Low-temperature magnetic behavior of nanostructured ferrite compositions prepared by plasma spraying

摘要

Peculiarities of low-temperature behavior of the magnetic properties of disordered spinel ferrites, prepared by means of dilution with the P_2O_5 amorphizing agent and by rapid quenching, were investigated. A sharp increase in the saturation magnetization σ_S, of ferrite compositions (1-x)MeFe_2O_4·xP_2O_5 (where Me is Ni, Fe, Mn, etc.), was observed at temperatures T < 80 K. It was established that the temperature dependences of σ_S and χ~(-1) (where χ is the magnetic susceptibility) of the nickel ferrite composition (x = 0.6) have an extremum at T = 11 K. In this case, the effect of "memory" is observed for σ_S(T), which represents the dependence of σ_S (T = 4.2 K) on the magnitude of the magnetic field in which cooling was carried out. The asymptotic Curie temperature was determined by extrapolation of the linear part of the χ~(-1)(T) dependence and found to be equal to -150 K. We present an analysis of the observed dependences from the viewpoint of a complex magnetic state, combining the features of the near antiferromagnetic and ferrimagnetic boundary-surface spin ordering.