Magnetic structure

About: Magnetic structure is a research topic. Over the lifetime, 10787 publications have been published within this topic receiving 207143 citations.

Neutron diffraction study of YVO 3 , NdVO 3 , and TbVO 3

Abstract: The structural and magnetic properties of YVO3, NdVO3 and TbVO3 were investigated by single-crystal and powder neutron diffraction. YVO3 shows a structural phase transition at 200 K from an orthorhombic structure with the space group Pbnm to a monoclinic one with the space group P21 /b. But supplementary highresolution synchrotron diffraction experiments showed that the monoclinic distortion is extremely small. A group theoretical analysis shows that this magnetic state in the monoclinic phase is incompatible with the lattice structure, unless terms of higher than bilinear order in the spin operators are incorporated in the spin Hamiltonian. This observation is discussed in the light of recent theories invoking unusual many-body correlations between the vanadium t2g orbitals. A structural phase transition back to the orthorhombic space group Pbnm is observed upon cooling below 77 K. This transition is accompanied by a rearrangement of the magnetic structure into a mode compatible with the lattice structure. The crystal structures of NdVO3 and TbVO3 are closely similar to that of YVO3. However, only a single magnetic phase transition was found in the vanadium sublattice down to 9.5 K. Below 60 K the magnetic moments of the Nd 3+ - and Tb 3+ -ions are gradually polarized by the ordered vanadium moments. Below 11 K, we found a noncollinear order of the terbium moments.

Oxygen stripes in La0.5Ca0.5MnO3 from ab initio calculations.

Abstract: We investigate the electronic, magnetic, and orbital properties of La 0 . 5 Ca 0 . 5 MnO 3 perovskite by means of an ab initio electronic structure calculation within the Hartree-Fock approximation. Using the experimental crystal structure reported by Radaelli et al. [Phys. Rev. B 55, 3015 (1997)], we find a charge-ordering stripelike ground state. The periodicity of the stripes, and the insulating magnetic structure, consisting of antiferromagneticaly coupled zigzag chains, are in agreement with neutron x-ray and electron diffraction experiments. However, the detailed structure is more complex than that envisaged by simple models of charge and orbital order on Mn d levels alone, and is better described as a charge-density wave of oxygen holes, coupled to the Mn spin/orbital order.

Layered Antiferromagnetic Ordering in the Most Active Perovskite Catalysts for the Oxygen Evolution Reaction

Abstract: We have performed an in-depth ab initio study of the magnetic structure within the most active perovskites for the oxygen evolution reaction. In all cases, the ground state exhibits an extended antiferromagnetic coupling in the unit cell. Layered antiparallel alignment of the magnetic moments appears to be related to their electrocatalytic activity. All the perovskites calculated within this paper show space-separated charge-transport channels depending on the spin orientation. Comparing the electronic structures with the reported activities, we find a direct correlation between the magnetic accumulation on the spin channels in the bulk material and the catalytic activity. We discuss the possible implications of such observations in terms of magnetic interactions. During oxygen evolution in water electrolysis, reactants and products do not preserve spin. For triplet state oxygen to evolve, the catalyst at the anode can speed up the reaction if it is able to balance the magnetism of the oxygen molecule by extracting electrons with an opposite magnetic moment, conserving the overall spin.