Tuning of current-induced effective magnetic field through Rashba effect engineering in hybrid multiferroic structures

Current-induced effective magnetic fields offer a new pathway through spin orbit interaction (SOI) to switch magnetization and have recently attracted great interest. In the conventional heavy metal/ferromagnetic metal/oxide (HM/FM/Oxide) structure, significant efforts have been made to study the role of the HM in determining effective magnetic fields. However, very little attention has been paid to the oxide layer and its interface with FM, where the Rashba effect may affect the effective field. In this report, we present a pathway to tune the effective magnetic field by engineering the Rashba effect in a hybrid multiferroic multilayer structure. A ferroelectric oxide of BaTiO3, whose polarizations either up or down are controlled by interface engineering, was introduced into the conventional SOI multilayer with the structure of BaTiO3/CoFeB/Pt. The current-induced effective magnetic fields increase by more than 200% when the ferroelectric polarization of BaTiO3 changes from up to down. The changes in the effective magnetic field are mainly attributed to the different Rashba effective fields induced by the opposite ferroelectric polarizations. Our study offers a new path towards controlling the current-induced effective magnetic field and may pave the way for integrating other functional oxides into the spintronic devices. Combining magnetic materials with oxides offers a route to low-power memories, according to research from scientists in Singapore. Locally switching the magnetization orientation of a permanent magnet is a way of storing binary data. The energy consumption of these magnetic memories is much lower if a local current, rather than an external magnetic field, induces the switch. Current-induced magnetization switching has previously been demonstrated in devices made by layering a heavy metal, a ferromagnetic material, and an oxide material. While many conventional oxide materials have been tried, Jingsheng Chen and Hyunsoo Yang and their colleagues from the National University of Singapore instead used BaTiO3, a ferroelectric oxide which has permanent internal electric fields. They showed that they could increase the current-induced magnetic fields by more than 200% by altering the ferroelectric polarization of the BaTiO3. Over 200% difference of the current-induced effective magnetic field was achieved through engineering the Rashba effect in a hybrid-multiferroic multilayer structure (BaTiO3/CoFeB/Pt), where the polarization of BaTiO3 with either up or down was controlled through interface engineering. Our works offer a new direction towards controlling the current-induced effective magnetic field and may pave the way to integrate other functional oxides into the spintronic devices.