Spin-reorientational phase transitions in yttrium-samarium ferrite garnets

Complex magnetic and structural studies are carried out in single crystals of the Smsub(x)Ysub(3-x)Fesub(5)Osub(12) (0.27 <= x <3) yttrium-samarium ferrite garnets. The orientational (x, T) phase diagram is plotted which indicates that the sequence of spin-reorientation phase transitions <111> reversible <110> reversible observed in ferrites with x>xsub(cr) approximately 1.1 on lowering of the temperature is the same as in the samarium ferrite garnet Sm3Fe5O12, the temperature of the transitions rapidly decreasing with growth of diamagnetic dilution. Only easy directions of the <111> type occur in ferrites with x<xsub(cr) at temperatures 1.7 K<T<Tsub(N). The orientation phase diagrams of Smsub(x)Ysub(3-x)Fesub(5)Osub(12) ferrites are calculated theoretically in the crystal field approximation. The calculation shows that all features of the diagram and also the change in sign of the anisotropy constant K2 on variation of the concentration x can be ascribed to the concentration dependence of only one of the nine crystal field parameters Bsub(kq) viz. B20