Parameter space for thermal spin-transfer torque

TL;DR

This paper investigates thermal spin-transfer torque in magnetic tunnel junctions with ultra-thin MgO barriers, demonstrating fabrication, characterization, and the potential for switching using laser-induced temperature gradients.

Contribution

It provides experimental fabrication and characterization of ultra-thin MgO barriers and demonstrates thermal spin-transfer torque switching with laser-generated temperature gradients.

Findings

Tunneling magneto resistance ratios of 55-64% for 3-4 monolayer barriers

Critical current for switching is 0.2 MA/cm$^2$

Temperature gradients of 20 K enable thermal switching

Abstract

Thermal spin-transfer torque describes the manipulation of the magnetization by the application of a heat flow. The effect has been calculated theoretically by Jia et al. in 2011. It is found to require large temperature gradients in the order of Kelvins across an ultra thin MgO barrier. In this paper, we present results on the fabrication and the characterization of magnetic tunnel junctions with 3 monolayer thin MgO barriers. The quality of the interfaces at different growth conditions is studied quantitatively via high-resolution transmission electron microscopy imaging. We demonstrate tunneling magneto resistance ratios of up to 55% to 64% for 3 to 4 monolayer barrier thickness. Magnetic tunnel junctions with perpendicular magnetization anisotropy show spin-transfer torque switching with a critical current of 0.2 MA/cm$^2$. The thermally generated torque is calculated ab initio using the Korringa-Kohn-Rostoker and non-equilibrium Green's function method. Temperature gradients generated from femtosecond laser pulses were simulated using COMSOL, revealing gradients of 20 K enabling thermal spin-transfer-torque switching.