Effect of configurational entropy on phase formation, structure, and magnetic properties of deeply substituted strontium hexaferrites

Solid solutions based on SrFe12O19 strontium hexaferrite with deep (up to at.67%) co-substitution of triply charged Fe3+ iron cations by triply charged diamagnetic Al3+ aluminum, Ga3+ gallium, and In3+ indium cations, as well as by paramagnetic Co3+ cobalt and Cr3+ chromium cations, were obtained by conventional ceramic technology. This type of substitution leads to the formation of high-entropy phases. The phase composition of the obtained samples was studied by powder X-ray diffraction. The configurational mixing entropy was calculated for all the obtained samples, and its influence on the processes of phase formation was studied. The unit cell parameters are calculated and their dependences on the average ionic radius of the iron sub-lattice are plotted. The average grain size varied within 2-5 mu m. The field and temperature properties of the magnetization of the obtained samples were studied. The Ms saturation magnetization is determined using the Law of Approach to Saturation. The Mr residual magnetization, SQR loop squareness and Hc coercivity are also determined. Based on the obtained data, the k magnetic crystallographic anisotropy coefficient and the Ha anisotropy field are calculated. All the obtained and calculated values are plotted depending on the average ionic radius of the iron sub-lattice. All plotted dependencies are non-linear. The Tmo magnetic ordering and Tf freezing temperatures are obtained from the ZFC and FC magnetization data. The cluster nature of the magnetic behavior for all the samples is revealed. The average cluster diameter reaches similar to 400 nm. The interpretation of the magnetic properties is made taking into account the effect of high configurational mixing entropy and magnetic dilution of the iron sub-lattice.

Automated summary

By using conventional ceramic technology, solid solutions based on SrFe12O19 strontium hexaferrite with deep co-substitution of Fe3+ iron cations by Al3+ aluminum, Ga3+ gallium, In3+ indium, Co3+ cobalt, and Cr3+ chromium cations were successfully obtained, resulting in the formation of high-entropy phases. The phase composition, unit cell parameters, and field and temperature properties of magnetization of the obtained samples were studied. The magnetic behavior revealed a cluster nature, with an average cluster diameter of about 400 nm, and was interpreted considering the effect of high configurational mixing entropy and magnetic dilution of the iron sub-lattice.