damping, and interfacial spin transport in Pt/LSMO bilayers

Abstract

We report ferromagnetic resonance measurements of magnetic anisotropy and damping in epitaxial La0.7Sr0.3MnO3 (LSMO) and Pt capped LSMO thin films on SrTiO3 (001) substrates. The measurements reveal large negative perpendicular magnetic anisotropy and a weaker uniaxial in-plane anisotropy that are unaffected by the Pt cap. The Gilbert damping of the bare LSMO films is found to be low α = 1.9(1) × 10−3, and two-magnon scattering is determined to be significant and strongly anisotropic. The Pt cap increases the damping by 50% due to spin pumping, which is also directly detected via inverse spin Hall effect in Pt. Our work demonstrates efficient spin transport across the Pt/LSMO interface.

Spin transport and dynamics in all-oxide perovskite La2/3Sr1/3MnO3/SrRuO3

“…Figure 4(b) summarizes the dependence of α on SRO-thickness, t SRO . For LSMO single-layer films we find α = (0.9 ± 0.2)×10 −3 , which is on the same order as previous reports of LSMO thin films [21][22][23]26 . This low damping is also comparable to the values reported in Heusler alloy thin films 45,46 and may arise from LSMO can thus be an efficient source of spin current generated resonantly by microwave excitation.…”

“…High crystallinity of the film gives rise to a nonnegligible in-plane magnetocrystalline anisotropy field, which manifests in an in-plane angular dependence of H FMR and introduces another adjustable parameter in the nonlinear Kittel equation for in-plane FMR. Moreover, ∆H in in-plane FMR of epitaxial thin films often depends strongly on the magnetization orientation and exhibits nonlinear scaling with respect to frequency due to two-magnon scattering, a non-Gilbert mechanism for damping 23,[32][33][34][35][36][37] . We indeed find that damping of LSMO in the in-plane configuration is anisotropic and dominated by two-magnon scattering.…”

“…A well-known non-Gilbert damping mechanism in highly crystalline ultrathin magnetic films is two-magnon scattering 23,[32][33][34][35][36][37]40,61,62 , in which uniformly precessing magnetic moments (a spin wave, or magnon mode, with wavevector k = 0) dephase to a k = 0 magnon mode with adjacent moments precessing with a finite phase difference. By considering both exchange coupling (which results in magnon energy proportional to k 2 ) and dipolar coupling (magnon energy proportional to −|k|) among precessing magnetic moments, the k = 0 and k = 0 modes become degenerate in the magnon dispersion relation 61 as illustrated in Fig.…”

“…Among these complex oxides, La 2/3 Sr 1/3 MnO 3 (LSMO) and SrRuO 3 (SRO) are attractive materials for epitaxial, lattice-matched spin-source/spin-sink heterostructures. LSMO, a metallic ferromagnet known for its colossal magnetoresistance and Curie temperature of >300 K, can be an excellent resonantly-excited spin source because of its low magnetization damping [21][22][23][24][25][26] . SRO, a room-temperature metallic paramagnet with relatively high conductivity 27 , exhibits strong spin-orbit coupling 28 that may be useful for emerging spintronic applications that leverage spin-orbit effects [2][3][4] .…”

“…However, it is generally a challenge to separate the inverse spin-Hall signal from the spin rectification signal, which is caused by an oscillating magnetoresistance mixing with a microwave current in the conductive magnetic layer [29][30][31] . Moreover, while the spin-mixing conductance is typically estimated from the enhancement in the Gilbert damping parameter α, the quantification of α is not necessarily straightforward in epitaxial thin films that exhibit pronounced anisotropic non-Gilbert damping 23,[32][33][34][35][36][37] . It has also been unclear how the Gilbert and non-Gilbert components of damping in LSMO are each modified by an adjacent SRO layer.…”