Structural phase transition in the two-dimensional triangular lattice antiferromagnet RbFe(MoO4)2 -: art. no. 174408

We report temperature-dependent x-ray powder diffraction patterns and single-crystal electron spin resonance (ESR) and Raman spectra of the two-dimensional triangular-lattice antiferromagnet RbFe(MoO4)(2). A structural phase transition is found to occur in this compound at T(c)similar or equal to190 K. By analyzing our data and the literature data on similar compounds, we conclude that the 190 K transition comprises rotations of MoO4 tetrahedra and is, most likely, a transformation from a highly symmetric P (3) over bar m1 room-temperature structure into a very similar but less symmetric P (3) over bar c1 low-temperature one. The shift of the ESR frequency and the ESR linewidth were found to be determined by the crystal field influence and are described well considering the single-ion anisotropy with the constant D/k(B)=0.25 K. The change of the crystal field at the iron site below the phase-transition point T-c is estimated.