We investigate the structural, electronic, and magnetic properties of the van der Waals antiferromagnet CrSBr under high pressure using ab initio calculations. At ambient pressure, CrSBr is a Mott insulator with A-type antiferromagnetic order and a local moment of similar to 3 mu(B) per Cr atom, originating from three electrons in the t(2g) manifold. Upon increasing pressure, the moment collapses to similar to 1 mu(B), accompanied by a volume reduction and an inversion of the distorted CrS4Br2 octahedron with elongated Cr-Br bonds. This transition is accompanied by an insulator-metal crossover, driven by crystal electric field reconstruction that redistributes the Cr 3d electrons among four low-lying states. Our results reveal a pressure-induced transition in CrSBr, from a Mott-localized high-spin state to an itinerant metallic state with a substantially reduced magnetic moment.

The magnetic structure of the intermetallic compound ErGa has been determined using high-resolution neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm, No. 63) CrB-type structure and orders ferromagnetically at 32 (2) K, with the Er moments initially aligned along the b axis. Upon cooling below 16 K, the Er magnetic moments cant away from the b axis towards the c axis. At 3 K, the Er moment is 8.7 (3) μB and the Er magnetic moments point in the direction 31 (3)° away from the crystallographic b axis, within the bc plane. 166Er Mössbauer spectroscopy work supports this structure and shows clear signals of the spin-reorientation in both the magnetic and electric quadrupole hyperfine interactions.

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1-xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has established that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the N & eacute;el temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 1 2 ], is maintained in the Lu-doped (Ho1-xLux)2Fe2Si2C compounds.

Symmetry-protected band degeneracy, coupled with a magnetic order, is the key to realizing novel magnetoelectric phenomena in topological magnets. While the spin-polarized nodal states have been identified to introduce extremely-sensitive electronic responses to the magnetic states, their possible role in determining magnetic ground states has remained elusive. Here, taking external pressure as a control knob, we show that a metal-insulator transition, a spin-reorientation transition, and a structural modification occur concomitantly when the nodal-line state crosses the Fermi level in a ferrimagnetic semiconductor Mn3Si2Te6. These unique pressure-driven magnetic and electronic transitions, associated with the dome-shaped Tc variation up to nearly room temperature, originate from the interplay between the spin-orbit coupling of the nodal-line state and magnetic frustration of localized spins. Our findings highlight that the nodal-line states, isolated from other trivial states, can facilitate strongly tunable magnetic properties in topological magnets.

We report the results of Raman spectroscopy on a self-intercalated van der Waals ferrimagnet Mn3Si2Te6. Using polarization-resolved Raman spectroscopy, we identify twelve phonon modes with Eg and A1g symmetries, in agreement with the first principle calculations. Below the ferrimagnetic transition temperature Tc∼ 78 K, we observed a significant deviation of the phonon frequency from the anharmonic model, accompanied by a strong line broadening, indicating a substantial spin-phonon coupling in Mn3Si2Te6. Among twelve phonon modes, this spin-phonon coupling is found to be strong mostly in the out-of-plane vibrational modes. These results highlight the dominant role of the interlayer superexchange interaction in determining the magnetic properties, reflecting the self-intercalated van der Waals structure of Mn3Si2Te6.

In this work, the enhanced superconductivity of SnSe 2 is reported in decompression and the key mechanism behind the decompression-driven superconductivity enhancement is revealed.

In this study, we synthesized La1-xMgxFeO3 (x = 0.1, 0.2, and 0.3) powdered ceramics using sol - gel and sintering methods and their structure, magnetic and electrical properties have been investigated. All samples showed the Pbnm single phase, and structural analyses revealed a lattice distortion due to the addition of Mg that increases with increasing Mg content. Transmission electron microscopy revealed a decrease in particle size with increasing Mg content. The M - H hysteresis loops of the samples revealed that the samples with Mg substitution at the La site exhibits weak ferromagnetic behaviour, and the hysteresis loops increases with an increase in Mg content. The magnetisation increases as the Mg content is increased, which is might be related to the lower crystallite and particle sizes, as well as higher Fe4+/Fe3+ ratio, as shown by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. Analysis of the electrical properties showed grain-grain boundary effect in the conduction mechanism and two relaxation mechanisms for low Mg contents (x <= 0.2), whereas only the grain effect and one relaxation mechanism were observed at higher Mg contents (x = 0.3). The temperature dependence of direct current conductivity obeys the Arrhenius law. The activation energy for the conduction mechanism decreased with an increase in the Mg content. These results contribute the important knowledge in promising the candidate electrode material in electrochemical application.

A highly tunable band gap of the layered semiconductor Zn3In2S6 under pressure is reported. The change in the band gap is strongly coupled to the variation and transformation of the crystal structure.

Two-dimensional magnetic materials (2DMMs) are significant not only for studies on the nature of 2D long-range magnetic order but also for future spintronic devices. Of particular interest are 2DMMs where spins can be manipulated by electrical conduction. Whereas Cr2Si2Te6 exhibits magnetic order in few-layer crystals, its large band gap inhibits electronic conduction. Here we show that the defect-induced short-range crystal order in Cr2Si2Te6, on the length scale below 0.6 nm, induces a substantially reduced band gap and robust semiconducting behavior down to 2 K that turns to metallic above 10 GPa. Our results will be helpful in designing conducting states in 2DMMs and call for spin-resolved measurement of the electronic structure in exfoliated ultrathin crystals.

As the pioneer semiconductor in transistor, germanium (Ge) has been widely applied in information technology for over half a century. Although many phase transitions in Ge have been reported, the complicated phenomena of the phase structures in amorphous Ge under extreme conditions are still not fully investigated. Here, we report the different routes of phase transition in amorphous Ge under different compression conditions utilizing diamond anvil cell (DAC) combined with synchrotron-based X-ray diffraction (XRD) and Raman spectroscopy techniques. Upon non-hydrostatic compression of amorphous Ge, we observed that shear stress facilitates a reversible pressure-induced phase transformation, in contrast to the pressure-quenchable structure under a hydrostatic compression. These findings afford better understanding of the structural behaviors of Ge under extreme conditions, which contributes to more potential applications in the semiconductor field.

Indium telluride (In2Te3) is a typical layered material among III-IV families that are extremely sensitive to pressure and strain. Here, we use a combination of high-pressure electric transport, Raman, XRD, and first-principles calculations to study the electronic properties and structural evolution characteristics of In2Te3 under high pressure. Our results reveal the evidence of isostructure electronic transitions. First-principle calculations demonstrate that the evolution of phonon modes is associated with the transition from semiconductor to metal due to the increase in the density of states near the Fermi level. The pressure-induced metalization as a precursor monitors the structural phase transition, and then the superconductivity is produced. Further, in decompression, Tc slightly increased and remained at 3.0 GPa, and then the disorder is present and the superconductivity is suppressed. Our work not only perfects the superconducting phase of the In-Te system under pressure but also provides a reference for further superconducting research and applications.

The importance of electronic structure evolutions and reconstitutions is widely acknowledged for strongly correlated systems. The precise effect of pressurized Fermi surface topology on metallization and superconductivity is a much-debated topic. In this work, an evolution from insulating to metallic behavior, followed by a superconducting transition, is systematically investigated in SnS2 under high pressure. In-situ X-ray diffraction measurements show the stability of the trigonal structure under compression. Interestingly, a Lifshitz transition, which has an important bearing on the metallization and superconductivity, is identified by the first-principles calculations between 35 and 40 GPa. Our findings provide a unique playground for exploring the relationship of electronic structure, metallization, and superconductivity under high pressure without crystal structural collapse.

A pressure-induced structural phase transition and its intimate link with the superconducting transition was studied for the first time in TiSe2 up to 40 GPa at room temperature using X-ray diffraction, transport measurement, and first-principles calculations. We demonstrate the occurrence of a first-order structural phase transition at 4 GPa from the standard trigonal structure (S.G.P3̅m1) to another trigonal structure (S-G-P3̅c1). Additionally, at 16 GPa, the P3̅c1 phase spontaneously transforms into a monoclinic C2/m phase, and above 24 GPa, the C2/m phase returns to the initial P3̅m1 phase. Electrical transport results show that metallization occurs above 6 GPa. The charge density wave observed at ambient pressure is suppressed upon compression up to 2 GPa with the emergence of superconductivity at 2.5 GPa, with a critical temperature (Tc) of 2 K. A structural transition accompanies the emergence of superconductivity that persists up to 4 GPa. The results demonstrate that the pressure-induced phase transitions explored by the experiments along with the theoretical predictions may open the door to a new path for searching and controlling the phase diagrams of transition metal dichalcogenides.

We report a novel method to synthesize bulk grain-size gradient polycrystalline Ni by AGG. By periodical sintering in the large volume press (LVP), AGG repeatedly occurs, resulting in exceptionally large grains on the sample surface, but the inner grains are still small. The formation of grain-size gradient profile is attributed to the uneven plastic deformation caused by compression in the LVP. Besides, the gradient structure can be achievable with uniformity by employing tungsten with a high shear modulus into the sample assembly. This work would guide us to design bulk heterogeneous gradient nanostructured materials with both excellent strength and ductility. The uniform grained gradient structure obtained with the improved LVP assembly. (a) The improved LVP assembly with W tablet used between Ni sample and outer Mo-capsule; (b) Inverse pole figure mapping characterization of uniform grain-size gradient structure comprised of smaller grains.

A key factor that determines the mechanical and electrical performance of graphene-based materials and devices is how graphene behaves under extreme conditions, yet the response of few-layer graphene to high shear stress has not been investigated experimentally. Here we applied high pressure and shear to graphene powder using a rotational diamond anvil cell and studied the recovered sample with multiple means of characterization. Sustaining high pressure and shear, graphene breaks into nanometer-long clusters with generation of large number of defects. At a certain stress level, it transforms to amorphous state and carbon onions. The reduction of infrared reflectivity in the severely sheared phase indicates the decrease in conductivity. Our results unveil the shear sensitive nature of graphene, point out the effects of shear on its physical properties, and provide a potential method to manipulate this promising material.

We report our investigations on the effects of pressure on the electronic and magnetic properties of magnetic Dirac semimetal EuMnBi2 by using electrical transport, synchrotron x-ray diffraction, and x-ray absorption spectroscopy. The antiferromagnetic interaction due to the Eu magnetic moment in EuMnBi2 is enhanced under pressure up to similar to 3.9GPa. The Neel temperature (T-N) is found to disappear above 4 GPa and a new transition T-t at around 29 K emerges above 6 GPa. T-t remains relatively constant up to 15 GPa, above which it increases with further compression, reaching similar to 60K at 22 GPa. Eu L-edge x-ray absorption spectroscopy revealed a valence change of Eu toward a trivalent state that begins above 6 GPa, which indicates that T-t is likely related to the valence transition temperature of Eu. Sign reversal of the Hall resistivity above 7 GPa suggests that the valence change of Eu also induces a Fermi surface modification.

Transition metal dichalcogenides (TMDs) have attracted wide attention due to their quasi-two-dimensional layered structure and exotic properties. Plenty of efforts have been done to modulate the interlayer stacking manner for novel states. However, as an equally important element in shaping the unique properties of TMDs, the effect of intralayer interaction is rarely revealed. Here, we report a particular case of pressure-tuned re-arrangement of intralayer atoms in distorted 1T-NbTe2, which was demonstrated to be a new type of structural phase transition in TMDs. The structural transition occurs in the pressure range of 16-20 GPa, resulting in a transformation of Nb atomic arrangement from the trimeric to dimeric structure, accompanied by a dramatic collapse of unit cell volume and lattice parameters. Simultaneously, a charge density wave (CDW) was also found to collapse during the phase transition. The strong increase in the critical fluctuations of CDW induces a significant decline in the electronic correlation and a change of charge carrier type from hole to electron in NbTe2. Our finding reveals a new mechanism of structure evolution and expands the field of pressure-induced phase transition.

The grain size doubling of nickel nanocrystals in calcination reveals that oriented attachment (OA), which generally involves the use of a liquid medium, can occur in solid state as well and dominate the nano-grain coarsening.

Charge density wave (CDW) systems have been widely studied and proposed to be potential candidates for next‐generation electronic devices. However, the lack of room‐temperature CDW materials has limited the development of CDW‐based electronic devices, and thus finding a way to manipulate the CDW transitions and orders toward room temperature will be of importance. Room‐temperature and above CDW transition in 1 T ‐VSe 2 is reported. The CDW transition is found to shift to ≈114 K at 0.7 GPa, and further compression enhances the transition temperature dramatically, reaching ≈358 K at 14.6 GPa. High‐pressure Raman spectroscopy measurement confirms that room‐temperature CDW order is achieved and persists up to 15 GPa. Such significant enhancement in CDW can be attributed to the pressure enhanced out‐of‐plane Fermi surface nesting and CDW gap in 1 T ‐VSe 2 . The observation of room‐ and high‐temperature CDW transition in 1 T ‐VSe 2 under pressure provides an engineering approach to optimizing the CDW as needed in applications, which does not only open up a new platform for searching and controlling novel states of two‐dimensional materials, but also promotes a practical development of CDW‐related technology and devices.