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There remains some disagreement in the literature on CeTiGe over the presence of a structural transition from the low temperature CeFeSi-type form to the high temperature CeScSi-type structure. We present a detailed study of the effect of temperature on this structural transition. Furthermore, the same hydride is obtained after hydrogenation of both forms. Using neutron powder diffraction we find that the structure of CeTiGeH 1.5 corresponds to a stuffed variant of the CeScSi-type structure with space group I 4 /mmm , a = 4.0785(1) A and c = 17.1060(8) A. The H atoms occupy both the Ce 4 tetrahedral sites and the Ti 4 Ce square based pyramidal sites for a total hydrogen occupancy of 1.5 H f.u. −1 . Preliminary examinations of the magnetic properties after hydrogenation reveal the onset of low temperature magnetic order around 3.5 K, suggesting for the first time a hydrogen induced magnetic order for an intermetallic with CeScSi-type structure.

International audience; The sequence of phase transformations in a Fe–Cr–Mn alloy (known as an austenitic stainless steel) are investigated in order to explore the potential of this rare earth-free material for magnetocaloric applications at high temperature. In the lack of high temperature X-ray diffraction the magnetic response and transition temperatures of alloys have been determined by using a Faraday’s Balance apparatus and an extraction vector magnetometer. These characterizations have been complemented by DCS and DTA measurements as well as thermodynamic calculations using Thermocalc. The retained nominal composition is Fe0.59Cr0.16Mn0.25 (referred to as FeCrMn 15/25) shows the targeted reversible transformation. Carbon addition is shown to shift the transition temperature to lower values. The effect of carbon addition on the phase transition and on the magnetocaloric response is discussed. A comparison is made with the chromium-poor Fe–Cr–Ni system.

International audience; The intermetallic NdNiMg15 is the Mg-richest phase (more than 88 atom % of Mg) discovered in the Mg–Nd–Ni system. Its structure was determined by X-ray diffraction on single crystal with the following crystal data: tetragonal system, P4/nmm, Z = 2, a = 10.0602(1) Å, c = 7.7612(2) Å, dcalc = 2.40 g·cm–3. Its structure is made of a three-dimensional framework of magnesium atoms showing channels filled by one-dimensional chain consisting of alternating Nd and Ni atoms along the c-axis. Anti-ferromagnetic ordering was observed with TN = 9 K, which is remarkably high considering the long distances between magnetic atoms, that is, Nd atoms. The effective magnetic moment μeff is equal to 3.58 μB, which is consistent with magnetic Nd3+ ions and weakly or nonmagnetic Ni atoms. Below TN, the M(H) curves show field-induced metamagnetic transitions at critical fields increasing with decreasing temperatures. The magnetic structure of NdNiMg15 was determined from neutron powder diffraction data by considering the propagation vector k = (1/2 1/2 0). This magnetic structure consists in ferromagnetic chains along the c-axis of Nd atoms carrying moments, only separated by Ni atoms. The chains are ferromagnetically coupled within planes perpendicular to the [110] direction, and these planes are anti-ferromagnetically coupled to neighboring planes forming a checkerboard-like magnetic structure.

In this study, we have expanded our previous work on the Gd 2 (Co 3-x Si x ) solid solution to form the family of R 2 ( T 3-x Si x ) compounds with a wide range of the rare earth metals (Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er) by variation of the composition and, where necessary, the transition element (Co and Ni). We report the crystallographic and the magnetic properties of this La 2 Ni 3 -type series. The R 2 Co 3-x Si x compounds with R = Pr, Nd, Sm and Gd, undergo ferro- or ferrimagnetic transitions at T C ranging from 64 K (Nd) to 338 K (Gd) and the R 2 Ni 3-x Si x phases with R = Gd-Er display ferromagnetic order below T C from 96 K (Gd) to 7 K (Er).

International audience; The investigation of layered intermetallic compounds containing light elements like hydrogen has great potential for superconductivity. We studied the insertion of carbon atoms in CeScSi-type intermetallics (an ordered variant of the La2Sb structure type), and here, we report the new carbide NdScSiC0.5. Carbon insertion keeps the pristine compound’s space group, I4/mmm, but causes an anisotropic expansion of the unit cell with an increase in the a parameter and a decrease of the c parameter. X-ray and neutron diffraction measurements indicate the existence of a NdScSiCx solid solution (0.2 < x ≤ 0.5) with carbon atoms occupying only the Sc4Nd2 octahedral sites while leaving the Nd4 tetrahedral sites vacant. Magnetization measurements unveil a linear reduction of the ferromagnetic ordering temperature from TC = ∼171 K to ∼50 K with increasing carbon content. The ferromagnetic structures of the pristine NdScSi and the filled NdScSiC0.5 have been determined from neutron diffraction measurements. Finally, we discuss the effect of carbon versus hydrogen insertion on electronic and magnetic properties based on density functional theory calculations. Although the unpaired spin density channels between Nd and Sc atoms (responsible of the high Curie temperature in NdScSi) are reduced upon carbon insertion, the strong Nd–C interaction, linked to a reduced c lattice parameter in NdScSiC0.5, ensures a strong magnetic coupling between the Nd double layer along the c axis and the ferromagnetic order is preserved.

Unconventional superconductivity has recently been discovered in the first iron-based superconducting silicide LaFeSiH. By using the complementary techniques of muon spin rotation, tunneling diode oscillator and density functional theory, we investigate the magnetic penetration depth and thereby the superconducting gap of this novel high-temperature superconductor. We find that the magnetic penetration depth displays a sub-$T^2$ behavior in the low-temperature regime below $T_c/3$, which evidences a nodal structure of the gap (or a gap with very deep minima). Even if the topology of the computed Fermi surface is compatible with the $s_\pm$-wave case with accidental nodes, its nesting and orbital-content features may eventually result in a $d$-wave state, more unusual for high-temperature superconductors of this class., Comment: 6 pages, 2 tables, 3 figures; v2: improved discussion and organization, 4 figs, 1 table

The intermetallic NdNiMg

We address the ferromagnetic tendencies detrimental for superconductivity that are related to the substitution of the pnictogen As atom with Ge or Si, together with additional substitutions in the spacer layers in 122 and 1111 Fe-based superconductors. Intermediate compounds in which these substitutions are realized individually are studied within density functional theory. We thus single out the control of spacer ions as an effective way to handle such a ferromagnetism, and we also show that it is suppressed in YFe$_2$Ge$_2$ under pressure ---which then can be expected to enhance its superconductivity., v1: 6 pages, 4 figures, 3 tables. v2: 7 pages, new figures 2 and 4 and extended discussion. v3: 7 pages, 4 figures, 4 tables. v4: published version

We show that it is possible to replace in Gd 2 In some amount of In by X=Al, Ga, Sn and Pb to obtain Gd 2 In 1− x X x samples after melting. The magnetic and magnetocaloric properties of the Gd 2 In 0.8 X 0.2 intermetallic compounds have been investigated through dc magnetization measurements. We evidence that the substitution of Al and Ga for In barely changes the Curie temperature T C but decreases the second magnetic transition temperature T ′ which corresponds to the transition from a ferromagnetic to an antiferromagnetic state. On the other hand, the substitution of Sn and Pb for In strongly increases T C and changes the nature or even suppresses the transition at lower temperature. This magnetic behavior gives rise to an interesting way to tune the Curie temperature near room temperature without diluting the Gd network and thus to modify the magnetocaloric effect in Gd 2 In 1− x X x compounds.

International audience; Intermetallic phases have been investigated with respect to their ability to accept small atoms in interstitial sites without changing the host structure. Among those, the intermetallic compounds crystallizing in the tetragonal CeScSi-type structure are able to absorb hydrogen atoms. These compounds are of particular interest because they can show electride-like character and, therefore, can be exploited as new catalysts. Here we report the case of GdScGe which uptakes hydrogen at 623 K and under a H2 gas pressure between 0.5 and 4 MPa. The formation of the hydride GdScGeH, with H atoms entering into the [Gd4] tetrahedra, preserves the host structure but induces an anisotropic volume expansion with a strong increase of the c-parameter and a slight decrease of the a-parameter. Interestingly, we show for the first time for this family of materials that hydrogen insertion reduces the dimensionality of the magnetic and transport properties from 3D to quasi-2D which results in a vanishing of the ferromagnetic order (TC = 350 K for GdScGe) and a change of the metallic conduction behavior to a nonmetallic one. As evidenced by density functional theory calculations, such drastic effects are accounted for through the Gd–H chemical bonding effect and the oxidizing effect of H whereas the volume expansion plays only a minor role.

International audience; We investigated the structural and magnetic properties of the boride Nd5Fe2B6 and of the deuteride Nd5Fe2B6D4.1 by means of magnetization and specific heat measurements, Mössbauer spectroscopy and neutron powder diffraction. In Nd5Fe2B6D4.1, deuterium atoms are located in two inequivalent interstitial sites: one octahedral D1 [Nd6] and one tetrahedral D2 [Nd3Fe], both avoiding B as near neighbor. This insertion induces a pronounced anisotropic unit cell expansion along the c-axis. While the Nd5Fe2B6 compound exhibits a magnetic ordering below about 68 K, the deuteride exhibits a lower ordering temperature of about 21 K as a consequence of D insertion in the Nd environment. For both compounds powder neutron diffraction investigations have evidenced a ferromagnetic structure with magnetic moments along the c-axis. However, in the deuteride, the Nd magnetic moments values are reduced and that of Fe vanishes. 57Fe Mössbauer spectroscopy confirms the existence of a small ordered magnetic moment on iron in Nd5Fe2B6 and the presence of two environments for Fe in the deuteride.

We report the synthesis and characterization of the novel silicide LaFeSiH displaying superconductivity with onset at 11 K. We find that this pnictogen-free compound is isostructural to LaFeAsO, with a similar low-temperature tetragonal to orthorhombic distortion. Using density functional theory we show that this system is also a multiband metal in which the orthorhombic distortion is likely related to single-stripe antiferromagnetic order. Electrical resistivity and magnetic susceptibility measurements reveal that these features occur side-by-side with superconductivity, which is suppressed by external pressure., Comment: 5 + epsilon pages, 7 figures, Supplemental Material on demand; v2 includes additional magnetization and resistivity data; v3 includes additional resistivity data from LaFeSiH single crystal

Polycrystalline CeNiZn (ZrNiAl type, P 6 ¯ 2 m , a = 715.6 (4), c = 388.4 (2) pm) forms a new hydride CeNiZnH 1.2(1) under hydrogen exposure (10 bar) at 423 K. The resulting hydride crystallizes in a hexagonal structure ( P 6/ mmm ) with the unit cell parameters a = 433.19 (2) and c = 424.37 (2) pm. Thus, hydrogen atom insertion yields a structural transition from a ZrNiAl- to an AlB 2 -type structure with a high volume cell expansion of +20.1%. The magnetic, thermal and transport properties of CeNiZnH 1.2(1) were investigated. Susceptibility and specific heat measurements do not reveal magnetic order down to 1.8 K but most likely the presence of ferromagnetic correlations due to the proximity of a ferromagnetic order or a nonmagnetic atom disorder spin-glass state. Moreover, the cerium valence is modified from an intermediate to a trivalent state, a change that results from the decrease of the hybridization strength between conduction and Ce (4 f ) electrons upon hydrogenation. Transport measurements also evidence a deviation from the typical resistivity behavior of metallic systems. Several scenarios are conceived to explain this change, in particular weak localization effect, knowing that it rarely occurs upon hydrogenation of intermetallics.

The title compound is prepared from mixtures of the elements (5 GPa, 720 K, 95% yield) and characterized by powder XRD, electrical measurements, and DFT band structure calculations.

NdScSi and NdScGe were synthesized from the elements via arc-melting and subsequent annealing. Their ordered La 2 Sb type structures, with space group I 4/ mmm , were refined from single crystal X-ray diffractometer data: a =428.94(6) and b =1570.5(3) pm, wR 2=0.0395, 309 F 2 values for NdScSi and a =431.2(1) and c =1581.3(5) pm, wR 2=0.1220, 227 F 2 values for NdScGe, with 11 variables per refinement. Hydrogen insertion was performed on both Nd-based intermetallics by solid/gas reaction. Hydrogen uptake keeps the pristine compound space group but yields an anisotropic expansion of the unit cell with a large increase of c (≈+7%) and a slight decrease of a (≈−1.7%) parameters. Hydrogen absorption at 350 °C and under 5 bar of H 2 pressure shows that the hydride NdScSiH 1.48(5) is formed. An in-situ neutron diffraction study during the deuteration of NdScSi reveals for the first time in a CeScSi-type compound, the possibility to fill two interstitial sites with deuterium atoms, leading to the composition NdScSiD 1.5 for the deuteride adopting then the La 2 Fe 2 Se 2 O 3 -type structure. From magnetization measurements, we evidence that hydrogenation strongly reduces the Curie temperature of NdScSi ( T C =175 K) and NdScGe ( T C =194 K) since NdScSiH 1.5 and NdScGeH x undergo a magnetic transition at 4 K and around 2 K, respectively.

Neutron powder diffraction experiments were performed on the moderate Kondo systems Ce6Ni1.67Si3 and Ce5Ni1.85Si3. These measurements have shown that Ce6Ni1.67Si3 does not present a long range magnetic order down to 1.6 K, but only short range ferromagnetic correlations. Ce5Ni1.85Si3 undergoes an antiferromagnetic transition at TN ≈ 6 K. Its magnetic structure at 1.5 K and zero field is collinear with the magnetic moments along the hexagonal axis and can be described with the propagation vector k = (1/2 0 0). This antiferromagnetic order coexists with a short range ferromagnetic component.

CeCoAl was synthesized by melting of the elements in a sealed niobium tube in an induction furnace. Annealing of the sample gave access to a single phase sample. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Above 271 K CeCoAl crystallizes in its own structure type in the space group C2/m [a = 1107.4(2), b = 440.6(1) and c = 479.6(1) pm, β = 104.6(1)°]. Data obtained at 300 K lead to 511 F 2 values with 20 variables and a residual of [I ≥ 3σ(I)] wR = 0.0539. Below 271 K satellites give rise to the superspace group C2/m(α0γ)00; α = 2/3, γ = 2/5 with a temperature independent q-vector. For the 90 K data (also for 180 and 220 K) the commensurate modulated structure could be refined with 4817 F 2 values, 129 variables and residuals of wR = 0.0347 (main), wR = 0.1927 (satellites 1st order), wR = 0.1541 (satellites 2nd order) and wR = 0.1768 (satellites 3rd order) [a = 1107.5(1), b = 440.3(1) and c = 479.0(1) pm, β = 104.7(1)°]. For the three temperatures only minor variations of the modulation amplitudes are observed. The relation of the low temperature (3+1)D 3a × 5c approximant and the room temperature 3D structure is discussed on the basis of a group–subgroup relation. By investigation of the heat capacity, the phase transition could be identified as a second order one with a transition temperature of 271 K. Magnetic measurements clearly prove the intermediate cerium valence which is in line with the short Ce–Co distances.

The new solid solution Gd2(Co3-xSix) (0.29 < x < 0.50) is obtained by arc-melting of the elements.

International audience; We report the discovery of a new solid solution Gd2(Co3-xSix) with 0.29 < x < 0.50 in the Gd-Co-Si ternary system. Members of this solid solution crystallize with the La2Ni3-type structure and correspond to the stabilization of "Gd2Co3" through silicon substitution. The structure of the member Gd2(Co2.53(3)Si0.47) was determined by X-ray diffraction on a single crystal. It crystallizes with the space group Cmce and cell parameters a = 5.3833(4), b = 9.5535(6), and c = 7.1233(5) Å. Co/Si mixing is observed on two crystallographic positions. All compounds studied in the solid solution present a ferrimagnetic order with a strong composition-dependent Curie temperature TC with 280 K < TC < 338 K. The magnetocaloric effect, which amounts to around 1.7 J K(-1) kg(-1) for ΔH = 2 T, is interestingly tunable around room temperature over a temperature span of 60 K through only 4-5% of composition change.

In this work we report the results of the neutron diffraction investigation performed on the germanides R 15 Ge 9 C, for R = Ce, Pr and Nd (La 15 Ge 9 Fe-type, hP 50, P 6 3 mc , Z = 2), to refine the crystal superstructure of these compounds and determine their magnetic structures. The interstitial carbon atoms occupy mainly the 2 b Wyckoff site in the position (1/3 2/3 ∼1/2) and also, with a smaller occupancy rate, the Wyckoff site 2 a at (0 0 ∼1/2). In the magnetic state, the three compounds display predominantly a ferromagnetic behavior with the propagation vector k = [0 0 0]. These results are in agreement with the magnetization measurements, with T C = 10, 30 and 80 K as Curie temperature of Ce 15 Ge 9 C, Pr 15 Ge 9 C and Nd 15 Ge 9 C, respectively. Ce 15 Ge 9 C and Nd 15 Ge 9 C present a ferromagnetic alignment of the R moments along the c -axis and an antiferromagnetic spin arrangement within the ( a – b ) plane. For Pr 15 Ge 9 C the ferromagnetic contribution is found within the ( a – b ) plane, as previously observed for the isotypic compound Tb 15 Si 9 C. The carbides crystal structure possesses four inequivalent rare earth sites carrying different magnetic moments, leading to mean values of 0.9 μ B /Ce, 1.1 μ B /Pr and 2.2 μ B /Nd for Ce 15 Ge 9 C, Pr 15 Ge 9 C and Nd 15 Ge 9 C, respectively. The magnetic structures of these R 15 Ge 9 C compounds differ strongly from those of their parent R 5 Ge 3 germanides, but present strong similarities with the structures of the R 15 Si 9 C compounds. The overall results indicate and confirm the drastic influence of carbon insertion in the rare earth environment.

International audience; The first compound in the cobalt bismuth system was synthesized by high-pressure high-temperature synthesis at 5 GPa and 450 °C. CoBi3 crystallizes in space group Pnma (no. 62) with lattice parameters of a = 8.8464(7) Å, b = 4.0697(4) Å and c = 11.5604(9) Å adopting a NiBi3-type crystal structure. CoBi3 undergoes a superconducting transition at Tc = 0.48(3) K as evidenced by electrical-resistivity and specific-heat measurements. Based on the anomaly of the specific heat at Tc and considering the estimated electron-phonon coupling, the new Bi-rich compound can be classified as a Bardeen-Cooper-Schrieffer-type superconductor with weak electron-phonon coupling. Density-functional theory calculations disclose a sizable influence of the spin-orbit coupling to the valence states and proximity to a magnetic instability, which accounts for a significantly enhanced Sommerfeld coefficient.

International audience; The hydrides RETXH (RE = rare earth, T = transition metal and X = Si, Ge) crystallizing in the tetragonal ZrSiCuAs-type are obtained by hydrogen absorption of the intermetallics adopting the tetragonal CeFeSi-type. The H-insertion induces interesting magnetic transitions governed by two effects: the increase of the unit cell volume linked to the H-absorption and the occurrence of the RE-H chemical bonding. Some typical examples are reported in this present brief review.

TbScGe is obtained as pure phase after melting of the constituents followed by an annealing at 1173 K. Contrary to what was suggested previously, this ternary germanide does not present a high temperature form with the hexagonal Ti 5 Ga 4 -type structure after melting and quenching; the as quenched sample is a mixture based on the two solid solutions (Tb 1− x Sc x ) 5 Ge 3 and Tb 1− x Sc x . TbScGe adopts the tetragonal CeScSi-type structure with a = 4.219 and c = 15.452 A as unit cell parameters. Its investigation by magnetization and specific heat measurements reveals a ferromagnetic behavior below T C = 250 K inducing a moderate magnetocaloric effect; for a magnetic field change of 2 T, the magnetic entropy change Δ S m is equal to −1.6 J K −1 kg −1 which corresponds to an adiabatic temperature change Δ T ad of 1.25 K.

NdCoSi is prepared by arc melting of the elements followed by annealing at 1073 K (30 d) and transformed to NdCoSiH under 4 MPa of H2 at 523 K.

International audience; Investigation of the Gd–Co system around the composition Gd4Co3 showed that this compound does not exist. When samples with the nominal composition Gd4Co3 are synthesized a mixture of Gd12Co7 and Gd6Co4.85(2) (=Gd4Co3.23(2)) is observed. Gd6Co4.85(2) is the only compound found around the composition Gd:Co = 4:3. Its structure was determined by means of X-ray diffraction on single crystal with the space group P63/m. The cell parameters are a = 11.593(2) Å and c = 4.0495(14) Å. Its structure is closely related to the Ho4Co3.07-type or to the Ce6Ni1.67Si3-type structure. Gd6Co4.85(2) exhibits only one ferro(ferri)magnetic transition at 219(1) K and the second magnetic transition at 163 K, wrongly attributed to a spin reorientation, corresponds indeed to the ferromagnetic transition of the impurity Gd12Co7. Gd6Co4.85(2) presents magnetocaloric properties with a maximal adiabatic temperature change ΔTad equal to 4.4 K for μ0ΔH = 4.5 T.

International audience; The hydride NdCoSiH obtained by exposure at 523 K of the ternary antiferromagnet NdCoSi under a pressure of 4 MPa of hydrogen crystallizes in the tetragonal ZrCuSiAs-type structure where H atoms occupy the tetrahedral [Nd4] site. The hydrogenation induces an increase in the unit cell volume close to 6%. The investigation of NdCoSiH by magnetization measurements reveals its ferromagnetic behavior below TC = 20.5(5) K. Neutron powder diffraction shows that the TC temperature is associated with a ferromagnetic arrangement of the Nd moments (2.3(2) μB at 1.5 K) parallel to the c axis as observed for NdFeSi. The magnetic properties, magnetic structure, and the value of the Nd ordered magnetic moment evidenced for NdCoSiH are discussed using both band structure calculations and a comparison with the behavior of NdCoSi and NdFeSi.

International audience; The ternary silicides RE6T1:67Si3 (RE = Ce, Pr, Nd, Gd, Tb and T = Co, Ni) crystallizing with the hexagonal Ce6Ni1:67Si3-type structure has been recently extensively studied. It has been shown that some of these compounds exhibit interesting magnetocaloric properties. In this work, the magnetic structures of the Nd6Ni1:67Si3 compound were determined by means of neutron powder di®raction. According to previous magnetization and speci¯c heat measurements, this compound exhibits two successive magnetic transitions at 84K and 38K. The ¯rst transition corresponds to a ferromagnetic arrangement of the Nd-moments along the c-axis and the second one to a non-collinear ferromagnetic arrangement yielding a conical structure. The magnetic structures of Nd6Ni1:67Si3 are compared to those of the Nd6Co1:67Si3 homologous ternary silicide.

International audience; Gd3NiSi2 annealed sample has been investigated by magnetization, electrical resistivity and specific heat measurements. This study reveals its ferromagnetic behavior below TC = 215 K; only the gadolinium carries a magnetic moment with a saturation magnetization of 7.19 μB/Gd mol. Gd3NiSi2 exhibits a magnetocaloric effect higher in magnetic entropy change than the one recently reported for Gd6Ni5/3Si3. This ternary silicide can be obtained as metallic ribbons where the structural disordering modifies strongly its magnetocaloric properties.

International audience; The hydride NdMnSiH obtained by exposure of the ternary silicide NdMnSi under a pressure of 4 MPa of hydrogen at 523 K crystallizes in the tetragonal ZrCuSiAs-type structure where H atom occupies the tetrahedral [Nd4] sites. The hydrogenation of NdMnSi induces an increase in the unit cell volume close to 3.3%. The investigation of NdMnSiH by magnetization and specific heat measurements reveals the existence of two antiferromagnetic ordering, respectively, at TN1=565(5) K and TN2=103(4) K. Neutron powder diffraction shows that these Néel temperatures are associated with an antiferromagnetic arrangement of the (i) Mn substructure (TN1) and (ii) Nd substructure linked to a reorientation of the Mn one (TN2). Comparison of the TN1 and TN2 temperatures of NdMnSiH to those reported for the initial compound NdMnSi indicates a strong increase in TN1 (280 K -> 565 K) and a significant decrease in TN2 (185 K -> 03 K). The magnetic properties, magnetic structures, and values of Nd and Mn ordered magnetic moments are discussed using both band structure calculations and comparison with the behaviors of other ternary silicides and germanides based on manganese and rare earth elements.

International audience; Neutron powder diffraction experiments have been carried out on the hexagonal ternary silicides Nd6Co1.67Si3 and Tb6Co1.67Si3 in order to determine their magnetic structures. These compounds exhibit two successive ferromagnetic transitions at TC = 84 K and T1 = 40 K for Nd6Co1.67Si3 and at TC = 186 K and T1 = 171 K for Tb6Co1.67Si3. Single-crystal x-ray diffraction and specific heat measurements have been realized on Tb6Co1.67Si3 in order to complete its characterization. Neutron diffraction investigation at 1.5 K reveals for both compounds a canted ferromagnetic structure with a propagation vector k = (0 0 0). The Nd moment values are, respectively, equal to μ1 = 2.06(10)μB and μ2 = 3.14(9)μB for Nd1 and Nd2 atoms whereas Tb1 and Tb2 atoms carry a magnetic moment of μ1 = 7.9(2)μB and μ2 = 8.9(2)μB in Tb6Co1.67Si3. Moreover, a transition from a canted ferromagnet to a pure ferromagnet occurs at T1 = 40 K in Nd6Co1.67Si3 while a spin reorientation of the non-collinear ferromagnetic structure occurs at T1 = 171 K for Tb6Co1.67Si3. These magnetic structures are discussed on the basis of the atomic disorder existing for Co atoms in these ternary silicides around the Nd1 and Tb1 atoms.

Single phases of Nd 6 Ni 1.67 Si 3 and Nd 6 Co 1.67 Si 3 were prepared by arc melting of a stoichiometric mixture of the elements followed by annealing at 1073 K. The structure of Nd 6 Co 1.67 Si 3 was determined from single-crystal X-ray data with the space group P 6 3 / m and the lattice parameters a = 11.950(4) A and c = 4.232(2) A. Its structure derives from the structure of the aristotype compound Ce 6 Ni 1.67 Si 3 . A strong disorder of cobalt atoms in the chains of face-shared octahedra of neodymium is observed. Magnetization measurements reveal the existence of two ferro(ferri)magnetic transitions at 84(1) K and 38(1) K for Nd 6 Ni 1.67 Si 3 . For Nd 6 Co 1.67 Si 3 it has been previously shown that also two ferro(ferri)magnetic transitions occur at 84 K and 35 K. The comparison between the magnetic properties of Nd 6 Ni 1.67 Si 3 and Nd 6 Co 1.67 Si 3 shows a significant difference of the behaviour of the magnetization M versus temperature and field μ 0 H below 84 K. The curves M = f ( T ) obtained by field-cooled (FC) process and under μ 0 H = 0.1 T show an increase of M below 35 K for Nd 6 Co 1.67 Si 3 and on the contrary, a decrease of M below 38 K for Nd 6 Ni 1.67 Si 3 . This difference suggests the occurrence at low temperature of different magnetic structures for these two ternary silicides.

Unlike Gd6Co5/3Si3, which is obtained as a single phase after melting of the constituents, annealing under vacuum at 1073 K for 1 month is necessary to prepare the new ternary silicide Gd6Ni5/3Si3. Indeed, after melting, this alloy is a mixture containing mainly Gd3NiSi2 and Gd5Si3. These two compounds, Gd6M5/3Si3 (M = Co or Ni), crystallize with the hexagonal Ce6Ni2−xSi3-type structure. The crystal structure of Gd6Ni5/3Si3, refined on a single crystal with space group P63/m and unit cell parameters a = 11.7433(1) A and c = 4.1857(1) A, is characterized by infinite chains of face-shared trigonal prisms [Gd6] filled by silicon or nickel atoms. These chains run along the c-axis and extend as triangular columns by sharing rectangular faces in the ab-plane. Between these columns, infinite chains of face-shared octahedra of Gd atoms partially are filled by Ni atoms. The strong delocalization of the electron density of Ni observed in these latter chains has been attributed to high steric strains. No diffuse sca...

International audience; Unlike Gd6Co5/3Si3, which is obtained as a single phase after melting of the constituents, annealing under vacuum at 1073 K for 1 month is necessary to prepare the new ternary silicide Gd6Ni5/3Si3. Indeed, after melting, this alloy is a mixture containing mainly Gd3NiSi2 and Gd5Si3. These two compounds, Gd6M5/3Si3 (M = Co or Ni), crystallize with the hexagonal Ce6Ni2−xSi3-type structure. The crystal structure of Gd6Ni5/3Si3, refined on a single crystal with space group P63/m and unit cell parameters a = 11.7433(1) Å and c = 4.1857(1) Å, is characterized by infinite chains of face-shared trigonal prisms [Gd6] filled by silicon or nickel atoms. These chains run along the c-axis and extend as triangular columns by sharing rectangular faces in the ab-plane. Between these columns, infinite chains of face-shared octahedra of Gd atoms partially are filled by Ni atoms. The strong delocalization of the electron density of Ni observed in these latter chains has been attributed to high steric strains. No diffuse scattering nor superstructure were observed from electron diffraction experiments. The magnetization measurements reveal that (i) Gd6Ni5/3Si3 orders ferromagnetically at 310 K, a Curie temperature higher than that observed for Gd6Co5/3Si3 (TC = 294 K) and pure gadolinium (TC = 294 K); (ii) Ni as well as Co carries no magnetic moment; and (iii) these ternary silicides exhibit interesting magnetocaloric properties; for instance, the magnetic entropy (ΔSm determined by magnetization measurements) of Gd6Ni5/3Si3 is at a maximum around 312 K with values of ΔSm = −2.93 and –5.72 J/K kg at applied magnetic fields of 2 and 4.8 T, respectively. These properties are compared to those existing for the most famous magnetocaloric materials as Gd or Gd5Ge2Si2.

Single phases of Nd 6 Ni 1.67 Si 3 and Nd 6 Co 1.67 Si 3 were prepared by arc melting of a stoichiometric mixture of the elements followed by annealing at 1073 K. The structure of Nd 6 Co 1.67 Si 3 was determined from single-crystal X-ray data with the space group P 6 3 / m and the lattice parameters a = 11.950(4) A and c = 4.232(2) A. Its structure derives from the structure of the aristotype compound Ce 6 Ni 1.67 Si 3 . A strong disorder of cobalt atoms in the chains of face-shared octahedra of neodymium is observed. Magnetization measurements reveal the existence of two ferro(ferri)magnetic transitions at 84(1) K and 38(1) K for Nd 6 Ni 1.67 Si 3 . For Nd 6 Co 1.67 Si 3 it has been previously shown that also two ferro(ferri)magnetic transitions occur at 84 K and 35 K. The comparison between the magnetic properties of Nd 6 Ni 1.67 Si 3 and Nd 6 Co 1.67 Si 3 shows a significant difference of the behaviour of the magnetization M versus temperature and field μ 0 H below 84 K. The curves M = f ( T ) obtained by field-cooled (FC) process and under μ 0 H = 0.1 T show an increase of M below 35 K for Nd 6 Co 1.67 Si 3 and on the contrary, a decrease of M below 38 K for Nd 6 Ni 1.67 Si 3 . This difference suggests the occurrence at low temperature of different magnetic structures for these two ternary silicides.

International audience; The hydride CeRuSiH is derived from the non-magnetic heavy-fermion ternary silicide CeRuSi that crystallizes in the tetragonal CeFeSi-type structure (P4/nmm space group). This hydride exhibits two antiferromagnetic transitions at TN1 = 7.5(2) K and TN2 = 3.1(2) K, evidenced by magnetization and specific heat measurements. Crystal and magnetic structures of CeRuSiH have thus been investigated by means of neutron powder diffraction, which has shown firstly that H-atoms are fully inserted in the [Ce4]-tetrahedra. Moreover, between TN1 and TN2, the Ce magnetic moments are ordered in a collinear antiferromagnetic sinusoidal structure associated with the propagation vector k = (kx, kx,1/2) (kx

The hydride $\mathrm{Ce}\mathrm{Ru}\mathrm{Si}{\mathrm{H}}_{1.0}$ with space group $P4∕nmm$ was synthesized by exposure at $523\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ of the heavy-fermion ternary silicide CeRuSi under $4\phantom{\rule{0.3em}{0ex}}\mathrm{MPa}$ of hydrogen gas. The investigation of the hydride by x-ray powder diffraction reveals that the hydrogenation induces a pronounced anisotropic expansion of the unit cell. Moreover, $\mathrm{Ce}\mathrm{Ru}\mathrm{Si}{\mathrm{H}}_{1.0}$ presents two antiferromagnetic transitions at ${T}_{N1}=7.5(2)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${T}_{N2}=3.1(2)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ evidenced by magnetization and specific heat measurements. Hydrogenation changes the moderate heavy-fermion compound CeRuSi, which has a $\ensuremath{\gamma}=220\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}∕\mathrm{mol}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{2}$, to an antiferromagnet, which has a smaller electronic coefficient $\ensuremath{\gamma}=26\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}∕\mathrm{mol}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{2}$. In other words, the hydrogen insertion diminishes the influence of the Kondo effect. The transition heavy-fermion $\text{behavior}\ensuremath{\rightarrow}\text{antiferromagnet}$ can be well understood in terms of the classical Doniach diagram where the hydrogenation plays a role opposite to the pressure. The expansion of the lattice induced by hydrogen insertion is here much more important than the role of Ce-H bonding observed in other hydrogenated compounds $\mathrm{Ce}\mathrm{Co}\mathrm{Si}{\mathrm{H}}_{1.0}$ or $\mathrm{Ce}\mathrm{Co}\mathrm{Ge}{\mathrm{H}}_{1.0}$, where an opposite transition ($\text{antiferromagnetic}\ensuremath{\rightarrow}\text{spin}$ fluctuation) was evidenced.

NdCoSi and NdCoGe order antiferromagnetically at TN = 7.5 and 8.3 K respectively. These ternary compounds absorb easily hydrogen at 523 K under a hydrogen pressure of 4 MPa; the resulting hydrides are stable in ambient conditions and crystallize in the tetragonal ZrCuSiAs-type structure. Investigation of the hydrides by magnetization and electrical resistivity measurements and also by neutron powder diffraction reveals their ferromagnetic behaviours appearing below TC = 20.5 and 15.9 K respectively for NdCoSiH and NdCoGeH. Their magnetic structures are collinear with Nd-moments (2.28 and 2.35 μB at 1.5 K for NdCoSiH and NdCoGeH respectively) aligned along the c-axis as observed previously for NdFeSi. The antiferromagnetic-ferromagnetic transition evidenced during the hydrogenation can be explained by a change of the number of conduction electrons linked to the H-insertion as observed by electronic structure determination.