Site substitution in GdMnO3: Effects on structural, electronic, and magnetic properties

We report on detailed structural, electronic, and magnetic studies of GdMn1-xCrxO3 for Cr doping levels; x = 0 <= x <= 1. X-ray diffraction studies suggest that GdMn0.5Cr0.5O3 has a monoclinic P2(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 Mn3+ ions gives rise to major changes in the be-plane sublattice and also an effective orbital ordering in the ab plane, which persist up to compositions x similar to 0.35. These distinct features in the lattice and orbital degrees of freedom are also correlated with be-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 >= 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.