Complex Cation and Spin Orders in the High-Pressure Ferrite CoFe3O5

A ferrite in the Sr2Tl2O5-type MFe3O5 family with M = Co has been synthesized at 12 GPa pressure. Neutron diffraction shows the sample to be Co deficient with composition Co0.6Fe3.4O5. The Co/Fe cation distribution is found to be profoundly different from those of MFe3O5 analogs and lies between normal and inverse limits, as Co2+ substitutes across trigonal prismatic and one of the two octahedral sites. CoFe3O5 shows complex magnetic behavior with weak ferromagnetism below TC1 ≈ 300 K and a second transition to ferrimagnetic order at TC2 ≈100 K. Spin scattering of carriers leads a substantial increase in the hopping activation energy below TC1, and a small negative magnetoresistance is observed at low temperatures.EPSRCDepto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu

A New Cation-Ordered Structure Type with Multiple Thermal Redistributions in Co₂InSbO₆

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO(3)) and LiNbO(3) type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO(3) derivative with R32 symmetry has never been observed. Here we show that Co(2)InSbO(6) recovered from high pressure has a new, ordered‐R32 A(2)BCO(6) variant of the corundum structure. Co(2)InSbO(6) is also remarkable for showing two cation redistributions, to (Co(0.5)In(0.5))(2)CoSbO(6) and then Co(2)InSbO(6) variants of the ordered‐LiNbO(3) A(2)BCO(6) structure on heating. The cation distributions change magnetic properties as the final ordered‐LiNbO(3) product has a sharp ferrimagnetic transition unlike the initial ordered‐R32 phase. Future syntheses of metastable corundum derivatives at pressure are likely to reveal other cation‐redistribution pathways, and may enable ABO(3) materials with the R32 structure to be discovered

YRuO3: A quantum weak ferromagnet

International audienceThe perovskite YRuO 3 containing low-spin d 5 Ru 3+ has a Pnma orthorhombic structure with elongated RuO 6 octahedra evidencing orbital order and is insulating to low temperatures with a band gap of 70 meV. Canted antiferromagnetic Ru 3+ spin order is observed below T C = 97 K, and magnetization plateaus that emerge below 62 K reveal a quantum weak ferromagnetic state where 1/8 of the spins are reversed, reflecting extreme singleion anisotropy resulting from the strong spin-orbit coupling of the d 5 Ru 3+ ion. Dynamic effects of the reversed spins give rise to an unusual negative AC susceptibility response, and a partial freezing of this motion occurs at 27 K