Low-temperature magnetic behavior of ball-milled copper ferrite

摘要

We present a study on magnetic properties of CuFe_2O_4 nanoparticles, produced by high-energy ball milling. The series of samples obtained, with average particle size ranging from 61 nm to 9 nm, display increasing relaxation effects at room temperature. Irreversibility of the magnetization and shifts to negative fields in the hysteresis loops are observed below T_F approx approx 55 K, indicating unidirectional magnetic anisotropy in milled samples. These features could be explanined by assuming the formation of a spin-disordered surface layer, which is exchange-coupled to the ferrimagnetic core. The temperature depenence of average hyderfine field, saturation mangetization and coercive field shows a change of slope at T_f, indicating the spin freezing of the disordered phase at F_f.