Synthesis, Crystal Structure, and Magnetic Properties of ϵ‐In x Fe 2– x O 3 Nanorod‐Shaped Magnets

A series of ϵ‐In x Fe 2– x O 3 nanorods are prepared by combining the reverse‐micelle and the sol–gel methods. Metal replacement was achieved in the region of 0 ≤  x  ≤ 0.24. The crystal structures are orthorhombic structures (space group: Pna 2 1 ), which are pyroelectric with an electric polarization along the c axis. The transmission electron microscopy images show that the particle sizes are (80 ± 40) × (23 ± 5) nm ( x  = 0), (65 ± 30) × (30 ± 10) nm ( x  = 0.12), and (80 ± 40) × (35 ± 15) nm ( x  = 0.24). The magnetization versus temperature curves of the samples with x  = 0, x  = 0.12, and x  = 0.24 show spontaneous magnetization with Curie temperatures of 495 K, 456 K, and 414 K, respectively. Their coercive fields at 300 K are 20 kOe ( x  = 0), 14 kOe ( x  = 0.12), and 9 kOe ( x  = 0.24). These samples show a spin reorientation with reorientation temperatures ( T p ) of 102 K ( x  = 0), 149 K ( x  = 0.12), and 180 K ( x  = 0.24). In particular, the samples with x  = 0.12 and x  = 0.24 show antiferromagnetic behavior below T p . This series of ϵ‐In x Fe 2– x O 3 is the first example of a pyroelectric material that exhibits a phase transition between ferrimagnetism and antiferromagnetism.