The effect of copper substitution on the magnetic properties of Ni(0.8-x)Zn0.2CuxFe2O4 (where, x = 0, 0.25, 0.42, 0.45, 0.5 and 0.55) calcined at 1000degreesC, were investigated. From XRD, a second phase, CuO had been found to exist beyond 0.42 mol fraction of Cu. High-resolution XPS in the Cu 2p(3/2) region showed an unequal distribution of Cu+ and Cu2+ cations in the tetrahedral and octahedral sites, which affected the dia-paramagnetic spin balance and caused the variation of overall spin and hence the magnetization. (C) 2003 Elsevier B.V. All rights reserved.