Modular thermal Hall effect measurement setup for fast-turnaround screening of materials over wide temperature range using capacitive thermometry

We demonstrate a simple and easy-to-build probe designed to be loaded into a widely available Quantum Design Physical Properties Measurement System (PPMS) cryostat, with a detachable shielded sample puck section and robust heat sinking of three pairs of coaxial cables. It can be in principle used with any low-temperature cryostat. Our modular puck design has a radiation shield for thermal isolation and protection of the delicate sample space while handling and allows any variety of experimental setup benefiting from shielded coaxial wiring to be constructed on a selection of sample pucks. Pucks can be quickly and easily switched, and the system makes use of the simple yet extremely stable temperature and magnetic field control of the easy-to-use PPMS system. We focus on a setup designed for measurements of the thermal Hall effect and show that this system can yield unprecedented resolution over a wide temperature range and with rapid sample mounting or changing—allowing a large collection of potential samples to be screened for this novel physics. Our design aims to make these sensitive but challenging measurements quick, reliable, cheap, and accessible, through the use of a standard, widespread base cryostat and a system of modular removable sample stage pucks to allow quick turnaround and screening of a large number of candidate samples for potential new thermal Hall physics

Pressure-induced shift of effective Ce valence, Fermi energy and phase boundaries in CeOs4Sb12

CeOs4Sb12, a member of the skutterudite family, has an unusual semimetallic low-temperature L-phase that inhabits a wedge-like area of the field H - temperature T phase diagram. We have conducted measurements of electrical transport and megahertz conductivity on CeOs4Sb12 single crystals under pressures of up to 3 GPa and in high magnetic fields of up to 41 T to investigate the influence of pressure on the different H-T phase boundaries. While the high-temperature valence transition between the metallic H-phase and the L-phase is shifted to higher T by pressures of the order of 1 GPa, we observed only a marginal suppression of the S-phase that is found below 1 K for pressures of up to 1.91 GPa. High-field quantum oscillations have been observed for pressures up to 3.0 GPa and the Fermi surface of the highfield side of the H-phase is found to show a surprising decrease in size with increasing pressure, implying a change in electronic structure rather than a mere contraction of lattice parameters. We evaluate the field-dependence of the effective masses for different pressures and also reflect on the sample dependence of some of the properties of CeOs4Sb12 which appears to be limited to the low-field region

Asymmetric phase diagram and dimensional crossover in a system of spin-spin- 1/2 dimers under applied hydrostatic pressure

We present the magnetic and structural properties of [Cu(pyrazine)0.5 (glycine)]ClO4 under applied pressure. As previously reported, at ambient pressure this material consists of quasi-two-dimensional layers of weakly coupled antiferromagnetic dimers which undergo Bose-Einstein condensation of triplet excitations between two magnetic field-induced quantum critical points (QCPs). The molecular building blocks from which the compound is constructed give rise to exchange strengths that are considerably lower than those found in other S=1/2 dimer materials, which allows us to determine the pressure evolution of the entire field-temperature magnetic phase diagram using radio-frequency magnetometry. We find that a distinct phase emerges above the upper field-induced transition at elevated pressures and also show that an additional QCP is induced at zero-field at a critical pressure of pc=15.7(5),kbar. Pressure-dependent single-crystal X-ray diffraction and density functional theory calculations indicate that this QCP arises primarily from a dimensional crossover driven by an increase in the interdimer interactions between the planes. While the effect of quantum fluctuations on the lower field-induced transition is enhanced with applied pressure, quantum Monte Carlo calculations suggest that this alone cannot explain an unconventional asymmetry that develops in the phase diagram

SquidLab

-- Updated to version 2.9.1! Oct 2021 -- Bugfixes and improvements on error handling, particularly in verifying the correct installation environment for new users. -- Updated to version 2.9! July 2021 -- See the changelog for full changes - Added 'Mirror positive field scans to create negative scans' checkbox. - Scan metadata changed to be Scan, rather than Session-specific. This metadata includes the x axis variable type (T or H), and fit geometry parameters to automatically pre-fill in the fitting panel. The main improvement is that now such details are not lost upon Saving and Loading a Session. -- Updated to version 2.8! Apr 2021 -- Added new importers to support use of the MPMS Reciprocating Sample Option (RSO). -- Updated to version 2.7! Oct 2020 -- See the changelog for full changes - Now have a built-in graphing tab for quickly comparing data and background sweeps, and the option to sort datasets by temperature or field when importing. -- Updated to version 2.6! July 2020 -- See the changelog - Can now save and load Sessions and collections of data for later processing, or to archive all background scans ready for action. -- Updated to version 2.5! Feb 2020 -- See the changelog - includes support for Cryogenic S700X datafiles. SquidLab is a Matlab library with a full user-friendly GUI for importing, analyzing and plotting scans taken from a SQUID magnetometer. It's designed to allow: • Easy fitting of dipoles from raw V(z) voltage data. • A unified import pipeline for the (often quite complex) raw scan data files. • Fully-featured post-processing to resolve common issues with the raw data. • Background subtraction of one scan from another. • Fitting to the raw scans to obtain moment as a function of temperature or field. The Quantum Design Magnetic Property Measurement System (we support other instruments too, but this is the most common so let us focus on it) is a very sensitive instrument for measuring magnetic properties based on the SQUID magnetometer. However, sometimes for magnetically dilute samples or bulky sample holders and environments, their magnetic response can be so weak that it is comparable to the response from the sample holder used. The fitting algorithm employed by the MultiVu software for obtaining the magnetic moment can become unreliable in such cases (gets trapped in local minima, or the data no longer resemble the assumed dipole etc), and even the subtraction of the fitted background moment from the fitted sample+background moment does not result in a satisfactory outcome. In such cases, it becomes necessary to work directly with the SQUID voltages vs position data of the [sample + background] and [background] in order to recover the magnetic response due to the sample only and fit that to obtain meaningful information about the magnetic moment of the sample. SquidLab is described in our paper 'SquidLab - A user-friendly program for background subtraction and fitting of magnetization data', Review of Scientific Instruments 91, 023901 (2020) available at https://doi.org/10.1063/1.5137820. Please cite this work if our software proves helpful to your research results. Thank you and good luck, happy subtracting

Electronic and vibrational properties of the two-dimensional Mott insulator V0.9PS3 under pressure

We present a Raman spectroscopic study of the layered antiferromagnetic Mott insulator V(0.9)PS(3 )and demonstrate the evolution of the spectra with applied quasihydrostatic pressure. Clear features in the spectra are seen at the pressures identified as corresponding to a structural transition between 20 and 80 kbar and the insulator-metal transition at 120 kbar. The feature at 120 kbar can be understood as a stiffening of interplanar vibrations, linking the metallization to a crossover from two- to three-dimensionality. Theoretical ab initio calculations, using the previously determined high-pressure structures, were able to reproduce the measured spectra and map each peak to specific vibration modes. We additionally show calculations of the high-pressure band structure in these materials, where the opening of a band gap with an included Hubbard U term and its subsequent closing with pressure are clearly demonstrated. This little-studied material shows great promise as a model system for the fundamental study of low-dimensional magnetism and Mott physics. ©2019 American Physical Societ

Dataset to support : Direct evidence from high-field magnetotransport for a dramatic change of quasiparticle character in van der Waals ferromagnet Fe3-xGeTe2

Magnetometry and magnetoresistance (MR) data taken on the van der Waals ferromagnet Fe3−xGeTe2 (FGT) reveal three distinct contributions to the MR: a linear negative component, a contribution from closed Fermi-surface orbits, and a H2 enhancement linked to a non-coplanar spin arrangement. Contrary to earlier studies on FGT, by accounting for the field dependence of the anomalous Hall effect, we find that the ordinary Hall coefficient decreases markedly below 80,K, indicating a significant change in character of the electrons and holes on the Fermi surface at this temperature. The resulting altered ground state eventually causes the Hall coefficient to reverse sign at 35,K. Our Hall data support the proposal that Kondo-lattice behavior develops in this d-electron material below 80 K. Additional evidence comes from the negative linear component of the MR, which arises from electron-magnon scattering with an atypical temperature dependence attributable to the onset of Kondo screening

Data for Local nuclear and magnetic order in the two-dimensional spin glass, Mn0.5Fe0.5PS3

We present a comprehensive study of the short-ranged nuclear and magnetic order in the twodimensional spin glass, Mn0.5Fe0.5PS3. Nuclear neutron scattering data reveal a random distribution of Mn2+ and Fe2+ ions within the honeycomb layers, which gives rise to a spin glass state through inducing competition between neighbouring exchange interactions, indicated in magnetic susceptibility data by a cusp at the glass transition, Tg = 35 K. Analysis of magnetic diffuse neutron scattering data collected for both single crystal and polycrystalline samples gives further insight into the origin of the spin glass phase, with spin correlations revealing a mixture of satisfied and unsatisfied correlations between magnetic moments within the honeycomb planes, which can be explained by considering the magnetic structures of the parent compounds, MnPS3 and FePS3. We found that, on approaching Tg from above, an ensemble-averaged correlation length of ξ = 5.5(6) ˚A developed between satisfied correlations, and below Tg, the glassy behaviour gave rise to a distanceindependent correlation between unsatisfied moments. Correlations between the planes were found to be very weak, which mirrored our observations of rod-like structures parallel to the c* axis in our single crystal diffraction measurements, confirming the two-dimensional nature of Mn0.5Fe0.5PS3

Magnetotransport of Sm2Ir2O7 across the pressure-induced quantum-critical phase boundary

Rare-earth pyrochlore iridates host two interlocking magnetic sublattices of corner-sharing tetrahedra and can harbour a unique combination of frustrated moments, exotic excitations and highly correlated electrons. They are also the first systems predicted to display both topological Weyl semimetal and axion insulator phases. We have measured the transport and magnetotransport properties of single-crystal Sm2Ir2O7 up to and beyond the pressure-induced quantum critical point for all-in-all-out (AIAO) Ir order at pc = 63 kbar previously identified by resonant X-ray scattering and close to which Weyl semimetallic behavior has been previously predicted. Our findings overturn the accepted expectation that the suppression of AIAO order should lead to metallic conduction persisting down to zero temperature. Instead, the resistivity-minimum temperature, which tracks the decrease in the AIAO ordering temperature for pressures up to 30 kbar, begins to increase under further application of pressure, pointing to the presence of a second as-yet unidentified mechanism leading to non-metallic behavior. The magnetotransport does track the suppression of Ir magnetism, however, with a strong hysteresis observed only within the AIAO phase boundary, similar to that found for Ho2Ir2O7 and attributed to plastic deformation of Ir domains. Around pc we find the emergence of a new type of electronic phase, characterized by a negative magnetoresistance with small hysteresis at the lowest temperatures, and hysteresis-free positive magnetoresistance above approximately 5 K. The temperature dependence of our low-temperature transport data are found to be best described by a model consistent with a Weyl semimetal across the entire pressure range

Direct evidence from high-field magnetotransport for a dramatic change of quasiparticle character in van der Waals ferromagnet Fe3−xGeTe2

Magnetometry and magnetoresistance (MR) data taken on the van der Waals ferromagnet Fe 3 − x GeTe 2 (FGT) reveal three distinct contributions to the MR: a linear negative component, a contribution from closed Fermi-surface orbits, and a H 2 enhancement linked to a non-coplanar spin arrangement. Contrary to earlier studies on FGT, by accounting for the field dependence of the anomalous Hall effect, we find that the ordinary Hall coefficient decreases markedly below 80,K, indicating a significant change in character of the electrons and holes on the Fermi surface at this temperature. The resulting altered ground state eventually causes the Hall coefficient to reverse sign at 35,K. Our Hall data support the proposal that Kondo-lattice behavior develops in this d-electron material below 80 K. Additional evidence comes from the negative linear component of the MR, which arises from electron-magnon scattering with an atypical temperature dependence attributable to the onset of Kondo screening