The Role Of Iron In Magnetic Damping Of Mg(Al,Fe)(2)O-4 Spinel Ferrite Thin Films

We have investigated magnesium aluminum ferrite thin films with a range of iron concentrations and identified the optimal iron content to obtain high crystalline quality thin films with the low magnetic damping required for spin current-based applications. EpitaxialMgAl2 - x FexO4 films with 0.8 < x<2.0 were grown by pulsed laser deposition on single crystal MgAl2O4 substrates and were characterized structurally and magnetically. We find that the x=1.5 composition minimizes the room-temperature magnetic damping with a typical Gilbert damping parameter ofalphaeff = 1.8 x10- 3. This minimized damping is governed by a competition between the more robust magnetic ordering with increased iron content, x, and the more defective structure due to larger film-substrate lattice mismatch with increased iron content. The temperature-dependent magnetization curves indicate that T-c is suppressed below room temperature for iron contentx <= 1.2 and eventually suppressed entirely for x=0.8. X-ray magnetic circular dichroism results indicate that for all x the magnetic moment is dominated byFe3 + cations distributed in a 60:40 ratio on the octahedral and tetrahedral sites, with minimal contribution fromFe2 + cations. Films withx = 1.4 - 1.6 exhibit very strong ferromagnetic resonance and low Gilbert damping withalphaeff = ( 1.8 - 6 ) x10- 3, making them ideal candidates for microwave and spintronic applications.