Magnetic properties of nanostructured CuFe2O4

The structural evolution and magnetic properties of nanostructured copper f errite, CuFe2O4, have been investigated by x-ray diffraction, Mossbauer spe ctroscopy, and magnetization measurements. Nanometre-sized CuFe2O4 particle s with a partially inverted spinel structure were synthesized by high-energ y ball milling in an open container with grain sizes ranging from 9 to 61 n m. Superparamagnetic relaxation effects have been observed in milled sample s at room temperature by Mossbauer and magnetization measurements. At 15 K, the average hyperfine held of CuFe2O4 decreases with decreasing average gr ain size while the coercive force, shift of the hysteresis loop, magnetic h ardness, and saturation magnetization at 4.2 K increase with decreasing ave rage grain size. At 295 K the coercive-held dependence on the average grain size is described, with particles showing superparamagnetic relaxation eff ects. At 4.2 K the relationship between the coercive field and average grai n size can be attributed to the change of the effective anisotropy constant of the particles. The interface anisotropy of nanostructured CuFe2O4 is fo und to be about 1.8(1) x 10(5) erg cm(-3). Although spin canting was presen t, approximately 20% enhancement of the saturation magnetization in CuFe2O4 nanoparticles was observed, which could be explained by a cation redistrib ution induced by milling. The high-held magnetization irreversibility and s hift of the hysteresis loop detected in our samples have been assigned to a spin-disordered phase, which has a spin-freezing temperature of approximat ely 50 K.