Crystal and magnetic structures of Y2CrS4

Chromium(II) sulfide, Y₂CrS₄, prepared by a solid-state reaction of Y₂S₃ and CrS, showed an antiferromagnetic transition at 65 K. The neutron diffraction patterns at 10 and 90 K were both well refined with the space group Pca2₁. At 90 K, cell parameters were a=12.5518(13) Å, b=7.5245(8) Å, and c=12.4918(13) Å. At 10 K, magnetic peaks were observed, which could be indexed on the same unit cell. Magnetic moments of chromium ions were parallel to the b-axis and antiferromagnetically ordered in each set of the 4a sites.     

Crystal engineering in two- and three-dimensional systems based on cyanomolybdates: structures, magnetism and intercalation properties

A design of infinite two- and three-dimensional cyano-bridged networks with useful properties has attracted a great deal of attention in contemporary science. A proposal described some investigations in crystal engineering, performed over the past few years on supramolecular coordination polymers based on [Mo(CN)_n]⁴⁻ (n=7,8) building blocks and on their magnetic and intercalation properties.     

Syntheses, crystal structure and luminescence property of novel 4f-3d heterometallic one-dimensional coordination polymers

Two 4f-3d heterometallic one-dimensional coordination polymers [ZnEu₂(Fur)₈·2H₂O]n and [ZnTb₂(Fur)₈·2H₂O]n (HFur=α-furancarboxylic acid) with good solubility were synthesized and characterized by infrared spectra, X-ray single crystal and powder diffractions, thermogravimetric and differential thermal analysis, and excitation and emission spectra. The X-ray diffraction analyses revealed that the two complexes are isomorphous. The Zn and Ln atoms are linked into one-dimensional chains by furancarboxylate ligands and the metal atoms are arranged in the ···Zn···Ln···Ln···Zn···Ln···Ln···order. Under the excitation of UV light, these coordination polymers emit intense characteristic luminescence of Eu³⁺ or Tb³⁺ ion, respectively. The influence of Zn²⁺ ion on the luminescence properties was also discussed here.     

A new quasi-one-dimensional molecular solid based on Ni(mnt)2 anion: Crystal structure and spin-gap transition

A new molecular solid, [1-(4′-bromo-2′-fluorobenzyl)-4-dimetylaminopyridinium]-bis(maleonitriledithiolato)nickel(III), (BrFBzPyN(CH₃)₂(Ni(mnt)₂)(1), has been prepared and characterized by elemental analyses, IR, ESI-MS spectra, single crystal X-ray diffraction and magnetic measurements. Compound 1 crystallizes in the orthorhombic space group Pnma, a=20.579(4) Å, b=7.078(1) Å, c=17.942(4) Å, α=β=γ=90°, V=2613.3(9) Å³, Z=4. The Ni(III) ions of 1 form a quasi-one-dimensional Zigzag magnetic chain within a Ni(mnt)₂⁻ column through Ni?S, S?S, Ni?Ni, or π?π interactions with an Ni?Ni distance of 4.227 Å. Magnetic susceptibility measurements in the temperature range 2-300 K show that 1 exhibits a spin-gap transition around 200 K, and antiferromagnetic interaction in the high-temperature phase (HT) and spin gap in the low-temperature phase (LT). The transition for 1 is second-order phase transition as determined by DSC analyses.     

EPR characterization of a nanoporous metal-organic framework exhibiting a bulk magnetic ordering

Magnetic properties of the open-framework structure [Cu₃(PTMTC)₂(py)₆(CH₃CH₂OH)₂(H₂O)] as well as those of a related evacuated sample have been analyzed on the basis of combined SQUID and EPR measurements. Such combined experiments demonstrate unambiguously the key role played by the radical ligand PTMTC in the promotion in both molecular magnets of magnetic exchange interactions through the open-framework structure.     

Structure and magnetic properties of perovskite Sr2CuNbO6−δ

Single phase perovskite Sr₂CuNbO_6−δ with a high proportion of Cu¹⁺ ions and oxygen vacancies was synthesized by solid-state reaction. The structure was determined by Rietveld method with space group Pm3m. Isotropic g value was evaluated from electron spin resonance (ESR) measurements. The ESR result is consistent with that of magnetic susceptibility.     

Organic radical molecular solids based on [(TCNQ)n] (n=1 or 2): Syntheses, crystal structures, magnetic properties and DFT analyses

Four molecular solids consisting of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical and benzylpyridinium or benzylquinolinium derivatives with molar ratios of 1:1 (1-3) and 2:1 (4) have been prepared and characterized. In the crystals of 1 and 3, TCNQ⁻ monoanions and the corresponding cations form segregated stacks, which are regular in 1 but irregular in 3. Instead of segregated stacks, TCNQ⁻ monoanions in 2 form isolated π-dimers. In the crystals of 4, two crystallographic independent TCNQ species possess almost equal fractional negative charge (ca. −0.5). Two types of TCNQ species form a tetrad, these tetrads make a TCNQ stack with the pattern …BAAB…BAAB… along the crystallographic a-b direction. The magnetisms for 1-4 can be simply explained by the formation of singlet spin state. A broken symmetry approach in a density functional theory framework at the ub3lyp/6-31 g level was used to calculate the magnetic exchange constants in 1-4. The results qualitatively demonstrate the observed magnetic properties.     

Electrical and magnetic features in the perovskite-type system Y(Co, Mn)O3

Electrical and magnetic properties of the perovskite-type solid solution YCo_xMn_1−xO₃ (x=0.20-0.60) have been studied at different temperatures and magnetic fields. Electrical conductivity measurements show a semi-conducting behaviour throughout the solid solution. The room-temperature conductivity increases with the Co content up to 33 at.%, and then decreases. The effective moment in the paramagnetic state shows a non-monotonic decrease, when the Co content increases. In the ordered state, the behaviour at low or null magnetic fields corresponds to a spin-glass or antiferromagnetic system, with a transition temperature, which raises with the Co content (up to 50 at.% Co), and then decreases. At high fields, all the solid solutions show a ferromagnetic behaviour, although there is a marked difference in their ferromagnetic cycles, at a threshold value of 33 at.% Co.     

Low-density core-shell composite hollow microspheres with tunable magnetic properties

Low-density (about 0.9 g/cm³) composite core-shell hollow microspheres with tunable magnetic properties were fabricated by Ni-Fe-P deposition on hollow glass microspheres (HGM) with modified electroless plating process. The effects of mole ratio of Fe²⁺/Ni²⁺, concentration of the reducer and pH value of the solution on the magnetic properties of the products were investigated. In conclusion, the increase in the mole ratio of Fe²⁺/Ni²⁺ and pH value of the solution could improve the soft magnetic properties of composite microspheres remarkably, while the increase in the concentration of NaH₂PO₂ had the opposite effect. The as-obtained metallic shells were amorphous and the crystallization got better with increased annealing temperature after plating. In addition, the saturation intensity of the composite microspheres was enhanced monotonically by increasing the annealing temperature. This work provided a facile and effective strategy to fabricate core-shell composite hollow microspheres with tailored magnetic properties.     

BaCO3 mediated modifications in structural and magnetic properties of natural nanoferrites

Preparing M-type barium hexaferrite and improving the magnetic response of natural ferrites by incorporating barium carbonate (BaCO₃) is ever-demanding. Series of barium carbonate doped ferrites with composition (100−x)Fe₃O₄·xBaCO₃ (x=0, 10, 20, 30 wt%) are prepared through solid state reaction method and sintered gradually at temperatures of 800 and 1000 °C. Nanoparticles of natural ferrite and commercial BaCO₃ are used as raw materials. Impacts of BaCO3 on structural and magnetic properties of these synthesized ferrites are inspected. The obtained ferrites are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) at room temperature. Uniform barium hexaferrite particles in terms of both morphology and size are not achieved. The average crystallite size of BaFe₁₂O₁₉ is observed to be within 30–600 nm. The sintering process results phase transformation from Fe₃O₄ (magnetite) to α-Fe₂O₃ (hematite) and the formation of hexagonal barium ferrite crystals. The occurrence of barium crystal is found to enhance with the increase of BaCO₃ concentrations up to 20 wt% and suddenly drop at 30 wt%. Saturation and remanent magnetization of the doped ferrites are significantly augmented up to 16.37 and 8.92 emu g⁻¹, respectively compared to their pure counterpart. Furthermore, the coercivity field is slightly decreased as BaCO₃ concentrations are increased. BaCO₃ mediated improvements in the magnetic response of natural ferrites are demonstrated.     

Structural and thermal studies of PVA:NH4I

Proton-conducting polymer electrolytes based on poly vinyl alcohol (PVA; 88% hydrolyzed) and ammonium iodide (NH₄I) has been prepared by solution casting method with different molar ratios of polymer and salt using DMSO as solvent. DMSO has been chosen as a solvent due its high dielectric constant and also its plasticizing nature. The ionic conductivity has been found to increase with increasing salt concentration up to 25 mol% beyond which the conductivity decreases and the highest ambient temperature conductivity has been found to be 2.5×10⁻³ S cm⁻¹. The conductivity enhancement with addition of NH₄I has been well correlated with the increase in amorphous nature of the films confirmed from XRD and differential scanning calorimetry (DSC) analyses. The temperature-dependent conductivity follows the Arrhenius relation. The polymer-proton interactions have been analyzed by FTIR spectroscopy.     

Sensitivity analysis for estimation of power losses in magnetic cores using neural network

Experimental data from a sample of 42 cores made from grain oriented 0.27 mm thick 3% SiFe electrical steel with dimensions ranging from 35 to 160 mm outer diameter, 25-100 mm inner diameter and 10-70 mm strip width and a flux density range 0.2-1.7 T have been obtained at 50 Hz and used as training data to a feed forward neural network. An analytical equation for prediction of power loss as depends on input parameters from the results of sensitivity analysis has been obtained. The calculated power losses with the analytical expression have also been compared with power loss obtained from the Preisach model after it has been applied to toroidal cores. The results show the proposed model can be used for estimation of power losses in the toroidal cores.     

Magnetic properties and magnetic structures of Sr3−xCaxRu2O7

We have measured magnetization curves and powder neutron diffraction of double-layered Ruddlesden-Popper type ruthenate Sr_3−xCa_xRu₂O₇ (x=1.5, 2.0 and 3.0). The field dependence of the magnetization revealed that the transition field of metamagnetic transition along the b-axis shifted to lower fields and that the transition became broad with increasing Sr content. The slope of the magnetization curve also increased with increasing Sr content below the metamagnetic transition. These results indicate that an itinerant component is partly introduced by the Sr substitution. From the magnetic reflection, on cooling below T_N, an additional reflection was observed at (0 0 1) for each x, and the amplitude increased with decreasing temperature. The observed diffraction patterns are very similar to those of Ca₃Ru₂O₇. We conclude that the magnetic structure of the antiferromagnetic ordered phase is basically the same structure with that of Ca₃Ru₂O₇.     

Crystal field and exchange interactions in rare earth transition metal salen compounds containing bipyridine, pyrazole complexes

Crystal field parameters for Pr³⁺ in {[Ni(salen)Pr-(hfac)₃](H₂O)} (noted as NiPr) and {[Ni(salen)Pr(hfac)₃(pyr)]-(CHCl₃)} (noted as NiPrpyr) have been found from a fit to the thermal variation in the magnetic susceptibility of NiPr and NiPrpyr. The nature of exchange interaction in [Cu(salen)Pr(hfac)3(pyr)] (noted as CuPrpyr), {[{Cu(salen)Pr(hfac)₃}₂(pyz)](H₂O)₃} (noted as Cu₂Pr₂pyz) and {[{Cu(salen)Pr(hfac)₃}₂(bpy)]-(CHCl₃)₂} (noted as Cu₂Pr₂bpy, bpy=4,4_-bipyridine) have been found using the derived results for NiPr and NiPrpyr. All the exchange interactions give significant contribution to the thermal variation in magnetic susceptibility below 50 K. The contribution due to Pr-Cu interaction is positive while that of the Cu-Cu and Pr-Pr interactions are negative. The behaviors below 10 K for Pr-Cu and Pr-Pr are difficult to explain, and point to a possible change in structure of CuPrpyr, Cu₂Pr₂pyz and Cu₂Pr₂bpy below 10 K. The theoretical thermal variations in the magnetic specific heat of NiPr and NiPrpyr are computed and discussed.     

Structural and magnetic ordering in the VxNb1+yS2 system

The influence of composition on the structural ordering and magnetism in the V_xNb_1+yS₂ system has been investigated by X-ray diffraction and magnetic measurements. Stoichiometric V_1/3NbS₂ did not exhibit the structural ordering of vanadium between the NbS₂ layers. In the ordered structure, the vanadium composition deviated from the ideal value of to both higher and lower values, while the niobium composition was in the range of 0.05?y?0.18. Excess niobium, y>0, is thought to play an essential role in the structural ordering in this system. For samples with excess niobium and ordered structures, a magnetic transition was observed at 20-50 K, depending on the composition. The spontaneous magnetization of 3-5×10⁻³ μ_B/V atom is thought to be intrinsic to this system. The magnetization curves consisted of a constant and a proportional parts of the magnetic field, which correspond to the spontaneous magnetization and high-field susceptibility, respectively. The magnetization curves and the temperature dependencies of the high-field susceptibility were quite similar to those of the canted antiferromagnetic NiS₂. A correlation between the structural and magnetic ordering is suggested.     

Crystal field investigation on the magnetic properties of Yb in Yb(CF3SO3)3·9H2O

Ytterbium tri-fluoromethanesulfonate (YbTFMS) single crystals are prepared from the slow evaporation of the aqueous solution of YbTFMS and the principal magnetic susceptibility perpendicular to the c-axis of the hexagonal crystal (χ_⊥) is measured from 300 K down to 13 K. Principal magnetic anisotropy Δχ(=χ_∥−χ_⊥) is measured from 300 K down to 80 K which provides principal magnetic susceptibility parallel to the c-axis (χ_∥) down to 80 K. Very good theoretical simulation of the observed magnetic properties of YbTFMS has been obtained using one electron crystal field (CF) analysis having C_3h site symmetry. No signature of ordering effect in the observed magnetic data is noticed down to the lowest temperature (13 K) attained, indicating the inter-ionic interaction to be of predominantly dipolar type. The calculated g-values are found to be g_∥=2.67 and g_⊥=2.51, respectively. CF analysis provides the electronic specific heat which gives two Schottky anomalies in its thermal variation down to ∼13 K. The temperature dependences of quadrupole splitting and hyperfine heat capacity are studied from the necessary information obtained from the CF analysis.     

Influence of particle size and compaction pressure on the magnetic properties of iron-phenolic soft magnetic composites

This paper investigates the effect of particle size and compaction pressure on the magnetic properties of iron-phenolic soft magnetic composites (50 Hz-1000 kHz). The results showed that the optimum amount of phenolic resin to attain maximum permeability and minimum loss factor at 10 kHz is 0.7 wt% for samples containing iron powder with average particle size ∼150 μm compacted at 800 MPa. In accordance with this resin content, at high frequencies (>300 kHz), the sample with lower particle size ∼10 μm exhibits higher magnetic permeability, higher operating frequencies and lower imaginary part of permeability. With increase in the compaction pressure, specific resistivity decreases and imaginary and real parts of permeability increase at low frequencies.     

Influence of cation substitution on the magnetic properties of the FeCr2S4 ferrimagnet

The influence of cation substitution on the magnetic properties of single and polycrystals of FeCr₂S₄ spinel has been studied. The tetrahedral A-site substitution of the Fe by Cu in Fe_1−xCu_xCr₂S₄ was found to increase significantly the value of temperature T_m of the spin-glass like magnetization anomaly, whereas the octahedral B-site substitution of the Cr by In decreases T_m. This effect is suggested to result from a structural transformation influenced by variation of internal (chemical) pressure due to lattice contraction (Cu) or expansion (In). The observed reduced values of the Curie temperature for Cu-substituted single crystals compared to that of the polycrystalline samples are attributed to presence of Cl ions in samples detected by electron-probe microanalysis. The observed reduced value of saturation magnetization in the polycrystals compared to the single crystals is ascribed to the effect of surface anisotropy. Based on the experimental data the superexchange is concluded to be the dominant exchange interaction for 0≤x≤0.5 in Fe_1−xCu_xCr₂S₄, whereas the indirect exchange through the charge carriers is considered of minor importance.     

Structural and magnetic ordering in the two-dimensional coordination polymer Co(ox)(bpy-d8), (ox=C2O4, bpy-d8=4,4′-bipyridine-d8)

Neutron diffraction and magnetic susceptibility studies of the two-dimensional coordination polymer Co(ox)(bpy-d8) are presented, where ox=C₂O₄²⁻ and bpy-d8=4,4′-bipyridine-d8 (fully deuterated). The neutron powder diffraction data reveal a second-order crystallographic phase transition at 290 K. Above 290 K, a disordered structure, space group Immm, is observed that is closely related to the ordered structure previously proposed on the basis of single crystal X-ray diffraction. At low temperatures, the structure is an ordered variant of the high-temperature phase with space group I222. In both phases, the Co ions are linked by the oxalate forming infinite chains that are crosslinked by the bpy ligands.The magnetic susceptibility follows qualitatively a quasi one-dimensional chain behavior. It exhibits a broad maximum around 35 K, corresponding to a strong antiferromagnetic coupling through the oxalate bridges. A kink at 9 K marks the onset of long-range antiferromagnetic ordering due to much weaker interchain magnetic interactions.The magnetically ordered structure determined from the low-temperature neutron diffraction data can be described with the propagation vector (1/2, 1/2, 1/2), i.e. a doubling of the unit cell in each principal direction. It is concluded that a significant antiferromagnetic interaction is mediated through the bpy ligands, although the Co-Co distance along these bridges is 11.4 Å.     

Influence of solvothermal growth condition on morphological formation of hematite spheroid and pseudocubic micro structures and its magnetic coercivity

Influence of solvothermal growth condition on morphological formation and population of defects of hematite spheroid and pseudocubic micro structures and its magnetic properties were studied. Spheroid shaped crystals with different size were obtained from growth solution made of methanol, methanol-water, propanol and pseudocubic crystallites with dimension of 1.281 μm size were obtained with propanol-water solution combination at a growth temperature of 200 °C. UV absorption and magnetic properties of spheroid and pseudocubic micro structures were size and shape dependant. Spheroid shaped sample grown from precursor solution made of methanol gives intense UV absorption peaks at 360 nm and high coercivity (5.23 KOe) at room temperature. Reduction in magnetic coercivity and remanence of all samples at 5 K with respect to 300 K is attributed to antiferromagnetic nature of hematite with spheroid and pseudocubic morphology. High coercivity (6.2 KOe) at room temperature was observed from micro pseudocubic sample grown with propanol-water combination which is contributed to high aspect ratio, inter particle interaction and crystalline defects.