Structure and magnetism of the Rh4+-containing perovskite oxides La0.5Sr0.5Mn0.5Rh0.5O3 and La0.5Sr0.5Fe0.5Rh0.5O3.

Synchrotron X-ray powder diffraction data indicate that La_0.5Sr_0.5Mn_0.5Rh_0.5O₃ and La_0.5Sr_0.5Fe_0.5Rh_0.5O₃ adopt distorted perovskite structures (space group Pnma) with A-site and B-site cation disorder. A combination of XPS and ⁵⁷Fe Mössbauer data indicate the transition metal cations in the two phases adopt Mn³⁺/Rh⁴⁺ and Fe³⁺/Rh⁴⁺ oxidation state combinations respectively. Transport data indicate both phases are insulating, with ρ vs. T dependences consistent with 3D variable-range hopping. Magnetisation data reveal that La_0.5Sr_0.5Mn_0.5Rh_0.5O₃ adopts a ferromagnetic state below T_c ∼ 60 K, which is rationalized on the basis of coupling via a dynamic Jahn–Teller distortion mechanism. In contrast, magnetic data reveal La_0.5Sr_0.5Fe_0.5Rh_0.5O₃ undergoes a transition to a spin-glass state at T ∼ 45 K, attributed to frustration between nearest-neighbour Fe–Rh and next-nearest-neighbour Fe–Fe couplings. [ABSTRACT FROM AUTHOR]