The Effect Of Oxygen Content On The Structure, Magnetic And Transport Properties For LaMn_0.7Fe_0.3O_3＋δ

Polycrystalline bulk samples of LaMn_0.7Fe_0.3O_3+δ were prepared with the standard solid-state reaction. The sample obtained by the solid-state reaction was annealed at 700℃,750℃,800℃and 850℃in N2 for 6 hours. XRD analysis of these samples indicated this series of polycrystalline samples possess perovskite structure at room temperature.The oxygen content of LaMn_0.7Fe_0.3O_3+δ series was determined by the iodometric titration, and the oxygen content decreased with increasing annealing temperature. IR results show that the frequency B-O bending mode did not change with increasing annealing temperature, while that of the streTching mode shifted to lower wavenumber, which indicates that oxygen content has significant influences on B-O bond length and little on bond angle.We presented a detailed set of dc magnetization, magnetic hysteresis loops, resistance measurements on polycrystals of LaMn_0.7Fe_0.3O₃ system. The thermomagnetic irreversibility exhibited by the zero-field-cooled (ZFC) magnetization and field-cooling magnetization (FC) in the dc magnetization measurement is indicative of the absence of long-range ferromagnetic order. It was explained well by the spin-cluster glass. The zero-field-cooled magnetization (ZFC) does not coincide with FC curves blow Tc, which is a characteristic of spin-cluster glass. On the other hand, field-cooling magnetization reaches saturation at the low temperature, shows the character is the ferromagnetism. These phenomena indicate that with decreasing the temperature, the system enters a mixed phase with the ferromagnetic phase and antiferromagnetic phase. The decrease of the Tc with the increase of the annealed temperature for the...