Effect of Ga substitution on grain orientation and magnetostrictive properties of polycrystalline CoFe2O4 ceramics prepared by the solid-state method

Abstract

As a kind of magnetostrictive ceramics, cobalt ferrites are widely concerned because of its large magnetostriction and high resistivity, which are ideal for high-frequency applications. But, the high driving magnetic field due to the high magnetocrystalline anisotropy limits the practical applications of cobalt ferrites, thus, it is a still a challenge to find a balance between high magnetostriction properties and low driving magnetic fields. In this work, we investigated the effects of partially substitution of Ga3+ for Fe3+ on grain orientation and magnetic properties, attempting to maintain high magnetostriction while reducing the driving magnetic field. The CoFe2-xGaxO4 (x=0, 0.05, 0.1, 0.15) with single-phase spinel structure were prepared by the conventional solid-state method. The saturation magnetization MS increased with the increase of Ga concentration, meanwhile the coercivity Hc and magnetocrystalline anisotropy constant K1 significantly decreased, which indicates the better soft magnetic characteristics of the Ga-doped cobalt ferrites. The oriented CoFe2-xGaxO4 samples were obtained using magnetic field orientation technique during the powder forming process. The <001> preferred orientation was achieved in CoFe2O4 samples. However, the <001> orientation degree decreased with the substitution of Ga, and the preferred orientation has changed into <111> at x=0.15. The Ga substitution affected the magnetocrystalline anisotropy and grain orientation, thereby affecting the magnetostrictive properties. As for the non-oriented samples, although the maximum magnetostrictive strain slightly decreased with Ga substitution, while there was a significant drop in the magnetostrictive saturation field. However, the magnetostriction of the oriented samples decreased significantly with the substitution of Ga due to the change of grain orientation from <001> to <111>.