24 research outputs found
Topological magnons driven by the Dzyaloshinskii-Moriya interaction in the centrosymmetric ferromagnet MnGe
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 MnGe 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 -axis with an applied magnetic field. Hence, MnGe
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 MnSi
The metallic compound MnSi 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
MnSi 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
Effects of Cr-doping on the Jahn-Teller, the orthorhombic to rhombohedral, and the magnetic transitions in LaMn1-xCrxO3 compounds
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
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 () of the two non-spin-flip polarization channels and is absent in the other one () 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
Total interference between nuclear and magnetovibrational one-phonon scattering cross sections
Spin Fluctuations Drive the Inverse Magnetocaloric Effect in MnSi
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
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