We have investigated the structural, magnetic and barrier properties for Co-ferrite thin films, which have been formed by plasma oxidization of the surface of Co33Fe67(CoFe2) underlayer deposited on MgO(001) single crystal substrates. XRD patterns and cross sectional TEM observation revealed that the Co-ferrite thin films grew epitaxially with the (001) orientations on (001)-oriented CoFe2 underlayer. The saturation magnetization of CoFe2 and Co-ferrite annealed at 523 K were 1.5 Wbm-2 and 0.44 Wbm-2, respectively. Magnetizations of these two layers were rotated simultaneously. Coercivity increased up to near 80 kAm-1 after postannealing. To evaluate barrier properties of Co-ferrite, we have fabricated magnetic tunnel junctions (MTJs) consisting of CoFe2/Co-ferrite/Ta on MgO(001) single crystal substrates through microfabrication technique. These MTJs exhibited the non-linear current density(J)-voltage(V) curves, revealing that Co-ferrite thin films acted as a barrier.
