A compact membrane-driven diamond anvil cell and cryostat system for nuclear resonant scattering at high pressure and low temperature

Robust magnetism and crystal structure in Dirac semimetal EuMnBi2under high pressure

Dirac materials offer exciting opportunities to explore low-energy carrier dynamics and novel physical phenomena, especially their interaction with magnetism. In this context, this work focuses on studies of pressure control on the magnetic state of EuMnBi2, a representative magnetic Dirac semimetal, through time-domain synchrotron Mössbauer spectroscopy in151Eu. Contrary to the previous report that the antiferromagnetic order is suppressed by pressure above 4 GPa, we have observed robust magnetic order up to 33.1 GPa. Synchrotron-based x-ray diffraction experiment on a pure EuMnBi2sample shows that the tetragonal crystal lattice remains stable up to at least 31.7 GPa.

Strong enhancement of magnetic ordering temperature and structural/valence transitions in EuPd3S4 under high pressure

We present a comprehensive study of the inhomogeneous mixed-valence compound, EuPd3S4, by electrical transport, X-ray diffraction, time-domain 151Eu synchrotron Mössbauer spectroscopy, and X-ray absorption spectroscopy measurements under high pressure. Electrical transport measurements show that the antiferromagnetic ordering temperature, TN, increases rapidly from 2.8 K at ambient pressure to 23.5 K at ~19 GPa and plateaus between ~19 and ~29 GPa after which no anomaly associated with TN is detected. A pressure-induced first-order structural transition from cubic to tetragonal is observed, with a rather broad coexistence region (~20 GPa to ~30 GPa) that corresponds to the TN plateau. Mössbauer spectroscopy measurements show a clear valence transition from approximately 50:50 Eu2+:Eu3+ to fully Eu3+ at ~28 GPa, consistent with the vanishing of the magnetic order at the same pressure. X-ray absorption data show a transition to a fully trivalent state at a similar pressure. Our results show that pressure first greatly enhances TN, most likely via enhanced hybridization between the Eu 4f states and the conduction band, and then, second, causes a structural phase transition that coincides with the conversion of the europium to a fully trivalent state.

Pressure effect on magnetism and valence in ferromagnetic superconductor Eu(Fe0.75Ru0.25)2As2

Eu(Fe_0.75Ru_0.25)₂As₂is an intriguing system with unusual coexistence of superconductivity and ferromagnetism, providing a unique platform to study the nature of such coexistence. To establish a magnetic phase diagram, time-domain synchrotron Mössbauer experiments in¹⁵¹Eu have been performed on a single crystalline Eu(Fe_0.75Ru_0.25)₂As₂sample under hydrostatic pressures and at low temperatures. Upon compression the magnetic ordering temperature increases sharply from 20 K at ambient pressure, reaching ∼49 K at 10.1 GPa. With further compression, the magnetic order is suppressed and eventually collapses. Isomer shift values from Mössbauer measurements and x-ray absorption spectroscopy data at EuL₃edge show that pressure drives Eu ions to a homogeneous intermediate valence state with mean valence of ∼2.4 at 27.4 GPa, possibly responsible for the suppression of magnetism. Synchrotron powder x-ray diffraction experiment reveals a tetragonal to collapsed-tetragonal structural transition around 5 GPa, a lower transition pressure than in the parent compound. These results provide guidance to further work investigating the interplay of superconductivity and magnetism.

Compression rate of dynamic diamond anvil cells from room temperature to 10 K

There is an ever increasing interest in studying dynamic-pressure dependent phenomena utilizing dynamic Diamond Anvil Cells (dDACs), devices capable of a highly controlled rate of compression. Here, we characterize and compare the compression rate of dDACs in which the compression is actuated via three different methods: (1) stepper motor (S-dDAC), (2) gas membrane (M-dDAC), and (3) piezoactuator (P-dDAC). The compression rates of these different types of dDAC were determined solely on millisecond time-resolved R1-line fluorescence of a ruby sphere located within the sample chamber. Furthermore, these different dynamic compression-techniques have been described and characterized over a broad temperature and pressure range from 10 to 300 K and 0-50 GPa. At room temperature, piezoactuation (P-dDAC) has a clear advantage in controlled extremely fast compression, having recorded a compression rate of ∼7 TPa/s, which is also found to be primarily influenced by the charging time of the piezostack. At 40-250 K, gas membranes (M-dDAC) have also been found to generate rapid compression of ∼0.5-3 TPa/s and are readily interfaced with moderate cryogenic and ultrahigh vacuum conditions. Approaching more extreme cryogenic conditions (<10 K), a stepper motor driven lever arm (S-dDAC) offers a solution for high-precision moderate compression rates in a regime where P-dDACs and M-dDACs can become difficult to incorporate. The results of this paper demonstrate the applicability of different dynamic compression techniques, and when applied, they can offer us new insights into matter's response to strain, which is highly relevant to physics, geoscience, and chemistry.

Adapting a continuous flow cryostat and a plate DAC to do high pressure Raman experiments at low temperatures

We present a method for modifying a continuous flow cryostat and a steel plate DAC (Diamond Anvil Cell) to perform high pressure micro-Raman experiments at low temperatures. Despite using a steel DAC with a lower specific heat capacity (∼335 J/kg K), this setup can routinely perform high pressure (∼10 GPa) measurements at temperatures as low as 26 K. This adaptation is appropriate for varying the temperature of the sample while keeping it at a constant pressure. We determined that the temperature variation across the sample chamber is about 1 K using both direct temperature measurements and finite element analysis of the heat transport across the DAC. We present Raman spectroscopy results on elemental selenium at high pressures and low temperatures using our modified setup.

Calibration of Manganin pressure gauge for diamond-anvil cells

Pressure calibration for most diamond-anvil cell (DAC) experiments is mainly based on the ruby scale, which is key to implementing this powerful tool for high-pressure study. However, the ruby scale can often hardly be used for programmably controlled DAC devices, especially the piezoelectric-driving cells, where a continuous pressure calibration is required. In this work, we present an effective pressure gauge for DACs made of Manganin metal based on the four-probe resistivity measurements. Pressure dependence of its resistivity is well established and shows excellent linear relations in the 0-30 GPa pressure range with a slope of 23.4 (9) GPa for the first-cycle compression, in contrast to that of multiple-cycle compression and decompression having a nearly identical slope of 33.7 (4) GPa likely due to the strain effect. In addition, the such-established Manganin scale can be used for continuously monitoring the cell pressure of piezoelectric-driving DACs, and the reliability of this method is also verified by the fixed-point method with a Bi pressure standard. Realization of continuous pressure calibration for programmably controlled DACs would offer many opportunities for the study of dynamics, kinetics, and critical behaviors of pressure-induced phase transitions.

High-pressure nuclear inelastic scattering with backscattering monochromatization

The capability to perform high-pressure low-temperature nuclear inelastic scattering on ¹²⁵Te and ¹²¹Sb with a sapphire backscattering monochromator is presented. This technique was applied to measure nuclear inelastic scattering in TeO₂ at pressures up to 10 GPa and temperatures down to 25 K. The evaluated partial Te densities of phonon states were compared with theoretical calculations and with Raman scattering measured under the same conditions. The high-pressure cell developed in this work can also be used for other techniques at pressures up to at least 100 GPa.