Size-Dependent Magnetization Switching in Magnetoelectric Heterostructures for Self-Biased MRAM Applications

Straintronic magnetic random access memory (MRAM) devices based on magnetoelectric heterostructures are gaining much attention because of their ability to perform energy-efficient, nonvolatile magnetization switching. However, practical applications of such devices are often restricted by the requirement of biasing magnetic field to provide the initial magnetization state. This work reports the self-biased, in-plane 180° magnetization switching of FeGaB nanomagnets on PMN-PT piezoelectric substrate. By varying the thickness of the nanomagnets with different aspect ratio, the self-biased operation is obtained for a particular range where the lower limit is imposed by the thermal stability and the upper limit is given by the shape anisotropy energy. We also demonstrate that in-plane 180° magnetization switching for larger aspect ratio nanomagnets is also limited because of the maximum achievable stress from the piezoelectric layer. The underlying physics, including the relationship between the critical switching time and energy, is delineated using finite difference method (FDM) micromagnetic model coupled with elastodynamic and electrostatic conditions.