Extraordinarily large perpendicular magnetic anisotropy in epitaxially strained cobalt-ferrite CoxFe3-xO4(001) (x=0.75, 1.0) thin films

Perpendicular magnetic anisotropy (PMA) of cobalt-ferrite CoxFe(3)-xO(4) (x 0.75 and 1.0) epitaxial thin films grown on MgO (001) by a reactive magnetron sputtering technique was investigated. The saturation magnetization was found to be 430 emu/cm 3 for x 0.75, which is comparable to that of bulk CoFe2O4 (425 emu/cm(3)). Torque measurements afforded PMA constants of Keff u 9: 0Merg= cm(3) dKu 10: 0Merg= cm(3) and Keff u 9: 7Merg= cm(3) for x 0.75 and 1.0, respectively. The value of Keff u extrapolated using Miyajima's plot was as high as 14.7 Merg/cm(3) for x 1.0. The in-plane four-fold magnetic anisotropy was evaluated to be 1.6 Merg/cm 3 for x 0.75. X-ray diffraction measurement revealed our films to be pseudomorphically strained on MgO (001) with a Poisson ratio of 0.4, leading to a considerable in-plane tensile strain by which the extraordinarily large PMA could be accounted for. (C) 2013 AIP Publishing LLC.