Comparative study of spin reorientation in orthoferrite NdFeO3 due to A- site doping in one case and B- site doping in another

Orthoferrites are pervoskite with general formula ABO3, where A-site is occupied by rare earth compounds and B-site by transition metals. The parent compound is NdFeO3, which is G-type antiferromagnetic in nature with the Néel temperature 670 K. From powder neutron diffraction studies, it has been found that with the lowering of temperature in the range 190 – 100 K, Fe3+ spins undergo gradual spin reorientation where easy axis changes from x to z direction leading to the change in magnetic structure Γ4 (Gx, Cy, Fz) → Γ2 (Fx, Cy, Gz). In the present work, we have studied the spin reorientation of Fe3+ spins as well as rare earth ordering in two ways i) by 50% doping of Mn ions on Fe site i.e. B- site ii) by 50% doping of Dy ions on Nd site i.e. A- site. In both the cases, crystal structure of the compound remains same as parent compound i.e. orthorhombic with Pbnm space group but there is change in Néel temperature as well as magnetic structure. In NdFe0.5Mn0.5O3, spin reorientation is observed in two temperature region with the easy axis of Fe3+/Mn3+ ions rotating gradually from x to y direction in the first region which is around Néel temperature (300-150 K) and  y to z direction in the lower temperature region (70-20 K). Nd3+ ion orders with a small ferromagnetic canting (Fx) below 4K. In Nd0.5Dy0.5FeO3, Fe3+ spins undergo gradual rotation from x to z direction till 20 K contradicting the abrupt spin reorientation from x to y direction as observed in DyFeO3 and again below 10 K Fe3+ spins started rotating along x direction. Rare earth ordering i.e. Nd3+/Dy3+ also started with Cy type ordering which is unusual as compared to parent compounds.