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

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 Mossbauer spectroscopy. The magnetic state of Ag2FeO2 changes successively through a second-order phase transition at T-p = 36 K and a crossover at T-c = 20 K. A partially disordered (PD) state appears below T-p, in which approximate to 2/3 spins are ordered and the remaining approximate to 1/3 spins fluctuate, which state persists at least down to 5 K. The spin correlation length starts to grow at T-p; however, it remains very short (approximate to 27 angstrom) below T-c. This exotic magnetism is concerned with strong frustration in the classic antiferromagnetic triangular lattice.