Parameter Space for Thermal Spin-Transfer Torque

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.

Time-resolved measurement of the tunnel magneto-Seebeck effect in a single magnetic tunnel junction

“…10, 16 The temperature difference across the 1.5 nm MgO layer resulting from the simulations is used in section IV A in combination with the measured voltage to calculate the Seebeck coefficients. …”

“…In non-local spin valves, thermally driven spin injection was discovered 13 and Peltier and Seebeck effects were studied 14 . The number of these new effects, combined with the proposed thermal spintransfer torque 15,16 might enable the fabrication of thermally driven Magnetoresistive Random Access Memory (MRAM) and other spintronic devices.…”

Perspective: Ultrafast magnetism and THz spintronics

“…Under different bias-voltages, the spin-dynamics have been studied using ultrafast lasers in search of a modification of the ultrafast demagnetization. 55 Spin-transfer torque driven by extreme temperature gradients seems feasible, 56,57 as indicated by researches published so far. 58,59 New concepts in spintronic devices focus on a more compact version of the magnetic device structures.…”

Thermoelectricity and disorder of FeCo/MgO/FeCo magnetic tunnel junctions

“…The TMR ratios calculated for barriers with different thicknesses are compared with experimental results in Table I. The thinnest MgO barrier that can currently be grown coherently comprises three ML [23,24]. In experiments [25], TMR ratios can be maximized through controlled annealing and other grow conditions, approaching our theoretical values for the clean interfaces.…”