Two ferromagnetic phases with different spin states of Mn and Ni in LaMn0.5Ni0.5O3 -: art. no. 184416

A ferromagnetic transition below 280 K is observed in the temperature variation of the magnetization, measured using high magnetic fields, for samples of LaMn0.5Ni0.5O3 synthesized by the high-temperature solid-state reaction method. On the other hand, two well-defined magnetic transitions, at similar to150 and similar to280 K, are observed in low-field zero-field-cooled (ZFC) magnetization (M-ZFC) measurements on these samples, indicating the possibility for the existence of two different ferromagnetic phases of the compound. LaMn0.5Ni0.5O3, synthesized by a low-temperature method, shows a single magnetic transition at similar to150 K for samples annealed below 500 degreesC and a single magnetic transition at 280 K for samples annealed above 1000 degreesC in the low-field M-ZFC measurements. Broad or multiple magnetic transitions are observed for the low-temperature samples annealed in the temperature range 500-1000 degreesC. High-temperature magnetic susceptibility, powder x-ray-diffraction, and core-level x-ray photoelectron spectroscopic studies on the single-phase samples (annealed at 400 and 1300 degreesC) indicate that the nanocrystalline material (obtained at 400 degreesC) with spin states of Mn and Ni as Mn4+ and Ni2+ undergoes a magnetic transition below 150 K, whereas high temperature (1300 degreesC) annealed material with spin states like Mn3+ and low-spin Ni3+ becomes ferromagnetic below 280 K. A charge disproportionation of the type Mn4++Ni2+-->Mn3++Ni3+ takes place when the low-temperature synthesized LaMn0.5Ni0.5O3 is annealed above 500 degreesC. The results give evidence for the existence of two different phases of LaMn0.5Ni0.5O3 with different crystal structures and different spin states of Mn and Ni.