Magnetic properties of Fe2P-type Tb6FeTe2, Tb6CoTe2, Tb6NiTe2 and Er6FeTe2 compounds

The magnetic ordering of the Fe₂P-type Tb₆FeTe₂, Tb₆CoTe₂ Tb₆NiTe₂ and Er₆FeTe₂ phases (space group P6¯2m) has been investigated through magnetization measurement and neutron powder diffraction. Tb₆FeTe₂, Tb₆CoTe₂ and Tb₆NiTe₂ demonstrate high-temperature ferromagnetic and low-temperature spin reorientation transitions, whereas Er₆FeTe₂ shows antiferromagnetic transition, only.The Tb₆FeTe₂ and Tb₆NiTe₂ phases show same high-temperature collinear ferromagnetic structure, whereas Tb₆FeTe₂ is the commensurate non-collinear ferromagnet and Tb₆NiTe₂ is the canted ferromagnetic cone with K₁=[0, 0, ±3/10] and K₂=[±2/9, ±2/9, 0] wave vectors at 2 K. The magnetic structure of Er₆FeTe₂ is a flat spiral with K₁=[0, 0, ±1/10] at 2 K. The magnetic entropy change for Tb₆NiTe₂ is ΔS_m=−4.86 J/kg K at 229 K for the field change Δμ₀H=0-5 T.In addition, novel Fe₂P-type Gd₆FeTe₂, Zr₆FeTe₂, Hf₆FeTe₂, Dy₆NiTe₂, Zr₆NiTe₂ and Hf₆NiTe₂ phases have been obtained.     

Magnetic and thermodynamic properties of NdT2Ge2 (T=Pd, Ag) compounds

Physical properties of NdPd₂Ge₂ and NdAg₂Ge₂, crystallizing with the tetragonal ThCr₂Si₂-type crystal structure, were investigated by means of magnetic, calorimetric, electrical transport as well as by neutron diffraction measurements. The specific heat studies and neutron diffraction measurements were performed down to 0.30 K and 0.47 K, respectively. Both compounds exhibit antiferromagnetic ordering below T_N equal to 1.5 K for NdPd₂Ge₂ and 1.8 K for NdAg₂Ge₂. Neutron diffraction data for the latter germanide indicate antiferromagnetic collinear structure described by the propagation vector k=(0.5, 0, 0.5). The Nd magnetic moments equal to 2.24(5) μ_B at 0.47 K are aligned along the a-axis and have the +− sequence within the crystal unit cell. For NdPd₂Ge₂ only very small Bragg peaks of magnetic origin were observed in the neutron diffraction patterns measured below T_N, thus hampering determination of the magnetic structure. Both compounds exhibit metallic-like electrical conduction. From the specific heat data the crystal electric field (CEF) levels schemes were determined. Difference between the overall CEF splitting in the two compounds is correlated with their structural parameters.     

Magnetic properties of DyCo5 and TbCo5 intermetallics from the electronic structure calculations

LSDA and LSDA+U calculations, with spin-orbit coupling (SOC) included, were performed for DyCo₅ and TbCo₅ intermetallic compounds. In the case of magnetic moments, LSDA-SOC calculations give results in good agreement with the experimental data. However, LSDA has shown to be unable to predict relative stabilities of ferromagnetic and ferrimagnetic configurations of the 4f and 3d spin sublattices giving the wrong result that the ferromagnetic configuration is more stable. LSDA+U method cures this problem and gives correct result. Additionally, within the accuracy of available experimental data, the corresponding effective exchange fields are in reasonable agreement with experiment.     

Magnetic properties of RE2MnGe6 (RE = La,Ce) and YMn0.3Ge2 germanides

The magnetic data of RE₂MnGe₆ (RE = La, Ce) and YMn_0.3Ge₂ are reported. La₂MnGe₆ and Ce₂MnGe₆ crystallize in the orthorhombic Ce₂CuGe₆ structure type, space group Amm2 (No. 38). The non-stoichiometric YMn_0.3Ge₂ compound crystallizes with the orthorhombic CeNiSi₂-type structure (space group Cmcm (No. 36)). The studied RE₂MnGe₆ (RE = La, Ce) intermetallics are characterized by ferromagnetic properties with Curie temperatures 177 (La) and 150 K (Ce), respectively. For YMn_0.3Ge₂ the low-field magnetic measurements indicate the antiferromagnetic property below 395 K with the small ferromagnetic component. The values of the magnetic moments in the ordered state indicate the ferromagnetic ordering in La₂MnGe₆ and complex magnetic order with the ferromagnetic component in YMn_0.3Ge₂ and Ce₂MnGe₆. The hysteresis loop and values of the coercivity field indicate that these compounds are soft magnetic materials.     

Exchange interactions in R2Fe17−xGax (R=Y, Sm, Gd, Tb, Ho and Tm) compounds

We calculated the molecular field coefficients, n_FeFe and n_RFe (R=Sm, Gd, Tb, Ho and Tm), for R₂Fe_17−xGa_x and the values of n_FeFe and n_SmFe for R₂Fe_17−xT_x (T=Al and Si) using the experimental values of the Curie temperature. The values of n_FeFe increase in spite of the decrease of μ_Fe for 0?x?5. The values of n_SmFe have large values when the magnetic anisotropy is axial. For 6?x?8, the values of n_FeFe, n_HoFe and n_TmFe increase largely, which is related to the change of the easy magnetization direction. For Y₂Fe_17−xT_x (T=Ga and Al), the values of n_FeFe have a maximum value with increasing those of μ_Fe. With increasing V⁻¹, the values of n_FeFe have a maximum value around the same value of V⁻¹ for Y₂Fe_17−xT_x (T=Ga and Al). For Y₂Fe_17−xSi_x, the values of n_FeFe increase with increasing V⁻¹.     

Magnetic and transport properties of RCr0.3Ge2 (R=Tb, Dy, Ho and Er) compounds

The magnetic and transport properties of ternary rare-earth chromium germanides RCr_0.3Ge₂ (R=Y and Tb-Er) have been determined. X-ray and neutron diffraction studies indicate that these compounds have the CeNiSi₂-type structure (space group Cmcm) [1]. Magnetic measurements reveal the antiferromagnetic ordering below T_N equal to 18.5 K (R=Tb), 11.8 K (Dy), 5.8 K (Ho) and 3.4 K (Er). From the neutron diffraction data the magnetic structures have been determined. For TbCr_0.3Ge₂ and DyCr_0.3Ge₂ at low temperatures the magnetic ordering can be described by two vectors k₁=(,0,0) and k₂=(,0,), and k₁′=(,0,0) and k₂′=(,0,), respectively. In HoCr_0.3Ge₂ and ErCr_0.3Ge₂ the ordering can be described by one propagation vector equal to (,,0) and (0,0,0.4187(2)), respectively. In DyCr_0.3Ge₂ some change in the magnetic ordering is observed at T_t=5.1 K. In temperature range from T_t to T_N the magnetic ordering is given by one propagation vector k=(,0,0). YCr_0.3Ge₂ is a Pauli paramagnet down to 1.72 K which suggests that in the entire RCr_0.3Ge₂ series the Cr atoms do not carry magnetic moments. All compounds studied exhibit metallic character of the electrical conductivity. The temperature dependencies of the lattice parameters reveal strong magnetostriction effect at the respective Nèel temperatures.     

Synthesis and crystal structure of RMgSi2 compounds (R=La, Ce, Pr, Nd), a particular example of linear intergrowth

A new series of rare earth compounds with stoichiometry RMgSi₂ (R=La, Ce, Pr, Nd) is reported. The single crystal X-ray diffraction showed that CeMgSi₂, which melts congruently at 1200 °C, crystallizes in a new tetragonal structure type (I4₁/amd, tI32, a=4.2652(4) Å, c=36.830(4) Å, Z=8; wR₂=0.042 (19 parameters, 393F₀²), R₁=0.018 (297F₀>4σF₀). The crystal structure of CeMgSi₂ can be formally built up by alternating along the z direction four CeMg₂Si₂-type CeMg₂Si₂ slabs with four AlB₂-type CeSi₂ slabs, one after the other. The structural model obtained from a CeMgSi₂ single crystal has been confirmed for the La, Pr and Nd homologous compounds by means of Rietveld refinement. The trend of the unit-cell parameters, plotted versus the R³⁺ ionic radius, shows a linear behaviour, which strongly suggests a trivalent state for the Ce atoms. An analysis of the features of this new structure is reported, in comparison with the other known CeMg₂Si₂/AlB₂-type linear intergrowth compounds.     

Magnetocaloric effect in the ternary DyCo3B2 compound

A large magnetocaloric (MCE) effect has been observed for the ternary compound DyCo₃B₂. This material shows the magnetic ordering below T_C = 22 K for H = 0 T. MCE has been determined based on the isothermal magnetization curves measurements and the isomagnetic heat capacity dependence on temperature. The maximum magnetic entropy change −ΔS_M = 17.5 J kg⁻¹K⁻¹ and the adiabatic temperature change ΔT_ad = 14 K have been observed in the neighborhood of the magnetic phase transition at the magnetic field change of 9 T. The analysis of the magnetic contribution to the specific heat indicates on the important role of the crystal electric field and the anisotropy for the properties of the DyCo₃B₂ compound.     

On phase equilibria and crystal structures in the systems Ce-Pd-B and Yb-Pd-B. Physical properties of R2Pd13.6B5 (R=Yb, Lu)

Phase equilibria and crystal structures of ternary compounds were determined in the systems Ce-Pd-B and Yb-Pd-B at 850 °C in the concentration ranges up to 45 and 33 at% of Ce and Yb, respectively, employing X-ray single crystal and powder diffraction. Phase relations in the Ce-Pd-B system at 850 °C are governed by formation of extended homogeneity fields, τ₂-CePd₈B_2−x (0.10<x<0.48); τ₃-Ce₃Pd_25−xB_8−y (1.06<x<1.87; 2.20<y<0.05), and CePd₃B_x (0<x<0.65) the latter arising from binary CePd₃. Crystallographic parameters for the new structure type τ₂-CePd₈B_2−x (space group C2/c, a=1.78104(4) nm, b=1.03723(3) nm, c=1.16314(3), β=118.515(1)° for x=0.46) were established from X-ray single crystal diffraction. The crystal structures of τ₂-CePd₈B_2−x and τ₃-Ce₃Pd_25−xB_3−y are connected in a crystallographic group-subgroup relationship. Due to the lack of suitable single crystals, the novel structure of τ₁-Ce₆Pd_47−xB₆ (x=0.2, C2/m space group, a=1.03594(2) nm, b=1.80782(3) nm, c=1.01997(2) nm, β=108.321(1)°) was determined from Rietveld refinement of X-ray powder diffraction data applying the structural model obtained from single crystals of homologous La₆Pd_47−xB₆ (x=0.19) (X-ray single crystal diffraction, new structure type, space group C2/m, a=1.03988(2) nm, b=1.81941(5) nm, c=1.02418(2) nm, β=108.168(1)°).The Yb-Pd-B system is characterized by one ternary compound, τ₁-Yb₂Pd₁₄B₅, forming equilibria with extended solution YbPd₃B_x, YbB₆, Pd₅B₂ and Pd₃B. The crystal structures of both Yb₂Pd₁₄B₅ and isotypic Lu₂Pd₁₄B₅ were determined from X-ray Rietveld refinements and found to be closely related to the Y₂Pd₁₄B₅-type (I4₁/amd). The crystal structure of binary Yb₅Pd_2−x (Mn₅C₂-type) was confirmed from X-ray single crystal data and a slight defect on the Pd site (x=0.06) was established.The three structures τ₁-Ce₆Pd_47−xB₆, τ₂-CePd₈B_2−x and τ₃-Ce₃Pd_25−xB_8−y are related and can be considered as the packings of fragments observed in Nd₂Fe₁₄B structure with different stacking of common structural blocks.Physical properties for Yb₂Pd_13.6B₅ (temperature dependent specific heat, electrical resistivity and magnetization) yielded a predominantly Yb-4f¹³ electronic configuration, presumably related with a magnetic instability below 2 K. Kondo interaction and crystalline electric field effects control the paramagnetic temperature domain.     

Structural and magnetic properties of Zn1−xSbxCr2−x/3Se4 (x=0.11, 0.16 and 0.20) single crystals

Single crystals of Zn_1−xSb_xCr_2−x/3Se₄ based on the ZnCr₂Se₄ spinel, which is known to exhibit interesting magnetic and electronic transport properties, have been prepared by solid state reaction from the appropriate selenides. Three compounds of different Sb content (x=0.11, 0.16, and 0.20) were studied by X-ray diffraction, X-ray photoelectron scattering technique and macroscopic magnetic measurements with the aim to determine (i) stability of the cubic symmetry and (ii) influence of the Sb admixture on the magnetic properties. The results show that the Sb³⁺ and Zn²⁺ ions share the tetrahedral sites in the spinel structure, while the Cr³⁺ions carrying magnetic moments, are located in the octahedral sites. The X-ray photoelectron spectroscopy (XPS) data indicate that in this series of compounds the chromium ions have a 3d³ electronic configuration. The three samples studied order antiferromagnetically at low temperatures, with the magnetic characteristics being hardly altered with respect to those reported for the parent ZnCr₂Se₄ compound.     

Preparation and structural study from neutron diffraction data of R2MoO6 (R=Dy, Ho, Er, Tm, Yb, Y)

The title compounds have been prepared as polycrystalline powders by thermal treatments of stoichiometric mixtures of R₂O₃ and MoO₃ in air. The room-temperature crystal structure for all the series has been refined from high-resolution neutron powder diffraction data. All the phases are isostructural (space group C2/c, Z=8) with the polymorph α-R₂MoO₆, typified by Sm₂MoO₆. The structure contains four zigzag, one-dimensional MoO₅ polyhedral rows per unit cell, running through the RO₈ polyhedral framework along the [001] direction. MoO₅ form discrete units (i.e. do not share common oxygen), with Mo-O distances ranging from 1.77 to 2.24 Å, although the oxygen coordination can be extended to distances of about 3.1 Å, giving rise to strongly distorted MoO₈ scalenohedra. Thus, MoO₈ and RO₈ polyhedra are fully ordered in R₂MoO₆ compounds, which in fact can be considered as superstructures of fluorite (M₃O₆), containing 24 MO₂ fluorite units per unit cell, with unit-cell parameters related to that of cubic fluorite ( Å). A bond valence study demonstrates that the present crystal structure is especially stable for small rare-earth cations, and becomes more unstable when the R³⁺ size increases, thus explaining the observed preference of the large rare-earth molybdates for polymorphs β and γ with the same stoichiometry.     

Structure and magnetic properties of rare-earth chromium germanides RECrxGe2 (RE=Sm, Gd-Er)

The ternary rare-earth chromium germanides RECr_xGe₂ (RE=Sm, Gd-Er) have been obtained by reactions of the elements, either in the presence of tin or indium flux, or through arc-melting followed by annealing at 800 °C. The homogeneity range is limited to 0.25?x?0.50 for DyCr_xGe₂. Single-crystal and powder X-ray diffraction studies on the RECr_0.3Ge₂ members revealed that they adopt the CeNiSi₂-type structure (space group Cmcm, Z=4, a=4.1939(5)-4.016(2) Å, b=16.291(2)-15.6579(6) Å, c=4.0598(5)-3.9876(2) Å in the progression for RE=Sm to Er), which can be considered to be built up by stuffing transition-metal atoms into the square pyramidal sites of a “REGe₂” host with the ZrSi₂-type structure. (The existence of YbCr_0.3Ge₂ is also implicated.) Only the average structure was determined here, because unusually short Cr-Ge distances imply the development of a superstructure involving distortions of the square Ge net. Magnetic measurements on RECr_0.3Ge₂ (RE=Gd-Er) indicated that antiferromagnetic ordering sets in below T_N (ranging from 3 to 17 K), with additional transitions observed at lower temperatures for the Tb and Dy members.     

Magnetic properties of EuLn2O4 (Ln=rare earths)

Ternary rare earth oxides EuLn₂O₄ (Ln=Gd, Dy-Lu) were prepared. They crystallized in an orthorhombic CaFe₂O₄-type structure with space group Pnma. ¹⁵¹Eu Mössbauer spectroscopic measurements show that the Eu ions are in the divalent state. All these compounds show an antiferromagnetic transition at 4.2-6.3 K. From the positive Weiss constant and the saturation of magnetization for EuLu₂O₄, it is considered that ferromagnetic chains of Eu²⁺ are aligned along the b-axis of the orthorhombic unit cell, with neighboring Eu²⁺ chains antiparallel. When Ln=Gd-Tm, ferromagnetically aligned Eu²⁺ ions interact with the Ln³⁺ ions, which would overcome the magnetic frustration of triangularly aligned Ln³⁺ ions and the EuLn₂O₄ compounds show a simple antiferromagnetic behavior.     

Magnetic properties and structural transitions of orthorhombic fluorite-related compounds Ln3MO7 (Ln=rare earths, M=transition metals)

Magnetic properties and structural transitions of ternary rare-earth transition-metal oxides Ln₃MO₇ (Ln=rare earths, M=transition metals) were investigated. In this study, we prepared a series of molybdates Ln₃MoO₇ (Ln=La-Gd). They crystallize in an orthorhombic superstructure of cubic fluorite with space group P2₁2₁2₁, in which Ln³⁺ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). All of these compounds show a phase transition from the space group P2₁2₁2₁ to Pnma in the temperature range between 370 and 710 K. Their magnetic properties were characterized by magnetic susceptibility measurements from 1.8 to 400 K and specific heat measurements from 0.4 to 400 K. Gd₃MoO₇ shows an antiferromagnetic transition at 1.9 K. Measurements of the specific heat for Sm₃MoO₇ and the analysis of the magnetic specific heat indicate a “two-step” antiferromagnetic transition due to the ordering of Sm magnetic moments in different crystallographic sites, i.e., with decreasing temperature, the antiferromagnetic ordering of the 7-coordinated Sm ions occur at 2.5 K, and then the 8-coordinated Sm ions order at 0.8 K. The results of Ln₃MoO₇ were compared with the magnetic properties and structural transitions of Ln₃MO₇ (M=Nb, Ru, Sb, Ta, Re, Os, or Ir).     

Metamagnetic transition in the 75 K antiferromagnet Gd4Co2Mg3

Gd₄Co₂Mg₃ (Nd₄Co₂Mg₃ type; space group P2/m; a=754.0(4), b=374.1(1), c=822.5(3) pm and β=109.65(4)° as unit cell parameters) was synthesized from the elements by induction melting in a sealed tantalum tube. Its investigation by electrical resistivity, magnetization and specific heat measurements reveals an antiferromagnetic ordering at T_N=75(1) K. Moreover, this ternary compound presents a metamagnetic transition at low critical magnetic field (H_cr=0.93(2) T at 6 K) and exhibits a magnetic moment of 6.3(1) μ_B per Gd-atom at 6 K and H=4.6 T. Due to this transition the compound shows a moderate magnetocaloric effect; at 77 K the maximum of the magnetic entropy change is ΔS_M=−10.3(2) J/kg K for a field change of 0-4.6 T. This effect is compared to that reported previously for compounds exhibiting a magnetic transition in the same temperature range.     

Structural and magnetic properties of RMn2−xFexD6 compounds (R=Y, Er; x≤0.2) synthesized under high deuterium pressure

RMn_2−xFe_xD₆ compounds were obtained by applying a deuterium pressure of several kbar to RMn_2−xFe_x compounds for x≤0.2 and R=Y, Er. These compounds are isostructural to RMn₂D₆ compounds and crystallize in a K₂PtCl₆ type structure with a random substitution of R and half the Mn atoms in the same 8c site whereas the other Mn atoms are located on the 4a site and surrounded by six D atoms (24e site). According to neutron powder diffraction analysis the Fe atoms are preferentially substituted on the 4a site. YMn_2−xFe_xD₆ compounds are paramagnetic and their molar susceptibility follows a modified Curie-Weiss law. ErMn_2−xFe_xD₆ compounds display a ferromagnetic behavior at 2 K, but their saturation magnetization (M_S∼4.0 μ_B/f.u.) is half that of their parent compounds (M_S∼8.0 μ_B/f.u.). The neutron diffraction patterns of ErMn_1.8Fe_0.2D₆ display below 13 K both ferromagnetic and antiferromagnetic short range order, which can be related to a disordered distribution of Er moments. The paramagnetic temperatures of ErMn_2−xFe_xD₆ compounds are negative and decrease versus the Fe content whereas they are positive and increase for their parent compounds.     

Neutron diffraction studies of RSn1+xGe1−x (R=Tb-Er) compounds

The magnetic structures of RSn_1+xGe_1−x (R=Tb, Dy, Ho and Er, x≈0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn_1.12Ge_0.88 is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1) μ_B at 1.62 K. It lies in the b-c plane and form an angle θ=17.4(2)° with the c-axis. This structure is stable up to the Nèel temperature equal to 31 K. The magnetic structures of RSn_1+xGe_1−x, where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2, 0) with the sequence (++−+) of magnetic moments in the crystal unit cell. In DySn_1.09Ge_0.91 and HoSn_1.1Ge_0.9 magnetic moments equal 7.25(15) and 8.60(6) μ_B at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to T_N=10.7 K. For ErSn_1.08Ge_0.92, the Er magnetic moment equals 7.76(7) μ_B at T=1.5 K and it is parallel to the b-axis. At T_t=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of k_x component and a quick decrease of k_y component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b-c plane and form an angle 48(3)° with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Nèel temperature is observed.     

Hexagonal perovskite-intergrowth manganates: Ln2Ca2MnO7 (Ln=La, Nd and Sm)

Two structures, all consisting of alternative stacking of hexagonal perovskite layer and graphite-like Ca₂O layer, were identified in Ln₂Ca₂MnO₇ systems (Ln=La, Nd and Sm). La₂Ca₂MnO₇ (1), crystallizing in the space group with the lattice constants a=5.62231(7)  Å and c=17.3192(4) Å, contains almost ideal close packed [LnO₃] arrays. While for the smaller rare earth cations, e.g., Nd₂Ca₂MnO₇ (2) and Sm₂Ca₂MnO₇ (3), the structure distorts to large unit cell (a′=2a and c′=c). Study of the substituted systems, LnLn′Ca₂MnO₇ (Ln or Ln′=La, Ce, Pr, Nd, Sm, Eu, Gd) and La_2−xSm_xCa₂MnO₇, shows a phase transformation from (1) to (2) at certain value of cation size. The MnO₆ octahedra in these compounds are isolated, thus the magnetic property is mainly paramagnetic.     

The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties

The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI₃ and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln₁₂(C₂)₃I₁₇-type compounds (C 2/c, a=19.610(1) and 19.574(4) Å, b=12.406(2) and 12.393(3) Å, c=19.062(5) and 19.003(5) Å, β=90.45(3)° and 90.41(3)°, for Pr₁₂(C₂)₃I₁₇ and Nd₁₂(C₂)₃I₁₇, respectively). All compounds contain infinite zigzag chains of C₂-centered metal atom octahedra condensed by edge-sharing into the [tcc]_∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd₁₂(C₂)₃I₁₇ sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln³⁺)₁₂(C₂^6-)₃(I⁻)₁₇(e⁻) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd₁₂(C₂)₃I₁₇, Gd₁₂(C₂)₃I₁₇ and Dy₁₂(C₂)₃I₁₇ indicate the coexistence of competing magnetic interactions leading to spin freezing at T_f=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at T_N=25 and 29 K, respectively. For Dy₁₂(C₂)₃I₁₇, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe.     

B-site disordering in Ba3Ln2MoO9 (Ln=Ho, Er) perovskites: A neutron diffraction study

We describe the preparation, structure determination and magnetic properties of two Ba perovskites containing rare-earth cations at the B-sublattice. Ba₃Ln₂MoO₉ (Ln=Ho³⁺ and Er³⁺) were synthesized by ceramic procedures. Joint X-ray (XRPD) and neutron (NPD) powder diffraction refinements were carried out to analyse the crystal structure. At room temperature, both phases are tetragonal, space group I4/mcm, Z=4. Ln and Mo atoms are found to be distributed at random over the octahedral sites of the perovskites. Magnetic measurements at 0.1 T show that both samples are paramagnetic between 3 and 300 K, following a Curie-Weiss law. M vs. H curves show a region of paramagnetic behaviour and above 2.5 T a magnetic saturated system is observed. Finally, the temperature evolution of the NPD patterns of Ba₃Ho₂MoO₉ reveals the absence of long-range magnetic ordering down to 2 K.