On the transition point of thermally activated conduction of spinel-type MFe2O4 ferrite thin films (M = Zn, Co, Ni)

Thin films of zinc ferrite (ZnFe2O4), cobalt ferrite, and nickel ferrite have been grown on SrTiO3(100) substrates. By changing the growth temperature T-G, the electrical conductivity sigma of the thin films can be switched from insulating to conducting. An increased lattice constant of thin films grown at low temperatures (e.g., TG(ZnFe2O4) < 450 degrees C) indicates the formation of defects, which seems to promote the hopping conductivity. Temperature-dependent measurements of sigma reveal two thermally activated conduction processes. Interestingly, the transition point of these two processes at T-x = 107K-140K is close to the Verwey transition known from structurally similar magnetite thin films. (C) 2013 AIP Publishing LLC.