Synthesis and magnetic structure of the YbMn2Sb2 compound

A neutron diffraction investigation has been carried out on the trigonal La₂O₃-type (hP5, space group , No. 164; also CaAl₂Si₂-type) YbMn₂Sb₂ intermetallic. A two-step synthesis route has been tried in this work, and successfully utilised to prepare single phase samples of this compound. This study shows that YbMn₂Sb₂ presents antiferromagnetic ordering below 120 K. The magnetic structure of this intermetallic consists of antiferromagnetically coupled magnetic moments of the manganese atoms, in the Mn1 (1/3, 2/3, Z_Mn) and Mn2 (2/3, 1/3, 1 − Z_Mn) sites; the direction of magnetic moments of manganese atoms forming a φ and a θ angle, respectively with the X- and the Z-axis. At 4 K the magnetic moment of the Mn1 atom is μ_Mn = 3.6(1) μ_B, with φ = 0° and θ = 62(4)°, whilst the Mn2 atom has a magnetic moment μ_Mn = 3.6(1) μ_B, with φ = 0° and θ = 242(4)°. On the other hand, in this compound no local moment was detected on the Yb site.     

Magnetocaloric effect in Pr6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Pr₆Co_1.67Si₃ compound have been investigated by magnetization measurements. The saturation moment at 5 K is found to be 10.7μ_B. The compound undergoes two magnetic transitions below Curie temperature T_C = 48 K and shows a reversible second-order magnetic transition around T_C. A magnetic entropy change ΔS = 6.9 J/(kg K) is observed for a magnetic field change from 0 to 5 T. The full width at half maximum of the ΔS peak is found to be about 38 K.     

Magnetic structures of Zr6CoAs2-type Ho6−xErxMnBi2 solid solutions

Investigations were made by neutron diffraction on Zr₆CoAs₂-type (space group no. 189) Ho_6−xEr_xMnBi₂ solid solutions. The ferromagnetic ordering temperature decreases from Ho₆MnBi₂ (T_C = 200(6) K) to Er₆MnBi₂ (T_C = 100(4) K), whereas temperatures of ferrimagnetic (or antiferrimagnetic) ordering (T_Ferri and T_AFerri) are found to have non-monotonic dependences on the content of Er: T_Ferri = 58(4) K for Ho₆MnBi₂, T_Ferri = 162(4) K for Ho_4.5Er_1.5MnBi₂, T_Ferri = 150(4) K for Ho₃Er₃MnBi₂, T_AFerri = 78(4) K for Ho_1.5Er_4.5MnBi₂ and T_AFerri = 52(4) K for Er₆MnBi₂.

In these compounds, no local moment was detected on the manganese ion site, except for Ho_1.5Er_4.5MnBi₂ and Er₆MnBi₂ compounds. The manganese magnetic moments (μ_Mn) is 1.5μ_B and these are antiferromagnetically coupled with that of rare earth moments.     

Magnetic ordering in Th3P4-type Tb4Sb3 compound

The nature of the magnetic ordering of Tb₄Sb₃ compound (Th₃P₄-type, cubic; cI28, space group , No. 220, a = 0.91518(7) nm) has been investigated by using the techniques of magnetization and neutron diffraction. AC and DC magnetisation measurements indicate antiferromagnetic ordering at 108 K in zero magnetic field that is accompanied by a field-induced metamagnetic transition to a ferromagnetic state, in fields above 0.3 T. Neutron diffraction experiment in zero applied magnetic field shows that below T_N = 112(4) K Tb₄Sb₃ exhibits an antiferromagnetic flat spiral-type ordering with propagation vector K₁ = [±1/8, ±1/8, ±1/8]. The magnetic moment of Tb atoms is found to be M_Tb = 6.7(3) μ_B at 80 K. The magnetic moment of Tb atoms lie in the (1 1 1) plane of Tb₄Sb₃ unit cell (the cone axis arranges along [1 1 1] direction with cone angle β = 90°). Below T_N2  50 K, Tb₄Sb₃ shows second antiferromagnetic transition with K₂ = [1/2, 1/2, 1/2] with possible re-orientation of Tb magnetic moments.     

Electronic structure and thermoelectric power of CeNi4Si

The studies of the thermoelectric power and band structure calculations for CeNi₄Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi₄Si is paramagnetic down to 2 K and follows the Curie–Weiss law with μ_eff = 0.52μ_B/f.u. and the paramagnetic Curie temperature θ_P = −2 K. This effective paramagnetic moment is lower than the free Ce³⁺ value. The obtained values for the f occupancy n_f and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi₄Si is characterized by γ = 16 mJ mol⁻¹ K⁻² and θ_D = 335 K.     

Study of structure and magnetic properties of the perovskite Tb0.5Sr0.5CoO3

The perovskite compound Tb_0.5Sr_0.5CoO₃ has been prepared and studied for the first time. We report here the structural and magnetic properties of the compound using the DC magnetization and powder neutron diffraction techniques. The compound is found to be orthorhombic with Pbnm space group. The magnetic ground state of the system is ferromagnetic with T_c = 120 K. The ordered magnetic moment is found to be 1.57 (4) μ_B/Co ion at 12 K along the crystallographic b-axis. The observed effective paramagnetic moment μ_eff = 2.54 μ_B/f.u. The role of ionic size effect on the magnetic and transport properties of the compound through the variation of CoOCo bond angles is highlighted.     

Electrical transport in UNi0.5Sb2 single crystals

Single crystals of UNi₀.₅Sb₂ were investigated by means of Seebeck coefficient and Hall effect measurements in the temperature range 5–300 K. The results corroborated the occurrence of two magnetic phase transitions: from para- to antiferromagnetic state at T_N = 161.5 K and a spin-reorientation near T_t = 64 K. The first-order character of the latter feature was proved by studying in detail the electrical resistivity and the magnetic susceptibility of single-crystalline UNi₀.₅Sb₂ in the vicinity of T_t.     

Magnetic structure of the HoPdSn compound

A polycrystalline sample of the HoPdSn compound was prepared and studied by powder neutron diffraction. This compound crystallizes in the orthorhombic TiNiSi-type structure (space group Pnma). The Ho atoms occupy the 4c position. Below T_N=3.7 K, the Ho moments equal to 6.0(1) μ_B form a magnetic structure described by the propagation vector k=(1/3,1/2,1/3) and are parallel to the a-axis.     

Structure and magnetic properties of pseudoternary ThMn12-type uranium compounds

Magnetic properties of UFe₉MnSi₂, UNiMnSi₂ and UNi_9.5Co_0.5Si₂ were investigated at temperature range 4.2–1000 K and in magnetic field up to 14 T at 4.2 K. The first compound is ferromagnetic below T_C=445 K with saturation magnetic moment about 7 μ_B/f.u. The derivatives of paramagnetic UNi₁₀Si₂ are both nonmagnetic. Additionally, ⁵⁷Fe Mössbauer effect was examined in UFe₉MnSi₂ in the temperature range between 20 K and about 500 K. This last experiment suggests that the magnetic order of the iron sublattice is not simple ferromagnetic.     

The effect of Hf substitution for Zr on glass forming ability and magnetic property of FeCoZrMoBAlY bulk metallic glasses

Bulk metallic glasses (BMGs) Fe₆₁Co₆Zr_8−xHf_xMo₇B₁₅Al₁Y₂ (x = 0–8) have been produced by copper mold casting technique using industrial raw materials. The effect of substitution of Hf for Zr on the glass forming ability (GFA) and the magnetic property has been studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). It was found that the substitution of an appropriate amount of Hf for Zr can improve the GFA of the base alloy Fe₆₁Co₆Zr₈Mo₇B₁₅Al₁Y₂, as demonstrated by the increase in reduced glass transition temperature T_rg (=T_g/T_l) and GFA parameters of γ (=T_x/T_g + T_l) and δ (=T_x/T_l − T_g). The Fe₆₁Co₆Zr₅Hf₃Mo₇B₁₅Al₁Y₂ alloy exhibits the highest GFA with the largest T_rg (0.612) and δ (1.633), and can cast a fully amorphous rod in 3 mm diameter. The substitution of Hf for Zr also enhances the magnetic properties, as verified by the increase in saturation magnetization (M_s) in the alloy of Fe₆₁Co₆Zr₃Hf₅Mo₇B₁₅Al₁Y₂, whose M_s is approximately 1.5 times higher than that of the base alloy (x = 0) at room temperature. Finally, the effect of the substitution of Hf for Zr on glass forming ability and magnetic properties is discussed.     

Hydrothermal synthesis and characterization of a new layered compound Li2VGeO5

The new compound Li₂VGeO₅ with a layered structure has been synthesized at 580 °C via the hydrothermal method. The compound crystallizes in the space group P4/n of the tetragonal system with two formula units in a cell of dimensions a=6.5187(9) Å, c=4.5092(9) Å (T=298 K), V=191.61(5) Å³. The structure is composed of layers made of repeating [(VO₅)(GeO₄)]¹⁻ units. Li⁺ ions reside between the layers. The magnetic susceptibility data show an antiferromagnetic coupling below 5 K with C=0.47 emu K mol⁻¹, and θ=−13 K with μ_eff=1.89μ_B for each Li₂VGeO₅ unit.     

Influence of A-site cation size-disorder on structural, magnetic and magnetocaloric properties of La0.7Ca0.3−xKxMnO3 compounds

The structural and magnetic properties of perovskite oxides La_0.7Ca_0.3−xK_xMnO₃ (0 ≤ x ≤ 0.15) have been investigated to explore the influence of the A-site cation size-disorder (σ²). The materials were prepared by the solid-state method and then characterized by X-ray diffraction (XRD). The XRD data have been analyzed by Rietveld refinement technique. For K doping concentration x ≤ 0.075, the samples crystallize in the orthorhombic structure, while for x ≥ 0.1, the structure becomes rhombohedral. The variation of the magnetization M as a function of the applied magnetic field μ₀H reveals the presence of a structural distortion leading to a reduction of the magnetization at low μ₀H values. When increasing μ₀H, the structural distortion decreases and for a high applied magnetic field, the M (μ₀H) curves saturate indicating the disappearance of the structural distortion. The influence of K doping concentration and the applied magnetic field on the magnetocaloric properties has been considered. A large magnetic-entropy change (|ΔS_M|  5 J/kg K) is obtained in all samples at Curie temperatures between 270 and 280 K for an applied magnetic field of 3 T. These results show that these materials can be used as candidates for magnetic refrigerants near room temperature.     

Crystal structure, thermal expansion and magnetic properties of new compound Dy1.2Fe4Si9.8

The new ternary compound Dy_1.2Fe₄Si_9.8 have been prepared and studied by means of X-ray powder diffraction technique and vibrating sample magnetometer. The ternary compound Dy_1.2Fe₄Si_9.8 crystallizes in the hexagonal Er_1.2Fe₄Si_9.8-type structure, space group P6₃/mmc (no. 194) with lattice parameters a = 0.39415(1) nm and c = 1.52771(3) nm. The crystal structural refinement of the compound Dy_1.2Fe₄Si_9.8 has been performed by using Rietveld method. Lattice thermal expansion studies on the compound were carried out in the temperature range from 298 to 1013 K. The variation of the unit cell parameters shows that the unit cell parameters increase with the increase in temperature. The coefficients of average lattice thermal expansion along various axes in the temperature range from 298 to 1013 K are , and . The temperature dependence of the magnetization for the compound was also investigated in the range from 90 to 300 K. The experimentally determined magnetic effective paramagnetic moment is μ_eff = 11.3μ_B per formula unit (10.3μ_B per Dy atom).     

Electronic structure and magnetism of PrNixPt1−x compounds

We have studied influence of the Pt–Ni substitution on the crystal structure and magnetic behavior of the PrNi_xPt_1−x compounds. Polycrystalline samples with x = 1, 0.9, 0.75, 0 were prepared and characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). The analysis of XRPD data confirmed that the orthorhombic CrB-type structure owned by the parent binary compounds remains conserved through the entire series. The samples were subsequently investigated by specific heat (C_p), magnetization (M) and ac susceptibility measurements in the temperature range 2–350 K and in magnetic fields up to 9 T. All compounds were found to order ferromagnetically. The T_C values monotonously increase with increasing Ni content. To inspect the crystal-field (CEF) effects and magnetocaloric properties specific-heat data were analyzed in detail and the magnetic contribution to the specific heat together with the magnetic entropy have been determined. The results of first principles electronic structure calculations of the PrNi and PrPt confirmed that besides the stable Pr magnetic moments due to localized 4f-electrons only a very small magnetic moments of at most 0.2μ_B is induced at the Ni (Pt) site due to the polarized 3d-electron states (5d-electron states) hybridizing with the Pr 5d-electron states, i.e. the Ni (Pt) moment plays only minor role in the total balance of the magnetic moments in these compounds.     

HfFe6Ge6-type YbMn6Ge6−xGax compounds (0.07≤x<0.72) with large magnetocrystalline anisotropy

The HfFe₆Ge₆-type YbMn₆Ge_6−xGa_x solid solution (0.07≤x≤0.72) has been studied by X-ray diffraction, microprobe analysis and powder magnetization measurements. All the compounds order antiferromagnetically between T_N=481 K for x=0.07 and T_N=349 K for x=0.72 and display more or less pronounced spontaneous magnetization at lower temperature. The corresponding Curie points increase from 40 K for x=0.07 to 319 K for x=0.72. The maximum magnetization values of the Ga-rich compounds (M≈5 μ_B/f.u. at 6 K) is compatible with a ferrimagnetic order of the Mn and Yb sublattices whereas the smaller values measured in the Ga-poor compounds suggest the stabilization of non-colinear magnetic structures. All the studied compounds are characterized by rather large coercive fields at low temperature (4.0≤H_c≤8.2 kOe).     

The crystal structure and magnetic properties of the Gd6Cr4Al43 compound

The crystal structure of intermetallic compound Gd₆Cr₄Al₄₃ has been investigated by means of X-ray diffraction data (Ho₆Mo₄Al₄₃ structure type, space group P6₃/mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å).

SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at T_N1 = 19.0(1) K and T_N2 = 6.8(1) K, respectively.     

Giant negative magnetoresistance in the vicinity of the ferromagnetic phase transition TC in Sm0.55Sr0.45MnO3

The temperature dependence of the resistance in Sm_0.55Sr_0.45MnO₃ at zero magnetic field and its first derivative served for the determination of T_C which turned out to be equal to 129.1 K. Then, the resistance measurements were carried out as functions of the stationary magnetic fields up to 14 T at the following temperatures: 118.6, 124.6, 133.6 and 139.7 K. Two of them are below and two of them are above T_C. It turned out that at all the four temperatures the resistance reveals a hysteresis. It turned also out that the closer the temperature to T_C the greater this hysteresis. At all the four temperatures the magnetoresistance is negative, its absolute value depends on the magnetic field and reaches 100% at 12 T. At lower fields the absolute value of the negative magnetoresistance increases monotonically with the decrease of temperature starting from 139.7 K. On the other hand, a maximum observed on all the primary and secondary curves above T_C moves with the decrease of temperature towards the lower magnetic fields and disappears on all the curves below T_C. On the secondary curves above T_C this maximum is flat.     

Ce(Au,Sb)2 with UHg2 structure type, a new member of the AlB2 family

A new ternary compound Ce(Au,Sb)₂, with a homogeneity range has been observed from X-ray powder diffraction of as cast alloys, a = 4.743–4.712 Å, c = 3.567–3.768 Å. Its crystal structure was investigated by X-ray diffraction from Ce(Au_1−xSb_x)₂ (x = 0.266) single crystal: CAD-4 automatic diffractometer, Mo K radiation, a = 4.7256(6) Å, c = 3.6711(6) Å, P6/mmm space group, V = 70.997(17) Å³, Z = 1, ρ = 10.732 Mg/m³, μ = 76.369 mm⁻¹, R₁ = 0.0415, wR₂ = 0.0793 for 99 reflections with I > 2σ(I₀). The coordination polyhedron of X (X = 0.734Au + 0.266Sb) atom is a full-capped trigonal prism [XCe₆X₃X₂]. Ce atom is coordinated by 14 atoms: [CeX₁₂Ce₂]. The compound is isotypic with UHg₂ structure, a deformation derivative of AlB₂ structure type. It forms isostructural compounds with La and Pr.     

On the crystal structure of new series of compounds, RPt2+xSb2−y (x = 0.125, y = 0.25; R = La, Ce, Pr)

A new compound CePt_2+xSb_2−y (x = 0.125, y = 0.25) was synthesized by arc-melting of the elements. The chemical and structural characterizations were carried out at room temperature on as-cast samples using X-ray diffractometry, metallographic analysis and EDS-microanalysis. According to the results of X-ray single crystal diffraction this antimonide crystallizes in I4cm space group (no. 108), Z = 32, ρ = 12.19 Mg/m³, μ = 89.05 mm⁻¹ (a = 12.5386(3) Å, c = 21.4692(6) Å (crystal I) and a = 12.5455(2) Å, c = 21.4791(5) Å (crystal II)). The structure and composition were confirmed by powder X-ray diffraction (a = 12.4901(2) Å, c = 21.3620(4) Å) and EDS-microanalysis respectively. Isotypic compounds were observed with La and Pr from X-ray powder diffraction of as-cast alloys at room temperature (a = 12.6266(4) Å, c = 21.4589(6) Å for LaPt_2+xSb_2−y and a = 12.5184(5) Å, c = 21.4178(7) Å for PrPt_2+xSb_2−y). The CePt_2+xSb_2−y structure is derived from CaBe₂Ge₂ (a = 2a₀ − 2b₀, b = 2a₀ + 2b₀, c = 2c₀) and comprises a new atomic arrangement with both vacancy on 4(b) pyramidal site and substitution of antimony atoms (X) by platinum (B) in the B–XX–B layers (referring to the subcell structure) forming two B––1/2B1/2XX–3/4B and two X–BB–X layers per cell. The structure of CePt_2+xSb_2−y is compared with those reported before for URh_1.6As_1.9 and CeNi_1.91As_1.94.     

Temperature dependent neutron powder diffraction study of the Laves phase compound TbCo2

The structure, magnetization and magnetostriction of Laves phase compound TbCo₂ are investigated by temperature dependent high resolution neutron powder diffraction. The compound crystallizes in the cubic Laves phase C15 structure above its Curie temperature T_C and exhibits a rhombohedral distortion (space group ) below T_C. By an appropriate extrapolation of the temperature factor of Co atom above T_C, the Rietveld refinement of the neutron powder diffraction data of the rhombohedral structure converges satisfactorily and reveals that the moments of Co1(3b) and Co2(9e) are almost equal. Tb moment follows well the Brillouin function. The total magnetic moment of TbCo₂ is about 5.8μ_B/f.u., the anisotropic magnetostriction constant λ₁₁₁ is about 4.6 × 10⁻³ and the volume magnetostriction ω_s is about 8.7 × 10⁻³ at 14 K.