Preparation and characterization of rare earth-zinc substituted X-type hexaferrites

Abstract

Abstract The preparation of a highly pure X-type hexaferrite phase is challenging, and critically dependent on the preparation method and the adopted experimental conditions, as it normally coexists at equilibrium with M and W phases at the formation temperature in the range 1250–1400 °C. In this article, we report the effects of partial rare-earth (RE) and Zn co-substitution on the structural and magnetic properties of Co2X hexaferrites (Ba2-xRExCo2ZnxFe28-xO46; RE: La, Nd, Pr). The RE-Zn substituted samples were prepared by ball milling and sintering at 1300 °C. Analysis of the XRD patterns indicated the coexistence of X, W, and M phases in all samples, with the X-type being the majority phase in all RE-Zn substituted samples. The weight fractions of the phases changed depending on the type and concentration (x) of RE-Zn substitution, and yields of X-type phase as high as 68 ± 3% and 67 ± 3% were observed for La-Zn (x = 0.1) and Pr-Zn (x = 0.2) substitutions, respectively. Also, the saturation magnetization varied slightly with the substitution, and the highest value of 76.8 emu/g (1 emu/g = 1 Am2/kg) was observed for the Pr-Zn substituted sample. All samples exhibited low coercivity in the range of 32–53 Oe (1 Oe = 79.58 A/m), and magnetocrystalline anisotropy field in the range 5.07–7.78 kOe, and the coercivity exhibited an increasing tendency with the increase of the anisotropy field. The magnetic phases in each sample were further confirmed by thermomagnetic measurements, and the corresponding Curie temperatures were determined. The thermomagnetic behavior indicated an enhancement of the superexchange interactions, and a corresponding increase of the Curie temperature of the W and X phases with the La-Zn and Nd-Zn substitutions, whereas the Pr-Zn substitution did not exhibit such enhancements in the W phase.