High field magnetization of aluminum-doped cobalt ferrite single crystals

Abstract

Magnetization measurements performed on single crystals of aluminum-substituted cobalt ferrites CoFe2−xAlxO4 are presented under a high magnetic field up to 20 T in the 4.2–300 K temperature range. Three substitution ranges (x=0.27, 0.46, and 1.05) are studied. In each case [100] is found to be the easy axis of magnetization as in pure cobalt ferrite while an abrupt field-induced transition is observed along the [111] direction below 200 K. When the temperature is greater than 100 K, saturation along [100] cannot be attained for x=1.05. A net decrease of the spontaneous magnetization due to the aluminum substitution on the octahedral B sites of the spinel lattice is found. Magnetization results are interpreted on the basis of the ionic distribution of the Co2+ and Fe3+ ions.