Gagor, A.; Zajdel, P.; Toebbens, D.M.: The phase transitions in CsFe(MoO4)2 triangular lattice antiferromagnet, neutron diffraction and high pressure studies. Journal of Alloys and Compounds 607 (2014), p. 104-109
10.1016/j.jallcom.2014.04.049

Abstract:
We report on the phase transitions in the triangular lattice antiferromagnet CsFe(MoO4)2 at low temperatures and high pressure using powder neutron and X-ray diffraction, specific heat, magnetic susceptibility and in situ high pressure Raman measurements. CsFe(MoO4)2 undergoes a structural phase transition induced by the rotation of (MoO4)2 tetrahedra at Tc = 220 K. The transformation is associated with a symmetry decrease from P-3m to P-3. Below 4.5 K the antiferromagnetic long range order appears that is related to the nuclear unit cell by the modulation vector q = (1/3 1/3 0.5). The system adopts '120°' spiral spin structure that has been found in several triangular lattice multiferroics. Under pressure CsFe(MoO4)2 undergoes a reconstructive phase transition to a much larger superstructure which preserves the super-exchange interactions at low temperatures and allows an additional magnetic long-range order at T ~ 20 K.