Wenli Bi

We report high-pressure x-ray diffraction and electrical resistance measurements on Sr(Co 0.88 Ni 0.12 ) 2 P 2 , an itinerant antiferromagnet with the highest Néel temperature ( T N = 36 K) among Sr(Co 1 − x Ni x ) 2 P 2 series. Room-temperature diffraction data reveal a pressure-induced transition from an uncollapsed tetragonal to a collapsed tetragonal (cT) structure, beginning near 8.4 GPa and completing before 12.4 GPa. This transition is characterized by an expansion of the in-plane a -lattice parameter and a contraction in the c -lattice parameter, resulting in a reduction of the axial ratio c / a . Resistance measurements show a low-pressure anomaly near 38 K, consistent with the reported antiferromagnetic transition. As the room temperature value of the applied pressure exceeds 8 GPa, signs of a partial cT transition appear on cooling with the full cT transition occurring for pressures exceeding 10 GPa. The cT phase is accompanied by a much higher-temperature transport anomaly that resembles the pressure-induced ferromagnetic transition reported for SrCo 2 P 2 , reaching approximately 190 K before gradually decreasing at higher pressures. These results demonstrate strong coupling between the lattice collapse and magnetic behavior in Sr(Co 0.88 Ni 0.12 ) 2 P 2 .

The determination of the orientations of the individual Dy ^III anisotropy axes in polynuclear complexes is challenging but crucial for the understanding of systems showing Single Molecule Magnet or Single Molecule Toroic behavior. In particular, the experimental proof of a toroidal ground state from magnetization data often remains ambiguous. Here, we report the coordination cluster [Co ^III ₃ Dy ^III ₃ (µ ₃ -OH) ₄ (O ₂ C-C ₆ H ₄ -p-Me) ₆ (pmide) ₃ (H ₂ O) ₃ ]Cl ₂ · 10MeCN (1) (H ₂ pmide = N-2-pyridylmethyldiethanolamine) which crystallizes with threefold symmetry and contains an equilateral Dy ^III ₃ triangle surrounded by a triangle of diamagnetic Co ^III ions. We also report a multi-technique investigation of its toroidal magnetic spin structure, including ¹⁶¹ Dy Synchrotron Mössbauer Spectroscopy which shows an abrupt transition from a non-magnetic to a magnetic state. The experimental orientations of the individual Dy ^III magnetic axes were assessed using torque magnetometry and micro-SQUID measurements and both experiments converged on a spin structure that is in very good agreement with ab initio calculations. Such a multi-technique approach, including ¹⁶¹ Dy Synchrotron Mössbauer Spectroscopy, provides a roadmap for the unambiguous identification of such toroidal states.

The coordination cluster [Co^III₃Dy^III₃(µ₃-OH)₄(O₂C-C₆H₄-p-Me)₆(pmide)₃(H₂O)₃]Cl₂∙10MeCN (1) (where H₂pmide = N-2-pyridylmethyldiethanolamine) crystallizes on a threefold site in the trigonal space group P 3 c1. The cluster core contains one equilateral Dy₃^III triangle and one triangle of diamagnetic Co^III ions to give a shuttlecock-like molecular structure. The magnetic spin structure has been investigated using a multi-technique approach. In addition to the magnetic susceptibility, we report ¹⁶¹Dy Synchrotron Mössbauer Spectroscopy (SMS) which shows an abrupt transition from a non-magnetic to a magnetic state which is in line with the transition observed in complementary measurements. The experimental orientations of the individual axes were independently assessed using torque magnetometry and micro-SQUID measurements and both experiments converged on a spin structure that can be correlated with the crystal structure. The results are also in agreement with those from ab initio CASSCF/SO-RASSI calculations, which also showed that a hydrogen-bonded chloride counterion has a significant effect on the magnetic structure.

ReMo binary alloy films with a maximum Mo content of 25 at. % are successfully electrodeposited using high concentration acetate solutions in the presence of citric acid. The electrochemical behavior of the ReMo alloy is studied using cyclic voltammetry and anodic stripping methods. Different techniques, including electron microscopy, x-ray diffraction, and four-point probe resistance measurements at cryogenic temperature, are used to characterize the surface morphology, crystal structure, and superconducting critical temperature of alloys, respectively. While all films exhibit a crystalline hcp phase after 700 °C annealing, the film with the highest 25 at. % Mo content shows a second crystalline cubic phase. Mo doping preserves the enhanced superconducting transition temperature (Tc) in electrodeposited amorphous Re films and improves the stability of Tc against thermal annealing at a temperature of 200 °C. This is the first successful demonstration to use a dopant to stabilize the enhanced Tc of electrodeposited films, enabling the fabrication and operation of superconducting connectors above the intrinsic Tc of the materials.

High-entropy alloys (HEAs) are a class of multi-element materials that exhibit unique structural and functional properties. This study reports on the synthesis and characterization of a superconducting HEA, (NbTa)0.55(HfTiZr)0.45 fabricated using the vacuum arc melting technique. Scanning electron microscopy and energy-dispersive x-ray spectroscopy were employed to analyze the material's morphology and composition. X-ray diffraction analysis revealed a single-phase body-centered cubic (BCC) structure with a measured nanoindentation hardness of 6.4 GPa and Young's modulus of 132 GPa. This HEA superconductor was investigated by x-ray diffraction at Beamline 13BM-C, Advanced Photon Source, and the BCC phase was stable to the highest pressure of 50 GPa. Superconductivity was characterized by four-probe resistivity measurements in a quantum design physical property measurement system, yielding a superconducting transition temperature (Tc) of 7.2 K at ambient pressure and reaching a maximum of 10.1 K at the highest applied pressure of 23.6 GPa. The combination of high structural stability enhanced superconducting performance under pressure and superior mechanical properties highlights (NbTa)0.55(HfTiZr)0.45 as a promising superconductor under extreme environments.