Nanoscale Multiferroics For Electro-Magnetic Devices

G.P. Carman
University of California, Los Angeles, US

Keywords: nanoscale multiferroics

Summary:

Present day electromagnetic devices (e.g. memory, antennas, and motors) rely on a discovery made by Oersted 200 years ago where a current passing through a wire generates a magnetic field. While extremely useful this approach has significant limitations in the nanoscale. Recent discoveries suggest that a ferromagnetic material’s intrinsic magnetization can be manipulated with an electric field (i.e. multiferroic) and thereby overcome the deficiencies associated with Oersted’s discovery. One multiferroic approach relies on mechanically coupling a piezoelectric material to a magnetostrictive material where an electric field induces a strain to reorient the magnetostrictive material’s magnetization state and thus electrically control magnetism. This multiferroic approach is substantially enhanced by using physical phenomenon present in nanoscale magnetic elements such as the elimination of domain walls. This presentation provides motivation, experimental/analytical data, and a description of two devices (memory and antennas) the new NSF Engineering Research Center ERC at UCLA entitled Translational Applications for Nanoscale Multiferroics TANMS is pursuing. The analytical/experimental data contained in this presentation focuses on strain-mediated multiferroics. Analysis consists of micromagnetic simulations (Landau-Lifshitz-Gilbert LLG) coupled with elastodynamics using the electrostatic approximation producing seven fully coupled partial differential equations. Qualitative and quantitative verification of the model is achieved with comparison to experimental data on single magnetic domain magnetostrictive elements. The modeling efforts guides fabrication and testing of a variety of structures including nanoscale ring and oval shapes to electrically and deterministically orient the local magnetic spin states (i.e. at the 5-100 nm level). Experimental data obtained from Photoemission Electron Microscopy PEEM, Magnetic Force Microscopy MFM, and Lorentz Transmission Electron Microscopy TEM demonstrates both multi-domain and single domain deterministic reorientation of the local magnetic spin states. These results guide the design of a memory element with predicted low write energies (sub femtojoule) and an experimental demonstration of an electromagnetic antenna receiver substantially smaller than the wavelength (<λ/100) in free space. These experimental/analytical results provide ample support that the nanoscale multiferroic approach using electric control of magnetization in the small scale is potentially superior to Oersted original discovery.