Successive magnetic transitions and frustrated magnetism in Fe2(HPO3)3 ⋅ 4H2O

Abstract

AbstractWe report the magnetic and optical properties of Fe2(HPO3)3 ⋅ 4H2O. By combined magnetic susceptibility and specific heat measurements, we find two antiferromagnetic (AFM) transitions (TN1=9 K, TN2=5 K) which originate from the AFM exchange interactions mediated by the (HPO3)2− anions. Compared with the non‐hydrated compound Fe2(HPO3)3, the magnetic interaction strength and ordering temperature of Fe2(HPO3)3 ⋅ 4H2O are both reduced by a factor of ~2. Through density functional theory (DFT) analysis we find almost degenerate AFM states in Fe2(HPO3)3 ⋅ 4H2O which are close in energy. The competition of these AFM states might lead to the two successive AFM phase transitions at low temperature. The low ordering temperature as well as competing AFM states both imply frustrated magnetism in Fe2(HPO3)3 ⋅ 4H2O, probably originating from the complex competing AFM interactions. The optical properties of Fe2(HPO3)3 ⋅ 4H2O are also investigated by photoluminescence and infrared spectroscopies.