Investigation on X-ray photoelectron spectroscopy, structural and low temperature magnetic properties of Ni-Ti co-substituted M-type strontium hexaferrites prepared by ball milling technique

The effect of substituting Fe3+ ions by a combination of divalent Ni2+ and tetravalent Ti4+ in SrM hexaferrites synthesized by mechanical ball-milling technique were reported. Standard SrFe12O19 hexagonal ferrite (P63/mmc) was confirmed by measured XRD patterns. The phase purity was also confirmed by the XPS. The SEM images showed a clear hexagonal-shape particles in the prepared ferrites. The elemental distribution obtained from EDX spectra for SrFe12–2xNixTixO19 (x = 0.2, 0.4, 0.6 and 0.8) was consistent with stoichiometry of the starting powder. X-ray photoelectron spectra confirmed the existence of Fe2+, Fe3+, Ni2+, Ni3+ and Ti4+ ions. The presence of Fe2+ and Ni3+ was correlated with an electron transfer between Fe3+ and Ni2+. By increasing the Ni concentration, we found that some Fe3+ ions are transferred to Fe2+ ions, while some of the Ni2+ ions are transferred to Ni3+ ions. Irreversible ZFC and FC curves were recorded in the 4–300 K temperature range. The isothermal magnetization curves confirmed the ferromagnetic behavior for all synthesized samples. A small variation in the saturation and remnant magnetizations along with a sharp reduction in the coercivity fields with the increase of x were observed in a wide range of temperatures. The broad peak observed in the temperature dependence of the saturation magnetization for x = 0.8 may be referred to the spin reorientation transition. The decrease in the coercivity agrees with the behaviour of the magneto crystalline anisotropy while the first anisotropy constant exhibits a fast decrease above x = 0.6.

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