Oxygen stoichiometry and magnetic properties of LuFe₂O_4+δ

We report a comprehensive investigation of the magnetic properties of LuFe₂O₄ (LFO) samples with different oxygen stoichiometries. Samples with excess oxygen exhibit spin glass behavior without long-range magnetic order, while three-dimensional ferrimagnetic order exists in a stoichiometric sample. Dissimilar experimental observations reported in several papers can be understood consistently when oxygen stoichiometry is taken into account. The stoichiometric sample orders magnetically below T_N = 243 K, and a monoclinic lattice distortion sets in below T_L = 175 K. This structural change is sensitive to the applied magnetic field, indicating strong spin-lattice coupling in this material. Unusual low-field thermal magnetization behavior was observed near T_L, and its origin is discussed.