Magnetic properties of La2CuO4 with slight amounts of excess oxygen

Temperature dependence of magnetic susceptibility is reported for polycrystalline samples of La2CuO4 prepared under several conditions to reduce excess oxygen. The sample calcined at 1050 degrees C in flowing argon and quenched shows a sharp peak at a Neel temperature T-N of 302K. The sample calcined at 1050 degrees C in flowing oxygen and quenched shows T-N of 292K, which increases up to 304K after deoxygenation at 500 degrees C in flowing argon. These results show that further deoxygenation in flowing argon is necessary in order to reduce excess oxygen completely. It should be noted that the sample with T-N of 292K shows another peak at 64K. This peak shifts to 20K after annealing at 1000 degrees C in flowing oxygen, indicating that the low temperature peak can not be related to existence of bulk oxygen. Neither existence of impurity phases nor distribution of T-N can explain appearance of the low temperature peaks. These results strongly suggest existence of some magnetic transition in La2CuO4 with fairly slight amounts of excess oxygen.