Magnetic structure and space group of the garnet Ca3Fe2(GeO4)3

Ca₃Fe₂(GeO₄)₃, is paramagnetic at room temperature with the cubic space group Ia3d. At 4.2 K the compound is magnetically ordered. From powder neutron diffraction data a pair of collinear, enantiomorphic magnetic structures is derived, the magnetic space group of which is I_p4₁ 22 or I_p4₁ ‘22’, respectively.     

The magnetic structure of cubic ErAl3

The magnetic structure of cubic or β-ErAl₃ has been investigated by neutron diffraction from powder samples. ErAl₃ undergoes a transition at 5·1°K, to an antiferromagnetic state with an enlarged tetragonal unit cell. The moments are directed perpendicular to the tetragonal c-axis. Crystal field effects are large and dominant in this compound. The extrapolated saturation moment is 5·1/μ_B, which corresponds to the Γ₈ ground state.     

Magnetic structure of the Mn5Si3-type Er5Ge3 compound

The Er₅Ge₃ compound (Mn₅Si₃-type, hP16, P6₃/mcm) at 4 K shows magnetic ordering of the antiferromagnetic type. Its magnetic structure consists of sine modulated collinear magnetic moments of Er that are parallel to the c axis (with a propagation vector k=[0 0 ±0.3]). This corresponds to the magnetic unit cell (a a 10c), the values of the magnetic moment of the Er atoms being, as a general formula, M_z≈M₀ cos [2π(Z–1/4)(1–kZ)], with M₀=9.2(2) μ_B at 4 K.     

A comparative study of electronic structure and magnetic properties of SrCrO3 and SrMoO3

A comparative study of electronic structure and magnetic properties of SrCrO₃ and SrMoO₃ has been carried out using FPLAPW method with density-functional theory. The calculated results suggest that both compounds are nonmagnetic (NM) metal in cubic structures at room temperature, and they exhibit very similar band structure and electronic properties except more extend Mo 4d orbitals than Cr 3d electronic states. However, the electronic structure and magnetic properties exhibit remarkable differences between them in the low temperature phases. SrCrO₃ is with a C-AFM ground state with magnetic moment of 1.18μ_B/Cr in the tetragonal structure, while SrMoO₃ is with a NM ground state in the orthorhombic structure. It is assumed that the extend 4d orbitals may be the reason which results in NM solution at low temperature phase of SrMoO₃.     

The magnetic structure of HoCo2Si2

We have carried out neutron diffraction on a HoCo₂Si₂ powder sample at 4.2 K. The magnetic structure of this compound is collinear antiferromagnetic with the holmium magnetic moments parallel to the c-axis of the crystal. The magnetic moment value of holmium is 9.85 μ_B. The magnetic space group is I4/mm'm' (Sh⁴¹⁰₁₂₈) k = 000 The ordering temperature is t_n = 12(1) K.     

A neutron diffraction study of the magnetic properties of PrTiO3 and NdTiO3

The magnetic properties of PrTiO₃ and NdTiO₃ were studied by neutron diffraction at several temperatures below 110 K. Although PrTiO₃ exhibits a T_N at 90 K no significant magnetic scattering was detected down to 65 K. The order at 90 K can be attributed to the Ti(III) below our detection limit of 0.25μ_B. Below 65 K magnetic reflections due to the Pr(III) sublattice develop consistent with a F_xC_y configuration. At 7 K the moment is 1.35(15)μ[inB] and lies at 45° (5) to the a or b axes. This structure is contrasted with that found for PrCrO₃. By comparing powder data at 50 and 7 K for NdTiO₃ it is concluded there is no evidence for magnetic order on either the Nd(III) or Ti(III) sublattices in agreement with bulk magnetic properties. The decrease in magnitude of the Ti(III) moment from LaTiO₃ to NdTiO₃ is compared to the known behavior of the La_1-xY_xTiO₃ system and is found to be consistent.     

The magnetic structure of the compound Ho5Sb3

We have investigated the magnetic behavior of Ho₅Sb₃ compound (Mn₅Si₃-type, hexagonal; a=0.8865(1) nm, c=0.6232(1) nm, as derived from X-ray Guinier powder pattern) by using the techniques of magnetization, electrical resistivity, heat capacity and neutron diffraction. We find that Ho₅Sb₃ exhibits a ferrimagnetic type (Ferrimagnet I) ordering below 60 K with propagation vectors K₀=[0, 0, 1] and K₁=[±K_x, 0, 0]. Below 40 K, the thermal variation of magnetic reflections and the appearance of an additional magnetic component with propagation vector K₂=[0, 1/2, 0] show the onset of an antiferromagnetic type of ordering in the magnetic structure; which evolves into yet another ferrimagnetic structure (Ferrimagnet II) as the temperature is lowered down to 2 K. The magnetic moments of the Ho atoms at the (4d) and (6g) sites with magnitudes of nearly 7.4 and 6.3 μ_B at 2 K, respectively, are inclined approximately at 70° to the c-axis.     

Field-induced structural transition and the related magnetic entropy change in Ni43Mn43Co3Sn11 alloy

Magnetic properties and magnetic entropy change ΔS were investigated in Heusler alloy Ni₄₃Mn₄₃Co₃Sn₁₁. With decreasing temperature this alloy undergoes a martensitic structural transition at T_M=188 K. The incorporation of Co atoms enhances ferromagnetic exchange for parent phases. Austenitic phase with cubic structure shows strong ferromagnetic behaviors with Curie temperature T_C^A at 346 K, while martensitic phase shows weak ferromagnetic properties. An external magnetic field can shift T_M to a lower temperature at a rate of 4.4 K/T, and a field-induced structural transition from martensitic to austenitic state takes place at temperatures near but below T_M. As a result, a great magnetic entropy change with positive sign appears. The size of ΔS reaches 33 J/kg K under 5 T magnetic field. More important is that the ΔS displays a table-like peak under 5 T, which is favorable for Ericsson-type refrigerators.     

Neutron diffraction study of β-UD3 and β-UH3

The results of a neutron powder diffraction study on β-UD₃ and β-UH₃ are reported. Diffraction patterns have been obtained both above (220 K) and below (10 K) the Curie temperature, in order to refine the crystal structure on the basis of a large number of resolved Bragg peaks and to obtain the ordered magnetic moment. The two kinds of uranium atoms present in the structure appear to be magnetically equivalent. The observed magnetic moment for β-UD₃ at T = 10 K is μ_ord = (1.45 ? 0.11) μ_B/U_atom     

Temperature and field dependent electronic structure and magnetic properties of LaCoO3 and GdCoO3

The transformation of the band structure of LaCoO₃ in the applied magnetic field has been theoretically studied. If the field is below its critical value B_C≈65 T, the dielectric band gap decreases with the field, thus giving rise to negative magnetoresistance that is highest at T≈300÷500 K. The critical field is related to the crossover between the low- and high-spin terms of Co³⁺ ions. The spin crossover results in an insulator–metal transition induced by an increase in the magnetic field. Similar calculations have been done for GdCoO₃ which is characterized by large spin gap∼2000 K.     

Magnetic structure of the Sm5Ge4-type Tb2Ti3Ge4

The orthorhombic Sm₅Ge₄-type Tb₂Ti₃Ge₄ shows square modulated non-collinear magnetic ordering with wave vector K=[±1/3, 1/2, 1/2] at 2 K. The terbium magnetic moments lie in the bc plane and magnetic moment value of 7.5(2) μ_B/Tb is obtained at 2 K.     

The magnetic field dependence of the structural transition temperature in La3S4 and La3Se4

The magnetic field dependence of the structural transition temperature T_m from the cubic to the tetragonal phase has been determined for single crystals of La₃S₄ and La₃Se₄. The observed field dependence of T_m can be accounted for by the band Jahn-Teller model of the coupling of an e_g-band to the shear mode of the cubic lattice without invoking any coupling to acoustic or optical phonons.     

The magnetic structures of LaTiO3 and CeTiO3

The basic features of the magnetic structures of LaTiO₃ and CeTiO₃ were determined by powder neutron diffraction. LaTiO₃ (T_N = 125 K) is a type G antiferromagnet with a moment on Ti (III) of 0.45(5)μ_B at 10 K. As bulk magnetic measurements indicate a weak ferromagnetic moment, a G_zF_x or G_xF_z configuration is implied. CeTiO₃ (T_N) = 116 K) shows more complex behaviour. At 81 K only G and F type reflections are observed. The most consistent interpretation is to assign G-type configuration to Ti(III) and an induced F_z on Ce(III). Moments are 0.36μ_B on Ti(III) and 0.4(1)μ_B on Ce(III). It is also possible to assign both G and F components to Ti(III). This demands a “canting angle” of 34° to explain the F moment. Below 80 K a C-type component develops. A model assuming a G_zF_x configuration for Ti(III) and a C_yF_x configuration for Ce(III) provides a good fit to the data. This assignment is consistent with Bertaut's symmetry considerations. Other models which violate Bertaut's rules also fit the data.     

Magnetic and ESR studies of Er3+ in lanthanum dihydride LaH2

Er³⁺ electron spin resonance ESR and magnetic susceptibility have been studied in metallic lanthanum dihydride host. The ESR spectrum contains a single asymmetrical line with g-factor g = 6.68 ± 0.05 close to that expected for Γ₇ as ground state. The experimental magnetic susceptibility was interpreted on the base of LLW cubic crystal field Hamiltonian. The best fit of the experimental data has been obtained for the following B₄ and B₆ crystal field parameters: B₄ = ?5.2 × 10^?3 K; B₆ = 3.8 × 10^?5 K which support the anionic-like character hydridic model of hydrogen atoms in this hydride.     

The antiferromagnetic structure of TbB4

The magnetic structure of the rare earth tetraboride TbB₄ (crystallographic space group P4/mbm) has been determined by neutron diffraction on a polycrystalline sample. Below the experimentally determined Néel temperature of T_N = (43±1) K TbB₄ is ordered antiferromagnetically. The data refinement yielded a magnetic moment value of (7.7 ± 0.2) μ_B/Tb ion at 4.2 K which we interpret as Tb⁴⁺. The magnetic structure is antiferromagnetic collinear with the moments perpendicular to the tetragonal axis.     

Van Vleck paramagnetism of the thulium garnet Tm3Al5O12

The magnetic susceptibility of the garnet-type single crystal Tm₃Al₅O₁₂ exhibits the typical Van Vleck temperature independent paramagnetism below ≈8 K. The temperature dependence of the susceptibility over the range 2.0-300 K has been analyzed on the assumption that the cubic crystal-electric-field dominates the energy level on ³H₆ (J=6) ground multiplet for Tm³⁺ ion having 12-electrons in 4f shell. The ground state of the ³H₆ is nonmagnetic with Γ₂ singlet, avoiding the Kramers doublet. The energy separation between Γ₂ and the first excited state Γ⁽²⁾₅ triplet is evaluated to be 68.0 K. The whole energy interval Δ between Γ₂ and the highest state Γ₁ in ³H₆ is estimated to be 339.5 K.     

Crystal structure and magnetism of UFe3B2

The structure of the UFe₃B₂ compound has been refined down to R=0.022 and wR₂=0.052 from single crystal X-ray diffraction data. This uranium boride crystallizes in the CeCo₃B₂ type-structure (P6/mmm space group no. 191, Z=1, ρ=10.79 g/cm³), with lattice parameters at room temperature a=0.5052(1) nm, c=0.3002(1) nm and V=0.664(1) nm³. Magnetization measurements made between 2 K and 800 K suggested that UFe₃B₂ is an antiferromagnet with a rather high Néel temperature of T_N=268±5 K. No other magnetic transitions were observed down to the lowest studied temperature.     

Crystal structure and magnetic properties of Mn substituted ludwigite Co3O2BO3

The needle shape single crystals Co_3−x Mn_xO₂BO₃ with ludwigite structure have been prepared. According to the X-ray diffraction data the preferable character of distinct crystallographic positions occupation by Mn ions is established. Magnetization field and temperature dependencies are measured. Paramagnetic Curie temperature value Θ=−100 K points out the predominance of antiferromagnetic interactions. Spin-glass magnetic ordering takes the onset at T_N=41 K. The crystallographic and magnetic properties of Co₃O₂BO₃:Mn are compared with the same for the isostructural analogs Co₃O₂BO₃ and CoO₂BO₃:Fe.     

Antiferromagnetic resonance in ferroborate NdFe3(BO3)4

The AFMR spectra of the NdFe₃(BO₃)₄ crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an “easy-plane” antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields H_a1=1.14 kOe and H_a2=60 kOe and magnetic excitation gaps Δν₁=101.9 GHz and Δν₂=23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width.At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed.     

Magnetic susceptibility studies of (CH2)3(NH3)2FeCl2Br2 and (CH2)6(NH3)2FeCl2Br2

The magnetic susceptibility of the layered compounds (CH₂)₃(NH₃)₂FeCl₂Br₂ and (CH₂)₆(NH₃)₂FeCl₂Br₂ has been measured in the range 80 < T < 300 K. The results follow a Curie-Weiss behavior in the range 120 < T < 300 K but are field dependent for T < 120 K. The results are interpreted in terms of a two-dimensional antiferromagnetic interaction which is canted. A comparison with the corresponding pure chloride compounds is given.