Search

Magnetic order consistent with multiferroism has been observed in the acentric LiNbO3-type, high pressure form II of MnTiO3 using neutron diffraction and magnetization measurements. Spin order below the 28 K magnetic transition has propagation vector (0 0 0), and spins lie in the ab plane. Representation synmietry analysis shows that the antiferromagnetic Mn2+ spin component observed by neutron scattering, of magnitude 3.9(1) /μB at 2 K, coexists with a weak ferromagnetic component of magnitude 0.0014 μB. This magnetization is perpendicular to the electrical polarization resulting from cation displacements in this acentric structure, permitting coupled switches of the two ferroic orders. The spin order is stable to fields of at least 5 T; however, facile domain reorientation within the ab plane enhances the antiferromagnetic susceptibility and a constant magnetization/field (M/H) is observed in field strengths greater than ∼1.5 T. Suppression of the {101} neutron intensity with field follows the same Brillouin-dependence as M/H and enables the antiferromagnetic easy axes to be identified as parallel to the ab plane hexagonal axes. [ABSTRACT FROM AUTHOR]

Spin-ordered structures of monoclinic brannerite-type CoV206 have been determined from neutron diffraction data recorded at 2 ? in applied magnetic fields of 0,2.5, and 5.0 T. Three collinear magnetic phases were observed as field increases: an antiferromagnetic state with propagation vector (0 1 ½). a ferrimagnetic (−⅓ 1 ⅓) phase, and a (0 0 0) ferromagnetic order. Co2+ moments of 4.4-5.0 µ? have a large orbital component and are aligned close to the c-axis direction in all cases. Spin-lattice coupling leads to a magnetostriction and volume expansion as field increases. The ferrimagnetic phase accounts for the previously reported 1 /3-magnetization plateau, and demonstrates that monoclinic CoV206 behaves as an accidental triangular antiferromagnetic lattice in which further frustrated orders may be accessible. [ABSTRACT FROM AUTHOR]

Abstract: A variable-temperature powder neutron diffraction study of the monoclinic brannerite-type CoV2O6 (space group C2/m, a=9.2531(2), b=3.5040(1), c=6.6201(1) Å and β=111.617(1)° at 300K) is reported. No structural transition is observed down to 4K, but a magnetostriction accompanying antiferromagnetic order at T N =15K is discovered. Antiferromagnetic order observed below T N has an a×b×2c supercell in which Co2+ moments of magnitude 4.77(4)μB at 4K lie in the ac plane and are ferromagnetically coupled within chains of edge-sharing CoO6 octahedra parallel to b. Ferromagnetic chains are coupled antiferromagnetically to neighbouring chains in the a and c directions, and a model for the interchain order in the reported 1/3 magnetization plateau region is proposed. [Copyright &y& Elsevier]

The magnetism of the A-site-ordered perovskite LaMm3V4O12 is studied comprehensively by means of neutron powder diffraction experiments and theoretical calculations. Magnetic neutron diffraction results show that a rhombohedral 60° spin structure emerges on the cubic lattice below a 44-K Néel transition. Ab initio electronic structure calculations confirm that high-spin Mn2+ moments are localized while V 3d-band states are itinerant, and that the noncollinear 60° spin structure is more stable than collinear ferromagnetic or G-type antiferromagnetic alternatives. Effective Heisenberg model calculations reveal that the appearance of such a nontrivial spin structure can be attributed to significant next-nearest-neighbor and third-nearest-neighbor magnetic interactions. [ABSTRACT FROM AUTHOR]

The magnetic and crystal structures of the title materials have been investigated using high-resolution neutron and synchrotron x-ray powder diffraction. Ferromagnetic Ru dimers are observed in the spin-ordered ground states of all three materials, evidencing an intradimer double exchange interaction. Antiferromagnetic order between dimers breaks the degeneracy of the triangular lattice but no distortion of the B′ = La and Y structures is observed. The magnetic ordering transition temperature increases with the radius of the B′ cation. An anomalous 120 K structural transition in Ba3NdRu2O9 is attributed to Jahn-Teller distortion, evidenced by large-amplitude Γ6 deformations of the NdO6 octahedra. Further lattice anomalies accompany magnetic ordering transitions at 24 and 18 K in Ba3NdRu2O9. Nd spins order ferromagnetically and a substantial magnetic anisotropy leads to large coercivity and 1/3-magnetization steps in the magnetic hysteresis loop. [ABSTRACT FROM AUTHOR]