Altermagnets are unconventional spin split magnets arising from the zero spin-orbit coupled limit. They host a magnetic multipolar order parameter yet direct real-space observation of these multipoles has remained elusive. Here we use polarized-neutron diffraction to reconstruct the three-dimensional magnetization density of the prototypical altermagnet MnF_2. By exploiting symmetry-selective magnetic reflections, we separate the dominant spherical Mn^2+ contribution from the much weaker anisotropic Mn magnetization and the covalent spin polarization of the fluorine ligands. The reconstructed spin density reveals a finite fluorine ion moment together with an anisotropic Mn magnetization consistent with the symmetry-allowed altermagnetic rank-5 magnetic multipole O_52(magnetic triacontadipole). These results provide direct real-space evidence of ferroic multipolar order in an altermagnet and establish polarized-neutron diffraction as a powerful probe of hidden magnetic multipoles in quantum materials.

This study focuses on a precursor of the synthesis of Laponite, named pre-Laponite. Pre-Laponite shares similar molecular formula and structure with Laponite, but it exhibits reduced long-range order. N2 adsorption isotherms reveal that both materials possess comparable BET (N2) specific surface areas and microporedominated textures consistent with slit-shaped pores. Notably, the study demonstrates a 1.4-fold improvement in hydrogen uptake for pre-Laponite compared to Laponite at-196 degrees C and 1 bar, pointing to new opportunities for designing clay-based materials for hydrogen storage application.

We investigate the spin state stability of Mn in alpha-Mn2O3 through the structural, insulator-to-metal transition under high pressure by x-ray emission spectroscopy (XES) and x-ray diffraction (XRD) up to 41 GPa. The XES spectra show a broadening of the main line and a weak shift of the satellite feature as pressure increases but no signature of spin transition while XRD confirms the full conversion to the Cmcm phase at high pressure. Using multiplet calculations, we suggest that the XES spectral changes under pressure is driven by the increased Coulomb interaction in the compressed lattice. The absence of spin transition through the phase transition could be caused by Jahn-Teller distortions on the Mn sites, which stabilize the spin state, possibly leading to hopping conductivity owing to polaronic effects.

Structural modifications of single-walled aluminosilicate clay nanotubes have been studied under hydrostatic pressure by in situ synchrotron X-ray scattering. Imogolite nanotubes (INT) of nominal composition (OH)(3)Al2O3SiOH, and methyl-modified imogolite nanotubes (m-INT), (OH)(3)Al2O3SiCH3, have hydrophilic and hydrophobic internal cavities, respectively. Nanotube chiralities also differ, with zigzag (INT) and armchair (m-INT) chirality. In this work, pressure-induced changes in nanotube morphology and atomic structure are studied as a function of chirality, affinity of the inner cavity, and the pressure-transmitting medium used. Radial deformation and collapse of nanotubes are evidenced below 3 GPa, followed by the formation of a lamellar phase at higher pressures. In the case of INT, the collapse pressure value depends on the pressure transmitting medium chosen. Axial compressibility is measured, and a pseudo Young's modulus Y is determined to be equal to similar to 265 GPa for INT and below 80 GPa for m-INT, underpinning the role of nanotube chirality in mechanical properties.

Antiferromagnetic intermetallic compound EuRhGe3 crystalizes in a non-centrosymmetric BaNiSn3-type (I4mm) structure. We studied its pressure-dependent crystal structure by using synchrotron powder x-ray diffraction at room temperature. Our results show a smooth contraction of the unit cell volume by applying pressure while preserving I4mm symmetry. No structural transition was observed up to 35 GPa. By the equation of state fitting analysis, the bulk modulus and its pressure derivative were determined to be 73 (1) GPa and 5.5 (2), respectively. Furthermore, similar to the isostructural EuCoGe3, an anisotropic compression of a and c lattice parameters was observed. Our experimental results show a good agreement with the pressure-dependent structural evolution expected from theoretical calculations below 13 GPa. Reflecting a strong deviation from integer Eu valence, the experimental volume data appear to be smaller than those of DFT calculated values at higher pressures.

The magnetic order in BaFe2Se3, an iron-based spin ladder that is superconducting under pressure, is intensely studied due to the intimate relation between magnetism and superconductivity. In the present paper, we have performed a comprehensive study of structural, magnetic, and electronic properties on Ba(Fe1-xNix)2Se3 (0 x 0.2) and BaFe2(Se1-yTey)3 (0 y 0.15). Neutron powder diffraction measurements were performed on the Ni-doped sample up to x = 0.1 and BaFe2(Se0.85Te0.15)3. Our results show that the block magnetic order remains as the ground state for x 0.05 in Ba(Fe1-xNix)2Se3. Additionally, for BaFe2(Se0.85Te0.15)3, the block magnetic structure is even more robust. As for the resistivity, it decreases with increasing Ni content while it barely changes with Te doping. The observed negligible change of the magnetic propagation wave vector as a function of Ni content seems to contradict the orbital selective Mott Phase proposed previously.

Supercrystals, extended lattices of closely packed nanoparticles (NPs), present exciting possibilities for various applications. Under high pressures, typically in the gigapascal (GPa) range, supercrystals undergo significant structural changes, including adjustable interparticle distances, phase transformations, and the formation of new nanostructures through coalescence. While prior research has focused on ligand engineering's impact on supercrystal mechanical response, the influence of NP shape remains unexplored, especially for NPs larger than 10 nm coated with hydrosoluble ligands. This study examines the effects of NP shape on the mechanical properties of supercrystals using high‐pressure small‐angle X‐ray scattering and focused ion beam–scanning electron microscopy tomography. Notably, supercrystals exhibit higher hardness levels compared to previously reported values for gold supercrystals, attributed to the use of larger NPs. Spherical and tetrahedral NPs rearrange before collapsing under pressure, whereas rods and octahedra coalesce without prior structural rearrangement, likely due to their higher packing fraction. Additionally, anisotropic deformation of NP lattices and sintering does not always correlate with deviatoric stresses. These findings refine the understanding of complex processes governing supercrystal structure under high pressure, opening new avenues for NP engineering and advancing plasmonic applications under extreme conditions.

In this paper, we investigate the physical properties of the type II multiferroic GdMn$_2$O$_5$ material by means of neutrons scattering, electric polarization and magnetization measurements. A complex $(T,H)$ phase diagram shows up, with especially a field induced magnetic transition around 12 T at low temperature. The high field phase is accompanied by an additional electric polarization along both the $a$ and $$b directions, as authorized by symmetry, but never observed experimentally up to now. While the magnetic properties recover their initial states after driving the field back to zero, the polarization along $a$ shows a significant increase. This behavior is observed for all directions of the magnetic field. It constitutes a novel and striking manifestation of the magneto-electric coupling, resulting in the establishment of a new ground state at zero magnetic field.

We report on the pressure evolution of the electronic and crystal structures of the noncentrosymmetric antiferromagnet EuCoGe3. Using a diamond anvil cell, we performed high pressure fluorescence detected near-edge x-ray absorption spectroscopy at the Eu L3, Co K, and Ge K edges and synchrotron powder x-ray diffraction. In the Eu L3 spectrum, both divalent and trivalent Eu peaks are observed from the lowest pressure measurement (~2 GPa). By increasing pressure, the relative intensity of the trivalent Eu peak increases, and an average Eu valence continuously increases from 2.2 at 2 GPa to 2.31 at~50 GPa. On the other hand, no discernible changes are observed in the Co K and Ge K spectra as a function of pressure. With the increase in pressure, lattice parameters continuously decrease without changing I4mm symmetry. Our study revealed a robust divalent Eu state and an unchanged crystal symmetry of EuCoGe3 against pressure.

We report here an extensive high pressure small-angle X-ray scattering study on 3D supercrystals self-assembled from colloidal spherical gold crystalline nanoparticule (NPs). We used a large variety of NPs with different gold core diameter, from 2 to 10 nm, grafted with different ligands: alkane-thiols or oleylamine. The self assembly of these various NPs leads to supercrystals of different structures: face centered cubic (FCC), body centered cubic (BCC), as well as the C14 Frank and Kasper phase. Using a Diamond Anvil Cell to apply pressure on these wide range of samples, we provide a unique overview on the mechanical properties of gold NPs supercrystals. In particular, bulk modulii have been determined from low pressure regime and the different behavior between FCC and BCC structures has been interpreted as due to an easier restructuring of the ligand conformation in the FCC structure compared to the BCC structure. At higher pressure, a fingerprint of irreversible structural transition has been observed. We have ascribed this irreversibility to the sintering of nanoparticles and confirmed this interpretation by transmission electron microscopy.

We report on the pressure evolution of the electronic and crystal structures of the noncentrosymmetric antiferromagnet EuCoGe3. Using a diamond anvil cell, we performed high pressure fluorescence detected near-edge x-ray absorption spectroscopy at the Eu L3, Co K, and Ge K edges and synchrotron powder x-ray diffraction. In the Eu L3 spectrum, both divalent and trivalent Eu peaks are observed from the lowest pressure measurement (similar to 2 GPa). By increasing pressure, the relative intensity of the trivalent Eu peak increases, and an average Eu valence continuously increases from 2.2 at 2 GPa to 2.31 at similar to 50 GPa. On the other hand, no discernible changes are observed in the Co K and Ge K spectra as a function of pressure. With the increase in pressure, lattice parameters continuously decrease without changing I4mm symmetry. Our study revealed a robust divalent Eu state and an unchanged crystal symmetry of EuCoGe3 against pressure.

We present in situ pressure experiments on aluminogermanate nanotubes studied by X-ray scattering and absorption spectroscopy measurements. Structural transformations under hydrostatic pressure below 10 GPa are investigated as a function of the morphology, organization, or functionalization of the nanotubes. Radial deformations, ovalization for isolated nanotubes, and hexagonalization when they are bundled are evidenced. Radial collapse of single-walled nanotubes is shown to occur, in contrast to the double-walled nanotubes. The effect of the transmitting pressure medium used on the collapse onset pressure value is demonstrated. Axial Young's moduli are determined for isolated (400 GPa) and bundled (600 GPa) single-walled nanotubes, double-walled nano-tubes (440 GPa), and methylated single-walled nanotubes (200 GPa).

The spin ladder system BaFe2Se3 presents puzzling magnetic behaviors, such as a spin-glass-like phase below similar to 50 K. In this paper, an exchange bias effect with a large vertical shift in the field-cooled hysteresis loop is observed below 50 K. We also evidence the existence of uncompensated spins by susceptibility, magnetic remanence, and hysteresis loop measurements. The thermoremanent and isothermoremanent magnetization curves evidence a two-dimensional diluted antiferromagnet (DAFF) nature. Moreover, a nanometer-sized layered structure is observed by scanning electron microscope (SEM) and confirmed by scanning transmission electron microscope (STEM) coupled with electron energy loss spectroscopy (EELS). The discovery of exchange bias in antiferromagnetic BaFe2Se3 crystals adds a new dimension to the research of its superconducting and multiferroic properties.

We report thermal conductivity measurements on single crystals of herbertsmithite, over a wide range of temperatures (0.05-120 K) in magnetic fields up to 15 T. We also report measurements of the thermal Hall effect, found to be vanishingly small. At high temperatures, in the paramagnetic regime, the thermal conductivity has a negligible field dependence. Upon cooling and the development of correlations, the onset of a clear monotonic field dependence below about 20 K signals a new characteristic temperature scale that may reflect the subtle crossover towards the quantum spin liquid regime. Deconfined spinons, if present, are not detected and phonons, as the main carriers of heat, are strongly scattered by the intrinsic spin excitations and the magnetic defects. In view of the colossal fields required to affect the intrinsic spins, most of the field-induced evolution is attributed to the progressive polarization of some magnetic defects. By elaborating a phenomenological model, we extract the magnetization of these main scattering centers which does not resemble the Brillouin function for free spins 1/2, requiring to go beyond the paradigm of isolated paramagnetic spins. Besides, the onset of a nonmonotonic field dependence below about 2 K underlines the existence of another characteristic temperature scale, previously highlighted with other measurements, and sheds new light on the phase diagram of herbertsmithite down to the lowest temperatures.

The spin dynamics in the block magnetic phase of the iron-based ladder compound \bfs\ has been studied by means of single crystal inelastic neutron scattering. Using linear spin wave theory and Monte-Carlo simulations, our analysis points to a magnetic Heisenberg model with effective frustrated antiferromagnetic couplings only, able to describe both the exotic block order and its dynamics. This new and purely antiferromagnetic picture offers a fruitful perspective to describe multiferroic properties but also understand the origin of the stripe-like magnetic instability observed under pressure as well as in other parent compounds with similar crystalline structure.

We report on High Pressure Small Angle X-ray Scattering (HP-SAXS) measurements on 3D face-centered cubic (FCC) supracrystals (SCs) built from spherical gold nanoparticles (NPs). Dodecane-thiol ligands are grafted on the surface and ensure the stability of the gold NPs by forming a protective soft layer. Under a hydrostatic pressure of up to 12 GPa, the SC showed a high structural stability. The bulk elastic modulus of the SC was derived from the HP-SAXS measurements. The compression of the SC undergoes two stages: the first one related to the collapse of the voids between the NPs followed by the second one related to the compression of the soft matrix which gives a major contribution to the mechanical behavior. By comparing the bulk modulus of the SC to that of dodecane, the soft matrix appears to be less compressible than the crystalline dodecane. This effect is attributed to a less optimized chain packing under pressure compared to the free chains, as the chains are constrained by both grafting and confinement within the soft matrix. We conclude that these constraints on chain packing within the soft matrix enhance the stability of SCs under pressure.

We report the exceptional structural and magnetic stability of SrFeO2 under pressure by X-Ray Magnetic Circular Dichroism (XMCD) and X-ray Diffraction (XRD) up to the Mbar range. The XMCD data confirm the onset of ferromagnetism above 30 GPa and its stability up to 102 GPa while XRD shows that SrFeO2 structure remains unchanged from 30 GPa up to 111 GPa without any sign of structural transition. Our results demonstrate the robustness of Fe properties under extreme conditions in the square planar environment.

M. J. Weseloh,1, 2, ∗ V. Balédent,3 W. Zheng,3 M. Verseils,4 P. Roy,4 J. B. Brubach,4 D. Colson,5 A. Forget,5 P. Foury-Leylekian,3 and M.-B. Lepetit1, 2, † 1Institut Néel, CNRS, 25 av. des Martyrs, 38042 Grenoble, France, Université Grenoble Alpes 2Institut Laue-Langevin, 71 av. des Martyrs, 38000 Grenoble, France 3Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405, Orsay, France 4Synchrotron SOLEIL, L ́ Orme des Merisiers, Saint Aubin BP 48, 91192, Gif-sur-Yvette, France 5SPEC, CEA, CNRS-UMR3680, Université Paris-Saclay, Gif-sur-Yvette Cedex 91191, France