Effect of reduction temperature on the structure and magnetic properties of nano FeCo/Al₂O₃ composites

Nano FeCo/Al₂O₃ composites were synthesized using a sol-gel technique combined with H-reduction method. The microstructure and magnetic properties of the samples were characterized by X-ray diffraction，transmission electron microscopy，vibrating sample magnetometer and Mssbauer spectroscopy. The results show that nano FeCo in FeCo/Al₂O₃ composites presents bcc structure. With the increasing of reducing temperature，the grain size of FeCo increases，while glomeration and growth of α-FeCo are rest ricted effectively due to the existence of Al₂O₃. With the increasing of the grain size of FeCo，the saturation magnetization of the samples increases，but the coercivity of the samples increases firstly then decreases. The maximum values of saturation magnetization and coercivity are 62.41 emu·g^-1 and 208.99 Oe respectively；FeCo/Al₂O₃ transforms from a mixed state containing superparamagnetism and magnetic-order to a complete magnetic-order state. The change of coercivity results from the transformation of magnetic structure from single-domain to multi-domain.