Spin pumping from permalloy into uncompensated antiferromagnetic Co doped zinc oxide

Abstract

Heterostructures of Co-doped ZnO and Permalloy were investigated for their static and dynamic magnetic interactions. The highly Co-doped ZnO is paramagnetic at room temperature and becomes an uncompensated antiferromagnet at low temperatures, showing a narrowly opened hysteresis and a vertical exchange-bias shift even in the absence of any ferromagnetic layer. At low temperatures in combination with Permalloy, an exchange bias is found causing a horizontal as well as a vertical shift of the hysteresis of the heterostructure together with an increase in coercive field. Furthermore, an increase in the Gilbert damping parameter at room temperature was found by multifrequency ferromagnetic resonance (FMR), indicating spin pumping. Temperature dependent FMR shows a maximum in magnetic damping close to the magnetic phase transition. These measurements also evidence the exchange-bias interaction of Permalloy and long-range ordered Co-O-Co structures in ZnO, which are barely detectable by SQUID due to the shorter probing times in FMR.