Strain-induced magnetic damping anomaly in La${}_{1-x}$Sr${}_x$MnO${}_3$ ($x=0.3$-$0.5$) thin films

Abstract

Magnetic properties of La${}_{1-x}$Sr${}_x$MnO${}_3$ (LSMO) are highly sensitive to various factors such as the Sr doping level $x$, lattice strain, and oxygen stoichiometry due to the strongly correlated nature of $3d$ electrons. For the development of energy-efficient spintronic devices with ultra-low magnetic damping of LSMO, a thorough understanding of its complex magnetization dynamics is of great importance. In this work, we have measured ferromagnetic resonance of LSMO thin films on Nb-doped SrTiO${}_3$ (Nb-STO) substrates over a wide temperature and frequency range and observed an anomalous increase in the Gilbert damping constant and a decrease in the effective saturation magnetization at temperatures below 100 K. The anomalies become more pronounced as the LSMO thickness decreases while they are not observed for LSMO on (LaAlO${}_3$)${}_{0.3}$(Sr${}_2$TaAlO${}_6$)${}_{0.7}$ substrates with relatively small epitaxial strain. The results suggest that the epitaxial strain-induced magnetically dead layer at the LSMO/Nb-STO interface acts as a spin sink and leads to the anomalies in the magnetization dynamics.

15 pages, 8 figures