Role of holes states on metal to insulator transition and collapse of magnetic ordering in LaFe1−xNixO3 (x = 0.0–0.5)

Polycrystalline LaFe1−xNixO3 (x = 0.0, 0.1, 0.3 and 0.5) have been prepared by the standard solid state reactions method. The phase formation has been confirmed by the powerful synchrotron X-ray diffraction experiment. In order to investigate the effects of Ni doping on the oxidation state, spin state and the magnetic ordering of the iron cations, 57Fe Mössbauer Spectroscopy has been carried out at room temperature. Iron is present as Fe3+ in high spin state in LaFeO3. Ni doping has no effect on the spin state of the Fe3+ cations. However, a progressive increase in the concentration of Fe4+ cations has been inferred. Relatively stronger covalent character of the Fe4+–O−2 bond causes a progressive collapse in the magnetic ordering and delocalization of the hole states.

► Possibility of any spin state transition of Fe3+ and its role to mediate the collapse in magnetic ordering has been excluded.
► Instead, the iron oxidizes partially to Fe4+ with more covalent Fe–O–Fe bond.
► Covalency of Fe–O–Fe bond increases and accounts for the magnetic collapse.
► MIT is partially contributed both by the electron interactions and disorder effects.
► Intermediate value of the IS in doped orthoferrites can be well described by the holes state which are of mainly O2p character.