Spin-glass Behavior in LuFe2O4+δ

We have carried out a comprehensive investigation of magnetic properties of LuFe2O4+δ, measuring ac susceptibility, dc magnetization, and specific heat. A magnetic phase transition around 236 K is identified as a paramagnetic to ferrimagnetic transition in accordance with previous studies. Upon further cooling below this temperature, highly relaxational magnetic behavior is observed: the dc magnetization exhibits history and time dependence, and the real and the imaginary parts of the ac susceptibility show large frequency dependence. Dynamic scaling of the ac susceptibility data suggests that this low-temperature phase can be described as a spin-glass phase. We also discuss the magnetic field dependence of the spin-glass transition and aging, memory, and rejuvenation effect below the glass transition temperature around 229 K.