Reorientation Phenomenon in a Magnetic Phase ofε-Fe2O3Nanocrystal

We observed an unusual magnetic phase transition in the magnetic phase of ε -Fe 2 O 3 nanorods (Néel temperature = 495 K). In the cooling process at 1 kOe, the magnetization value ( M ) of the ε -Fe 2 O 3 phase decreased at 154 K and then sharply decreased between T =115 and 70 K. During the heating process, the M value returned to the original value at T =125 K with a thermal hysteresis of 10 K. This phase transition is accompanied by a decrease in coercive field from 21 kOe (200 K) to 0.6 kOe (100 K). This unusual magnetic phase transition is interpreted as a spin reorientation phenomenon due to the compensation between the magnetic dipole–dipole interaction and the single-ion anisotropy.