Neutron diffraction studies of the magnetic disorder in Zn_xMg_0.8-xNi_0.2Fe₂O₄ ferrite with x = 0.0, 0.2, 0.4 and 0.6

Magnetic properties of Zn_xMg_0.8-xNi_0.2Fe₂O₄ ferrite system with x = 0.0, 0.2, 0.4 and 0.6 have been investigated in the neutron diffraction technique. Neutron diffraction measurements of all the four samples are performed at a number of temperatures ranging from 823 down to 15 K. The observed sublattice moments do not follow the smooth trend as expected in collinear ferrimagnetic structure. A sluggish and step-like behavior in the temperature dependence of the magnetic moment has been observed below T_C which manifests the presence of spin clusters superimposed on the infinite magnetic network. For the sample with x = 0.6 the ordered moment in the B sublattice reduces drastically indicating the presence of strong noncollinearity in the B site. But the absence of (2 0 0) reflection in the neutron patterns at all temperatures suggests that there is no long range spatial ordering of the transverse spin components. However, for this sample there is considerable broadening of the (1 1 1) diffraction peak at 15 K due to diffuse signal. The presence of this diffuse scattering and the decrease in the B site moment at temperatures below 50 K indicates that a re-entrant or semi-spin-glass like structure is more probable for the composition with x = 0.6. The results are described qualitatively in the light of the existing theories and experimental observations.