Magnetism and spin-dependent transport phenomena across Verwey and Morin transitions in iron oxide/Pt bilayers

Abstract

Understanding the influence of phase coexistence and phase transitions on spin transport properties in a ferromagnet/heavy metal (FM/HM) system is of utmost importance for spintronics. Here, we report a comprehensive investigation of the magnetic and spin transport properties of biphase iron oxide (BPIO = α-Fe2O3 + Fe3O4)/Pt films over a wide temperature range, 10K≤T≤300K. In-plane (IP) and out-of-plane (OOP) magnetometry and radio frequency transverse susceptibility measurements confirm the characteristic features of the Verwey and Morin transitions at TV ∼ 120 K and TM ∼ 200 K, respectively. Anisotropic magnetoresistance (AMR) is observed in the BPIO film, which arises mainly from the spin polarized tunneling of conduction electrons between neighboring uniformly magnetized grains through the resistive grain boundary. Spin Hall magnetoresistance (SMR) and spin Hall anomalous Hall effect (SH-AHE) are detected in the BPIO/Pt films. Around the TV, the temperature evolution of SMR shows a sharp maximum, while SH-AHE exhibits a steep decrease. Both SMR and SH-AHE are strongly susceptible to the Verwey transition but the Morin transition, indicating that the interfacial magnetism of our BPIO/Pt film is dominated by the Fe3O4 phase rather than the α-Fe2O3 phase.