Multiferroic Micro-Motors with Deterministic Single Input Control

This paper describes a method for achieving continuous deterministic 360$^{\circ} $ magnetic moment rotations in single domain magnetoelastic discs, and examines the performance bounds for a mechanically lossless multiferroic bead-on-a-disc motor based on dipole coupling these discs to small magnetic nanobeads. The continuous magnetic rotations are attained by controlling the relative orientation of a four-fold anisotropy (e.g., cubic magnetocrystalline anisotropy) with respect to the two-fold magnetoelastic anisotropy. This approach produces continuous rotations from the quasi-static regime up through operational frequencies of several GHz. Driving strains of only $\approx$90 to 180 ppm are required for operation of motors using existing materials. The large operational frequencies and small sizes, with lateral dimensions of $\approx$100s of nanometers, produce large power densities for the rotary bead-on-a-disc motor, and a newly proposed linear variant, in a size range where power dense alternative technologies do not currently exist.