Magnetic and crystallographic phase transitions in Dysub(p)Gdsub(1-p)VO4

The compositional vanadate system Dysub(p)Gdsub(1-p)VO4(O<=p<=1) displays successive crystallographic and magnetic phase transitions below 14 K. An experimental investigation of these phase changes has been made with thermal expansion methods and Moessbauer spectroscopy. It is found that there is a surprising variation of the compositional dependence of the transition temperatures Tsub(D)(p) and Tsub(N)(p), which cannot be adequately explained by conventional pseudo-spin molecular field and pair model approximations. A detailed formalism has been developed that accounts for the observations in terms of a magneto-strictively induced quadrupole moment on the Gd3+ ions in the mixed crystal system and concomitant quadrupole interactions between the Dy3+ and Gd3+ ions. The application of the formalism to the corresponding variation of Tsub(D)(p) in the simple diluent system Dysub(p)Ysub(1-p)VO4(O<=p<=1) is also discussed. (author)