Partially disordered state with short-range spin correlation in S=5/2 classical triangular antiferromagnet Ag2FeO2

Abstract

A triangular-lattice antiferromagnet of Ag2FeO2 was synthesized under high pressure. Its magnetism was studied in terms of electrical resistivity, magnetic susceptibility, heat capacity, powder neutron scattering, and Mössbauer spectroscopy. The magnetic state of Ag2FeO2 changes successively through a second-order phase transition at Tp=36 K and a crossover at Tc=20 K. A partially disordered (PD) state appears below Tp, in which ≈2/3 spins are ordered and the remaining ≈1/3 spins fluctuate, which state persists at least down to 5 K. The spin correlation length starts to grow at Tp; however, it remains very short (≈27 Å) below Tc. This exotic magnetism is concerned with strong frustration in the classic antiferromagnetic triangular lattice.