Anisotropy Stabilized Magnetic Phases of the Triangular Antiferromagnet RbFe(MoO4)2

Abstract

The magnetic H–T phase diagram of a quasi-two-dimensional easy plane antiferromagnet RbFe(MoO₄)₂ (S = 5/2) with an equilateral triangular lattice structure is studied with ⁸⁷Rb NMR technique for field directed along hard axis C₃. The studies confirm the two step transition from the low field umbrella-like incommensurate magnetic phase to the paramagnetic state observed recently (H. Mitamura et al., J. Magn. Magn. Mater. 400, 70 (2016)). The transitions were identified as a lambda anomaly in the spin-lattice relaxation rate and a step increase of magnetic susceptibility at intermediate transition. The ⁸⁷Rb NMR study precludes the possibility of either V or fan spin textures in the new high field phase. The additional transition is presumably associated with loss of inter plane magnetic order before the transition to paramagnetic state of individual triangular planes.