Magnetic and dielectric properties of RbCoBr3. Inspected from nonmagnetic impurity effect

Through magnetic and dielectric measurements, a simultaneous phase transition of spin and lattice systems observed previously at 37.2 K of RbCoBr3 have been investigated by doping with nonmagnetic Mg impurities. A mutual reduction in the ferroelectric Curie temperature TC and the Neel temperature TN due to the enhancement of Mg doping confirms the occurrence of the synergistic ordering of both. A broad peak of the real part of dielectric constant along the c axis, ε'c (T), at approximately 32 K of the pure system splits into two sharp peaks in mixed systems. This suggests the presence of successive structural phase transitions at around this temperature. A probable sequence of crystal and magnetic structures was discussed for the successive phase transitions of RbCo1-xMgxBr3. The interplay between the spin and lattice variables of RbCoBr3 was interpreted by taking account of spin-dependent polarizability and spin-dependent spontaneous polarization. A dielectric anomaly observed at 9.0 K in RbCoBr3, where ε'c(T) has a sharp peak, was ascribed to the occurrence of another structural transition. (author)