Probing VCMA in MTJs with in-plane magnetization

M Williamson,W Wang,X Chao,H Almasi,M De Rozieres,M Tsoi,J.-P Wang

doi:10.1063/1.5008379

Abstract

Voltage controlled magnetic anisotropy (VCMA) is a novel method to switch magnetizations in low-power and ultra-fast applications based on magnetic tunnel junctions (MTJs). Here we explore the ferromagnetic resonance (FMR) technique to probe VCMA in situations where other methods cannot be applied. We quantify VCMA in CoFeB/MgO/CoFeB MTJ nanopillars with in-plane magnetizations where our FMR method is unique in providing direct information about VCMA. We observe a quadratic shift of the FMR resonance field when a voltage bias is applied across the MTJ. The VCMA energy corresponding to the quadratic shift varies with an energy factor of 8.2μJ/m2 for 1 V2/nm2. These results are important for understanding magnetodynamics in MTJ-based applications with in-plane magnetizations.

Highlights

Control and manipulation of magnetic moments is the central theme of spintronics research
In this work we show that the ferromagnetic resonance (FMR) technique can be used to provide direct information about Voltage controlled magnetic anisotropy (VCMA) in magnetic tunnel junctions (MTJs) with in-plane magnetizations
Other dips/peaks are associated with FMR of the reference MTJ layer and other resonance modes of the free layer as will be described later

Summary

INTRODUCTION

Control and manipulation of magnetic moments is the central theme of spintronics research. By measuring the effective coercive field as a function of the applied voltage the VCMA field can be probed directly because it is parallel/antiparallel to the out-of-plane applied field and adds up to the MTJ’s intrinsic coercivity at zero voltage bias.[7,8] This simple method, cannot be used in MTJs with in-plane magnetizations because the in-plane switching is not controlled by a perpendicular (VCMA) field.[9] Instead, the perpendicular anisotropy energy should be deduced from the integral of magnetic hysteresis loop[10,11] which quantifies the work done on the material by the applied field. In this work we show that the ferromagnetic resonance (FMR) technique can be used to provide direct information about VCMA in MTJs with in-plane magnetizations

SAMPLES AND SET-UP

RESULTS AND DISCUSSION

CONCLUSION