Anisotropic Topological Hall Effect with Real and Momentum Space Berry Curvature in the Antiskrymion Hosting Heusler Compound Mn1.4_{1.4}PtSn

The topological Hall effect (THE) is one of the key signatures of topologically non-trivial magnetic spin textures, wherein electrons feel an additional transverse voltage to the applied current. The magnitude of THE is often small compared to the anomalous Hall effect. Here, we find a large THE of 0.9 $\mu\Omega$cm that is of the same order of the anomalous Hall effect in the single crystalline antiskyrmion hosting Heusler compound Mn$_{1.4}$PtSn, a non-centrosymmetric tetragonal compound. The THE is highly anisotropic and survives in the whole temperature range where the spin structure is noncoplanar (<170 K). The THE is zero above the spin reorientation transition temperature of 170 K, where the magnetization will have a collinear and ferromagnetic alignment. The large value of the THE entails a significant contribution from the momentum space Berry curvature along with real space Berry curvature, which has never been observed earlier

Detection of antiskyrmions by topological Hall effect in Heusler compounds

Heusler compounds having D2d crystal symmetry gained much attention recently due to the stabilization of a vortexlike spin texture called antiskyrmions in thin lamellae of Mn1.4Pt0.9Pd0.1Sn as reported in the work of Nayak et al. [Nature (London) 548, 561 (2017)10.1038/nature23466]. Here we show that bulk Mn1.4Pt0.9Pd0.1Sn undergoes a spin-reorientation transition from a collinear ferromagnetic to a noncollinear configuration of Mn moments below 135 K, which is accompanied by the emergence of a topological Hall effect. We tune the topological Hall effect in Pd and Rh substituted Mn1.4PtSn Heusler compounds by changing the intrinsic magnetic properties and spin textures. A unique feature of the present system is the observation of a zero-field topological Hall resistivity with a sign change which indicates the robust formation of antiskyrmions. © 2020 authors. Published by the American Physical Society

Neutron diffraction as a probe for the characterization of biological entities

International audienceUsing the neutron as a probe, investigations at the interface between physics, chemistry and medicine can provide major information to the clinician, and the goal of this short review is to assess the different information which can be retrieved. Varied research issues can be approached, such as the interaction of tissues with trace elements, the mechanical deformation of prosthesis, the effect of diseases affecting bones or kidney stones composition and microstructure, as well as the dissolution process induced by drugs on kidney stones

Lack of linear magnetoelectric effect in ferrimagnetic distorted honeycomb Ni 4 Nb 2 O 9

International audienceM4A2O9 transition metal oxides, with M a divalent cation and A Nb or Ta, that exhibit a structure derived from corundum constitute an interesting class of materials due to their possible magnetoelectric properties. The lack of a linear magnetoelectric effect in Ni4Nb2O9, unlike Mn4Nb2O9 or Co4Nb2O9, is explained by a comprehensive investigation, combining synchrotron x-ray and neutron diffraction with magnetization, dielectric, and polarization measurements. The m′m′m magnetic point group associated with the Pb′cn′ ferrimagnetic structure induced below 76 K by the orthorhombic Pbcn structure of Ni4Nb2O9 forbids indeed such an effect. The crystal structure and magnetic ground state of Ni4Nb2O9 are discussed and compared with those of magnetoelectric P3¯c1M4A2O9 compounds whose structure derives from corundum

Ageing and Langmuir Behavior of the Cage Occupancy in the Nitrogen Gas Hydrate

Clathrate hydrates are ice-like systems in which nanometric water cages encapsulate guest molecules. Functionalizing clathrate hydrates is an important issue, accomplished by playing with their chemical composition and their cage structure. In this issue, the cage occupancy and its kinetics constitute key information for future developments. In many aspects, nitrogen gas hydrate represents an interesting system not only for its applied relevance (e.g., gas separation and methane/carbon dioxide exchange), but also for its fundamental interest (e.g., structural metastability and kinetics). Thanks to the complementarity of neutron diffraction and Raman scattering, the vibrational signatures of the so-called SI and SII clathrate structures of the nitrogen hydrates are reviewed. Moreover, the investigation of the ageing of the SII structure is reported together with its interpretation in the frame of the Langmuir behavior of the cage filling at low temperature. The cage filling is monitored with the help of a time-dependent analysis of the Raman scattering signals (over several months). The SII large cage filling decreases with a kinetic rate of 5.9 ± 3.3 × 10 − 3 h−1 at 77 K and atmospheric pressure, so that equilibrium is reached after ca. eight weeks. Isotherm measurements of the guest Raman signatures lead to revealing a Langmuir constant higher in the small cage than in the large cage at 150 K. Such a behavior might thus be correlated with the nitrogen depletion with time, observed in the large cage of the SII nitrogen hydrate

Ordering of (Cr,V) Layers in Nanolamellar (Cr 0.5

International audienceNanolamellar MAX phase compounds (Cr0.5V0.5)n+1AlCn are formed with n = 1, 2 and 3, and their 300 K structure is studied in detail by high-resolution neutron diffraction. While the n = 1 compound is found to have complete disordering of vanadium and chromium in the metallic layers, the n = 2 and 3 compounds show strong tendency for these elements’ ordering, with the layer in the 2a(0,0,0) site of (Cr0.5V0.5)3AlC2 fully occupied by vanadium. The thermal expansion dependency of temperature is also studied by neutron diffraction for 2 < T < 550 K, revealing a negligible thermal expansion below 100 K for all of the compounds

Unraveling the metastability of the SI and SII carbon monoxide hydrate with a combined DFT-neutron diffraction investigation

International audienceClathrate hydrates are crystalline compounds consisting of water molecules forming cages (so-called “host”) inside of which “guest” molecules are encapsulated depending on the thermodynamic conditions of formation (systems stable at low temperature and high pressure). These icelike systems are naturally abundant on Earth and are generally expected to exist on icy celestial bodies. Carbon monoxide hydrate might be considered an important component of the carbon cycle in the solar system since CO gas is one of the predominant forms of carbon. Intriguing fundamental properties have also been reported: the CO hydrate initially forms in the sI structure (kinetically favored) and transforms into the sII structure (thermodynamically stable). Understanding and predicting the gas hydrate structural stability then become essential. The aim of this work is, thereby, to study the structural and energetic properties of the CO hydrate using density functional theory (DFT) calculations together with neutron diffraction measurements. In addition to the comparison of DFT-derived structural properties with those from experimental neutron diffraction, the originality of this work lies in the DFT-derived energy calculations performed on a complete unit cell (sI and sII) and not only by considering guest molecules confined in an isolated water cage (as usually performed for extracting the binding energies). Interestingly, an excellent agreement (within less than 1% error) is found between the measured and DFT-derived unit cell parameters by considering the Perdew-Burke-Ernzerhof (denoted PBE) functional. Moreover, a strategy is proposed for evaluating the hydrate structural stability on the basis of potential energy analysis of the total nonbonding energies (i.e., binding energy and water substructure nonbonding energy). It is found that the sII structure is the thermodynamically stable hydrate phase. In addition, increasing the CO content in the large cages has a stabilizing effect on the sII structure, while it destabilizes the sI structure. Such findings are in agreement with the recent experimental results evidencing the structural metastability of the CO hydrate

High temperature spin-driven multiferroicity in ludwigite chromocuprate Cu 2 CrBO 5

International audienceWe report spin-driven multiferroicity above 100 K in the ludwigite Cu(II) oxyborate Cu2CrBO5. Spontaneous polarization, which reaches 35 µC.m-2 at 5 K, appears below 120 K, concomitantly with an incommensurate antiferromagnetic order and complex magnetodielectric effects. In magnetically induced ferroelectrics, multiferroicity usually appears at low temperature, because of the competing magnetic exchanges needed to stabilize a magnetic spiral : the remarkably high transition temperature observed in Cu2CrBO5 originates from the presence of strong Cu-O-Cu magnetic super-exchange interactions, which are not weakened by Cu/Cr cationic disorder. Our result provides an important contribution to the search for high temperature spindriven multiferroics amongst low-dimensional cuprates

Magnetic Investigation of an Atypical Three-Dimensional Bimetallic Oxalate-Based Magnet

International audienceDetailed magnetic measurements and powder neutron diffraction studies have been performed on a three-dimensional (3D) oxalate-based metal–organic framework (NH4)5[Mn2Cr3(ox)9]·10H2O (ox2– = C2O42–). The thermal variations of the magnetic susceptibilitiy measured via field-cooled and zero-field-cooled procedures are compatible with an antiferromagnetic spin organization in the presence of some single-ion anisotropy. This is supported by the metamagnetic behavior observed at 0.7 T in the magnetization curve at 2 K. Temperature-dependent neutron diffraction experiments have been performed between 2.5 and 300 K on the powdered sample. The structural part of the neutron diffraction pattern matches with the C2/c space group found by single-crystal X-ray diffraction. Below 6 K, the long-range magnetic ordering leads to the observation of a single magnetic peak at 0.386 Å–1. The refinement of the neutron diffractogram allows to propose a magnetic structure where the magnetic moments of the manganese(II) and chromium(III) ions are noncollinear with a maximum angle of almost 70°. In agreement with an orbital analysis, the coupling between these magnetic moments bridged in a bis(bidentate) oxalate ligand is mainly ferromagnetic whereas it is mainly antiferromagnetic for metal ions bridged in a monodentate-bidentate mode