Effect of heat treatment on the anisotropy field in Ni1+xGexFe2-2xO4

Heating and subsequent quenching of single crystals of Ni1+xGexFe2-2xO4causes Ni²⁺ions to migrate and occupy sites. Since in these sites their orbital state is triply degenerate, they furnish a and . On the other hand, they do not participate in cubic anisotropy while in the sites. Thus the measurement of anisotropy by ferrimagnetic resonance techniques enables one to study with some precision the cationic migration. For quenched samples the anisotropy decreases in its absolute value and changes its sign at lower temperatures. This change observed in the anisotropy due to quenching is seen to decrease with increase in Ge⁴⁺ion content. The relation between , the Ge⁴⁺ion content, and the quench temperature Tqhas been studied and interpreted. The results reveal the various factors which govern the migration of Ni²⁺ions and yield also the activation energies involved for the various cases. The migration of Ni²⁺ions is seen to be more complicated than that of Al³⁺or Ga³⁺in garnets. Finally, decreasing the anisotropy field in such ferrites by quenching serves as a very simple method of decreasing polycrystalline linewidth, particularly at low temperatures.