Contrasting Magnetic Behaviors in Rhodium- and Ruthenium-Doped Cubic Perovskite SrFeO 3 : Nearly Ferromagnetic Metal versus Spin-Glass Insulator.

The effects of Rh and Ru doping for SrFeO3 , a helimagnetic metal with a cubic perovskite structure, are studied by magnetic and resistivity measurements. Although SrRhO3 is a paramagnetic metal and SrRuO3 is a ferromagnetic one, the Rh doping induces a nearly ferromagnetic metallic state, whereas the Ru doping induces a spin-glass insulating state. Mössbauer measurements evidence a marked difference between SrFe0.8 Rh0.2 O3 and SrFe0.8 Ru0.2 O3 in the formal valences of Fe, which are estimated to be 4+ and 3.75+, respectively. The contrasting magnetic behaviors of Rh- and Ru-doped SrFeO3 are discussed in terms of the subtle balance between the double-exchange ferromagnetism and the superexchange antiferromagnetism.