Incoherent effect of Fe and Ni substitutions in the ferromagnetic-insulator La_(0.6)Bi_(0.4)MnO_(3+δ)

摘要

A comparative study of the effect of Fe and Ni doping on the bismuth based perovskite La_(0.6)Bi_(0.4)MnO_(3.1), a projected spintronics magnetic semiconductor has been carried out. The doped systems show an expressive change in magnetic ordering temperature. However, the shifts in ferromagnetic transition (T_c) of these doped phases are in opposite direction with respect to the parent phase T_c of 115 K. The Ni-doped phase shows an increase in T_c ～200 K, whereas the Fe-doped phase exhibits a downward shift to T_c～95 K. Moreover, the Fe-doped is hard-type whereas the Ni-doped compound is soft-type ferromagnet. It is observed that the materials are semiconducting in the ferromagnetic phase with activation energies of 77 & 82 meV for Fe & Ni-doped phases, respectively. In the presence of external magnetic field of 7 T, they exhibit minor changes in the resistivity behaviors and the maximum isothermal magnetoresistance is around -20% at 125 K for the Ni-phase. The results are explained on the basis of electronic phase separation and competing ferromagnetic and antiferromagnetic interactions between the various mixed valence cations.