Current-driven magnetic resonances in La_1-xNa_xMnO₃

In recent years, the inverse spin Hall effect (ISHE) in ferromagnetic/non-magnetic bilayers has become an indispensable tool to characterize the nature of the interface between them[1]. In a typical ISHE experiment, the magnetization of a ferromagnetic film placed on a microwave current-carrying coplanar waveguide or resonant cavity is driven into resonance while externally dc magnetic field applied is slowly swept and the spin current pumped into the adjacent non-magnetic metal is converted into a charge current by spin-orbit interaction and detected as a dc voltage in the non-magnetic film. However, reports on the electrical detection of magnetic resonance in bulk materials are very scarce as of now[2]. Here, we report the electrical detection of ferromagnetic and paramagnetic resonances in bulk ceramic oxides of Na-doped LaMnO₃ by passing microwave current directly through them. As Na is monovalent, double the number of holes are doped when La³⁺ is partially replaced by Na¹⁺ in La_1-xNa_xMnO₃ in contrast to an equal number of holes doped by divalent cation (Sr^2+, Ca²⁺, etc) substitution[3]. Thus, double exchange interaction becomes effective for small concentrations of Na and as a result La_1-xNa_xMnO₃ changes from antiferromagnetic to ferromagnetic at room temperature for x ≥ 0.1. We measured high-frequency magnetoresistance and magnetoreactance in x = 0.0-0.3 samples at room temperature for frequencies varying from f = 0.01 MHz to 3 GHz. Unlike the dc magnetoresistance which is negative in sign, the high-frequency magnetoresistance increases with the field and exhibits a peak at a specific field H_r which increases with the frequency of of the current. Analysis of the microwave magnetoresistance data led us to conclude that the observed features are caused by current-driven paramagnetic resonance in x ≤ 0.1 and ferromagnetic resonance for x ≥ 0.15 samples.



[1] M. Harder, Y. Gui, and C.-M. Hu, Phys. Rep. 661, 1 (2016).

[2] U. Chaudhuri et al., Appl. Phys. Lett. AIP Advances, 9, 125035 (2019).

[3] X. Zhu et al., J. Alloy & Comp. 459, 83 (2008); A. Ghosh et al., J. Appl. Phys.125, 153902(2019).