NiI₂ and NiBr₂ are archetypal van der Waals (vdW) triangular-lattice multiferroics that host incommensurate helimagnetic order at the lowest temperatures and undergo a transition to collinear antiferromagnetic order upon heating. Focusing on NiBr₂, we reveal that both antiferromagnetic phases exhibit a pronounced sensitivity to hydrostatic pressure. The Néel temperature of the collinear phase increases steeply at ~20 K/GPa, reaching ~100 K at 3 GPa without any indication of saturation, whereas the helimagnetic phase is completely suppressed only above ~0.8 GPa. This behavior contrasts sharply with NiI₂, in which both helical and collinear phases are strengthened until a moderate pressure of ∼6 GPa, above which the helical phase instantly disappears. Ab initio calculations identify the second-nearest interlayer exchange interaction j₂′ as the primary driver stabilizing the collinear AFM phase in NiBr₂. In addition, the in-plane exchange ratio renders the helical order in NiBr₂ considerably more fragile, enabling its suppression under relatively small pressures. These results underscore the dominant role of interlayer interactions in governing the distinct pressure responses of the magnetic phases in NiBr₂ and NiI₂. NiBr₂ and NiI₂ are van der Waals multiferroics with magnetic phase transitions from incommensurate helimagnetic order at low temperatures to collinear antiferromagnetic order upon heating. Here, the authors demonstrate that hydrostatic pressure significantly affects the antiferromagnetic phases in NiBr₂, with ab initio calculations highlighting interlayer interactions as key to stabilizing the collinear order, and reveal a contrasting pressure response in NiI₂, offering insights into pressure-induced magnetic phase control.

A2Ir2O7iridates were proven to crystallise in the geometrically frustrated pyrochlore structure, which remains stable upon rare-earth cation substitution, temperature variation, and external pressure application. However, the change of interatomic distances and local distortions in the lattice frequently leads to complex electronic properties. The low-temperature behaviour in light-A iridates has been thoroughly investigated, including its evolution with pressure. The present pressure study reports the electrical transport and magnetotransport properties in heavy rare-earth Lu2Ir2O7and Er2Ir2O7. Both compounds reveal a semiconductor-insulator transition induced by the antiferromagnetic ordering of the all-in-all-out (AIAO) type in the Ir sublattice. The transition monotonously shifts to a higher temperature under applied pressure by approximately 20 K at 3 GPa. As the transition in resistivity originates in the antiferromagnetic order, the latter is expected to be enhanced with the applied pressure as well. Upon cooling the compound in a magnetic field, the AIAO/AOAI domain structure with non-zero net magnetic moment is formed, mirroring itself in an asymmetric term in the magnetoresistivity of Lu2Ir2O7. The application of pressure then enhances the asymmetric term. The same behaviour is proposed for the whole heavy rare-earth A2Ir2O7series (A= Gd-Lu), although with magnetoresistivity features masked significantly by a stronger response of magneticAcations.

Magnetic and structural properties of tetragonal R2Cu2In intermetallics are presented for R = Dy, Tm, and Lu. The neutron diffraction experiment clarifies the nature of magnetic order in Dy2Cu2In and Tm2Cu2In. While Tm2Cu2In orders ferromagnetically below TC = 31K with magnetic space group (MSG) P4/mb'm', Dy2Cu2In forms a non-collinear ferromagnetic state below 50K (MSG P2'/m') with another k = (½, ½, ½) component of magnetic moment (MSG Ibam.1'c) appearing at 20K. The ground-state magnetic structure is described by the MSG Im'm'a with a magnetic moment of 9.35 μB. This subsequent transition is accompanied by the changes in the T-dependence of anisotropy constants, however, no related anomaly is observed in specific heat dominated by the CF and exchange interaction effects. Magnetic properties are discussed in the context of lattice response to temperature and pressure variations. The experimental results are supported by the analysis of the non-magnetic Lu analogue and by the first-principles calculations (electronic structure and material properties) based on Density Functional Theory (DFT).

A thorough study of EuZn2P2 single crystals, which were grown from Sn flux, was performed using both bulk (heat capacity, ac susceptibility, dc magnetization, electrical resistivitivity, magnetoresistance) and microscopic (M & ouml;ssbauer spectroscopy) techniques. Electrical resistance and magnetic susceptibility were measured also under high pressure conditions (up to 19 and 9.5 GPa, respectively). Further insight into electronic properties and phonons is provided by ab initio calculations. The results indicate that EuZn2P2 is an antiferromagnet with strong Eu-Eu exchange coupling of ferromagnetic type within the basal plane and weaker antiferromagnetic interaction along the c axis. The Eu magnetic moments are tilted from the basal plane. Hydrostatic pressure strongly affects both magnetic (increase of the N & eacute;el temperature) and electronic (suppression of the band gap and semimetallic behavior) properties, indicating a strong interplay of structure with magnetic and electronic degrees of freedom.

Structural and magnetic properties of the Shastry-Sutherland material Yb2Pt2Pb were studied in single-crystalline form under pressures up to 10 GPa, magnetic fields up to 17 T, and temperatures down to 0.3 K. Surprisingly robust magnetic order is observed with the N & eacute;el temperature T-N = 2.1 K stable up to 8.1 GPa. Indication of an additional magnetic phase formation can be traced in resistivity data for magnetic field along the c-axis exceeding the (pressure-dependent) metamagnetic transition. The related anomaly shifts to higher temperatures with increasing field, merging T-N at the tricritical point. Experiments with mu H-0 // [110] revealed the pressure stabilization of observed magnetic phases with respect to the magnetic field. The crystal-structure type is stable up to 10 GPa, without any sign of symmetry change, exhibiting moderate volume compressibility with bulk modulus B = 116(13) GPa, in good agreement with B = 118 GPa provided by the density functional theory.

Ce2Pd2In (Mo2FeB2-type of crystal structure) with the ferromagnetic ground state based on Ce-4f(1) states exhibits two distinct phases of pressure-driven destruction of magnetic order. For pressures up to 3 GPa, a gradual buildup of Kondo interactions and of incommensurate spin-density wave are observed, while the ordering temperature remain in the range 4-5 K. A gradual but fast suppression of magnetism and formation of heavy fermion state (estimated Sommerfeld coefficient gamma exceeding 400 mJ mol(-1) K-1) could be placed into the context of pressure evolution of crystal lattice, in which all nearest neighbors in the basal plane converged to the same value, forming a frustrated triangular lattice.

Tm2Cu2In belonging to the family of R2T2X intermetallics is a ferromagnet with glassy features. This work describes results of high-pressure studies of its magnetic behavior. While TC exhibits only a weak and non-monotonous response to hydrostatic pressure, the pressure impact on frequency dependence of AC susceptibility can be interpreted as due to gradual increase of relaxation time and decrease of the activation energy barrier. Since the magnetic behavior is strongly related to the details of crystal structure, the temperature and pressure effects on the lattice are presented, as well. First principles calculations based on the density functional theory provide a background information.

Lattice and electronic properties of La2Pd2In were studied at ambient and elevated pressures so as to determine features related to a specific atomic coordination without any influence of magnetism. We describe temperature dependences of lattice parameters, heat capacity and electrical resistivity of single-crystalline La2Pd2In (s.g. P4/mbm) in a broad temperature range 0.09- 300 K. Together with the anisotropic effect of hydrostatic pressure, showing that the lattice is more compressible in the basal plane, we can conclude that the lattice is affected by degrees of freedom of the La atoms with positions not imposed by symmetry. The lattice anisotropy is smaller than that found for isostructural ferromagnet Ce2Pd2In. The equilibrium bulk modulus B0 = (48 +/- 3) GPa was determined on the basis of individual linear compressibilities. Measurement of electrical resistivity indicated a superconducting state below T = 0.59 K with a low critical field 0.005 T at T = 380 mK. The onset of superconducting state as a bulk property of La2Pd2In was confirmed by measurements of specific heat and AC magnetic susceptibility. Experimental data can be accounted by first-principles electronic-structure calculations based on density-functional theory. The measured Sommerfeld coefficient. = 10.6 mJ mol(-1) K-2, only marginally exceeding the calculated. = 9.34 mJ mol(-1) K-2, indicates only weak electronic correlations.

CeCuAl3 belongs to the Ce-based family of intermetallic compounds crystallizing in a non-centrosymmetric tetragonal BaNiSn3-type structure. Multiple members of the family exhibit pressure-induced superconductivity, unconventional superconductivity, as the crystallographic lattice lacks a centre of inversion. Several indications have suggested the existence of superconductivity also in CeCuAl3. Such assumption is supported by presented measurements of anisotropic compressibility. Our measurements of the electrical resistance of a CeCuAl3 single crystal in significantly expanded pressure and temperature regions up to 10 GPa and down to 9 mK, however, indicate no transition to the superconducting state. A standard saturation of resistance to residual value and its temperature evolution attributed to Fermi-liquid behaviour is observed at low temperatures throughout the experiment. At higher temperatures, the pressure dependence of an anomaly ascribed to the Kondo effect as well as two anomalies connected to the crystal field excitations is followed and discussed with respect to heavy-fermion properties and crystal field scheme of CeCuAl3.

Elastic constants, thermal expansion, magnetostriction and heat capacity measurements were performed with and without applied magnetic field on a single crystal of UIrSi$_3$. The elastic properties were interpreted within the theory of the strain-exchange effect. The exchange-striction model together with the Ising model for the behavior of magnetic localized 5$f$ electrons and itinerant electrons of uranium correctly reproduces the main features of our magneto-acoustic experiments in UIrSi$_3$. Data on thermal expansion and magnetostriction confirm the conclusion that the dominant contribution of the measured temperature and field change in the speed of sound comes from the change in the elastic modulus itself. Based on the analysis of heat capacity measurements in the magnetic field, we explain the significant anomalies at the second-order branch of the phase transition boundary as a manifestation of the tricritical fluctuations, dominating the region below the tricritical point. The outcome confirms the 3D Ising model, at zero and low magnetic fields, with a crossover to the mean-field tricritical behavior at fields close to the tricritical point, where tricritical fluctuations dominate the temperature evolution of the given property.

Evolution of magnetism in single crystals of the van der Waals compound VI3 in external pressure up to 7.3 GPa studied by measuring magnetization and ac magnetic susceptibility is reported. Four magnetic phase transitions, at T1 = 54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 K, respectively have been observed at ambient pressure. The first two have been attributed to the onset of ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is characterized by the magnetic ordering transition at Curie temperature TC and the transition between two different ferromagnetic phases TFM, accompanied by a structure transition from monoclinic to triclinic symmetry upon cooling. The pressure effects on magnetic parameters were studied with three independent techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa whereas TFM increases rapidly with increasing pressure and reaches TC at a triple point at ~ 0.85 GPa. At higher pressures, only one magnetic phase transition is observed moving to higher temperatures with increasing pressure to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization is dramatically reduced by applying pressure (by more than 50% at 2.5 GPa) suggesting a possible pressure-induced reduction of vanadium magnetic moment. We discussed these results in light of recent theoretical studies to analyze exchange interactions and provide how to increase the Curie temperature of VI3.

The EuRu2P2 single crystal was investigated by means of magnetic, transport and thermodynamic studies at ambient and hydrostatic pressures. A small magnetocrystalline anisotropy with crystallographic [100] direction as an easy magnetization direction was found by experimental measurements and confirmed by first-principles calculations. We connect a previously reported change in the compressibility observed at room temperature to a rapid change of ordering temperature under applied hydrostatic pressure. (C) 2021 Elsevier B.V. All rights reserved.

The $5f$-based ferromagnet $\mathrm{U}{\mathrm{Ga}}_{2}$ with the Curie temperature ${T}_{\mathrm{C}}=125\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ was investigated by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments at the $\mathrm{U}--{M}_{4,5}$ and Ga--K edges. The position of the $\mathrm{U}--{M}_{4}$ white line, determined in the high-energy resolution fluorescence detection XAS, suggests that $\mathrm{U}{\mathrm{Ga}}_{2}$ is neither a localized $5{f}^{2}$ nor an itinerant system with $5f$ occupancy close to ${n}_{5f}=3$. The analysis of the acquired ${M}_{4,5}$ XANES and XMCD spectra indicates the $5f$ occupancy close to 2.5 and a large orbital magnetic moment of the uranium $5f$ states (3.18 ${\ensuremath{\mu}}_{\mathrm{B}}$) that is partly compensated by the antiparallel spin moment (1.31 ${\ensuremath{\mu}}_{\mathrm{B}}$). Thus, the total $5f$ magnetic moment of 1.87 ${\ensuremath{\mu}}_{\mathrm{B}}$ is obtained, which is smaller than the known bulk magnetization of 3.0 ${\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit, while the magnetic moments of the Ga atoms are negligible. Several methods based on density-functional theory were applied and the obtained results were compared with XAS spectral features, the Sommerfeld coefficient of the electronic specific heat, and the size of the U moments and $5f$ occupancies. A clear correlation is revealed between the $\mathrm{U}--{M}_{4}$ white-line position of three metallic uranium compounds and the calculated uranium ionicity. It is demonstrated that only electronic structure methods taking appropriate care of orbital magnetism and related atomic multiplet effects can successfully describe all considered properties.

A resistivity study of a single crystal of ${\mathrm{U}}_{2}{\mathrm{Ni}}_{2}\mathrm{Sn}$ has been performed at ambient pressure and under hydrostatic pressure up to $p=3.3\phantom{\rule{4pt}{0ex}}\mathrm{GPa}$. It revealed Fermi-liquid behavior accompanied by spin excitations with an energy gap $\mathrm{\ensuremath{\Delta}}=30\text{--}55\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in the whole pressure range. The N\'eel temperature varies with pressure in a nonmonotonous way. It increases at the rate $d{T}_{\mathrm{N}}/dp=+0.6\phantom{\rule{4pt}{0ex}}\mathrm{K}/\mathrm{GPa}$, and later, after passing through the maximum at \ensuremath{\approx}3 GPa, it starts to decrease quickly. High-pressure x-ray diffraction indicated that an orthorhombic distortion of the tetragonal structure takes place around the pressure of this ${T}_{\mathrm{N}}$ maximum. The computational study based on the density functional theory illustrates that the loss of magnetism in ${\mathrm{U}}_{2}{\mathrm{Ni}}_{2}\mathrm{Sn}$ with pressure is primarily due to $5f$-band broadening, which results from the collapse of the U spacing within the U-U dimers.

Among a large group of R2T2X intermetallics (R = rare earth, T = transition element, X = p-metal) crystallizing in the Shastry-Sutherland-like tetragonal structure, Ce2Pd2In represents a rare example of Ce-based ferromagnet, reached, however via an antiferromagnetic phase stable at higher temperatures. Here we describe the development of magnetism in Ce2Pd2In under external hydrostatic and uniaxial pressure, monitored by means of electrical resistivity, magnetization, and AC magnetic susceptibility experiments on a high-quality single crystal. The experiments prove a stability of the 4f magnetism in pressures up to 3 GPa. At these pressures only slightly reduced spontaneous magnetization in the FM state and enhanced electrical resistivity with signs of Kondo lattice behavior are observed. The AFM Neel temperature (T-N = 4.65 K) is essentially pressure independent, while the Curie temperature (T-C = 4.16 K at ambient pressure) significantly decreases under hydrostatic pressure. The fact that the ferromagnetic phase can be re-entered in weak magnetic fields (0.05 T) proves that the two types of magnetic order are effectively degenerate. Interestingly, T-C is not affected by uniaxial pressure applied along the tetragonal c-axis, T-N value exhibits only a weak decrease of 0.25 K GPa(-1) under such uniaxial pressure. The crystal structure of Ce2Pd2In exhibits a strongly anisotropic thermal expansion with anomalous expansion of the c-parameter with decreasing T. Modest size of magnetostriction effects, observed by dilatometry at ambient pressure, indicates only regular magnetovolume interactions. (C) 2021 Elsevier B.V. All rights reserved.

There is an ongoing dispute in the community about the absence of a magnetic quantum critical point (QCP) in the noncentrosymmetric heavy fermion compound CeRhSi3. In order to explore this question we prepared single crystals of CeRh(Si1-xGex)3withx= 0.05 and 0.15 and determined the temperature-pressure (T-p) phase diagram by means of measurements of the electrical resistivity. The substitution of isoelectronic but large Ge enforces a lattice volume increase resulting in a weakening of the Kondo interaction. As a result, thex= 0.05 andx= 0.15 compound exhibit a transition into the antiferromagnetic (AFM) at higher temperatures beingTN= 4.7 K andTN1= 19.7 K, respectively. Application of pressure suppressesTN(TN1) monotonically and pressure induced superconductivity is observed in both Ge-substituted compounds abovep⩾ 2.16 GPa (x= 0.05) andp⩾ 2.93 GPa (x= 0.15). Extrapolation ofTN(p) → 0 of CeRh(Si0.95Ge0.05)3yields a critical pressure ofpc≈ 3.4 GPa (in CeRh(Si0.85Ge0.15)3 pc≈ 3.5 GPa) pointing to the presence of an AFM QCP located deep inside the superconducting state.

Pressurizing strategically selected compositions of the $\mathrm{EuC}{\mathrm{u}}_{2}{(\mathrm{G}{\mathrm{e}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{i}}_{x})}_{2}$ series affords an opportunity for gaining microscopic insight into the ground-state properties and interplay between magnetism and valence fluctuations across a quantum critical point. This is investigated by way of systematic $^{151}\mathrm{Eu}$ M\"ossbauer spectroscopy measurements on $x=0$ and $x=0.5$ compositions in the series, pressurized up to 7 GPa including variable temperature scans in the range 300--4.2 K. In $\mathrm{EuC}{\mathrm{u}}_{2}\mathrm{G}{\mathrm{e}}_{2}$ the temperature and pressure dependences of the hyperfine interaction parameters indicate that both the magnetic and divalent state, $\mathrm{E}{\mathrm{u}}^{\ensuremath{\nu}+}$ where $\ensuremath{\nu}=2$, are stable up to 6--7 GPa, thus serving as a useful reference. Whereas in the $x=0.5$ composition which initially involves $\mathrm{E}{\mathrm{u}}^{2+}$, collapse of the magnetically ordered state is onset at \ensuremath{\sim}1.3 GPa and there is emergence of a nonmagnetic intermediate valence state coexisting with the magnetically ordered state. This regime of mixed states is a precursor of a quantum phase transition to a nonmagnetic homogeneous intermediate valence state $\ensuremath{\nu}\ensuremath{\sim}2.45$, across a quantum critical point at 3.6 GPa, suggesting a first-order phase transition. X-ray-diffraction pressure studies at 300 K up to 6 GPa of the $x=0.5$ composition indicate there is no change in lattice symmetry from the tetragonal $\mathrm{ThC}{\mathrm{r}}_{2}\mathrm{S}{\mathrm{i}}_{2}$-type structure. There are also no obvious discontinuities in pressure dependences of the lattice parameters upon evolving through the quantum critical point at 3.6 GPa. Increasing pressure changes the starting $\mathrm{E}{\mathrm{u}}^{2+}$ valence monotonically, until the mean valence attains its largest value $\ensuremath{\nu}\ensuremath{\sim}2.45$ indicative of enhanced charge fluctuations at the quantum critical point and plateaus thereafter. High-pressure resistance measurements at low temperatures down to 40 mK near the quantum critical point reveal no evidence for superconductivity.

ABSTRACT Characterization of a new pressure medium Daphne Oil 7575 using a set of three manganin coils, a superconducting temperature of lead and the response of two perpendicular strain-gages down to low temperatures is presented. A complementary study of Daphne Oil 7474 and Daphne Oil 7373 employing identical methods is included as well. Temperature dependence of the solidification point of Daphne Oil 7575 follows the behavior of its predecessor, Daphne Oil 7474, shifted to slightly higher pressure by about 0.2 GPa. Both Daphne Oil 7474 and Daphne Oil 7575 exhibit larger pressure decrease – between the pressure at room temperature and that at low temperature – than Daphne Oil 7373. On the other hand the solidification pressure of the two media is more than 1 GPa higher than for their ancestor, making them more suitable for experiments in frequently used piston pressure cells with nominal pressure of about 3 GPa.

Pressure variations of the Curie temperature of the 5f ferromagnet beta-UH3 were studied using the Mo-alloyed hydride (UH3)(0.)Mo-82(0).18, which is stable in air and has very similar T-C and magnetization per U atom. By means of ac magnetic susceptibility a linear decrease of T-C was observed for pressures up to 3.2 GPa. The coefficient dT(C)/dp = -2.05 K/GPa gives dlnT(C)/dp = 1/T*dT(C)/dp approximate to -0.011 GPa(-1). This value is smaller than expected for a 5f-band ferromagnet with relatively short U-U distances and suggests that UH3 may be more localized than expected. Among AnX compounds, similar dependence was found e.g. for US. Revisiting existing data on lattice elasticity for beta-UH3, bulk modulus B approximate to 100 GPa can be assumed, leading to dlnT(C)/dlnV = 1.1. Experimental data are confronted with results of GGA + U electronic structure calculations. Plausible values of direct Coulomb U and Hund's exchange J are deduced. The lattice compression was found to reduce predominantly the orbital moments.

Magnetic phase transitions under high pressure are reported for the diamond lattice antiferromagnet Co 3−x Rh x O 4 in the range of 0 ≤ x ≤ 2.0, which is an isostructural S = 3/2 system for the well-known frustrated antiferromagnet CoAl 2 O 4 . In the Co 3−x Rh x O 4 system, magnetic and specific-heat measurements at ambient pressure revealed that a second-order antiferromagnetic transition occurred at the Néel temperature ( T N ) which exhibits a nonmonotonic x -variation. The physical pressure variations of T N were determined by ac-calorimetry under hydrostatic pressures up to p = 2.6 GPa for Co 2 RhO 4 and CoRh 2 O 4 . The rates of change of T N with pressure (i.e., the pressure coefficients), 1.93 and 1.61 K GPa −1 , respectively, were comparable to those for CoAl 2 O 4 and Co 3 O 4 , respectively. The pressure coefficients of magnetic ordering temperature for these A-site spinel compounds were considerably larger than those for other spinel and iron-garnet compounds which follow the empirical ‘10/3 law’. Simple analysis of the chemical and physical pressure coefficients of T N revealed that T N depended on both the lattice volume and the oxygen positional parameter u .