Magnetic properties and colossal magnetoresistance of La_0.67Ca_0.33Mn_0.99Fe_0.01O₃ materials

Abstract

Polycrystalline perovskite with composition La_0.67Ca_0.33Mn_0.99Fe_0.01O₃ has been produced by a metal- salt routed sol-gel processing method. Colossal magnetoresistance of La_0.67Ca_0.33Mn_0.99Fe_0.01O₃ has been studied with x-ray diffraction, Rutherford back-scattering spectroscopy, Möossbauer spectroscopy and vibrating sample magnetometer. Crystalline La_0.67Ca0.33Mn_0.99Fe_0.01O₃ was perovskite cubic structure with a lattice parameter a₀=3.868 Å. Mössbauer spectra of La_0.67Ca_0.33Mn_0.99Fe_0.01O₃ have been at various temperature ranging from 4.2 K to room temperature. Analysis of ⁵⁷Fe Mössbauer data in terms of the local configurations of Mn atoms has permitted the influence of the magnetic hyperfine interactions to be monitored. The values of the isomer shifts show that all iron ions are in the Fe³⁺ state. For magnetic fields > 8 kOe and T < 100 K the magnetic moment is saturated at the value is 85 emu/g. The Curie temperature, T_c, is determined to be 270 K. The doping of ⁵⁷Fe reduces Curie temperature and saturation magnetization. The temperature dependence of the resistance for La_0.67Ca_0.33Mn_0.99Fe_0.01O₃ under zero and 10kOe applied field is shown that a semiconductor-metal transition, T_SC-M, occurs at 250 K. The relative magnetoresistance, MR, defined as : [R(0) -R(H)]/ R(H), is about 33 %.