A-Site Cation Size Effect on Structure and Magnetic Properties of Sm(Eu,Gd)Cr(0.2)Mn(0.2)Fe(0.2)Co(0.2)Ni(0.2)O(3) High-Entropy Solid Solutions

Three high-entropy Sm(Eu,Gd)Cr(0.2)Mn(0.2)Fe(0.2)Co(0.2)Ni(0.2)O(3) perovskite solid solutions were synthesized using the usual ceramic technology. The XRD investigation at room temperature established a single-phase perovskite product. The Rietveld refinement with the FullProf computer program in the frame of the orthorhombic Pnma (No 62) space group was realized. Along with a decrease in the V unit cell volume from ~224.33 Å(3) for the Sm-based sample down to ~221.52 Å(3) for the Gd-based sample, an opposite tendency was observed for the unit cell parameters as the ordinal number of the rare-earth cation increased. The average grain size was in the range of 5–8 μm. Field magnetization was measured up to 30 kOe at 50 K and 300 K. The law of approach to saturation was used to determine the M(s) spontaneous magnetization that nonlinearly increased from ~1.89 emu/g (Sm) up to ~17.49 emu/g (Gd) and from ~0.59 emu/g (Sm) up to ~3.16 emu/g (Gd) at 50 K and 300 K, respectively. The M(r) residual magnetization and H(c) coercive force were also determined, while the SQR loop squareness, k magnetic crystallographic anisotropy coefficient, and H(a) anisotropy field were calculated. Temperature magnetization was measured in a field of 30 kOe. ZFC and FC magnetization curves were fixed in a field of 100 Oe. It was discovered that the T(mo) magnetic ordering temperature downward-curve decreased from ~137.98 K (Sm) down to ~133.99 K (Gd). The spin glass state with ferromagnetic nanoinclusions for all the samples was observed. The <D> average and D(max) maximum diameter of ferromagnetic nanoinclusions were calculated and they were in the range of 40–50 nm and 160–180 nm, respectively. The mechanism of magnetic state formation is discussed in terms of the effects of the A-site cation size and B-site poly-substitution on the indirect superexchange interactions.