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

Abstract

Solid solutions based on SrFe 12 O 19 strontium hexaferrite with deep (up to at.67%) co-substitution of triply charged Fe 3+ iron cations by triply charged diamagnetic Al 3+ aluminum, Ga 3+ gallium, and In 3+ indium cations, as well as by paramagnetic Co 3+ cobalt and Cr 3+ 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 〈r B 〉 average ionic radius of the iron sub-lattice are plotted. The average grain size varied within 2–5 μm. The field and temperature properties of the magnetization of the obtained samples were studied. The M s saturation magnetization is determined using the Law of Approach to Saturation. The M r residual magnetization, SQR loop squareness and H c coercivity are also determined. Based on the obtained data, the k magnetic crystallographic anisotropy coefficient and the H a anisotropy field are calculated. All the obtained and calculated values are plotted depending on the 〈r B 〉 average ionic radius of the iron sub-lattice. All plotted dependencies are non-linear. The T mo magnetic ordering and T f 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 ∼ 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.