UCLA

The recent interest in non-volatile memory and logic devices has encouraged the scientific community to develop improved magnetic control mechanisms. In the present work, control of magnets by magnetoelastic anisotropy is investigated within the context of magnetoelectric (ME) heterostructures of different geometry and scale. The ME heterostructure is an artificial multiferroic material which exhibits both a coexistence and coupling of ferromagnetic and ferroelectric ordering. This device architecture provides a route to control magnetism with electric fields via interfacial mechanical stress. In the present work, the initial magnetization morphology and behavior under mechanical stress is investigated for bulk laminate composites, thin film heterostructures, patterned single domain nanostructures, and ring shaped nanostructures. Significant differences were observed in the magnets' response to magnetoelastic anisotropy depending on the scale and or geometry of the magnetic material. Generally speaking, as the scale and aspect ratio of a magnetic system is reduced, the intrinsic magnetostatic and shape anisotropy energies are also reduced thus increasing the relative magnitude (and influence) of magnetoelastic anisotropy. The unambiguous control of a magnet's easy axis is here called deterministic control and this is achieved experimentally in single domain and ring shaped magnets. The magnetization of these nanostructures is shown to rotate 90° with an applied electric field, an important proof of concept for the proposed strain-based magnetic writing devices. The experimental results are confirmed by multiple characterization techniques including magnetic force microscopy (MFM), magneto optic Kerr effect (MOKE), photo emission electron microscopy (PEEM), and Lorentz transmission electron microscopy (TEM). This work thus provides significant evidence of the viability of magnetoelastic anisotropy as a means to control magnetoelectric heterostructures in future spintronic device research.