Giant strain control of magnetoelectric effect in Ta|Fe|MgO

Abstract

The exploration of electric field controlled magnetism has come under scrutiny for its intriguing magnetoelectric phenomenon as well as technological advances in spintronics. Herein, the tremendous effect of an epitaxial strain on voltage-controlled perpendicular magnetic anisotropy (VPMA) is demonstrated in a transition-metal|ferromagnet|MgO (TM|FM|MgO) heterostructure from firstprinciples electronic structure computation. By tuning the epitaxial strain in Ta|Fe|MgO as a model system of TM|FM|MgO, we find distinctly different behaviours of VPMA from V-to Λ-shape trends with a substantially large magnetoelectric coefficient, up to an order of 10 3 fJV −1 m −1 . We further reveal that the VPMA modulation under strain is mainly governed by the inherently large spin-orbit coupling of Ta 5d-Fe 3d hybridized orbitals at the TM|FM interface, although the Fe 3d-O 2p hybridization at the FM|MgO interface is partly responsible in determining the PMA of Ta|Fe|MgO. These results suggest that the control of epitaxial strain enables the engineering of VPMA, and provides physical insights for the divergent behaviors of VPMA and magnetoelectric coefficients found in TM|FM|MgO experiments.Intensive and extensive attentions have been drawn to transition-metal capped ferromagnets on insulating MgO (TM|FM|MgO) as a promising candidate in spin-transfer torque (STT) memory, due to the significant magnetoresistence and perpendicular magnetic anisotropy (PMA), where the spin-polarized current manipulates the spin orientation of a ferromagnet free-layer 1-3 . On the other hand, more recent studies on these magnetic tunnel junctions (MTJs) focus on another alternative approach that utilizes an electric field (E-field) through the voltage to achieve magnetization switching 4,5 . The latter is expected to overcome the large critical current density that is required for STT switching. In particular, a small switching energy per bit, preferably less than 1 fJ, is indispensable, which in STT is in an order of 100 fJ 6 . The large PMA and magnetoelectric (ME) coefficient are favored to lower the switching bit energy in voltage-controlled PMA (VPMA) junctions.While PMA is discovered in several TM|FM|MgO heterostructures, diverse trends of the E-field dependence of VPMA have been demonstrated ranging from linear to V-to Λ -shape behaviors. For example, Ta|CoFeB|MgO and Au|CoFe|MgO exhibit the linear VPMA with magnetoelectric coefficients of − 33 and − 38 fJV −1 m −1 , respectively 7,8 . On the other hand, nonlinear Λ -and V-shape VPMA have also been reported when Fe-rich layers are used as a FM constitute in V|Fe|MgO 9 and MgO|FeB|MgO 10 , which have significantly large magnetoelectrics of − 1150 and 108 fJV −1 m −1 , respectively. There have been numerous subsequent studies since then to clarify the origin of such a wide range of VPMA and ME coefficients. However, the underlying mechanism remains unclear. It is indeed challenging to straightforwardly answer within a theoretical model because of the limited understanding on a detailed atomic st...

Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage

“…In the present study, the VCMA can be determined by the curve slope of the electric-field or n e dependence of MAE. The nonlinear parabola-like shape behavior of the VCMA within a small range of n e (−1 < n e < +1) is quite typical in most magnetoelectric materials, as reported in previous calculations [50][51][52] and experiments [53][54][55].…”

Interfacial magnetic-phase transition mediated large perpendicular magnetic anisotropy in FeRh/MgO by a heavy transition-metal capping

“…This implies that the AFM-FM transition at the interface accompanies the strong out-of-plane orbital ( and ) hybridization between the Ta 5 d and Fe 3 d states. A similar argument applies to the FeRh/MgO interface, as addressed in previous ab initio calculations 5 , 22 .

Figure 3 Spin and d -orbital decomposed PDOS of ( a ) Fe(I V ) in FeRh/MgO and ( b ) Fe(I Ta ) and ( c ) Ta(I) in Ta/FeRh/MgO multilayers.

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“…The other spin-antiparallel configurations, i.e., Type-I (or A-AFM) and Type-III (or C-AFM), have been excluded because they were found to have relatively high energies than those for the AFM-II and FM phases 21 . The preferred adsorption sites of Fe atoms were atop O at the FeRh/MgO interface and a hollow site at the Ta/FeRh interface, which are analogues to a Ta/Fe/MgO multilayer 22 . An experimental lattice constant (4.212 Å) for MgO was adopted for the in-plane lattice of supercells, which was matched to the optimized bulk lattices of AFM-II and FM FeRh within 0.5 and 1.1%, respectively 5 .…”

Recent Progress in the Voltage-Controlled Magnetic Anisotropy Effect and the Challenges Faced in Developing Voltage-Torque MRAM

“…Recently, strain-induced modulation of electronic structures and its influence on the VCMA effect has attracted attention [130,131]. For example, Hibino et al reported a high VCMA coefficient of +1600 fJ/Vm in a Pt/Co/Pd/MgO structure at 10 K [95].…”