Magnetic properties of orthorhombic fluorite-related oxides Ln3SbO7 (Ln=rare earths)

Ternary rare earth antimonates Ln₃SbO₇ (Ln=rare earths) were prepared and their structures were determined by X-ray diffraction measurements. They crystallize in an orthorhombic superstructure of cubic fluorite (space group Cmcm for Ln=La, Pr, Nd; C222₁ for Ln=Nd-Lu), in which Ln³⁺ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). Their magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 1.8 to 400 K. The Ln₃SbO₇ (Ln=Nd, Gd-Ho) compounds show an antiferromagnetic transition at 2.2-3.2 K. Sm₃SbO₇ and Eu₃SbO₇ show van Vleck paramagnetism. Measurements of the specific heat down to 0.4 K for Gd₃SbO₇ and the analysis of the magnetic specific heat indicate that the antiferromagnetic ordering of the 8-coordinated Gd ions occur at 2.6 K, and the 7-coordinated Gd ions order at a furthermore low temperature.     

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).     

Synthesis and magnetic properties of 12L-perovskites Ba4LnIr3O12 (Ln=lanthanides)

New quadruple perovskite oxides Ba₄LnIr₃O₁₂ (Ln=lanthanides) were prepared and their magnetic properties were investigated. They crystallize in the monoclinic 12L-perovskite-type structure with space group C2/m. The Ir₃O₁₂ trimers and LnO₆ octahedra are alternately linked by corner-sharing and form the perovskite-type structure with 12 layers. The Ln and Ir ions are both in the tetravalent state for Ln=Ce, Pr, and Tb compounds , and for other compounds (Ln=La, Nd, Sm-Gd, Dy-Lu), Ln ions are in the trivalent state and the mean oxidation state of Ir ions is . An antiferromagnetic transition has been observed for Ln=Ce, Pr, and Tb compounds at 10.5, 35, and 16 K, respectively, while the other compounds are paramagnetic down to 1.8 K.     

Mild hydrothermal synthesis, crystal structure, spectroscopic and magnetic properties of the [M=Fe, x=2.08, y=1.58; M=Co, Ni, x=2.5, y=2] compounds

The [M=Fe (1), x=2.08, y=1.58; M=Co (2), x=2.5, y=2; Ni (3), x=2.5, y=2] compounds have been synthesized using mild hydrothermal conditions at 170 °C during five days. Single-crystals of (1) and (2), and polycrystalline sample of (3) were obtained. These isostructural compounds crystallize in the orthorhombic system, space group Aba2, with a=9.9598(2), b=18.8149(4) and c=8.5751(2) Å for (1), a=9.9142(7), b=18.570(1) and c=8.4920(5) Å for (2) and a=9.8038(2), b=18.2453(2) and c=8.4106(1) Å for (3), with Z=8 in the three phases. An X-ray diffraction study reveals that the crystal structure is composed of a three-dimensional skeleton formed by [MO₅F] and [MO₄F₂] (M=Fe, Co and Ni) octahedra and [HPO₃] tetrahedra, partially substituted by [PO₄] tetrahedra in phase (1). The IR spectra show the vibrational modes of the water molecules and those of the (HPO₃)²⁻ tetrahedral oxoanions. The thermal study indicates that the limit of thermal stability of these phases is 195 °C for (1) and 315 °C for (2) and (3). The electronic absorption spectroscopy shows the characteristic bands of the Fe(II), Co(II) and Ni(II) high-spin cations in slightly distorted octahedral geometry. Magnetic measurements indicate the existence of global antiferromagnetic interactions between the metallic centers with a ferromagnetic transition in the three compounds at 28, 14 and 21 K for (1), (2) and (3), respectively. Compound (1) exhibits a hysteresis loop with remnant magnetization and coercive field values of 0.72 emu/mol and 880 Oe, respectively.     

High-pressure synthesis and structures of lanthanide germanides of LnGe5 (Ln=Ce, Pr, Nd, and Sm) isotypic with LaGe5

A series of lanthanide penta-germanides LnGe₅ (Ln=Ce, Pr, Nd and Sm) has been prepared by high-pressure (5–13 GPa) and high-temperature (500–1200 °C) reaction. CeGe₅ crystallizes in an orthorhombic unit cell (S.G. Immm (71)) with a=4.000(5) Å, b=6.192(5) Å, c=9.86(1) Å, and V=244.1(5) Å³. The new germanides are isotypic with LaGe₅ consisting of a Ge covalent network with tunnels where guest ions Ln³⁺ are situated. The network is composed of sublayers with edge-sharing Ge six-membered rings with only boat conformation. The sublayers are connected by rare eight-coordinated Ge atoms. The cell volume of the compounds systematically decreases from La to Sm compounds, except for CeGe_5, owing to the lanthanide contraction. The lattice constants of CeGe₅ are smaller than those of the Pr compound because it contains Ce⁴⁺ ions. CeGe₅ is paramagnetic above 2 K, but does not obey the Curie–Weiss law. PrGe₅ and NdGe₅ are Curie–Weiss type paramagnets with Weiss temperatures of –3.3 and –18.4 K. SmGe₅ shows an antiferromagnetic transition at 10.4 K.     

Structural and magnetic properties of the solid solution () YMn1−x(Cu3/4Mo1/4)xO3

Recently, the ferroelectromagnet YMnO₃ has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature 80 K) and ferroelectricity (Curie temperature 914 K). There have been no reports of complete YMn_1−xM_xO₃ solid solutions in which substitution of the foreign M cation preserves the hexagonal P6₃cm structure. In contrast there exist several homeotypic phases with the general formula, Ln_1+nCu_nMO_3+3n (n=1 (M=Ti), 2 (M=V) and 3 (M=Mo); Ln: lanthanide). Several YMn_1−x(Cu_3/4Mo_1/4)_xO₃ compounds have been synthesized. The solid solution, from YMnO₃ (x=0) to YCu_3/4Mo_1/4O₃ (x=1) has been characterized by X-ray diffraction and transmission electron microscopy study. For 0<x<0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P6₃cm, of YMnO₃. The Mn-free end member, x=1, crystallizes in a complex multiple cell, the superstructure being associated to Cu³⁺/Mo⁶⁺ cationic ordering. Dilution of the Mn³⁺ magnetic array by the paramagnetic (Cu²⁺) and diamagnetic (Mo⁶⁺) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x0.5 compositions.     

Magnetic properties of lanthanide rhenium oxides Ln3ReO7 (Ln=Sm, Eu, Ho)

Ternary lanthanide rhenium oxides Ln₃ReO₇ (Ln=Sm, Eu, Ho) were prepared and their structures were determined by X-ray diffraction measurements. They crystallize in an orthorhombic superstructure of cubic fluorite (space group Cmcm for Ln=Sm, Eu; C222₁ for Ln=Ho). The magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 1.8 to 400 K. The Sm₃ReO₇ shows an antiferromagnetic transition at 1.9 K. The Eu₃ReO₇ indicates a magnetic anomaly at 12 K. On the other hand, the results of the specific heat measurements indicate that both Sm₃ReO₇ and Eu₃ReO₇ undergo a structure transition at 270 and 350 K, respectively. The Ho₃ReO₇ is paramagnetic down to 1.8 K.     

Magnetic ordering of divalent europium in double perovskites Eu2LnTaO6 (Ln=rare earths): Magnetic interactions of Eu ions determined by magnetic susceptibility, specific heat, and Eu Mössbauer spectrum measurements

Structures and magnetic properties of double perovskite-type oxides Eu₂LnTaO₆ (Ln=Eu, Dy-Lu) were investigated. These compounds adopt a distorted double perovskite structure with space group P2₁/n. Magnetic susceptibility, specific heat, and ¹⁵¹Eu Mössbauer spectrum measurements show that the Eu²⁺ ions at the 12-coordinate sites of the perovskite structure are antiferromagnetically ordered at ∼4 K, and that Ln³⁺ ions at the 6-coordinate site are in the paramagnetic state down to 1.8 K.     

Studies on magnetic susceptibility and specific heat for 6H-perovskite-type oxides Ba3LnIr2O9 (Ln=La, Nd, Sm-Yb)

Magnetic properties of the 6H-perovskite-type oxides Ba₃LnIr₂O₉ (Ln=La and Nd: monoclinic; Ln=Sm-Yb: hexagonal symmetry) were investigated. For all the title compounds, a specific heat anomaly was found at 5.3-17.4 K. At the corresponding temperatures, the magnetic susceptibilities show a slight variation in its gradient. These magnetic anomalies suggest the magnetic ordering of the magnetic moments (S=1/2) remaining in the Ir^4.5+₂O₉ face-shared bioctahedra. In addition, the Ln³⁺ ions show the onset of the antiferromagnetic ordering around these temperatures. The Ba₃NdIr₂O₉ only shows a ferromagnetic behavior below 17.4 K with a remnant magnetization of 1.25 μ_B. This behavior may be due to the ferromagnetic ordering of the Nd³⁺ moments.     

Ln2Sr2PtO7+δ (Ln=La, Pr, and Nd): Three new Pt-containing [AnBn−1O3n]-type hexagonal perovskites

Polycrystalline samples of Ln₂Sr₂PtO_7+δ (Ln=La, Pr, Nd) were prepared by conventional solid state synthesis. The three compounds are new examples for n=2 members of the [A_nB_n−1O_3n] family of hexagonal perovskites containing platinum as the B-type cation. XRD Rietveld refinements show the platinates to crystallize in space group and, in the case of Pr and Nd, revealed a complete ordering of Ln/Sr on the two distinct A-type positions, while for La a partial disorder was observed. By XANES investigations at the Pt-L_III threshold the oxidation state +4 for platinum was found. Thermogravimetry revealed a small oxygen excess for Ln=La and Pr (δ=0.13 and 0.07), pointing to the presence of peroxide ions as already observed for isostructural Ru- and Ir-based compounds. UV–Vis measurements were done for the yellow lanthanum and the green neodymium compound. They revealed two optical band gaps of 2.52 and 3.05 eV, respectively. Magnetic measurements showed La₂Sr₂PtO_7+δ to be diamagnetic as expected for Pt⁴⁺ with low-spin configuration. For Ln=Pr and Nd the observed strong paramagnetism can be explained solely by the magnetic moments of the rare earths.     

Crystal structures and magnetic properties of fluorite-related oxides Ln3NbO7 (Ln=lanthanides)

Crystal structures and magnetic properties of the ternary oxides Ln₃NbO₇ (Ln=La, Pr, Nd, Sm-Lu) are reported. Their powder X-ray diffraction measurements and Rietveld analyzes show that they have the fluorite-related structures with space group Pnma (Ln=La, Pr, Nd), C222₁ (Ln=Sm-Tb), or Fm-3m (Ln=Dy-Lu). Magnetic susceptibility measurements were carried out from 1.8 to 400 K. The Ln₃NbO₇ compounds for Ln=Pr, Gd, Dy-Yb show Curie-Weiss paramagnetic behavior, and Sm₃NbO₇ and Eu₃NbO₇ show van Vleck paramagnetism. On the other hand, two magnetic anomalies were observed for both Nd₃NbO₇ (0.6 and 2.7 K) and Tb₃NbO₇ (2.0 and 3.2 K). From the results of specific heat measurements, it was found that these anomalies are due to the antiferromagnetic ordering of Ln ions in two different crystallographic sites (the 8-coordinated and 7-coordinated sites).     

K3Ln[OB(OH)2]2[HOPO3]2 (Ln=Yb, Lu): Layered rare-earth dihydrogen borate monohydrogen phosphates

Two isotypic layered rare-earth borate phosphates, K₃Ln[OB(OH)₂]₂[HOPO₃]₂ (Ln=Yb, Lu), were synthesized hydrothermally and the crystal structures were determined by single-crystal X-ray diffraction (R3?, Z=3, Yb: a=5.6809(2) Å, c=36.594(5) Å, V=1022.8(2) ų, Lu: a=5.6668(2) Å, c=36.692(2) Å, V=1020.4(1) ų). The crystal structure can be described in terms of stacking of Glaserite-type slabs consisting of LnO₆ octahedra interlinked by phosphate tetrahedra and additional layers of [OB(OH)₂]^- separated by K⁺ ions. Field and temperature dependent measurements of the magnetic susceptibility of the Yb-compound revealed Curie-Weiss paramagnetic behavior above 120 K (μ_eff=4.7 μ_B). Magnetic ordering was not observed down to 1.8 K.     

Syntheses and Structures of the Quaternary Copper Tellurides K3Ln4Cu5Te10 (Ln=Sm, Gd, Er), Rb3Ln4Cu5Te10 (Ln=Nd, Gd), and Cs3Gd4Cu5Te10

Six quaternary alkali-metal rare-earth copper tellurides K₃Ln₄Cu₅Te₁₀ (Ln=Sm, Gd, Er), Rb₃Ln₄Cu₅Te₁₀ (Ln=Nd, Gd), and Cs₃Gd₄Cu₅Te₁₀ have been synthesized at 1123 K with the use of reactive fluxes of alkali-metal halides ACl (A=K, Rb, Cs). All crystallographic data were collected at 153 K. These compounds crystallize in space group Pnnm of the orthorhombic system with two formula units in cells of dimensions (A₃Ln₄, a, b, c (Å)): K₃Sm₄, 16.590(2), 17.877(2), 4.3516(5); K₃Gd₄, 16.552(4), 17.767(4), 4.3294(9); K₃Er₄, 16.460(4), 17.550(4), 4.2926(9); Rb₃Nd₄, 17.356(1), 17.820(1), 4.3811(3); Rb₃Gd₄, 17.201(2), 17.586(2), 4.3429(6); Cs₃Gd₄, 17.512(1), 17.764(1), 4.3697(3). The corresponding R₁ indices for the refined structures are 0.0346, 0.0315, 0.0212, 0.0268, 0.0289, and 0.0411. The three K₃Ln₄Cu₅Te₁₀ structures belong to one structure type and the Rb₃Ln₄Cu₅Te₁₀ (Ln=Nd, Gd) and Cs₃Gd₄Cu₅Te₁₀ structures belong to another one, the difference being the location of one of the three unique Cu atoms. Both structure types are three-dimensional tunnel structures that contain similar Ln/Te fragments built from LnTe₆ octahedra and CuTe₄ tetrahedra. The CuTe₄ tetrahedra form ¹_∞[CuTe⁵⁻₃] and ¹_∞[CuTe³⁻₂] chains. The alkali-metal atoms, which are in the tunnels, are coordinated to seven or eight Te atoms.     

Magnetic and electrical properties of quadruple perovskites with 12 layer structures Ba4LnM3O12 (Ln=rare earths; M=Ru, Ir): The role of metal-metal bonding in perovskite-related oxides

Structures and magnetic and electrical properties of quadruple perovskites containing rare earths Ba₄LnM₃O₁₂ (Ln=rare earths; M=Ru, Ir) were investigated. They crystallize in the 12L-perovskite-type structure. Three MO₆ octahedra are connected to each other by face-sharing and form a M₃O₁₂ trimer. The M₃O₁₂ trimers and LnO₆ octahedra are alternately linked by corner-sharing, forming the perovskite-type structure with 12 layers. For Ln=Ce, Pr, and Tb, both the Ln and M ions are in the tetravalent state (Ba₄Ln⁴⁺M⁴⁺₃O₁₂), and for other Ln ions, Ln ions are in the trivalent state and the mean oxidation state of M ions is +4.33 (Ba₄Ln³⁺M^4.33+₃O₁₂). All the Ba₄Ln³⁺Ru^4.33+₃O₁₂ compounds show magnetic ordering at low temperatures, while any of the corresponding iridium-containing compounds Ba₄Ln³⁺Ir^4.33+₃O₁₂ is paramagnetic down to 1.8 K. Ba₄Ce⁴⁺Ir⁴⁺₃O₁₂ orders antiferromagnetically at 10.5 K, while the corresponding ruthenium-containing compound Ba₄Ce⁴⁺Ru⁴⁺₃O₁₂ is paramagnetic. These magnetic results were well understood by the magnetic behavior of M₃O₁₂. The effective magnetic moments and the entropy change for the magnetic ordering show that the trimers Ru^4.33+₃O₁₂ and Ir⁴⁺₃O₁₂ have the S= ground state, and in other cases there is no magnetic contribution from the trimers Ru⁴⁺₃O₁₂ or Ir^4.33+₃O₁₂.Measurements of the electrical resistivity of Ba₄LnM₃O₁₂ and its analysis show that these compounds demonstrate two-dimensional Mott-variable range hopping behavior.     

Magnetic properties of quadruple perovskites Ba4LnRu3O12 (Ln=La, Nd, Sm-Gd, Dy-Lu)

Quadruple perovskites Ba₄LnRu₃O₁₂ (Ln=La, Nd, Sm-Gd, Dy-Lu) were prepared and their magnetic properties were investigated. They adopt the 12L-perovskite-type structure consisting of Ru₃O₁₂ trimers and LnO₆ octahedra. All of these compounds show an antiferromagnetic transition at 2.5-30 K. For Ba₄NdRu₃O₁₂, ferrimagnetic ordering has been observed at 11.5 K. The observed magnetic transition is due to the magnetic behavior of the Ru^4.33+₃O₁₂ trimer with S=. Magnetic properties of Ba₄LnRu₃O₁₂ were compared with those of triple perovskites Ba₃LnRu₂O₉ and double perovskites Ba₂LnRuO₆.     

EuTZn (T=Pd, Pt, Au) with TiNiSi-type structure—Magnetic properties and Eu Mössbauer spectroscopy

The europium compounds EuTZn (T=Pd, Pt, Au) were synthesized from the elements in sealed tantalum tubes in an induction furnace. These intermetallics crystallize with the orthorhombic TiNiSi-type structure, space group Pnma. The structures were investigated by X-ray diffraction on powders and single crystals: a=732.3(2), b=448.5(2), c=787.7(2) pm, R₁/wR₂=0.0400/0.0594, 565 F² values for EuPdZn, a=727.8(3), b=443.7(1), c=781.7(3) pm, R₁/wR₂=0.0605/0.0866, 573 F² values for EuPtZn, and a=747.4(2), b=465.8(2), c=789.1(4) pm, R₁/wR₂=0.0351/0.0590, 658 F² values for EuAuZn, with 20 variables per refinement. Together the T and zinc atoms build up three-dimensional [TZn] networks with short T–Zn distances. The EuTZn compounds show Curie–Weiss behavior in the temperature range from 75 to 300 K with μ_eff=7.97(1), 7.70(1), and 7.94(1) μ_B/Eu atom and θ_P=18.6(1), 34.9(1), and 55.5(1) K for T=Pd, Pt, and Au, respectively, indicating divalent europium. Antiferromagntic ordering was detected at 15.1(3) K for EuPdZn and canted ferromagnetic ordering at 21.2(3) and 51.1(3) K for EuPtZn and EuAuZn. ¹⁵¹Eu Mössbauer spectroscopic measurements confirm the divalent nature of the europium atoms by isomer shift values ranging from −8.22(8) (EuPtZn) to −9.23(2) mm/s (EuAuZn). At 4.2 K full magnetic hyperfine field splitting is observed in all three compounds due to magnetic ordering of the europium magnetic moments.     

On the crystal structures of Ln3MO7 (Ln=Nd, Sm, Y and M=Sb, Ta)—Rietveld refinement using X-ray powder diffraction data

We have investigated, using X-ray powder diffraction data, the crystal structures of some fluorite derivatives with the formula Ln₃MO₇ (Ln=lanthanide or Y and M=Sb and Ta). In these compounds ordering of Ln and M occurs, leading to a parent structure in Cmmm. Tilting of the MO₆ octahedra causes doubling of one of the cubic axes, leading to a number of non-isomorphic subgroups, e.g. Cmcm, Ccmm and Cccm. We have identified an alternative space group Ccmm instead of C222₁ for those compounds containing a medium sized lanthanide or Y and M being Sb or Ta. Interestingly this is an alternative setting for the space group of the structure obtained when Ln is large (Cmcm). However, there tilting of the octahedra is around the a-axis of the parent structure, rather than around the b-axis as it is found in the compounds which we are reporting on here.In one compound, Nd₃TaO₇, both tilts occur. The phase transition between the two possible structures is a slow and difficult process above 80 K, allowing both phases to coexist.     

Magnetic structure and properties of Cu3(OH)4SO4 made of triple chains of spins s=1/2

Cu₃(OH)₄SO₄, obtained by hydrothermal synthesis from copper sulfate and soda in aqueous medium, is isostructural with the corresponding antlerite mineral, orthorhombic, space group Pnma (62), with a=8.289(1) b=6.079(1) and c=12.057(1) Å, V=607.5(2) ų, Z=4. Its crystalline structure has been refined from X-ray single crystal and powder neutron diffraction data at room temperature. It consists of copper (II) triple chains, running in the b-axis direction and connected to each other by sulfate groups. The magnetic structure, solved from powder neutron diffraction data at 1.4 K below the transition at 5 K evidenced by susceptibility and specific measurements, reveals that, inside a triple chain, the magnetic moments of the copper ions (μ_B=0.88(5) at 1.4 K) belonging to outer chains are oriented along the c-axis of the nuclear cell, with ferromagnetic order inside a chain and antiferromagnetic order between the two outer chains. No long-range magnetic order is obtained along the central chain with an idle spin behavior.     

Magnetic properties of ternary sodium oxides NaLnO2 (Ln=rare earths)

Magnetic properties of ternary sodium oxides NaLnO₂ (Ln=rare earths) are investigated. Their crystal structures are grouped into three types of structures, which are α-LiFeO₂, β-LiFeO₂, and α-NaFeO₂, depending on the size of rare earths. Their magnetic susceptibilities and specific heats have been measured from 1.8 to 300 K. Among them, NaGdO₂, NaDyO₂, and NaHoO₂ show antiferromagnetic transitions at 2.4, 2.2, and 2.4 K, respectively, and NaNdO₂ transforms to the ferromagnetic state below 2.4 K. NaSmO₂, NaErO₂, and NaYbO₂ exhibit a magnetic anomaly below 1.8 K.