Manipulation of magnetization switching and tunnel magnetoresistance via temperature and voltage control.

Houfang Liu,Zhenchao Wen,Peng Guo,Hongxiang Wei,Xiufeng Han,Yang Ji,Ran Wang,Shufeng Zhang,Jiafeng Feng

doi:10.1038/srep18269

Abstract

Magnetization switching between parallel and antiparallel alignments of two magnetic layers in magnetic tunnel junctions (MTJs) is conventionally controlled either by an external magnetic field or by an electric current. Here, we report that the manipulation of magnetization switching and tunnel magnetoresistance (TMR) in perpendicularly magnetized CoFeB/MgO/CoFeB MTJs can be achieved by both temperature and voltage. At a certain range of temperature, coercivity crossover between top and bottom magnetic layers is observed in which the TMR ratio of the MTJs is almost unmeasurable. Furthermore, the temperature range can be tuned reversibly by an electric voltage. Magnetization switching driven by the voltage reveals an unconventional phenomenon such that the voltage driven coercivity changes with temperature are quite different for top and bottom CoFeB layers. A model based on thermally-assisted domain nucleation and propagation is developed to explain the frequency and temperature dependence of coercivity. The present results of controlling the magnetization switching by temperature and voltage may provide an alternative route for novel applications of MTJs based spintronic devices.

Highlights

Electric voltage, exhibiting quasi-linear function; while at low temperature an even function voltage dependence for top CoFeB layer is observed but almost no change in bottom CoFeB layer
A semi-quantitative model of thermal-assisted magnetization reversal qualitatively accounts for the experimental data on the frequency and temperature dependence of the coercive fields of both top and bottom magnetic layers
Two other structures with a single magnetic layer consisting of substrate/Ta(5)/MgO(2)/CoFeB(1.4)/Ta(5) in which CoFeB is on the top of MgO layer (t-CoFeB) and substrate/ Ta(5)/CoFeB(1.2)/MgO(2) /Ta(5) with CoFeB on the bottom of MgO (b-CoFeB) are fabricated for magnetic property studies

Summary

Method

The multilayers of Ta(5)/Ru(10)/Ta(5)/CoFeB(1.2)/MgO(2)/CoFeB(1.4)/Ta(5)/Ru(6), Ta(5)/MgO(2)/CoFeB(1.4)/ Ta(5) (t-CoFeB) and Ta(5)/CoFeB(1.2)/MgO(2)/Ta(5) (b-CoFeB) (all thicknesses in nm) were deposited on oxidized silicon wafer by the sputtering system. The dynamic hysteresis loops of t-CoFeB and b-CoFeB MTJs are measured by a MOKE (magneto-optical Kerr effect) system setup with a 632.8 nm laser beam spot of diameter in tens of microns. The inductance of electromagnet coil is about 90 mH With these parameters, we are able to achieve the amplitude of the ac field more than 1 kOe at 50 Hz. To make the hysteresis loops contain enough points without distortion, a data acquisition (DAQ) card with the acquisition bandwidth up to 2 MHz per channel is used to record periodic magnetic field H and Kerr signal M simultaneously. From low to high temperatures, the hysteresis loops are collected by two sets of procedures: varying the voltage applied to the electromagnet with a gradually increasing amplitude of the external field at a constant frequency, or with a gradually increasing frequency of the external field at a fixed amplitude. Each MOKE signals for dynamics coercivity are averaged by at least 10 cycles

Author Contributions

Findings

Additional Information