Effect of Zn substitution on temperature dependent magnetic properties of BaFe12O19 hexaferrites

Abstract

Zinc doped barium hexaferrite powders with chemical composition BaFe12-xZnxO19 (0.0 ≤ x ≤ 0.3) were synthesized by sol-gel auto combustion method. The effect of zinc ion concentration on the temperature-dependent magnetic properties of BaFe12-xZnxO19 hexaferrites has been comprehensively investigated in the temperature range of 10–300 K and magnetic field of ±50 kOe. XRD powder patterns showed a pure single phase structure. The Rietveld refinement of the XRD patterns revealed the existence of hexagonal structure with P63/mmc space group. The average crystallite size of the powders was found to be in the range of 46–51 nm. The ratio of lattice constants (c/a) lower than 3.98 proves that BaFe12-xZnxO19 hexaferrite powders have a M-type hexagonal ferrite structure. The nonmagnetic zinc ions strongly affect the magnetic properties of the powders. The magnetic hysteresis loops were fitted by using a ‘law of approach to saturation’. From the linear fitting, the magnetic parameters were calculated such as saturation magnetization, effective magnetic anisotropy and anisotropy field. The saturation magnetization values close to bulk values were determined as 66.67 and 95.47 emu/g for 300 and 10 K, respectively, which makes the samples a promising candidate for electronic applications. The saturation magnetization slowly decreases and then increases, whereas the coercive field continuously decreases with the increasing of Zn2+ concentration (x). The squareness ratio (Mr/Ms) of about 0.5 confirmed that the hexaferrite powders have a uniaxial anisotropy. The effective magnetic anisotropy constant (Keff) was observed to decrease with the increase in Zn2+concentration. When the temperature increases, the saturation magnetization continuously decreases because of the weakening of superexchange interaction and the coercive field increases due to the increasing of anisotropy field. FMR measurements confirmed the ferromagnetic behaviour of the substituted barium hexaferrite powders. The high resonance field values of the powders (a maximum resonance field of 16 kOe) originate from the hard magnetic property of the hexaferrites used in this study. The absorption curves have a broad FMR linewidth due to an anisotropy axis randomly distributed and the competing between anisotropy and exchange fields.