Magnetic properties and colossal magnetoresistance of La_5/6Na_1/6Mn_1-yFe_yO₃ with 0 ≤ y ≤ 0.10

The effect of Fe doping (0 ≤ y ≤ 0.10) in Mn site was studied for the colossal magnetoresistance material La_5/6Na_1/6MnO₃. The same size of Fe³⁺ and Mn³⁺ causes no structure change in the series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Doping with Fe causes no dominant lattice effects. It depopulates the hopping electrons and weakens the double exchange. ZFC and FC magnetization curve at 0.01 T field shows irreversibility. The temperature dependence of resistivity shows that all samples undergo a transition from paramagnetic to ferromagnetic with the decrease of temperature. However, for y = 0.10 sample, two obvious peaks are observed in the magnetoresistance versus temperature curve at 5 T field. The high-field MR effect may have its origin in a small canting of the manganese moments inside each domain even for H > H_s. The canting angle becomes smaller and therefore electrons transfer more easily between pairs of Mn³⁺ and Mn⁴⁺ions under high field. This will lead to a MR effect.