Electrical transport and magnetic properties of room temperature ferromagnetism Sr_4-xEr_xCo₄O_10.5+δ(0.6≤x≤1.2) polycrystalline

Sr_4-xEr_xCo₄O_10.5+δ (0.4≤x≤1.2) polycrystalline were prepared by conventional solid state reaction, the effect of Er doping on the crystalline structure, electrical transport and magnetic properties were investigated. X-ray diffraction results show that the space groups were P3^-m3 with cubic crystal system and I4/mmm with tetragonal system when x=0.4 and 0.6≤x≤1.2, respectively, the lattice constant of tetragonal structure decreases with the increasing of Er doping. SEM results show that with the increasing of Er doping, the grain size decreases and the grain boundaries increase. The resistivity dependence of the temperature curves were measured by four-probe method, the results show that the polycrystalline bulks exhibit insulating behavior in the range of 80-300 K, and the resistivity as well as the thermal activation energy increases with the Er doping increasing. The magnetization and hysteresis loops were measured by superconducting quantum interference device, the results show that Sr_4-xEr_xCo₄O_10.5+δ (0.6≤x≤1.2) exhibits room temperature ferromagnetic with the curie temperature of 320-335 K, which may be derived from the peculiar Sr/Er ordering and the uncompensated magnetic moment of Co ions in CoO_4.5+δ.