Site substitution in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>GdMnO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>: Effects on structural, electronic, and magnetic properties

Abstract

We report on detailed structural, electronic, and magnetic studies of ${\mathrm{GdMn}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{3}$ for Cr doping levels; $x=0 \ensuremath{\le}\phantom{\rule{4pt}{0ex}}x\phantom{\rule{4pt}{0ex}}\ensuremath{\le}$ 1. X-ray diffraction studies suggest that ${\mathrm{GdMn}}_{0.5}{\mathrm{Cr}}_{0.5}{\mathrm{O}}_{3}$ has a monoclinic $P{2}_{1}/b$ structure with alternate arrangements of Mn and Cr atoms along the [001] direction. In the solid solutions, the Jahn-Teller distortion associated with ${\mathrm{Mn}}^{3+}$ ions gives rise to major changes in the $bc$-plane sublattice and also an effective orbital ordering in the $ab$ plane, which persist up to compositions $x\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 0.35. These distinct features in the lattice and orbital degrees of freedom are also correlated with $bc$-plane anisotropy of the local Gd environment. A gradual evolution of electronic states with doping is also clearly seen in O $K$-edge x-ray absorption spectra. Evidence of magnetization reversal in field-cooled-cooling mode for $x\phantom{\rule{4pt}{0ex}}\ensuremath{\ge}$ 0.35 coinciding with the Jahn-Teller crossover suggests a close correlation between magnetic interaction and structural distortion. These observations indicate a strong entanglement between lattice, spin, electronic, and orbital degrees of freedom. The nonmonotonic variation of remnant magnetization can be explained by doping-induced modification of magnetic interactions. Density-functional-theory calculations are consistent with layer-by-layer-type arrangements of Cr ions and Mn ions with ferromagnetic (antiferomagnetic) coupling between Mn (Cr) ions for intermediate compounds ($x=0.5$). For $x=0.25$ compositions, we found alternate layers of Mn and mixed Mn-Cr atoms stacked along the $c$ axis with intralayer ferromagnetic coupling and interlayer antiferromagnetic coupling. For $x=0.75$ compositions, there exists strong antiferomagnetic coupling between half-filled ${t}_{2g}$ orbitals of in-plane Cr ions along with a feromagnetic Mn-Cr coupling.

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