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

Abstract

Peculiarities of low-temperature behavior of the magnetic properties of disordered spinel ferrites, prepared by means of dilution with the P2O5 amorphizing agent and by rapid quenching, were investigated. A sharp increase in the saturation magnetization σS, of ferrite compositions (1-x)MeFe2O4·xP2O5 (where Me is Ni, Fe, Mn, etc.), was observed at temperatures T < 80 K. It was established that the temperature dependences of σS 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 σS(T), which represents the dependence of σS (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.