Quantitative Evaluation of Voltage-Induced Magnetic Anisotropy Change by Magnetoresistance Measurement

Abstract

We investigated the voltage-induced perpendicular magnetic anisotropy change in an epitaxial magnetic tunnel junction (MTJ) with an ultrathin FeCo layer. Tunneling magnetoresistance (TMR) curves were measured under various bias voltage applications for different FeCo thicknesses. Clear changes in the shape of TMR curves were observed depending on the voltage-controlled perpendicular magnetic anisotropy. By evaluating the relative angle of two ferromagnetic layers, we could estimate the anisotropy energy change quantitatively. The realization of voltage-induced anisotropy change in the MTJ structure makes it possible to control the magnetization dynamics, leading to a new area of electric-field-based spintronics devices. #

Electric-field control of domain wall motion in perpendicularly magnetized materials

“…Both these parameters depend on the magnetic properties of the sample, which are altered by the electric field. In the Supplementary Methods, we show that the exponent in equation (1) scales approximately linearly with the voltage, assuming that the perpendicular anisotropy scales linearly with voltage, which is supported by Shiota et al 13 , and pinning is caused by variations in the anisotropy over the sample. The derivation shows that a voltage-induced change in PMA, be it through a change of the surface anisotropy or the saturation magnetization, should be at the origin of the demonstrated sensitivity of v DW to the electric field.…”

“…This effect has first been demonstrated in semiconducting magnetic materials at cryogenic temperatures 5 , and has more recently been demonstrated at room temperature in ferromagnetic metals 6,7 . The prospect of low-power voltage-controlled magnetic switching has recently led to a large number of experimental observations of the effect in various materials [6][7][8][9][10][11][12][13][14][15][16][17] , demonstrating the manipulation of properties such as magnetic anisotropy 7 , saturation magnetization 12 , and Curie temperature 17 . Theoretical studies into the nature of the electric-field effect suggest that charging of the ferromagnet/ oxide interface changes the occupation of surface states, modifying the net anisotropy 18 .…”

Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet

“…Despite the limited penetration depth of an E-field in metals, the charge induced at the metal/dielectric interface on the topmost atomic layers is sufficient to modify the surface magnetic anisotropy energy (MAE) by a non negligible amount in ultrathin ferromagnetic layers as suggested by electronic structure calculations [9][10][11] . This has a particular impact in systems where the different anisotropy contributions almost cancel each other out, resulting in a large relative variation of the total effective MAE when the surface contribution is modified with the voltage [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . We have studied here a Pt/Co/AlOx sample where the surface MAE could be varied in two ways : charging the metal/dielectric interface and modifying its oxidation.…”

Ferroelectric control of magnetic domains in ultra-thin cobalt layers

“…10 Thus, a weak change of charge density induced by the electric field at the extremely narrow interface-adjacent layer is sufficient for a substantial change of coercivity, 5-7 T C , 8,9 and magnetic domain kinetics. 11,12 In context of these findings, the ferroelectric/ferromagnetic heterostructures become of interest for electronic elements operational within the conventional temperature range. First principles calculations performed for multilayers combining ultra-thin Co layers and P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) ferroelectric copolymer confirm an appreciable multiferroic coupling.…”

“…The other implication of the field-effect-tuned MAE is a possibility to change the domain wall (DW) velocity. [10][11][12] In order to directly observe the impact of the ferroelectric gate polarization on the DW propagation, we study a different area in a thinner part of the Al wedge resulting in a more oxidized Co/AlOx interface and greater MAE. Due to the relatively high MAE, the switching is triggered in a very limited number of reversed domains and develops further through the expansion of these domains (as shown in Movies 3 and 4 in the supplementary material 18 ).…”