Magnetic transition and defect characteristics of multiferroic CuFe1-xGaxO2 studied by positron annihilation spectra

Abstract

The structure, crystal defects and magnetic properties of multiferroic CuFe1-xGaxO2 (CFGO; x = 0–0.07) ceramics are studied systemically. Substitution of Ga3+ for Fe3+ shrinks the CFO lattice, decreases the particle size, and causes small liquid phase formation. Positron annihilation spectroscopy demonstrates that all samples contain a considerable number of vacancy defects. The overall defect environment is virtually unaffected by Ga3+ doping, but the open-volume of the defects is redistributed. Magnetic susceptibility measurements show that Ga doping enhances the strength of the antiferromagnetic interaction between high-spin Fe3+ ions as a result of reduced magnetic correlation length, but decrease the stability of the antiferromagnetic phase. The antiferromagnetic transition temperature, TN2, decreases from 11 K for x = 0 to 8 K for x = 0.07, and this destabilization of the antiferromagnetic phase is closely related to the crystal structure and defects, which are discussed in detail in this work.