24 research outputs found

    Topological magnons driven by the Dzyaloshinskii-Moriya interaction in the centrosymmetric ferromagnet Mn5_5Ge3_3

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    The phase of the quantum-mechanical wave function can encode a topological structure with wide-ranging physical consequences, such as anomalous transport effects and the existence of edge states robust against perturbations. While this has been exhaustively demonstrated for electrons, properties associated with the elementary quasiparticles in magnetic materials are still underexplored. Here, we show theoretically and via inelastic neutron scattering experiments that the bulk ferromagnet Mn5_5Ge3_3 hosts gapped topological Dirac magnons. Although inversion symmetry prohibits a net Dzyaloshinskii-Moriya interaction in the unit cell, it is locally allowed and is responsible for the gap opening in the magnon spectrum. This gap is predicted and experimentally verified to close by rotating the magnetization away from the cc-axis with an applied magnetic field. Hence, Mn5_5Ge3_3 realizes a gapped Dirac magnon material in three dimensions. Its tunability by chemical doping or by thin film nanostructuring defines an exciting new platform to explore and design topological magnons. More generally, our experimental route to verify and control the topological character of the magnons is applicable to bulk centrosymmetric hexagonal materials, which calls for systematic investigation.Comment: 24 pages, 4 figures. Accepted in Nature Communication

    An overview of the spin dynamics of antiferromagnetic Mn5_5Si3_3

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    The metallic compound Mn5_5Si3_3 hosts a series of antiferromagnetic phases which can be controlled by external stimuli such as temperature and magnetic field. In this work, we investigate the spin-excitation spectrum of bulk Mn5_5Si3_3 by combining inelastic neutron scattering measurements and density functional theory calculations. We study the evolution of the dynamical response under external parameters and demonstrate that the spin dynamics of each phase is robust against any combination of temperature and magnetic field. In particular, the high-energy spin dynamics is very characteristic of the different phases consisting of either spin waves or broad fluctuations patterns.Comment: 5 figure

    Effects of Cr-doping on the Jahn-Teller, the orthorhombic to rhombohedral, and the magnetic transitions in LaMn1-xCrxO3 compounds

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    We report on the electrical resistivity, the specific heat, and differential thermal analysis of LaMn1-xCrxO3 (x = 0.00–0.35) polycrystalline compounds at T > 300 K, as well as on their magnetic properties in the temperature range from 80 K to 280 K. The transport and the thermal results show that the isovalent substitution of Mn3+ by Cr3+ decreases the cooperative Jahn-Teller distortion and consequently affects orbital ordering in the whole concentration range. It is found that Cr drastically reduces the entropy change associated to the Jahn-Teller transition to negligible values for x ≥ 0.20. The orthorhombic to rhombohedral transition is also displaced to lower temperatures by Cr-doping, however exhibiting non-zero associated enthalpy changes for all x. A ferromagnetic contribution develops in orbitally disordered alloys with x ≥ 0.20. The paramagnetic to ferromagnetic transition temperatures show a similar variation upon increasing x as for the LaMn1-xGaxO3 system, implying a common origin for the ferromagnetic interaction in both systems. © 2020 Elsevier B.V

    Total interference between nuclear and magnetovibrational one-phonon scattering cross sections

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    A full phonon intensity cancellation is reported in a longitudinal polarized inelastic neutron scattering experiment performed on the magnetocaloric compound MnFe4Si3, a ferromagnet with TCurie ≈ 305 K. The TA[100] phonon polarized along the c-axis measured from the Brillouin zone center G=(0, 0, 2) is observed only in one (σz++\sigma _z^{ + + }) of the two non-spin-flip polarization channels and is absent in the other one (σz\sigma _z^{ - - }) at low temperatures. This effect disappears at higher temperatures, in the vicinity of TCurie , where the phonon is measured in both channels with nonetheless marked different intensities. The effect is understood as originating from nuclear-magnetic interference between the nuclear one-phonon and the magnetovibrational one-phonon scattering cross-sections. The total cancellation reported is accidental, i.e. does not correspond to a systematic effect, as established by measurements in different Brillouin zones

    Spin Fluctuations Drive the Inverse Magnetocaloric Effect in Mn5_5Si3_3

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    Inelastic neutron scattering measurements are performed on single crystals of the antiferromagnetic compound Mn5Si3 in order to investigate the relation between the spin dynamics and the magnetothermodynamics properties. It is shown that, among the two stable antiferromagnetic phases of this compound, the high temperature one has an unusual magnetic excitation spectrum where propagative spin waves and diffuse spin fluctuations coexist. Moreover, it is evidenced that the inverse magnetocaloric effect of Mn5Si3, the cooling by adiabatic magnetization, is associated with field induced spin fluctuations

    Synthesis and detailed characterization of bulk Sr2PdO3

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    Bulk Sr2PdO3 was synthesized by a modified solid state reaction and a detailed characterization was carried out using both microscopic and macroscopic experimental techniques. Pd site exhibits an electric field gradient of 5.9(1) ⋅ 1017 V/cm2 due to the anisotropic local atomic configuration. A Curie - paramagnetic susceptibility indicating antiferromagnetic interactions superimposed to a core diamagnetic state is confirmed. A linear volume thermal expansion with a coefficient of 3.0(1) ⋅ 10−5 K−1 at room temperature is extracted. A collection of Einstein oscillators, with an Einstein temperature of about 115 K, is involved in the thermal transport. Large atomic displacements were observed in Sr vibrations. No Pd or Sr valence change is observed up to 900 K. A moderate anharmonicity is identified and quantified in a macroscopic Grüneisen parameter of 2.5(1) at room temperature. The electrical resistivity reveals a semiconducting behaviour. A systematic reduction in electrical resistivity and a change in the conduction mechanism is observed upon thermal cycling which indicates that a peculiar electronic mechanism is involved. © 2018 Elsevier B.V
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