Abstract
Voltage control of magnetic anisotropy (VCMA) in magnetic heterostructures is a key technology for achieving energy-efficiency electronic devices with ultralow power consumption. Here, we report the first demonstration of the VCMA effect in novel epitaxial Ru/Co2FeAl(CFA)/MgO heterostructures with interfacial perpendicular magnetic anisotropy (PMA). Perpendicularly magnetized tunnel junctions with the structure of Ru/CFA/MgO were fabricated and exhibited an effective voltage control on switching fields for the CFA free layer. Large VCMA coefficients of 108 and 139 fJ/Vm for the CFA film were achieved at room temperature and 4 K, respectively. The interfacial stability in the heterostructure was confirmed by repeating measurements. Temperature dependences of both the interfacial PMA and the VCMA effect were also investigated. It is found that the temperature dependences follow power laws of the saturation magnetization with an exponent of ~2, where the latter is definitely weaker than that of conventional Ta/CoFeB/MgO. The significant VCMA effect observed in this work indicates that the Ru/CFA/MgO heterostructure could be one of the promising candidates for spintronic devices with voltage control.
Highlights
Giant voltage control of magnetic anisotropy (VCMA) effect as high as 1000 fJ/Vm in the CFA/MgO structure was theoretically proposed by first principles calculations[31]
From an experimental point of view, complicated interface reactions and/or inter-diffusions could occur in practical ultrathin heterostructures, such as boron diffusion in Ta/CoFeB/MgO structures[32,33], which is significant for both the interfacial PMA and the VCMA effect
A large coercivity change induced by voltages was observed for the CFA layer in perpendicularly magnetized magnetic tunnel junctions (MTJs) (p-MTJs) with the structure of CFA/MgO/CoFeB/Ta/[TbCo/Co]25 where the CFA was a free layer and the CoFeB/Ta/[TbCo/ Co]25 composited layer acted as a reference layer
Summary
Where MS is the saturation magnetization of the CFA film. the PMA energy density Ku can be calculated as,. The Ms2(T) power law indicates that the Ru/CFA/MgO system processes a strong spin-orbit interaction where localized moment or two-ion anisotropic exchange makes a main contribution to the temperature dependence of magnetic anisotropy[39,40]. Theoretical calculations will be strongly required for further understanding of the mechanisms to explain the observed temperature and magnetic anisotropy dependences of the VCMA effect. It was found that temperature dependences of both the interfacial PMA and the VCMA effect followed power laws of the saturation magnetization with a material-specific exponent. This study indicates the Ru/CFA/MgO heterostructure could be a promising candidate for spintronic applications with voltage-controlled magnetism
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