Spin reorientation in NdFe${}_{0.5}$Mn${}_{0.5}$O${}_3$: Neutron scattering and \emph{Ab-initio} study

Abstract

The structural, magnetic, and electronic properties of NdFe${}_{0.5}$Mn${}_{0.5}$O${}_3$ have been studied in detail using bulk magnetization, neutron/x-ray diffraction and first principles density functional theory calculations. The material crystallizes in the orthorhombic $Pbnm$ structure, where both Mn and Fe occupy the same crystallographic site ($4b$). Mn/Fe sublattice of the compound orders in to a G-type antiferromagnetic phase close to 250\,K where the magnetic structure belongs to ${\Gamma }_1$ irreducible representation with spins aligned along the crystallographic $b$ direction. This is unconventional in the sense that most of the orthoferrites and orthochromites order in the ${\Gamma }_4$ representation below the Néel temperature.This magnetic structure then undergoes a complete spin reorientation transition with temperature in the range 75\,K$\gtrsim$ T $\gtrsim$ 25\,K where the magnetic structure exists as a sum of two irreducible representations (${\Gamma }_1$+${\Gamma }_2$) as seen from neutron diffraction measurements. At 6\,K, the magnetic structure belongs entirely to ${\Gamma }_2$ representation with spins aligned antiferromagnetically along the crystallographic $c$ direction having a small ferromagnetic component ($F_x$). The unusual spin reorientation and correlation between magnetic ground state and electronic structure have been investigated using first principles calculations within GGA+U and GGA+U+SO formalisms.