Tunable magnetic anisotropy and ultra-low damping through Al substitution in lithium ferrite thin films

The development of ferromagnetic insulators with ultra-low damping, perpendicular magnetic anisotropy (PMA) and tunable magnetic properties are of great interest for the development of pure spin based spintronics. We have developed epitaxial thin films of the ferrimagnetic spinel structure Li_0.5(Al,Fe)_2.5O₄ (LAFO) with ultra-low magnetic damping and tunable magnetic properties. In this talk, we investigate an array of LAFO compositions deposited on spinel structure MgGa₂O₄ substrates with Al substitution ranging from 0.5 to 1.0. Al substitution modifies both the saturation magnetization as well as the magnetic anisotropy by changing the lattice constant. X-ray diffraction confirms excellent crystalline quality in all of our films. X-ray circular magnetic dichroism shows varying Fe cation distribution on the octahedral and tetrahedral sites of the spinel structure as a function of Al doping. SQUID magnetometry shows increasing saturation magnetization with decreasing Al as expected. Using broad band ferromagnetic resonance, we find that all compositions show ultra-low damping with Gilbert damping parameters ranging from 2x10^-4 to 1x10^-3. In addition, for Al substitution of 0.7 and above, LAFO films are under enough tensile strain and exhibit perpendicular magnetic anisotropy. These epitaxial, low damping LAFO films with variable Al composition exhibit a range of magnetic properties, making them promising for future spin wave spintronics applications.