Microwave and Thermally Driven Spin Currents in Tm3Fe5O12/Pt with Perpendicular Magnetic Anisotropy

Abstract

Ferrimagnetic insulator garnet films play an important role in magnon spintronics where magnon-mediated spin currents are used to carry, transport, and process information. This wave-based computing technologies lead to energetically more efficient devices and allows a decrease in the footprint of computing elements [1]. When a magnetic insulator (MI) film is combined with a non-magnetic (NM) spin current detector material like platinum, it is possible to electrically control the MI’s magnetization via the spin-orbit torque (SOT) effect. If the MI presents a perpendicular magnetic anisotropy (PMA), the electrical current density required to switch the magnetization is lower, and the process is faster. This makes the magnetoresistive random access memories based on SOT (SOT-MRAM) challenge the MRAMs based on the spin-transfer torque effect (STT-MRAM) [2]. Moreover, ferrimagnetic garnets with PMA enables high-speed domain-wall (DW) motion that also can be driven by electrical currents via SOT and are ideal materials for developing efficient DW racetrack memories [3]. Thulium iron garnet (TIG – Tm3Fe5O12) is a good candidate due to its high critical temperature of 549 K, a Gilbert damping of 10-2, and negative magnetostriction constant that favors the control of the PMA [4]. When combined with Pt, TIG/Pt is a reach system for the study of spin waves and the observation of spin-orbit effects. We investigate the generation and detection of magnon-based spin currents driven by microwaves and heat currents via the spin pumping (SPE) and spin Seebeck (SSE) effects in TIG(60 nm)/Pt(4 nm), at room temperature. The TIG film was deposited over GGG (Gd3Ga5O12) substrate using the sputtering technique and presented a flat surface with an RMS roughness of 0.1 nm. The magnetization saturation was ~ 100 emu/cm3, and the Gilbert damping parameter was 0.02. The results showed an effective spin-to-charge conversion via the inverse spin Hall effect (ISHE). It made it possible to detect a micro-voltage at the edges of the Pt film and confirmed high spin transparency of the interface TIG/Pt. The spin Seebeck coefficient was 0.54 μV/K, whereas the ratio between the microwave-driven voltage and the microwave power was 4μV/W.