Direct Detection of Transient Spin Pumping during Phase Transition of FeRh

Abstract

The dynamics of magnetization generates a spin current, which is referred to as spin pumping [1]. The spin pumping has been intensively studied because it can be utilized in quantifying spin related parameters, such as spin Hall angle, spin diffusion length and spin mixing conductance [2, 3]. In ferromagnet (FM) / heavy metal (HM) layers, which has been a central focus of research during last decade [2-4], the magnetization dynamics of FM generates a spin current in the HM layer, and the spin current is converted into the tangible charge current via inverse spin Hall effect (ISHE) [2-4]. However, the spin pumping efficiency is still low to be used directly for spintronic applications.Here we demonstrate a giant spin pumping induced by a phase transition of FeRh. FeRh is metallic alloy with CsCl structure which undergoes a phase transition from antiferromagnetic to ferromagnetic phase near 370 K [5]. We measured the transient ISHE voltage in FeRh/Pt bi-layer and found that the spin pumping signal appears during the phase transition of FeRh. Notably, the observed spin pumping signal is at least 2 orders of magnitude larger than those of previous reports [6, 7], suggesting that the spin pumping can be utilized in spintronic applications, e.g., magnetization switching [8]. The large transient spin pumping signal is ascribed to the total angular momentum change between antiferromagnet and ferromagnet during the phase transition, which accompanies the sign change of the exchange interaction. Our work provides a novel method to generate a large spin current, which could be utilized in spintronics application.