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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 t...

The magnetic properties of newly prepared Tm2Ir2O7 were investigated by means of magnetization and specific heat measurements and compared to the properties of other heavy rare-earth pyrochlore iri...

We present an extensive powder and single-crystal neutron scattering investigation of the crystallographic structure and magnetic order of the frustrated metallic $f$-electron magnet $\mathrm{U}{\mathrm{Ni}}_{4}\mathrm{B}$. We carry out a full refinement of the crystallographic structure and conclude that the low-temperature lattice symmetry is orthorhombic [space group Pmm2; cell parameters: $a=6.963(4)$, $b=14.793(9)$, $c=17.126(8)$ \AA{}]. We determine the magnetically ordered structure, concluding that below ${T}_{\mathrm{N}}=19.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, the material undergoes a transition into a partially ordered antiferromagnetic state. The magnetic structure is consistent with the existence of toroidal order in this material. We further test the proposal of a second magnetic transition occurring at $330\phantom{\rule{0.28em}{0ex}}\mathrm{mK}$, concluding that the thermodynamic anomalies observed at these temperatures do not reflect modifications of the magnetic structure. Our study provides a consistent picture of the interrelationship of structural and magnetic properties in the frustrated magnet $\mathrm{U}{\mathrm{Ni}}_{4}\mathrm{B}$ previously unresolved.

Low-temperature magnetic properties of Er2Zr2O7 were studied by magnetization measurements on a newly prepared single crystal. Simultaneously, powder neutron diffraction was employed to investigate its microscopic properties down to 0.3 K. Our low-temperature data demonstrate the presence of a magnetic signal (short-range correlations) by (i) bifurcation of zero-field-cooled (ZFC) and field-cooled (FC) data, and (ii) diffuse magnetic scattering signal developing well in agreement with the temperature development of bulk properties. The presented data are discussed in the frame of a spin-glass ground state in Er2Zr2O7.

The present study is focused on the structural phase transition in (La,Ce)Pd2Al2−xGax investigated by low temperature X-ray powder diffraction. All parent compounds crystallize in the tetragonal CaBe2Ge2 structure type (P4/nmm, 129) at room temperature and undergo structural phase transitions at low temperatures. Rietveld analysis of the measured patterns shows that the low temperature structures of (La,Ce)Pd2Al2 and (La,Ce)Pd2Ga2 have the same space groups and Wyckoff positions, but exhibit different magnitude of distortion and different characteristics of the structural transition. A small continuously appearing distortion is present in the Al parent compounds while the Ga ones exhibit a large discontinuously appearing distortion. These low temperature structures can be described using the C m m e , 67 space group which is translationengleiche subgroup of the tetragonal P 4 / n m m , 129 space group. The concentration dependence of the temperature where the distortion occurs has a minimum or is almost suppressed at a concentration of x ∼ 0.4 (cerium series) and x ∼ 1.6 (lanthanum series). To support our experimental findings we also present density function theory calculations which confirm the structural stability as experimentally observed. We discuss the impact of structural properties in the studied series on the previously observed development of physical properties such as superconductivity and magnetic excitations in neutron scattering spectra.

Magnetic properties of PrCuAl3 and NdCuAl3 single crystals, adopting the tetragonal BaNiSn3-structure-type, are reported. Our magnetization and specific heat measurements revealed no magnetic ordering in PrCuAl3, while NdCuAl3 orders antiferromagnetically below TN = 2.45 K. The paramagnetic regime was investigated for both analogues revealing (i) the a-axis as the easy direction of magnetization with (ii) a relatively high uniaxial anisotropy energy of 13.2 meV for PrCuAl3 compared to a smaller value of 4.7 meV for NdCuAl3. The measured data are well explained by rare-earth ground state multiplet splitting in crystal electric field. A powder neutron diffraction experiment confirmed PrCuAl3 to remain paramagnetic down to 1.5 K. On the other hand, NdCuAl3 orders antiferromagnetically below TN with an incommensurate magnetic structure described by two propagation vectors k1 = (1/3 - δ1, 0, 0) and k2 = (1/7 - δ2, 1/7 - δ2, 0), where δ1 = 0.035(1) and δ2 = 0.007(1). The magnetic moments (of both magnetic modulations) are arranged within the basal plane with a small z-component moment allowed by the symmetry. Our results are discussed with respect to other RCuAl3 compounds.

Structural and magnetic properties of the prominent magnetic shape memory alloy Ni2MnGa have been investigated in detail, as well as their evolution with tuning parameters – most frequently stoichiometry changes in the Ni-Mn-Ga system or substitution of one or more elements in the parent alloy by other d- and/or p-electron elements. Surprisingly, Ga-Ge substitution, although one of the most natural substitutions, has largely been neglected. We present our study on the preparation, phase and structural characterization, and magnetization properties of alloys within the Ni2MnGa1-xGex series. The isostructural substitution of Ga by Ge results in (i) a significant decrease of the melting point of the alloy, (ii) a contraction of the L21 crystal lattice following the Vegard’s law, (iii) a suppression of martensitic transformation of the lattice for x ≥ 0.25, and (iv) a substantial decrease of ferromagnetic Curie temperature with Ge content increasing above x = 0.4. Tentative signs of a possible martensitic transition are observed also for the other parent compound Ni2MnGe. The crucial role of sample annealing on its overall properties is demonstrated. The presented data are discussed in the frame of previous results on the parent alloy and other related doped systems.

The effects on the rare-earth crystal-field-splitting schemes of incorporation of large spin-orbit coupling ($5d$) ions, such as ${\text{Ir}}^{\text{4}}+$, into the rare-earth pyrochlores are largely unknown. We report on the preparation, specific heat, magnetization, and inelastic neutron-scattering study of ${\text{Er}}_{\text{2}}{\text{Ir}}_{\text{2}}{\text{O}}_{\text{7}}$ pyrochlore. An anomaly in specific heat and bifurcation of zero-field cooled and field cooled magnetization indicates an ordering of the Ir sublattice below 140 K, in good agreement with other rare-earth pyrochlore iridates. The Er sublattice ordering below 2 K can be considered short range as well, following the development of specific-heat and magnetization data down to low temperatures. The inelastic neutron scattering allowed us to unambiguously determine the crystal-field (CF) eigenenergies and parameters of ${\text{Er}}_{\text{2}}{\text{Ir}}_{\text{2}}{\text{O}}_{\text{7}}$, which are dictated dominantly by nearest-neighbor anions (the oxygen cage around the Er cation). The influence of the magnetic iridium cations on the erbium CF scheme is rather moderate despite the strong spin-orbit coupling expected in a $5d$ metal, which is evident when comparing the energy spectra of this iridate and other $3d$- or $4d$-metal containing erbium pyrochlores. The determined CF parameters were subsequently utilized for calculations of magnetization and specific-heat CF contributions, leading to an excellent agreement with experimental data.

Pressure induced superconductivity in non-centrosymmetric CeRhSi

Anisotropy of bulk magnetic properties and magnetic structure studies of a Tb

Pressure induced superconductivity in non-centrosymmetric CeRhSi$_{3}$ and CeIrSi$_{3}$ compounds has attracted significant attention of the scientific community since its discovery 15 years ago. Up-to-date, all reported experimental results were obtained employing the hybrid-cylinder piston pressure cells with a maximum reachable pressure of 3 GPa. Present study focuses on the superconducting state at higher, so far unreported, pressures using the Bridgman anvil cell and a CeRhSi$_{3}$ single crystal synthesized by the Sn-true-flux method. The initial increase of superconducting critical temperature from 0.4 K at 1.1 GPa to 1.1 K at 2.4 GPa is followed by a gradual suppression of SC state upon increasing the pressure above 3.0 GPa, forming a typical dome. The pressure induced superconductivity is expected to be completely suppressed in the pressure region between 4.5 and 5.0 GPa. Temperature dependence of electrical resistivity in constant magnetic fields and high pressures, as well as the magnetoresistance measurements, reveal a large critical field, exceeding 19 T at 0.6 K and 2.4 GPa, sharply decreasing receding the superconductivity dome. The previously reported $\it{T-p}$ and $\it{H-T}$ phase diagrams are completed by our high-pressure data and discussed in the frame of previous results., Comment: 16 pages, 5 figures

The magnetic properties of pyrochlore iridate Dy2Ir2O7 prepared by CsCl flux method were investigated by means of heat capacity and magnetization measurements. The low temperature behaviour was confirmed to be consistent with previously published results, whereas the high temperature data and their analysis are presented for the first time. The bifurcation of zero field-cooled and field-cooled magnetization curves coincides well with the onset of the anomaly in specific heat pointing to an ordering of the iridium sublattice. We confront the previously determined Dy3+ CF scheme with our high-temperature magnetization and specific heat data. The difference between calculations and experimental data, represented by 20 K specific heat anomaly, suggests the behaviour beyond the mean field approximation. The Dy2Ir2O7 differs from the rest of the heavy rare-earth pyrochlore iridates, where the mean field approximation constitutes an adequate description. The deeper understanding of the Dy2Ir2O7 magnetic behaviour requires, among others, also the phonon spectra studies.

Anisotropy of bulk magnetic properties and magnetic structure studies of a Tb2Pd2In single crystal by means of bulk magnetization methods and neutron diffraction techniques confirmed the antiferromagnetic order below the N el temperature 29.5 K. The collinear magnetic structure of Tb magnetic moments aligned along the tetragonal c axis is characterized by a propagation vector k 1 4, 1 4, 1 2 , yielding an equal moment structure with alternating coupling between nearest as well as next nearest Tb neighbors within the basal plane and antiferromagnetic coupling between the c axis neighbors. In the context of magnetism of R2T2X compounds, where R stands for rare earth or actinide element, such collinear structure with long wavelength periodicity represents a new type of magnetic structure.

We present the preparation and characterization of an $\mathrm{E}{\mathrm{r}}_{2}\mathrm{Z}{\mathrm{r}}_{2}{\mathrm{O}}_{7}$ single crystal. The material was studied by means of x-ray and neutron diffraction, magnetization, AC susceptibility, and specific heat measurements. The defect-fluorite type of cubic structure, previously reported as the crystal structure of $\mathrm{E}{\mathrm{r}}_{2}\mathrm{Z}{\mathrm{r}}_{2}{\mathrm{O}}_{7}$, is consistent with our x-ray powder diffraction data. The measurements of physical properties were performed in magnetic field applied along principal crystallographic directions. A negligible directional dependence of physical properties is observed at temperatures down to 3 K, and only minor differences can be traced at lower temperatures. A low-temperature anomaly in magnetization and specific heat data and its evolution with applied magnetic field is followed. A frequency-dependent shift of freezing temperature was observed in AC susceptibility. Several origins of the observed anomaly are discussed, leaving a spin-glass state as the most probable explanation.

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 (TN = 4.65 K) is essentially pressure independent, while the Curie temperature (TC = 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, TC is not affected by uniaxial pressure applied along the tetragonal c-axis, TN 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.

Modulated structure of Ni–Mn–Ga-based alloys is decisive in their magnetic shape memory (MSM) functionality. However, the precise nature of their five-layered modulated 10M martensite is still an open question. We used x-ray and neutron diffraction experiments on single crystals to investigate structural changes within 10M-modulated martensite of the Ni50Mn27Ga22Fe1 MSM alloy. The modulation vector gradually increases upon cooling from commensurate q = (2/5) g 110, where g 110 is the reciprocal lattice vector, to incommensurate with q up to pseudo-commensurate q = (3/7) g 110. Upon heating, reverse changes are observed with a thermal hysteresis of ≈60 K. The same hysteretic behaviour was detected in the electrical resistivity and the effective elastic modulus. Scanning electron microscopy showed that the changes are accompanied by the refinement of the a/b laminate. These observations indicate that the commensurate state is a metastable form of 10M martensite. Upon cooling, this phase evolves through nanotwinning into a more irregular and more stable incommensurate structure.

CeCuAl3 crystallizing in the tetragonal BaNiSn3-type structure and CeCuxAl4–x solid solutions were investigated by means of elastic and inelastic neutron scattering. Powder neutron diffraction brought information on both temperature evolution of crystallographic parameters and magnetic order at low temperatures. No structural change was observed in the investigated temperature range from 1.5 to 300 K. Weak magnetic peaks outside nuclear Bragg positions observed in solid solutions with 0.90 ≤ x ≤ 1.10 were described by the propagation vector k = (0.40 + δx, 0.60 + δy, 0), where δx ≈ 0.02 and δy ≈ 0.01. The magnetic structure of CeCu0.75Al3.25 consists of two components: an anti-ferromagnetic one described by the same k and a ferromagnetic one with k0 = (0, 0, 0) and magnetic moments lying within the tetragonal basal plane. The evolution of magnetic excitations as a function of Cu–Al concentration in CeCuxAl4–x was studied by inelastic neutron scattering. The measured spectra of CeCuAl3 and the solution wit...

CeCuAl

An extensive experimental investigation of Fe-based Heusler alloys has been performed in order to potentially prepare new materials which are tetragonally distorted and have large perpendicular magnetic anisotropy crucial not only for the STT-MRAM applications but also for magnetic shape memory devices. Based on criteria demanded for the MSM applications 25 Fe2YZ various compounds were selected for the synthesis using arc melting from more than 60 systems suggested theoretically. Only four compounds Fe2MnSn, Fe2NiSi, Fe2NiGe, and Fe3Ga were homogeneous single phase. None of the studied Fe-based materials exhibited the predicted tetragonal structure. Magnetic measurements confirmed that all investigated compounds are soft ferromagnets with no sign of a structural transition. Our results contradict the ab-initio calculations showing the limits of theoretical predictions by incomplete high throughput calculations as well as the limitations of the standard synthesis techniques.

A systematic structural and magnetic study of an extensive list of Co2YZ and Rh2YZ alloys (Y = d-elements, Z = p-elements) has been performed to identify new materials structurally related to the Ni2MnGa alloys. The target compositions were selected according to theoretical predictions of a tetragonal distortion of an ideally Heusler lattice. Based on the X-ray diffraction, microprobe, and differential scanning calorimetry results, the quality of individual samples was determined and 11 systems, including the novel Co3Sn, Co2NiSn, Co2NiSi, Co2CuGa, and Co2RhGe alloys, were found to be phase-pure or containing only a minor fraction of any secondary phases. The analysis of X-ray diffraction patterns confirmed the tetragonal structure of the Rh2YZ alloys, space group P 42/n c m, as predicted by DFT calculations. However, the crystal structure of Co2YZ is not consistent with the predicted tetragonal structure. Instead, a hexagonal structure, space group P 6/m m m, was determined. Magnetization measurements revealed that all the Rh- and Co-based alloys order ferromagnetically below 450 K and 1000 K, respectively. Additional anomalies of Co3Sn and Co2NiSn in the magnetization data and the peaks in differential scanning calorimetry profiles evidence the respective phases are metastable below ~900 K and transform to equilibrate phases above this temperature. The experimental results, both structural and magnetic properties, are discussed in the framework of previous experimental and theoretical studies.

The solid-state reaction, hydrothermal synthesis and CsCl flux methods were employed preparing Er2Ir2O7 pyrochlore iridate. A mixture of initial Er2O3 and IrO2 oxides was thermally treated, following the temperature evolution of individual phases by means of x-ray diffraction and energy dispersive x-ray spectroscopy. Reactions by hydrothermal synthesis, using various commonly used mineralising agents, showed negligible increase in the pyrochlore phase fraction. The solid-state reaction method allowed a preparation of Er2Ir2O7, however the reacted mixture contained a high percentage (60%) of initial unreacted Er2O3. Adding an excess of IrO2 to the initial content improved the composition of the reacted sample (50% of Er2Ir2O7 for initial Er2O3:IrO2 ratio 0.9:2.1). Nevertheless, a secondary Er–Ir–O phase with slightly larger crystallographic unit cell was also created as an additional product. An optimised flux synthesis, consisting of repeated heating and regrinding cycles at 800 °C and using CsCl as a flux, provided the best conditions for single phase pyrochlore preparation. A sample with 94% Er2Ir2O7 was further improved by repeated reaction with additional excess IrO2 oxide. A successful preparation route for (at least) the heavy-rare earth pyrochlore iridates is established.

In this report we describe the synthesis and characterization of several members of the Ni2YZ (Y = V, Cr; Z = Ga, Ge) family. While the Heusler alloy Ni2VGa was prepared phase pure, the Ni2CrGa sample consisted of a slightly Cr-deficient alloy and elemental Cr inclusions. The Ge analogues, Ni2VGe and Ni2CrGe, were also prepared as primarily Y-element deficient alloys, with minor secondary phases to balance the starting composition. Despite the minor secondary phases, all Ni2VGa, Ni2CrGa, and Ni2CrGe have diffraction patterns consistent with the cubic Heusler structure (a = 5.814(5), 5.765(3), and 5.788(8) A, respectively). Ni2VGe was concluded to consist of at least two highly off-stoichiometric phases and was excluded from further study. Specific heat and magnetization measurements on the prepared samples demonstrated they are non-magnetic or only weakly paramagnetic down to lowest temperature. No measurable magnetic moment was found in phase pure Ni2VGa down to 2 K, while only low moments (µ7T2K = 0.027(1) μB and 0.170(2) μB) were observed in Ni2CrGa and Ni2CrGe. Low values of magnetic moments were discussed from the viewpoint of magnetic Cr impurities in a non-magnetic lattice. Such interpretation was well supported by the specific heat data revealing a strong lowest-temperature contribution ascribed to ferromagnetic Cr clusters in the material. The impact of atomic disorder is discussed, particularly with respect to previous theoretical studies and the predicted properties.

We have studied the pressure effect on the magnetic phase diagram of tetragonal Nd 2 RhIn 8 . The magnetization under uniaxial pressure up to 5.3 kbar applied along the tetragonal c -axis and the heat capacity under hydrostatic pressure were measured in magnetic fields up to 7 and 14 T, respectively. Both types of measurements reveal an increase of T N with increasing pressure; the effect is considerably stronger for the uniaxial pressure. Considering also the anisotropic compressibility in this family of compounds, we conclude that T N increases with decreasing c / a . The phase boundary between the ground-state AF1 phase and the field-induced AF2 phase shifts slightly to higher magnetic fields with increasing pressure. The ground state phase is thus stabilized by applying pressure. The magnetic phase diagram is constructed.

A Ce2Pd2In single crystal was synthesized employing the Czochralski growth method from a stoichiometric melt. It was found to crystallize in the tetragonal Mo2FeB2-type structure. The investigation by means of X-ray diffraction, magnetization, specific heat, and electrical resistivity measurements revealed two successive magnetic phase transitions at around 4.5 and 4.1 K in the possibly slightly off-stoichiometric (Pd rich) crystal. Ferromagnetic ground state changes into the paramagnetic state through an intermediate antiferromagnetic phase. The measured magnetization and specific heat data were discussed in the view of first principles calculations of crystal field for Ce2Pd2In. Uniaxial magnetic anisotropy confining Ce moments into the c-axis has rather high energy exceeding 5 meV. Full ordered Ce-4f1 moments 2.14 μ B do not indicate any Kondo-type interaction, no many body enhancement of the Sommerfeld coefficient can be deduced.

The magnetization and electrical resistivity measurements on a CePdIn single crystal as well as its preparation and structural characterization are presented. The negative paramagnetic Curie temperatures indicate antiferromagnetic ground state, the anisotropy of the paramagnetic Curie temperature amounts 22.7 K. No ferromagnetic correlations were indicated. Powder neutron diffraction experiment performed at temperatures down to 0.4 K did not lead to observation of any magnetic peak in diffraction patterns. We estimate the magnetic moment on Ce atoms to be significantly lower than 0.5-B. The temperature development of lattice parameters documents the standard thermal expansion of the unit cell; no signs of structural phase transition were observed., The most of experiments were performed in MLTL (//mltl.eu/), which is supported within the program of Czech Research Infrastructures (project no. LM2011025). The work was supported within the program of Large Infrastructures for Research, Experimental Development and Innovation (Project No. LM2015050) and research project LTT17019 financed by the Ministry of Education, Youth and Sports, Czech Republic. We would like to acknowledge Helmholz Zentrum Berlin. This research project has been supported by the 7th Framework Programme through the “Research infrastructures” action of the “Capacities” Programme, CP-CSA_INFRA-2011-1.1.17 Number 233883 NMI3 II.

A new simplified synthesis of an Er 2 Ti 2 O 7 single crystal is presented. The single crystal was prepared by a floating zone technique from the unreacted stoichiometric mixture of starting oxides Er 2 O 3 and TiO 2 . No intermediate reactions of constituent oxides were conducted in contrast to previous studies. We demonstrate a good quality of prepared single crystal by both thorough (microscopic) chemical and structural characterization of the material and measurements of previously reported low-temperature properties: An Er 2 Ti 2 O 7 single crystal was characterized by means of x-ray, electron and neutron diffraction techniques, and magnetization and specific heat measurements. The low-temperature magnetization was investigated by indirect measurement employing pre-calibrated Hall probes. The obtained low-temperature data are well comparable with previous reports and document a high quality of the prepared single crystal. Presented single crystal synthesis from an unreacted precursor is prospectively applicable to other rare-earth RE 2 Ti 2 O 7 pyrochlores.

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-x Ge x )3 with x = 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, the x = 0.05 and x = 0.15 compound exhibit a transition into the antiferromagnetic (AFM) at higher temperatures being T N = 4.7 K and T N1 = 19.7 K, respectively. Application of pressure suppresses T N (T N1) monotonically and pressure induced superconductivity is observed in both Ge-substituted compounds above p ⩾ 2.16 GPa (x = 0.05) and p ⩾ 2.93 GPa (x = 0.15). Extrapolation of T N(p) → 0 of CeRh(Si0.95Ge0.05)3 yields a critical pressure of p c ≈ 3.4 GPa (in CeRh(Si0.85Ge0.15)3 p c ≈ 3.5 GPa) pointing to the presence of an AFM QCP located deep inside the superconducting state.

We report on structural and magnetic properties of a SmCuAl3 single crystal. The sample quality, phase and structure purity were investigated by means of x-ray and neutron diffraction, BSE electron microscopy and EDX analysis. The crystal structure was identified to be of a tetragonal BaNiSn3-type (space group I4mm, 107). Magnetization measurements revealed two magnetic phase transitions: from paramagnetic to ferromagnetic state at Tc = 28 K and another transition at TN = 6.6 K connected with a development of the antiferromagnetic component of magnetic moments. Both ferromagnetic and antiferromagnetic components are followed down to lowest temperature. Possible origins of the phase transition at 28 K are discussed. Paramagnetic data are well described assuming a Sm3+ ground-state-multiplet splitting in crystalline environment. Crystal field parameters are estimated and used for magnetization and specific heat calculations revealing a qualitatively good agreement with the experimental data., This work was supported by the Czech Science Foundation under Grant No. 17-04925J. The work was supported within the program of Large Infrastructures for Research, Experimental Development and Innovation (project No. LM2015050) and project LTT17019 financed by the Ministry of Education, Youth and Sports, Czech Republic.

YFeO

In a cubic ferromagnet, small spontaneous lattice distortions are expected below the Curie temperature, but the phenomenon is usually neglected. This study focuses on such an effect in the ${\mathrm{U}}_{4}{\mathrm{Ru}}_{7}{\mathrm{Ge}}_{6}$ compound. Based on DFT calculations, we propose a lattice distortion from the cubic $Im\text{\ensuremath{-}}3m$ space group to a lower, rhombohedral, symmetry described by the $R\text{\ensuremath{-}}3m$ space group. The strong spin-orbit coupling of the uranium ions plays an essential role in lowering the symmetry, giving rise to two different U sites (U1 and U2). Using polarized neutron diffraction in applied magnetic fields of 1 and $9\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ in the ordered state ($1.9\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) and in the paramagnetic state ($20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), we bring convincing experimental evidence of this splitting of the U sites, with different magnetic moments. The data have been analyzed both by maximum entropy calculations and by a direct fit in the dipolar approximation. In the ordered phase, the ${\ensuremath{\mu}}_{\mathrm{L}}/{\ensuremath{\mu}}_{\mathrm{S}}$ ratio of the orbital and spin moments on the U2 site is remarkably lower than for the free ${\mathrm{U}}^{3+}$ or ${\mathrm{U}}^{4+}$ ion, which points to a strong hybridization of the U $5f$ wave functions with the $4d$ wave functions of the surrounding Ru. On the U1 site, the ${\ensuremath{\mu}}_{\mathrm{L}}/{\ensuremath{\mu}}_{\mathrm{S}}$ ratio exhibits an unexpectedly low value: the orbital moment is almost quenched, like in metallic $\ensuremath{\alpha}$-uranium. As a further evidence of the $5f\text{\ensuremath{-}}4d$ hybridization in the ${\mathrm{U}}_{4}{\mathrm{Ru}}_{7}{\mathrm{Ge}}_{6}$ system, we observe the absence of a magnetic moment on the Ru1 site, but a rather large induced moment on the Ru2 site, which is in closer coordination with both U positions. Very similar results are obtained at $20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in the ferromagnetic regime induced by the magnetic field of $9\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. This shows that applying a strong magnetic field above the Curie temperature also leads to the splitting of the uranium sites, which further demonstrates the intimate coupling of the magnetic ordering and structural distortion. We propose that the difference between the magnetic moment on the U1 and U2 sites results from the strong spin-orbit interaction with different local point symmetries.

CePd 2 Al 2 single crystal was investigated by means of magnetization, specific heat and electrical resistivity measurements including the resistivity measurement under hydrostatic pressure. The antiferromagnetic phase transition with Neel temperature of 2.7 K was confirmed by all types of measurements as well as the first order structural phase transition from tetragonal to orthorhombic structure around 13 K. The long-range magnetic order with magnetization easy basal-plane was found. The thorough analysis of magnetization and specific heat was done to discuss the results in context of previous inelastic neutron scattering experiment and the crystal-field scheme. The electrical resistivity under hydrostatic pressure revealed a shift of the structural transition to the higher temperatures, while the magnetic transition temperature remains constant. The resistivity behavior at the structural transition indicates a change of the low-temperature crystal structure in pressures above 0.6 GPa.

CeCuAl

${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}$ compounds crystallizing in the tetragonal ${\mathrm{CaBe}}_{2}{\mathrm{Ge}}_{2}$-type structure (space group $P4/nmm$) and undergoing a structural phase transition to an orthorhombic structure ($Cmme$) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$ is described by an incommensurate propagation vector $\stackrel{P\vec}{k}=({\ensuremath{\delta}}_{x},\frac{1}{2}+{\ensuremath{\delta}}_{y},0)$ with ${\ensuremath{\delta}}_{x}=0.06$ and ${\ensuremath{\delta}}_{y}=0.04$. The magnetic moments order antiferromagnetically within the $ab$ planes stacked along the $c$ axis and are arranged along the direction close to the orthorhombic $a$ axis with a maximum value of 1.5(1) ${\ensuremath{\mu}}_{\mathrm{B}}/{\mathrm{Ce}}^{3+}$. ${\mathrm{CePd}}_{2}{\mathrm{Ga}}_{2}$ reveals a magnetic structure composed of two components: the first is described by the propagation vector $\stackrel{P\vec}{{k}_{1}}=(\frac{1}{2},\phantom{\rule{0.16em}{0ex}}\frac{1}{2},\phantom{\rule{0.16em}{0ex}}0)$, and the second one propagates with $\stackrel{P\vec}{{k}_{2}}=(0,\frac{1}{2},0)$. The magnetic moments of both components are aligned along the same direction---the orthorhombic [100] direction---and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors $\stackrel{P\vec}{{k}_{1}}$ and $\stackrel{P\vec}{{k}_{2}}$ describe also the magnetic structure of substituted ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}$ compounds, except the one with $x=0.1.\phantom{\rule{0.28em}{0ex}}{\mathrm{CePd}}_{2}{\mathrm{Al}}_{1.9}{\mathrm{Ga}}_{0.1}$ with magnetic structure described by $\stackrel{P\vec}{k}$ and $\stackrel{P\vec}{{k}_{1}}$ stays on the border between pure ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$ and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$, while only two crystal field (CF) excitations are expected from the splitting of ground state $J=\frac{5}{2}$ of the ${\mathrm{Ce}}^{3+}$ ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$. A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound ${\mathrm{CePd}}_{2}{\mathrm{Ga}}_{2}$ does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}$ series is discussed and crystal field parameters determined.

Magnetic structure of tetragonal UAu$_2$Si$_2$ was investigated by single-crystal neutron diffraction experiments. Below $T_{\rm N}$ = 20 K it orders antiferromagnetically with a propagation vector of $k = (2/3, 0, 0)$ and magnetic moments of uranium ions pointing along the tetragonal $c$-axis. Weak signs of the presence of a ferromagnetic component of magnetic moment were traced out.Taking into account a group theory calculation and experimental results of magnetization and $^{29}$Si-NMR, the magnetic structure is determined to be a squared-up antiferromagnetic structure, with a stacking sequence ($+ + -$) of the ferromagnetic $ac$-plane sheets along the $a$-axis. This result highlights similar magnetic correlations in UAu$_2$Si$_2$ and isostructural URu$_2$Si$_2$., Comment: 7 pages, 7 figures

We report on specific heat of (Ce,La)Pd2 X 2 compounds. The antiferromagnetic ground state is revealed in Ce-based analogues. The field induced ferromagnetic order is observed in magnetic fieldsss higher than 1 T. The structural phase transition on specific heat data is well pronounced in both Ce compounds and LaPd2Ga2. The thorough analysis of specific heat data is presented.

We present magnetic phase diagrams of Nd2RhIn8 and Tb2RhIn8 determined by magnetization and magnetoresistivity measurements on single crystals, including high-field magnetization up to 60 T. Both compounds order antiferromagnetically with the c-axis as the easy magnetization axis. Their magnetic phase diagrams are qualitatively rather similar. At low temperatures up to 1 / 2 T N , when applying the field along the tetragonal c-axis, we observe first-order transition to another magnetic phase prior to transition to the ferromagnetic order. The magnetic phase diagrams resemble those of other R2RhIn8 or RRhIn5 compounds.

CePtIn crystallizes in a hexagonal ZrNiAl-type structure and exhibits the properties varying between the magnetically ordered state and valence fluctuating state. The competition between RKKY and Kondo interaction in this compound is most significant among the CeTX family. Moreover, the signs of non-Fermi liquid behavior are observed in specific heat and electrical resistivity measurements at low temperatures. Until now all properties have been measured only on polycrystals, often with suspicion of foreign phase in the samples. The preparation of CePtIn single crystal as well as its structure and chemical characterization are presented in detail in this paper.

The compounds from CePd 2 Al 2 - x Ga x series were studied by means of magnetization and electrical resistivity measurements. The electrical resistivity was measured also on LaPd 2 Al 2 - x Ga x counterparts. The development of structural phase transition with Ga content was investigated and its connection with presence of vibron states was discussed. The structural parameters of CePd 2 Ga 2 were determine for both tetragonal and triclinic structure from powder neutron diffraction data. All studied compounds order antiferromagnetically, the Neel temperature slightly decreases with increasing Ga content. Simultaneously, ferromagnetic correlations are observed in the series and become stronger with Ga concentration. The powder neutron diffraction on CePd 2 Ga 2 proved the antiferromagnetic ground state, which is suppressed by magnetic field of 5 T. We found several possible propagation vectors describing observed magnetic reflection.

We present the crystal structure investigation of CeCuAl 3 compound. Our X-ray diffraction study confirms unambiguously BaNiSn 3 -type structure as the crystal structure of CeCuAl 3 in whole temperature range. Moreover, phase transition around 300 °C was found by our high-temperature powder X-ray diffraction measurement. This transition preserves BaNiSn 3 -type structure, only structural parameters change during the transition. The study is provided on single crystalline and polycrystalline samples as well as on La counterpart to compare mainly high-temperature behavior of these compounds.

We have studied development of structural and magnetic properties of TbNiAl single crystal under applied hydrostatic and uniaxial pressure. TbNiAl crystallizes in the hexagonal ZrNiAl-type structure. The lattice parameters show a transition between two phases with different c/a ratio around 120 K as evidenced by X-ray diffraction, resistivity and thermal expansion measurements. The application of hydrostatic pressure stabilizes the low c/a phase. The transition shifts consequently to lower temperatures with applied pressure and vanishes for pressure above 0.55 GPa. The magnetic properties are characterized by antiferromagnetic order below TN = 45 K. The application of magnetic field of 0.3 T along the c-axis leads to a metamagnetic transition to ferromagnetic order. The critical field of this transition shifts considerably to higher values with hydrostatic pressure whereas the uniaxial pressure applied along the c axis moves the transition to lower fields. TbNiAl represents thus a rare example of a well localized system where the magnetic ground state is strongly influenced by external pressure. This behavior is discussed in connection with the structural parameters.