Five characteristic temperatures of TM = 148 K, TN = 142 K, Tt = 138 K, Tf ~ 125 K and Tg ~ 50 K were found by the measurements of the magnetization curves at various temperature. The spontaneous magnetization appears below TM. It increases up to M_{
S} simeq 2 times 10^{-4} mu_{B} at Tt and then decreases steeply below Tt, which qualitatively agrees with the temperature dependence of magnetization obtained under field-cooling (FC) condition. On the other hand, the slope of the magnetization curve, namely the magnetic susceptibility, drops below TN, which coincides with the temperature dependence of magnetization obtained under zero-FC condition, although the magnetization curves were obtained under FC condition. The temperature dependence of the spontaneous magnetization shows a minimum at Tf and a drop at Tg although there is no anomaly in the temperature dependence of FC or ZFC magnetization.
