Voltage-controlled magnetic anisotropy in Pt/Fe/MgO and 2D dielectric LaOBr-capped Pt/Fe/MgO heterostructures

Abstract

Low power consumption and fast response enabled by voltage control are core advantages of field-effect transistors. Similarly, in magnetoelectric random access memory (MeRAM), voltage-controlled magnetic anisotropy (VCMA) offers comparable advantages in assisting or directly inducing magnetization switching. Enhancing the VCMA coefficient is essential for fully realizing this functionality. In this work, first-principles calculations reveal that the Pt/Fe/MgO heterostructure exhibits a significant VCMA coefficient (β = −4394 fJ/V·m), which is mainly contributed by the Pt layer. It has been demonstrated that the large VCMA coefficient originates from four indispensable determinants associated with the Pt layer: (1) the strong spin–orbit coupling constant, (2) the high induced spin polarization, (3) electron accumulation/depletion on the Pt layer, and (4) the presence of Pt dz2 orbital states near the Fermi level. In consideration of practical application scenarios, Pt/Fe/MgO was further capped with an Au electrode layer and a dielectric BaTiO3 layer. However, the calculated results reveal a significant reduction in the VCMA coefficient for both structures. In contrast, introducing a 2D dielectric material, LaOBr, as a gate layer atop Pt/Fe/MgO, a comparably large VCMA coefficient (β = −4373 fJ/V·m) is obtained. This is attributed to the van der Waals nature of the LaOBr/Pt interface, which allows the Pt layer to meet the four determinants mentioned above. The insights into the factors governing the VCMA coefficient and the design of the LaOBr/Pt/Fe/MgO heterostructure provide valuable guidance for the development of next-generation, high-performance MeRAM devices with large VCMA.