Magnetic structure

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

Observation of topological Hall effect in Mn2RhSn films

Abstract: Recently non-collinear magnetic structures have attracted renewed attention due to the novel Hall effects that they display. In earlier work evidence for a non-collinear magnetic structure has been reported for the ferromagnetic Heusler compound Mn2RhSn. Using sputtering techniques we have prepared high quality epitaxial thin films of Mn2RhSn by high temperature growth on MgO (001) substrates. The films are tetragonally distorted with an easy magnetization axis along the c-axis. Moreover, we find evidence for an anomalous Hall effect whose magnitude increases strongly below the Curie temperature that is near room temperature. Consistent with theoretical calculations of the anomalous Hall conductivity that we have carried out by deriving the Berry curvature from the electronic structure of perfectly ordered Mn2RhSn, the sign of the anomalous Hall conductivity is negative, although the measured value is considerably smaller than the calculated value. We attribute this difference to small deviations in stoichiometry and chemical ordering. We also find evidence for a topological Hall resistivity of about 50 nΩ cm, which is ~5% of the anomalous Hall effect, for temperatures below 100 K. The topological Hall effect signifies the presence of a chiral magnetic structure that evolves from the non-collinear magnetic structure that Mn2RhSn is known to exhibit.

The magnetic structure and electronic ground states of mott insulators GeV4S8 and GaV4S8

Abstract: The ground states of magnetic Mott insulators GaV4S8 and GeV4S8 were calculated with full-potential LAPW methods using the LDA + U approach. Both compounds undergo structural distortions from cubic to rhombohedral (GaV4S8) or orthorhombic (GeV4S8) symmetry at low temperatures. GaV4S8 is ferromagnetic below TC = 10 K, whereas GeV4S8 shows antiferromagnetic order with TN = 13 K. The spin structure of GeV4S8 was determined by neutron diffraction and described in the magnetic space group Pbmn21. The magnetic propagation vector is [1/2, 1/2, 0] relating to the cubic paramagnetic unit cell. The LDA + U calculations (U = 2 eV) confirm the magnetic insulating ground states for the first time with magnetic moments and energy gaps in very good agreement with the experimental data. This method also reproduces the antiferromagnetic spin ordering of GeV4S8. The Jahn−Teller instability of the degenerated levels in the V4 cluster MO drives the structural distortions, depending on the cluster electron count. Our results ...

Helifan: A new type of magnetic structure.

Abstract: The magnetic phases which have earlier been observed when a magnetic field is applied in the plane of the helical magnetic structure of Ho are identified with structures, intermediate between the helix and the fan, which we call helifans. A number of helifan structures have been calculated by a self-consistent mean-field method, and one of them accounts very well for the observed neutron-diffraction pattern. Different sequences of helifans may, in principle, be produced by varying the magnetic field and temperature, and modifying the exchange by alloying.

Nanocrystalline Nd2Fe17 synthesized by high-energy ball milling: crystal structure, microstructure and magnetic properties.

Abstract: Nanocrystalline Nd2Fe17 powders have been obtained by means of high-energy ball milling from nearly single-phase bulk alloys produced by arc melting and high temperature homogenization annealing. The rhombohedral Th2Zn17-type crystal structure of the bulk alloy remains unaltered after the milling process, with almost unchanged values for the cell parameters. However, the severe mechanical processing induces drastic microstructural changes. A decrease of the mean crystalline size down to around 10 nm is observed, giving rise to a considerable augmentation of the disordered inter-grain boundaries. This modification of the microstructure affects the magnetic behaviour of the milled powders, although the magnetic structure remains collinear ferromagnetic. While a unique ferro-to-paramagnetic transition temperature, TC = 339 ± 2 K, is observed in the bulk alloy, the nanocrystalline samples exhibit a more likely distribution of TC values. The latter seems to be responsible for the significant broadening of the temperature range in which magneto-caloric effect is observed, and the lowering of the maximum value of the magnetic entropy change. (Some figures in this article are in colour only in the electronic version)

Interactions in various magnetic compounds

Abstract: Susceptibility measurements on single crystals of KFe11O17 show an anomalous antiferromagnetic behavior, which we propose to call antiferrimagnetism. The behavior follows from Weiss field theory on a simplified (i.e., two‐sublattice) model.The magnetic structure of K2NiF4 has been determined by neutron diffraction by Legrand and Plumier at C.E.N., Mol (Belgium). Measurements on their single crystal show that χ∥ and χ⊥ become nearly equal at ≈100°K, i.e., far below the temperature where χ is maximum. This is believed to be due to a gradual breaking up of the long‐range order in the basal layers. Results obtained on powders of La0.5Sr1.5MnO4 and La1.5Sr0.5CoO4 are also given.Pure polycrystalline samples of EuS, EuSe, and EuTe with rocksalt structure show θ values of +16, +6, and −7°K; EuTe has a Neel temperature at +11°K. The ferromagnetism of EuO, EuS, and EuSe is due to a predominant direct positive exchange interaction Eu‐Eu, the antiferromagnetism of EuTe to a predominant next‐nearest neighbor superexch...