Complex Ferrimagnetism and Magnetoresistance Switching in Ca-Based Double Double and Triple Double Perovskites

Cation ordering in ABO₃ perovskites can lead to interesting and useful phenomena such as ferrimagnetism and high magnetoresistance by spin polarized conduction in Sr₂FeMoO₆. We used high pressures and temperatures to synthesize the cation ordered AA′BB′O₆ perovskites CaMnFeReO₆, CaMnMnReO₆, and Ca­(Mn_0.5Cu_0.5)­FeReO₆. These have columnar A/A′ and rocksalt B/B′ cation orders, as found in the recently discovered double double perovskite MnNdMnSbO₆, and partial Mn/Cu order over tetrahedral and square planar A′ sites in Ca­(Mn_0.5Cu_0.5)­FeReO₆ demonstrates that triple double cation order is possible. Neutron diffraction reveals complex ferrimagnetic orders in all three materials; CaMnFeReO₆ and Ca­(Mn_0.5Cu_0.5)­FeReO₆ have large room temperature magnetizations with low temperature switching of magnetoresistance in the latter material, and CaMnMnReO₆ displays a high coercivity of 1.3 T at low temperatures

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

Spin order in the charge disproportionated phases of the A-site layer ordered triple perovskite LaCa2Fe3O9

International audienceThe coupling between spins and charge disproportionation states has been investigated in the LaCa 2 Fe 3 O 9 oxide with neutron powder diffraction. This A-site layer ordered triple perovskite LaCa 2 Fe 3 O 9 undergoes charge disproportionation on cooling and shows two different charge ordering patterns. At 230 K, Fe 3.67+ disproportionates into a 2:1 ratio of Fe 3+ :Fe 5+ which order in a layered manner along the <010> direction of the pseudocubic unit cell. At lower temperatures (T < 170 K), the charge ordering pattern changes to a layered arrangement along the <111> direction. Neutron powder diffraction data shows that in the intermediate temperature range (170 K < T < 230 K) the spins order into a cycloidal structure on the ac plane for the Fe 3+ cations while the Fe 5+ cations remain paramagnetic. For the lowest temperature range (2 K < T < 190 K), the spin structure follows the charge ordering and evolves to a <111> layered magnetic structure. Introduction

Lock-in spin structures and ferrimagnetism in polar Ni2−xCoxScSbO6 oxides

International audienceThe new phase Co2ScSbO6 and Ni2-xCoxScSbO6 solid solutions adopt the polar Ni3TeO6-type structure and order magnetically below 60 K. A series of long-period lock-in [0 0 1/3n] spin structures with n = 5, 6, 8 and 10 is discovered, coexisting with a ferrimagnetic [0 0 0] phase at high Co-contents. The presence of electrical polarisation and spontaneous magnetisations offers possibilities for multiferroic properties

Stabilization of cubic Sr₂FeMoO₆ through topochemical reduction

Cubic Sr2FeMoO6 has been stabilized at room temperature, through topochemical de-intercalation of oxygen anions, whilst leaving magnetic ordering intact.</p

Incommensurate spin order in the metallic perovskite MnVO3

Incommensurate Mn spin order has been discovered in the perovskite MnVO3 containing localized 3d5 Mn2+ and itinerant 3d1 V4+ states. This phase has a distorted Pnma crystal structure (a = 5.2741(6) Å, b = 7.4100(11) Å, and c = 5.1184(8) Å at 300 K) and is metallic at temperatures of 2-300 K and at pressures of up to 67 kbar. Neutron scattering reveals a (0.29 0 0) magnetic vector below the 46 K spin ordering transition, and both helical and spin density wave orderings are consistent with the diffraction intensities. Electronic structure calculations show large exchange splittings of the Mn and V 3d bands, and (kx 0 0) crossings of the Fermi energy by spin up and down V 3d bands may give rise to Ruderman-Kittel-Kasuya-Yosida coupling of Mn moments, in addition to their superexchange interactions. © 2011 American Physical Society

Incommensurate spin order in the metallic perovskite MnVO₃

Incommensurate Mn spin order has been discovered in the perovskite MnVO3 containing localized 3d(5) Mn2+ and itinerant 3d(1) V4+ states. This phase has a distorted Pnma crystal structure (a = 5.2741(6) angstrom, b = 7.4100(11) angstrom, and c = 5.1184(8) angstrom at 300 K) and is metallic at temperatures of 2-300 K and at pressures of up to 67 kbar. Neutron scattering reveals a (0.29 0 0) magnetic vector below the 46 K spin ordering transition, and both helical and spin density wave orderings are consistent with the diffraction intensities. Electronic structure calculations show large exchange splittings of the Mn and V 3d bands, and (k(x) 0 0) crossings of the Fermi energy by spin up and down V 3d bands may give rise to Ruderman-Kittel-Kasuya-Yosida coupling of Mn moments, in addition to their superexchange interactions