Structure determination, magnetic and optical properties of a new chromium(II) thioantimonate, [Cr((NH2CH2CH2)3N)]Sb4S7

The chromium(II) antimony(III) sulphide, [Cr((NH₂CH₂CH₂)₃N)]Sb₄S₇, was synthesised under solvothermal conditions from the reaction of Sb₂S₃, Cr and S dissolved in tris(2-aminoethyl)amine (tren) at 438 K. The products were characterised by single-crystal X-ray diffraction, elemental analysis, SQUID magnetometry and diffuse reflectance spectroscopy. The compound crystallises in the monoclinic space group P2₁/n with a=7.9756(7), b=10.5191(9), c=25.880(2) Å and β=90.864(5)°. Alternating SbS₃³⁻ trigonal pyramids and Sb₃S₆³⁻ semi-cubes generate Sb₄S₇²⁻ chains which are directly bonded to Cr(tren)²⁺ pendant units. The effective magnetic moment of 4.94(6)μ_B shows a negligible orbital contribution, in agreement with expectations for Cr(II):d⁴ in a ⁵A ground state. The measured band gap of 2.14(3) eV is consistent with a correlation between optical band gap and framework density that is established from analysis of a wide range of antimony sulphides.     

Preparation and structural study of LaMnO3 magnetic material

We report the crystallographic parameters of LaMnO₃ obtained from X-ray diffraction data and electronic properties predictions using the density functional theory (DFT). LaMnO₃ was prepared by the citrate precursor method (CPM). The initial solution was 0.1 M of each cation and the citrate nitrate relation was one. The solution was dried at 373 K; the yielded foam was annealed at 873 K and then was characterized by X-ray diffraction. Diffraction peaks show that the space group is R-3c (#167) with a=b =5.523 Å and c=13.324 Å (rhombohedrally distorted perovskite). Structural results of the Rietveld method have a matching of 97% with that obtained from the Structure Prediction Diagnostic Software. DFT calculation reveals a half-metallic character and its magnetic moment is about 2.0 μ_B.     

Structural and magnetic properties of double-perovskite Ba2MnMoO6 by density functional theory

Perovskite-like materials which include magnetic elements have relevance due to the technological perspectives in the spintronics industry. In this work, we report the studies of Ba₂MnMoO₆ material by using the density functional theory. The interchange-correlation potential was included through the generalized gradient approximation. Our structural calculations are in agreement with the experimental results which show that the material crystallizes in the 225 space group (Fm3¯m) and has a lattice parameter of about 8070 Å. The density of states study was carried out by considering the up and down spin orientations. Results show that Ba₂MnMoO₆ has a conductor behavior due to dominant Mn spin-up and Mo spin-down contributions. The magnetic moment was calculated to be 2.9 μ_B.     

High-temperature ferromagnetism in Zn1−xMnxO semiconductor thin films

Clear evidence of ferromagnetic behavior at temperatures >400 K as well as spin polarization of the charge carriers have been observed in Zn_1−xMn_xO thin films grown on Al₂O₃ and MgO substrates. The magnetic properties depended on the exact Mn concentration and the growth parameters. In well-characterized single-phase films, the magnetic moment is 4.8 μ_B/Mn at 350 K, the highest moment yet reported for any Mn doped magnetic semiconductor. Anomalous Hall effect shows that the charge carriers (electrons) are spin-polarized and participate in the observed ferromagnetic behavior.     

Ab initio study of electronic structure and magnetic properties of copper (II) terephthalate

The first principles within the full potential linearized augmented plane wave (FP-LAPW) method was applied to study the compound of Cutp(OH₂)₂. The density of states, the electronic band structure and the spin magnetic moment are calculated. The calculations reveal that the compound has a ferromagnetic interaction arising from the bridging water molecule. The spin magnetic moment 1.0μ_B per molecule mainly comes from the Cu ion with little contribution from O, C anion.     

Antiferromagnetically coupled multilayers of (Co90Fe10 tF/Ru tRu)×N and (Ni81Fe19 tF/Ru tRu)×N prepared by ion beam deposition

This work describes multilayers of Co₉₀Fe₁₀ t_F/Ru t_Ru/Co₉₀Fe₁₀ t_F and Ni₈₁Fe₁₉ t_F/Ru t_Ru/Ni₈₁Fe₁₉ t_F (20 Åt_F200 Å) prepared at ambient temperature by ion beam deposition on Si/SiO₂ 3 kÅ substrates. The samples exhibited a maximum antiferromagnetic coupling with t_Ru=3.2 Å and M–H curves characterized by zero remanent magnetic moment and enhanced saturation field. Antiferromagnetic peaks were present with t_Ru17 and 30 Å.     

Mechanism of ferromagnetism in(Fe,Co)-codoped 4H-SiC from density functional theory

First-principles calculations are performed to investigate the electronic structures and magnetic properties of(Fe, Co)-codoped 4H-SiC using the generalized gradient approximation plus Hubbard U method. We find that 4H-SiC doped with an isolated Fe atom and an isolated Co atom produces a total magnetic moment of 5.98 μ_B and 6.00 μ_B respectively. We estimate T_C of about 263.1 K for the(Fe, Co)-codoped 4H-SiC system. We study ferromagnetic and antiferromagnetic coupling in(Fe, Co)-codoped 4H-SiC. Ferromagnetic behavior is observed.The strong ferromagnetic couplings between local magnetic moments can be attributed to p–d hybridization between Fe, Co and neighboring C. However, the(Fe, Co, V_(Si))-codoped 4H-SiC system shows antiferromagnetic coupling when an Si vacancy is introduced in the same 4H-SiC supercell. The results may be helpful for further study on transition metal-codoped systems.     

Magnetic phase transition in (Fe,Mn)65Ni35 alloys

Magnetization measurements on the Fe₆₀Mn₅Ni₃₅ and Fe₅₀Mn₁₅Ni₃₅ alloy samples were carried out in the temperature range 80T300 K and in magnetic fields up to 8 kOe. The Fe₆₀Mn₅Ni₃₅ was found to order ferromagnetically with a Curie temperature, T_c, above 300 K. From the temperature dependence of the spontaneous magnetization, M_s, it was concluded that the magnetic behavior of Fe₆₀Mn₅Ni₃₅ follows Wohlfarth theory of weak itinerant ferromagnet. The Fe₅₀Mn₁₅Ni₃₅ sample exhibits a magnetic phase transition from ferromagnetism to paramagnetism at T_c=242 K. The critical amplitudes and critical exponents (β, γ and δ) have been determined by using Arrott plots, Kouvel–Fisher method and scaling plots of the reduced magnetization and reduced magnetic field. The values of β, γ and δ are discussed and compared with the results obtained for various theoretical models and also with the experimentally determined values for related systems obtained by others.     

Magnetic properties of YCo5 (70%wt)+Y2Co17 (30%wt) nanocomposite powders at low temperatures

Nanostructured YCo₅ (70%wt)+Y₂Co₁₇ (30%wt) composite powders were prepared by mechanical milling and subsequent annealing at 1073 K for 1.5 min. The average grain size D of the YCo₅ and Y₂Co₁₇ phases, obtained from XRD data, was 14 and 12 nm, respectively. The temperature dependence of the magnetic properties was studied by DC magnetization measurements at temperatures T ranging from 3 to 300 K. Hysteresis loops (H_max=70 kOe) show that both the coercivity H_C and the squareness σ_r/σ_max are temperature-dependent. The coercivity increases from 12 kOe at room temperature to 18 kOe at T=3 K. The observed enhanced remanence (σ_r/σ_max>0.5) indicates that a strong exchange coupling is present at all temperatures used in this study. The maximum magnetization σ_max changes little with temperature and has a value of about 70% of the effective saturation magnetization of the title compound.     

Structural properties of diamond fine particles and clusters prepared by detonation and decomposition of TNT

The thermal parameter B for three different particle sizes of diamond samples (bulk powder 1–4 μm, fine particle 144–195 Å and cluster 55–61 Å) was determined by the grazing incidence X-ray diffraction method. The values of B were found to be in the range 0.50–0.70 Å² for particles in the size range 195–55 Å and 0.27 Å² for 1–4 μm. All of them are larger than that of diamond bulk. A clear size dependence of B, increasing with decreasing particle size, was found. By analysing X-ray diffraction data at several temperatures the magnitude of B was found to be due to B_S (static part) instead of B_T (dynamic part). The average B_S values obtained were 0.04 Å², 0.19 Å² and 0.27 Å² for bulk powder, fine particle and cluster samples respectively. Ultrahigh resolution transmission electron microscope (TEM) observation confirmed the presence of strain, distortion, roughness and dislocation lines in many particles. TEM images of particles indicate that the clusters were not spherical in shape; they were mostly cubiform and some were truncated prism-like polyhedral. The present study reveals that the B_S component is responsible for the large B value in diamond fine particles and clusters. No clear surface local atomic distortion was found in the particles.     

Investigation of the static and dynamic magnetic properties of CoFe2O4 nanoparticles

We have investigated the magnetic behavior of cobalt ferrite nanoparticles with a mean diameter of 7.2 nm. AC susceptibility of colloidal cobalt ferrite nanoparticles was measured as a function of temperature T from 2 to 300 K under zero external DC field for frequencies ranging from f=10 to 10,000 Hz. A prominent peak appears in both χ′ and χ″ as a function of T. The peak temperature T₂ of χ″ depends on f following the Vogel–Fulcher law. The particles show superparamagnetic behavior at room temperature, with transition to a blocked state at T_B^m94 K in ZFC and 119 K in AC susceptibility measurements, respectively, which depends on the applied field. The saturation magnetization and the coercivity measured at 4.2 K are 27.3 emu/g and 14.7 kOe, respectively. The particle size distribution was determined by fitting a magnetization curve obtained at 295 K assuming a log-normal size distribution. The interparticle interactions are found to influence the energy barriers yielding an enhancement of the estimated magnetic anisotropy, K=6×10⁶ erg/cm³. Mössbauer spectra obtained at higher temperatures show a gradual collapse of the magnetic hyperfine splitting typical for superparamagnetic relaxation. At 4.2 K, the Mössbauer spectrum was fitted with two magnetic subspectra with internal fields H_int of 490, 470 and 515 kOe, corresponding to Fe³⁺ ions in A and B sites.     

Aspects of “low field” magnetotransport in epitaxial thin films of the ferromagnetic metallic oxide SrRuO3

Epitaxial thin films of the conductive ferromagnetic oxide SrRuO₃ were grown on an (0 0 1) SrTiO₃ (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]_S and [0 0 1]_S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ₀H=9 T; T)−ρ( μ₀H=0 T; T)]/ρ( μ₀H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, T_C 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO₃ films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization.     

Structural and optical properties of thermally evaporated Bi2Te3 films

Bi₂Te₃ films were prepared by thermal evaporation technique. X-ray diffraction analysis for as-deposited and annealed films in vacuum at 150 °C were polycrystalline with rhombohedral structure. The crystallite size is found to increase as the film thickness increases and has values in the range 67–162 nm. The optical constants (the refractive index, n, and absorption index, k) were determined using transmittance and reflectance data in the spectral range 2.5–10 μm for Bi₂Te₃ films with different thicknesses (25–99.5 nm). Both n and k are independent on the film thickness in the investigated range. It was also found that Bi₂Te₃ is a high refractive index material (n has values of 4.7–8.8 in the wavelength range 2.5–10 μm). The allowed optical transitions were found to be direct optical transitions with energy gap  eV. The optical conductivities σ₁ = ƒ(hν) and σ₂ = f(hν) show distinct peaks at about 0.13 and 0.3 eV, respectively. These two peaks can be attributed to optical interband transitions.     

Effective Ru moment in RuSr2Eu2−xCexCu2O10 from high-temperature magnetic susceptibility

We have made high-temperature (250 K<T<800 K) DC susceptibility measurements in the compounds RuSr₂Eu_2−xCe_xCu₂O₁₀ for x=0.6,0.8, and 1.0 in order to determine the Ru effective magnetic moment. After carefully subtracting all contributions to the magnetic susceptibility except that of the Ru ions, we have been able to fit the Ru susceptibility with a law χ_Ru=χ₀+C_Ru/(T−Θ_Ru). We have found that the Ru effective moment falls between the values expected for Ru⁵⁺ in spin states and . We have also found a dependence of μ_eff(Ru) and Θ_Ru with the Ce content x.     

Dielectric and magnetic properties of xNiFe2O4+(1−x)Ba0.9Sr0.1TiO3 composites

Magnetoelectric composites, namely, xNiFe₂O₄+(1−x)Ba_0.9Sr_0.1TiO₃ were prepared by standard double sintering ceramic method. The X-ray diffraction analysis was carried out to check the phases formed during sintering and to calculate the lattice parameters. Scanning electron microscope (SEM) micrographs were taken to understand the microstructure of the samples. The dielectric constant (ε′) and loss tangent (tan δ) were measured as a function of frequency in the frequency range 100 Hz–1 MHz. Variation of dielectric constant and loss tangent with temperature and composition has been reported. The hysteresis measurements were done to determine saturation magnetization (M_S) and coersivity (H_c). The variation of saturation magnetization and magnetic moment is interpreted in terms of composition.     

Crystal structure and phase transitions of [(C2H5)4N]6Bi8Cl30

A new [(C₂H₅)₄N]₆Bi₈Cl₃₀ crystal of the family of alkylammonium halogenobismuthates was grown. X-ray diffraction studies showed that the crystals are monoclinic, space group C2/m with a = 20.117(5), b = 12.682(3), c = 20.396(5) Å, β = 93.03(3), Z =2. The lattice consists of (C₂H₅)₄N⁺ cations and a new type of Bi₈Cl⁶⁻₃₀ anion. Dielectric studies revealed two closely-lying structural phase transitions around 241 K (on cooling). They were interpreted as due to a freezing of the rotational motions of tetraethylammonium cations.     

Ab initio study of cubic complex Bi2CrCuO6 perovskite

We report a detailed calculation of the structural and electronic properties for the cubic complex Bi₂CrCuO₆ perovskite material by density functional theory. The exchange-correlation potential was included through the generalized gradient approximation. From the adjusting of Murnaghan state equation to the energy as a function of volume data, we obtain an ideal lattice parameter of 7.763 Å. The density of states study was carried out considering the two spin polarizations. Results reveal that this material behaves as a conductor to the spin-down polarization and evidence a semiconductor tendency to the spin-up configuration. This tendency to the half-metallicity character is corroborated by the integer number of magnetic moment (3.0 μ_B), which is attributed to the Cr-spin-up orbital contribution.     

Anisotropic dielectric properties of PbYb1/2Ta1/2O3 single crystals

PbYb_1/2Ta_1/2O₃ single crystals were obtained for the first time. They were grown by the flux method. The PbOPbF₂B₂O₃ system was used as a solvent. Dielectric investigations were carried out in 1 0 0_c, 1 1 0_c and 1 1 1_c pseudocubic directions. These studies pointed to anisotropy of dielectric properties. Frequency-independent ε′(T) and ε″(T) maxima related to the antiferroelectric–paraelectric (AFE—PE) phase transition are observed for all directions at 562 K. The frequency-dependent ε′(T) and ε″(T) maxima near 400 K related to the ferroelectric (FE)–AFE phase transition are observed only in 1 1 1_c direction. The hysteresis loops were observed in this direction only. These results point that ferroelectric relaxor properties appear only in 1 1 1_c direction. We propose to consider the ferroelectric phase as ferrielectric one.     

Magnetic properties of UFe5Sn single crystals

Millimetre-size UFe₅Sn single crystals were grown by the top seed solution growth method and characterized by magnetization, ⁵⁷Fe Mössbauer spectroscopy and specific heat measurements in order to study the magnetic transitions detected in powder samples at 248 and 178 K. The magnetization measurements show different behaviour along the three crystallographic directions but with similar values of spontaneous magnetization along a and c. The transition at 248 K is associated with ferromagnetic ordering of iron moments along the c-axis, while the transition at lower temperature is associated with a reorientation towards b. Mössbauer data show that this reorientation is concomitant to the ordering of the Fe2 sites, which in a large proportion remain paramagnetic between the two transition temperatures. Specific heat measurements are consistent with the establishment of magnetic ordering at 248 K, followed by a spin reorientation at 178 K, yielding γ(0 K)140 mJ/(mol K²) and θ290 K for UFe₅Sn.     

X-ray and high resolution selenium-77 solid state NMR spectroscopy as complementary probes to structural studies of organophosphorus diselenides

high resolution solid state NMR spectroscopy was employed to study structural properties of bis(diisopropoxyphosphorothioyl) diselenide 1 and bis(dineopentoxyphosphorothioyl) diselenide 2. The principal elements T_ii of effective dipolar/chemical shift tensor were calculated from spinning sideband intensities employing the WIN-MAS program. The values of anisotropy and asymmetry parameters reflect the distortion of the selenium environment. It was found that the T₃₃ component mostly contributes to changes in the isotropic chemical shifts. CP/MAS experiments were used to decide the assignment of space group by counting the number of crystallographically unique selenium centers in the unit cell. Crystals of diselenide 1 are triclinic, space group P with a=8.485(3) Å, b=8.508(1) Å, c=8.511(2) Å, =98.835(15)°, β=111.653(24)°, γ=93.524(21)°, V=559.5(3) ų, D_c=1.544(2) g/cm³ and Z=1. Refinement using 2222 reflections for 157 variables gives R=0.037. Crystals of diselenide 2 are triclinic, space group P1 with a=9.1418(8) Å, b=9.1465(8) Å, c=9.9200(9) Å, =74.751(8)°, β=74.629(7)°, γ=82.216(7)°, V=769.7(1) ų, D_c=1.365(2) g/cm³ and Z=1. Refinement using 3316 reflections for 297 variables gives R=0.0272.