Differential Susceptibility Measurements Research Articles

Structure and Magnetic Properties of a Nanosized Iron-Doped Bismuth Titanate Pyrochlore.

The nanosized (50-70 nm) pyrochlore Bi1.5Fe0.5Ti2O7-δ was prepared by a coprecipitation technique. Characterization of Bi1.5Fe0.5Ti2O7-δ was carried out by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Raman spectroscopy, Mössbauer spectroscopy, and magnetic susceptibility measurements. The study of Fe doping in Bi2Ti2O7 was performed by means of density functional theory (DFT) calculations. The nanosized Bi1.5Fe0.5Ti2O7-δ sample crystallizes in the structural type of pyrochlore (Fd3̅m). The distribution of Fe atoms over the sites of Bi and Ti was studied from DFT simulations and then confirmed by the XRD analysis and Mössbauer method. The local distribution, electronic structure, and magnetic behavior of nanosized Bi1.5Fe0.5Ti2O7-δ are determined by the local microstructure of the metastable nanosized sample. Based on the examination of the Mössbauer spectrum of the Bi1.5Fe0.5Ti2O7-δ nanopowder, the following states of oxidation were revealed for iron atoms: Fe4+ in the titanium sites with a fraction of ∼5.7% and two states of Fe3+ (in the Bi and Ti sites) with different geometries of the oxygen surrounding. The ratio of Fe3+ distributed over the sites correlates well with the distribution in the ceramic sample. The presence of Fe4+ was found only in the nanosized Bi1.5Fe0.5Ti2O7-δ. The experimental effective magnetic moment of Fe atoms in the nanosized Bi1.5Fe0.5Ti2O7-δ appeared noticeably lower than that in the ceramic sample. The temperature dependence of μeff within the temperature range of 50-300 K is adequately described by the model of coexistence of Fe3+ and Fe4+ and the existence of clusters.

Magnetic and electrical properties of postannealed Co2MnSi Heusler alloy films

The Co2MnSi (CMS) Heusler alloy compound with ordered crystalline structure is attractive for a number of applications due to soft ferromagnetic properties, high Curie temperature (TC ≅ 985 K), high saturation magnetization (Ms ≅ 5.1 µB/f.u), and predicted full spin polarization of carriers. In this work, we report preparation and properties of nanocrystalline CMS films with thickness d = 120 nm magnetron sputtered onto Si(100) substrates followed by annealing in vacuum at Ta = 300 ÷ 500 °C. Nanocrystalline structure of partially ordered cubic B2 phase with grain diameter d = 15 ÷ 30 nm increasing gradually with Ta has been indicated after annealing at Ta ≥ 400 °C. The angle-dependent differential susceptibility measurements revealed an interesting evolution of magnetic properties of the films in a course of postdeposition annealing at Ta=500 °C. Formation of isolated FM particles demonstrating the angle-dependent coercivity Hc(α) following the well-known Stoner–Wohlfarth model has been indicated after 0.5 h annealing. However, the Kondorsky low Hc ~ 1/cosα demonstrating a strong pinning of domain walls has been certified for similar films after 1.5 h annealing. At the same time, long-term (~ 5 h) annealing at 500 °C revealed reduced magnetization of the films due to a decomposition of the material. Nevertheless, electrical transport measurements revealed low field magnetoresistance of these films of about 0.1% and 0.05% at 80 and 295 K, respectively, demonstrating tunneling of spin-polarized carriers between nanocrystalline grains.

Resin‐Assisted Constructive Synthesis of Spin‐Crossover Nanorod Arrays

Spin‐crossover (SCO) nanorod arrays have been fabricated by a very simple construction method with cation‐exchange polymer resin beads as templates. The nucleation and growth mechanism of the nanorod arrays was studied by SEM. The spin‐crossover properties of nanorod arrays with different growth times were characterized by differential scanning calorimetry (DSC), Mössbauer spectroscopy, and magnetic susceptibility measurements. The transition temperatures of the obtained nanorod arrays increase as the immersion time of the nanorods increases. The hysteresis loop widths of these nanorod arrays are larger than that reported for [Fe(Htrz)2(trz)][BF4] (Htrz = 1,2,4‐triazole) as bulk powder and nanoparticles. This offers a new route for the fabrication of ordered SCO nanorod arrays by a self‐assembly method.

Effect of heat treatment on martensitic transformation of Ni47Mn40Sn13 ferromagnetic shape memory alloy prepared by mechanical alloying

In this paper, an attempt has been made to synthesis of the nanostructured Ni47Mn40Sn13 ferromagnetic shape memory alloy by ball milling of Ni, Mn and Sn powder mixture. The structure and magnetic evaluation of samples were investigated by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and AC susceptibility measurements. The results showed that after 20 hours of ball milling, the nanostructured L21-Ni47Mn40Sn13 powder was formed with an average particle size of 5 nm. In the as-milled specimen, the martensitic transformation (MT) was not observed. This was basically due to the atomic disordering and large lattice strain in nanoparticles. However, the annealing of milled specimens at temperatures above 1023K for 16 hours led to the occurrence of MT in nanostructured Ni47Mn40Sn13 powders. We also calculated t-he activation energy of MT by using Kissinger method and it was estimated to be about 52 kJ mol−1. The results demonstrate that a combination of MA and subsequent heat treatment has the potential to produce Ni-Mn-Sn magnetic shape memory.

Intrinsic nanostructure in Zr2−xFe4Si16−y(x = 0.81, y = 6.06)

We present a study of the crystal structure and physical properties of single crystals of a new Fe-based ternary compound, Zr2−xFe4Si16−y(x = 0.81, y = 6.06). Zr1.19Fe4Si9.94 is a layered compound, where stoichiometric β-FeSi2-derived slabs are separated by Zr-Si planes with substantial numbers of vacancies. High resolution transmission electron microscopy (HRTEM) experiments show that these Zr-Si layers consist of 3.5 nm domains where the Zr and Si vacancies are ordered within a supercell sixteen times the volume of the stoichiometric cell. Within these domains, the occupancies of the Zr and Si sites obey symmetry rules that permit only certain compositions, none of which by themselves reproduce the average composition found in x-ray diffraction experiments. Magnetic susceptibility and magnetization measurements reveal a small but appreciable number of magnetic moments that remain freely fluctuating to 1.8 K, while neutron diffraction confirms the absence of bulk magnetic order with a moment of 0.2μB or larger down to 1.5 K. Electrical resistivity measurements find that Zr1.19Fe4Si9.94 is metallic, and the modest value of the Sommerfeld coefficient of the specific heat γ = C/T suggests that quasi-particle masses are not particularly strongly enhanced. The onset of superconductivity at Tc ≃ 6 K results in a partial resistive transition and a small Meissner signal, although a bulk-like transition is found in the specific heat. Sharp peaks in the ac susceptibility signal the interplay of the normal skin depth and the London penetration depth, typical of a system in which nano-sized superconducting grains are separated by a non-superconducting host. Ultra low field differential magnetic susceptibility measurements reveal the presence of a surprisingly large number of trace magnetic and superconducting phases, suggesting that the Zr-Fe-Si ternary system could be a potentially rich source of new bulk superconductors.

FT‐Raman spectroscopic spectra on 3‐phenylpropylamine inclusion compounds

AbstractSome new Hofmann‐3‐phenylpropylamine‐type clathrates with chemical formulae of M(3‐phenylpropylamine)2 Ni(CN)4. 2G (MNi or Co, G = 1,2‐dichlorobenzene or 1,3‐dichlorobenzene) have been prepared and their Fourier transform infrared(FT‐IR; 4000–400 cm−1), far‐infrared (600–100 cm−1) and FT‐Raman (4000–60 cm−1) spectra are reported. The ligand molecule, guest molecules, polymeric sheet and metal‐ligand bands of the clathrates are assigned in detail. The compounds are also characterized by thermal gravimetric analysis (TGA), differential thermal analysis (DTA), elemental analysis and magnetic susceptibility measurements. From the results, the monodentate 3‐phenylpropylamine ligand molecule bonds to the metal atom of |M‐Ni(CN)4 | ∞ polymeric layers in the trans‐gauche‐gauche (TGG) form, and 1,2‐dichlorobenzene or 1,3‐dichlorobenzene molecules are guested by this structure revealing the inclusion ability of the host complexes. Copyright © 2010 John Wiley & Sons, Ltd.

Unusual Meissner state of the superconducting ferromagnet UCoGe revealed by differential susceptibility measurements with a polycrystalline sample

UCoGe is a ferromagnet with a Curie temperature TC∼3K at ambient pressure and superconductivity appears within the ferromagnetic phase with a superconducting transition temperature TSC∼0.8K. We have investigated magnetic properties of the ferromagnetic superconductor UCoGe in superconducting states by the differential susceptibility measurements with a polycrystalline sample. We observed unusual diamagnetic signals for magnetic field dependence of the differential susceptibility in superconducting state. We have revealed the sharp peak for the butterfly-shaped hysteresis loop of ferromagnetism observed even in Meissner state and point out the possible coexistence of ferromagnetism and superconductivity inhomogeneously in real space.

Measurement of the differential susceptibility of soft magnetic ribbons under applied tensile and compressive stress

This paper presents a method which allows the determination of the magnetisation curve of thin ribbons and its stress dependence for both tensile and compressive stress. In the case of the latter, the sample is agglutinated between two polymer sheets to prevent buckling. This sandwich is then mounted in a mechanical set-up, where the stress is applied by means of a spiral spring and a worm drive. The sample is ac magnetized and the flux is measured inductively yielding the stress dependent hysteresis curve as a basis for the determination of the differential susceptibility.

Crystal Structures, Dimorphism and Lithium Mobility of Li7MO6 (M = Bi, Ru, Os)

AbstractLi7MO6 (M = Bi, Ru, Os) have been synthesized by solid state reaction of Li2O with Bi2O3, or MO2 (M = Ru, Os) and characterized using powder X‐ray diffraction, differential scanning calorimetry, magnetic susceptibility (for M = Ru, Os), ionic conductivity and 6Li solid state NMR (for M = Bi) measurements. All three compounds exhibit a temperature induced triclinic – rhombohedral phase transition. Structures of the new low temperature triclinic phases have been refined by the Rietveld method from powder X‐ray data using atomic parameters of Li7TaO6 as a starting model (Li7BiO6: triclinic, $P{\bar 1}$, a = 5.5071(1), b = 6.0425(1), c = 5.5231(1) Å, α = 116.912(1), β = 120.867(1), γ = 62.234(1)°, V = 133.96(1) Å3, Z = 1, T = 230 K; Li7RuO6: triclinic, $P{\bar 1}$, a = 5.3654(1), b = 5.8584(1), c = 5.3496(1) Å, α = 117.182(1), β = 119.117(1), γ = 62.632(1)°, V = 124.43(1) Å3, Z = 1, T = 295 K; Li7OsO6: triclinic, $P{\bar 1}$, a = 5.3786(1), b = 5.8725(1), c = 5.3591(1) Å, α = 117.193(1), β = 119.277(1), γ = 62.700(1)°, V = 125.15(1) Å3, Z = 1, T = 295 K). Upon cooling, Li7RuO6 and Li7OsO6 undergo a magnetic transition at 12 and 13 K, respectively, from the paramagnetic to the antiferromagnetic state. The higher ionic conductivity of Li7BiO6 at T < 300 °C, as compared to Li7RuO6 and Li7OsO6, can be ascribed to the undergoing of the triclinic – rhombohedral transition at a much lower temperature. At T > 300 °C, the ionic conductivity of all three compounds increases sharply due to the melting of the lithium sublattice; for Li7RuO6 and Li7OsO6 the latter effect is superimposed by the phase transitions to the rhombohedral modifications.

Studies on some alkali-phosphate glasses containing antimony and iron oxides

The effect of heat treatment on the Fe 2+/Fe 3+ ratio in some alkali phosphate glasses containing antimony and iron oxides has been investigated. Differential thermal analysis, Mossbauer spectroscopy, magnetic susceptibility and density measurements as well as the molar volume calculations were used in this study. The obtained data indicate that all glasses show approximately unchangeable stability. It is found, from the area under the Mossbauer absorption spectra that ferrous transformed gradually to ferric ions and the transformation rate constant was found to be 48 min −1. The elapsed time was found to be 160 min. This transformation represents a first-order solid state reaction. The molar magnetic susceptibility measurements confirm the above results.

X-Ray Diffraction, Differential Thermal Analysis and Magnetic Susceptibility Measurements on Nominally CuFeCrSe3

X-Ray Diffraction, Differential Thermal Analysis and Magnetic Susceptibility Measurements on Nominally CuFeCrSe3

The Pr(Ba 1− xPr x) 2Cu 3O 7+ δ solid solution. : A crystal structure and phase diagram study

Samples of nominal composition Pr(Ba 1− x Pr x ) 2Cu 3O 7+ δ with −0.15≤ x≤0.6 and Nd(Ba 0.6Nd 0.4) 2Cu 3O 7+ δ were characterized by X-ray powder diffraction combined with Rietveld analysis, differential thermal analysis (DTA), thermogravimetry (TG), and AC susceptibility measurements. Pr(Ba 1− x Pr x ) 2Cu 3O 7+ δ is formed by the peritectic reaction Pr 2CuO 4+L→Pr(Ba 1− x Pr x ) 2Cu 3O 7+ δ at 1060±10°C with x≈0.35 and the homogeneity range extends from x≈0.06 at 975±10°C to x≈0.45 at 1012±10°C which is consistent with the X-ray diffraction results. As for the Nd(Ba 1− x Nd x ) 2Cu 3O 7+ δ solid solution, three distinct domains were found. In the Ba-rich region (0< x<0.15), the structure is tetragonal or orthorhombic depending on oxygen content. On the contrary, the structure of the 1212 phase is always tetragonal in the intermediate region (0.15≤ x≤0.30) and always orthorhombic in the Pr-rich region (0.30< x≤0.45). In addition, the composition range with respect to oxygen is significantly reduced compared to RBa 2Cu 3O 7− δ . The transition from the tetragonal intermediate domain to the orthorhombic Pr-rich domain results in the expected eightfold coordination for Pr atoms on Ba site when the Pr/Ba ratio for this site approaches unity. No evidence of a superstructure was found for either Pr- or Nd-containing 1212 phases.

Cu 2(1 − z) Mn zln 2Se 4 alloys; phase diagram and effects of Mn ordering on magnetic behaviour

X-ray powder diffraction, differential thermal analysis and magnetic susceptibility measurements on polycrystalline samples were used to determine the details of the T( z) phase diagram of the alloy system Cu 2(1 − z) Mn z ln 2Se 4. At room temperature, the terminal solid solutions extend over the ranges 0 < z < 0.30 and 0.90 < 1.0. Values of Curie-Weiss θ from magnetic susceptibility data were determined for single phase samples in each range and used to determine the ordering of the Mn in each case. The magnetic data indicate that for 0 < z < 0.30 and T > 200 °C, the Mn is randomly distributed over the cation sublattice, the phase having space group 142d. However, at lower temperatures, for 0.05 < z < 0.30, the Mn atoms order to occupy only the 4a sites resulting in probable antiferromagnetic behaviour. The high z alloys all show a random distribution of Mn on the cation sties, and the compound Mnln 2Se 4 ( z = 1.0) was found to be spinglass, with T g = 2.7 K and θ = −94 K.

Magnetism in the series (FexMn1−x)5(PO4)2(PO4H)2(H2O)4

Differential magnetic susceptibility measurements in synthetic polycrystals of the hureaulite series (FexMn1−x)5(PO4)2(PO4H)2(H2O)4 (0 ≤ x ≤ 1) are reported for the first time. Its structure consists essentially of a condensation of pentamers formed by distorted edge-sharing octahedra whose centres are occupied by Mn2+ or Fe2+ ions and disposed in three different crystallographic sites in the proportion (III):(II):(I) = 2:2:1. The results from high temperature susceptibility measurements show an effective magnetic moment ranging from 11.89 to 13.53 μB/f.u., suggesting that the spins in the pentamers are all parallel except one, which was attributed to the central one, that would have its spin reversed. The compound with x = 1 (ferrous compound) behaves as a normal canted antiferromagnet down to the Néel temperature, 12.7 K. Below this temperature the susceptibility tends to zero with the temperature. It was shown that the replacement of Fe2+ by Mn2+ introduces ferromagnetic correlations in the neighbourhood of the critical temperature due to anisotropic exchange interactions (weak ferromagnetism). The compound for x = 0 (manganous compound) is a weak ferromagnet with Néel temperature of 6.0 K. It was also observed that for x ≤ 0.40 a second phase transition begins to appear due, possibly, to a rearrangement of spins.

Synthesis and phase characterization of the intermetallic compounds Ln(Pt,Au) 2+δB 2C, where Ln = La, Pr, Nd, Dy and Y

The new superconducting intermetallic compounds Ln(Pt,Au) 2+δB 2C, where Ln = La, Pr and Y, as well as non-superconducting compounds with Ln = Nd and Dy have been studied in detail with regard to preparation conditions, microstructure and superconducting or magnetic properties. To this purpose X-ray diffraction, scanning electron microscopy with EDX/WDX for local element analysis, differential thermal analysis and AC susceptibility measurements have been employed. The appropriate arc-melting synthesis conditions, that lead to reproducible good-quality samples, have been optimized by varying the boron and carbon contents in the vicinity of the nominal composition LnPt 1.5Au 0.6B 2C. The best samples show the onset of the superconducting transition at 11 K, 6.5 K and 11 K for La, Pr and Y, and magnetic ordering at 9.6 K and 5.9 K for Nd and Dy, respectively. The local phase analysis of the superconducting phase yields practically no gold, resulting in an overall composition very close to LnPt 2.1B 2C. A sample prepared without any gold substitution for platinum showed similar superconducting properties as the ones with gold. This indicates that gold is principally unnecessary for the synthesis of the platinum-based borocarbides and that the nonmetallic elements play an essential role in the phase formation of these compounds.

The London penetration depth λ ab evolution with T c in the TI-2201 overdoped superconductor

The Cu-O monolayer Tl 2Ba 2CuO 6±δ is known to be an overdoped cuprate and T c is controlled by the oxygen off-stoechiometry parameter δ. Samples with T c ranging from ∼ 40K to 92K for orthorhombic and tetragonal phases have been prepared and systematically investigated by magnetization and differential susceptibility measurements in the reversible regime. This allows the deduction of the in-plane London penetration depth λ ab. We show the evolution of λ ab with T c which does not fall on the Uemura plot established for the underdoped high T c superconductors.

Structural transitions in a TiNiFe shape memory alloy

Results for resistance versus temperature, differential scanning calorimetry (DSC), Mössbauer spectroscopy, and magnetic susceptibility measurements in a Ti 50Ni 47Fe 3 sample are presented. The resistance versus temperature curve shows a sharp increase at 245K and then rises slowly until a maximum is attained at ∼150K. The DSC curve also exhibits a peak at the former temperature. The room temperature Mössbauer spectrum consists of a single line. As the temperature is lowered to 270K, a small asymmetric quadrupole doublet appears. The isomer shift and quadrupole splitting values of this doublet increase with decreasing temperature until almost constant values are achieved at temperatures ∼100K. The magnetic susceptibility curve shows a sharp decrease that begins at 255K and then an unexpected increase at 90K. We relate these observations with a charge density wave-driven premartensitic transition in this system, and with the final martensitic phase.

Synthesis and decomposition of ferrous oxalato hydrazinate precursors to obtain magnetic oxides

The preparation of γ-Fe2O3 from the thermal decomposition of ferrous oxalate dihydrate and ferrous oxalato hydrazinate precursors was studied employing differential thermal analysis (DTA), X-ray diffraction (XRD), infrared and magnetic susceptibility measurements. Ferrous oxalate dihydrate was precipitated from solution following the standard precipitation technique. The synthesis of ferrous oxalato hydrazinate was carried out by two methods. The wet chemical method reported in the literature was adopted to precipitate the compound from ferrous chloride solution. In the second method ferrous oxalate dihydrate was equilibrated with hydrazine hydrate vapour in a desiccator. The resultant product was found to be anhydrous ferrous oxalato hydrazinate. The decomposition end-products of these complexes were X-ray characterized and magnetic measurements were done. Ferrous oxalate dihydrate yielded mainly γ-Fe2O3 upon controlling the atmosphere during decomposition. However, autocatalytic decomposition of hydrazinated complexes formed a mixture of γ-Fe2O3 and α-Fe2O3. Efforts were made to increase the γ-Fe2O3 content by controlling the atmosphere during decomposition of these complexes.

Hyperfine field and reentrant spin glass behavior in amorphous LuFe alloys

Temperature dependence of the differential susceptibility and of Mössbauer spectra has been investigated for high Fe concentrated amorphous LuFe alloys. Amorphous Lu x Fe 100− x ( x = 10.5, 15, 20.7) alloys show cusps at the Curie temperature T c and the spin freezing temperature T f and a broad peak at the spin-canting temperature T g. The average hyperfine field H ̄ hf of the morphous Lu 20.7Fe 79.3 alloy was found to increase with decreasing temperature below T c = 180 K. An additional increase in H ̄ hf was observed below the spin-canting temperature T g= 60 K, being consistent with the results of the differential susceptibility measurements. The Mössbauer spectra were analyzed by both conventional and modified Hess-Rübartsch methods. The results obtained by the latter for the amorphous Lu 20.7Fe 79.3 alloy show no anti-ferromagnetic component in the hyperfine fields.

Magnetization of electron spin pairs in a free radical at low temperatures in a high magnetic field

Differential susceptibility measurements in pulsed magnetic fields up to 25 T in the spin system of orthorhombic DPPH were performed at liquid helium temperatures. The results can be very well described by a Gaussian distribution for the intra-pair interaction strength which is interpreted as fluctuations in the vibrational ground state of the molecules.