Diamagnetic and Electrical Properties of Si x Mo2S3−x (x=0.1, 0.2, 0.33, 0.5) and A0.1Mo2S3−x (A=C, B, and Ru)

Mo₂S₃ doped with Si, C, B, and Ru, is identified to bear the same crystalline structure P2₁/m as that of Mo₂S₃ through XRD analysis. Diamagnetic transitions with χ _m ～10^?4 emu/g?Oe at temperature ranging from 2 K to 6 K were observed in the doped samples of Si _x Mo₂S_3?x (x=0.1, 0.2, 0.33, 0.5). And both of the x=0.2 and 0.5 samples were found to have double diamagnetic transitions with higher T _c at the same temperature of 6.01 K, while Si _x Mo₂S_3?x of x=0.33 displayed an extra ferromagnetic-like response at 63 K. The corresponding transition in resistivity of Si _x Mo₂S_3?x with x=0.1 was noticed to show a mild drop with less than 10 % of its original transition values as measured down to 2 K. But a superconducting-like magnetic field dependence on the phase transition of resistivity was also noted. Its diamagnetic signals were greatly reduced when the applied magnetic fields were raised to 10³ Oes. In the doped samples of A_0.1Mo₂S_2.9 (A=C, B, and Ru), the phase transition in resistivity at 4.08 K, 4.62 K, and 4.35 K, respectively, exhibited similar fashion as that in the case of Si_0.1Mo₂S_2.9.     

Dielectric and optical properties of TlGa1 − x Er x S2 (x = 0, 0.001, 0.005, 0.01) single crystals

TlGa_{1 ? x} Er _x S₂ (x = 0, 0.001, 0.005, 0.01) solid solutions, based on the layered compound TlGaS₂, have been prepared by direct elemental synthesis. The effect of Er concentration on the dielectric and optical properties of the TlGa_{1 ? x} Er _x S₂ solid solutions has been studied. The results demonstrate that increasing the Er content of the TlGa_{1 ? x} Er _x S₂ solid solutions decreases the real part of their complex dielectric permittivity and increases their dielectric loss tangent. The conductivity (σ) of the TlGa_{1 ? x} Er _x S₂ solid solutions in the frequency range f = 1 to 35 MHz exhibits σ ～ f ^0.8 behavior, indicative of hopping charge transport through their band gap. We have evaluated the key parameters of this charge transport mechanism. We have studied temperature-dependent optical properties of the TlGa_{1 ? x} Er _x S₂ solid solutions. At temperatures in the range T = 77–200 K, the TlGa_0.999Er_0.001S₂ solid solution has an absorption band near its fundamental absorption edge, which is due to transitions to a direct exciton state.     

Structural, Electronic and Magnetic Properties of Zinc-Blende Ga1−x TM x N (TM = Cr, Mn, Fe, V)

In this paper, we present a theoretical study of structural, electronic and magnetic properties for zinc-blende Ga_1?x TM _x N(TM = Cr, Fe, Mn, V) using the full-potential augmented plane wave (FP-APW) method with local-spin density approximation (LSDA). We have analysed the dependence of structural parameters values on the composition x in the range of x=0.25, x=0.50. Also, the role of p–d hybridisation is analysed by partial (PDOS) and total density of states (TDOS). The magnetic moment of Ga_1?x TM _x N has been studied by increasing the concentration of TM atom. The TM atom is the most important source of the total magnetic moment in these alloys, while the contributions from Ga and N are minor. In addition our results verify the half-metallic ferromagnetic character of TM doped GaN.     

Magnetic and Charge-Ordering Properties of Bi0.2?x Pr x Ca0.8MnO3 (0.0=x=0.20) Perovskite Manganite

We have studied structure, magnetic and transport properties of polycrystalline samples synthesized with nominal compositions Bi_0.2?x Pr _x Ca_0.8MnO₃ (x=0.00, 0.02, 0.04, 0.08, 0.12, 0.16 and 0.20) via a solid-state reaction route. Magnetic measurements show that substitution of Pr at Bi site strongly affect the magnetic and charge-ordering properties. It has been found that the charge-ordering temperature (T _CO) decreases with increasing x up to x=0.12 and then after it increases with x up to x=0.20. A spin glass (SG) state has been observed at ??105 K in all the samples. Pr doping also leads to enhancement in the magnetic moment up to x=0.12 and then after a decrease in magnetic moment up to x=0.20. A concomitant increase in resistivity up to x=0.04 and then decrease in resistivity up to x=0.20 is also observed. We propose that the local lattice distortion induced by the size mismatch between the A-site cations and 6s² character of Bi³⁺ lone pair electron are responsible for the observed variation in the physical properties with doping content of Pr.     

Fluctuation Conductivity of RE1−2x Ca x M x Ba2Cu3O7−δ (RE=Nd,Y and M=Pr,Th) Superconductors

Polycrystalline samples of RE_1?2x Ca _x M _x Ba₂Cu₃O_7?δ with RE=Nd, Y and M=Pr, Th (with 0.0≤x≤0.10), superconductors were prepared by the standard solid-state method. Resistivity was measured as a function of temperature and doping concentration x. Excess conductivity was analyzed using the modified Lawrence-Doniach (LD) expressions. The fluctuation regions, crossover temperatures, coherence lengths, and effective layer thickness were obtained and the values were compared for both samples. For both samples, it was found that with increasing doping, the crossover temperatures were reduced, while the coherence length decreased. The upper critical field and critical current density were increased with increasing doping concentration due to the introduction of disorder and the enhancement of flux pinning by charge neutral doping. Furthermore, the coherence lengths of the Nd-based samples are larger than that for the Y-based samples by a factor 2. It was found that the value of critical current density in Nd(CaPr)-123 is higher than Y(CaTh)-123, from which it is suggested that CaPr doping is more effective than CaTh doping.     

Local Atomic and Electronic Structure with Magnetism of La0.7Ca0.3Mn1?x Cu x O3 (x=0, 0.03, 0.06, 0.1)

Local atomic and electronic structure with magnetic properties, especially Griffiths phase, of polycrystalline samples La_0.7Ca_0.3Mn_1?x Cu _x O₃ (x=0, 0.03, 0.06, 0.1) have been studied. The X-ray absorption spectra (XAS) of Cu 2p core level prove that the valence state of Cu ions exhibits trivalent state when doping content x≤0.06 and divalent Cu²⁺ ions begin to show for x=0.1. For the valence states of Mn ions, the X-ray photoelectron spectroscopy data show that they are in mixed states of Mn³⁺ and?Mn⁴⁺, and a shift to lower binding energy is observed, which is not attributed to the variation of valence states of Mn ions but the change of crystallographic surroundings, because there is no obvious change detected by X-ray absorption fine structure spectroscopy (XAFS). The Debye-Waller factor (σ ²) of x=0.1 sample is only slightly larger compared to x=0, which may be the origin of enhancement of Griffiths phase observed in the inverse-susceptibility as a function of temperature (H/M～T). The H/M～T curves of Cu doped samples indicate coexistence of FM, AFM and PM phase above Curie temperature?T _C , which may be related to the strong hybridization of O 2p and Mn 3d reflected by O 1s XAS spectra.     

The Influence of Vanadium on Magnetism and Magnetocaloric Properties of Fe 8 0 − x V x B12Si8 (x = 8, 10, and 13.7) Amorphous Alloys

Amorphous soft magnetic Fe_80?x V _x B₁₂Si₈ ribbons (0 ≤ x ≤ 14) have been fabricated by melt spinning technique, and their magnetic and magnetocaloric properties have been studied. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. The addition of vanadium to the ternary Fe₈₀B₁₂Si₈ alloy results in a decrease of the Curie temperature of amorphous alloys, T _C, from 473.5 to 335 K. With an increasing V content, the average magnetic moment of Fe atom and the magnetic entropy change also decrease. Fe_66.3V_13.7B₁₂Si₈ alloy exhibits the highest refrigeration capacity of 93.7 J kg^?1 and moderate peak magnetic entropy of 1.034 J kg^?1 K^?1 (T _C = 335 K) under the maximum applied field of 2 T. The results from this work showed that V containing amorphous alloy 13.7 at. % is an interesting material and potential candidate for magnetic refrigerants working near room temperature. The observed ?ΔS_M ^max values compare favorably with other amorphous Fe-based alloys.     

Mössbauer spectroscopic studies of the crystallization of amorphous Fe80B20−x Si x (x=0, 2, and 8) alloys

The crystallization process of amorphous Fe₈₀B_20–x Si _x (x=0, 2, and 8) ferromagnetic alloys has been studied by using ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction studies. Results for samples heat treated at different temperatures for different times show that the crystallization of Fe₈₀B_20–x Si _x samples having x=0 and 2 leads to -Fe and t-Fe₃B, while for x=8, it leads to -Fe, t-Fe₂B, and perhaps Fe-Si. It is further observed that the addition of silicon to the Fe-B system improves the thermal stability of the system.     

The thermal conductivity and Lorenz function of the tin-lead alloy system Sn x Pb1 − x (x = 0.85, 0.7 0.5 0.3)

The thermal conductivity and electrical resistivity of the tin-lead alloy system Sn _x Pb_{1 – x} (x = 0.85, 0.7 0.5 0.3) were measured in the temperature range 7–300 K. The thermal conductivity was analyzed at temperature T 20K, assuming 1//T+Tⁿ, where , , and n are constants. The analysis shows that n < 2, and not n 2, which would be expected for a normal pure metal. The electrical resistivities could be represented by a T ⁵ relation for temperatures up to about 60 K. The characteristic temperature _R appears to decrease with increasing weight percent of lead. The total Lorenz functions were high, indicating the presence of phonon conductivity. The phonon conductivity _g appears to vary with T, and can be represented by _g=a/Tⁿ (a > 0) and n2.Work supported by the Universiti Sains Malaysia.     

Structural and Magnetic Studies of Ca2?x Sm x MnO Compounds (x=0–0.4)

The Ca_2?x Sm _x MnO₄ (x=0?C0.4) compounds were synthesized by a solid?Csolid method and characterized by XRD at room temperature. The XRD profiles were indexed with a tetragonal structure (I/4mmm space group) for x??0.3 and orthorhombic one (Pnma space group) for x=0.4. The magnetic measurements were studied as a function of temperature (T=2?C300?K) and applied field (?? ₀ H=0?C10?T). When the temperature decreases, each compound has shown first a ferromagnetic?Cparamagnetic (FM?CPM) transition and then an antiferromagnetic?Cferromagnetic (AFM?CFM) one. The transition temperatures are found to be Sm-doping dependent. For all compounds, a spin-glass phenomenon is evidenced by FC/ZFC magnetization curves.     

Synthesis, Crystal Growth, and Acoustophotovoltaic Effect of TlIn1 – x Pr x Se2 and TlIn1 – x Pr x Te2

Procedures were developed for growing perfect TlIn_{1 – x} Pr _x Se₂ and TlIn_{1 – x} Pr _x Te₂ (0 x 0.08) single crystals. The growth charges were synthesized by a process involving partial cooling of a tilted, rotating tube. The crystals grown by the floating zone technique were found to readily cleave in two, mutually perpendicular mirror planes to give rectangular parallelepipeds. The crystals were shown to exhibit a sizeable acoustophotovoltaic effect: a combined action of radiation and sound waves produced an emf between the electrodes or a short-circuit current.     

Structural, transport, magnetic, and dielectric properties of La1−x Te x MnO3 (x = 0.10 and 0.15)

In this study, we have investigated the structure, temperature-dependent resistivity, magnetization, and dielectric properties of La_1?x Te _x MnO_3±δ (x = 0.10 and 0.15). X-ray diffraction analysis confirms the rhombohedral crystal symmetry with space group R $ \overline{3} $ c. For both the samples, the temperature dependence of magnetization plots show paramagnetic-to-ferromagnetic phase transition. The Curie temperature (T _c) and magnitude of magnetization increase with the Te concentration. Field-dependent magnetization produces the asymmetric hysteresis loop that has been attributed to the magneto crystalline anisotropy induced by lattice distortion and the rare earth spin coupling at room temperature. Temperature-dependent resistivity plots exhibit metal–insulator transition (MIT) and charge-ordering state. These plots have been fitted using variable range hopping model, and the density of states [N(E_F)] has been estimated. Magnetoresistance is measured as a function of temperature in the field of 1T, 5T, and 8T. The dielectric constant shows an anomaly near MIT. The dielectric constant exhibits a peaking behavior with the applied frequency and the temperature dependence of dielectric constant attains colossal values at high temperatures.     

Electrical resistivity and Seebeck coefficient of La1−x M x MnO3 (M = Ca,Sr) single crystals

The temperature dependence of the electrical resistivity and Seebeck coefficient was measured on single crystals of La_1–x Ca _x MnO₃(0 <x 0.3) and La_1–x Sr _x MnO 3 (0 <x 0.4) grown by the arc-image floating zone method. The electrical conduction for La_1–x crystals withx 0.2 was of the activation type aboveT _c and of the degenerate type belowT _c, while that for the crystal withx = 0.1 was of the activation type over the whole measured temperature range between –170 and 400°C. The conduction behaviour of La_{1– x} Sr _x MnO₃ was essentially the same as that of La_1–x Ca _x MnO₃ except that the conduction of the crystals withx = 0.3 and 0.4 was of the degenerate type aboveT _c. A distinct difference in Seebeck data was observed between the calcium and the strontium compounds.     

Low Temperature Giant Magnetocaloric Effect and Critical Behavior in Amorphous Co100−xEr x (x = 55, 65) Alloys

We report on the magnetic properties, magnetocaloric effect (MCE) and critical exponents in amorphous Co_100?xEr _x (x = 55 and 65), prepared by liquid quenching technique. The transition temperature from ferromagnetic to paramagnetic state has been evaluated according to M(T) measurements, and it is found to be 26 and 15 K for Co₄₅Er₅₅ and Co₃₅Er₆₅, respectively. The magnetization dependence M(H, T) on the temperature T and magnetic field H was measured carefully in the critical region. Magnetic entropy change (– ΔS _M ) allowing estimation of the MCE was determined based on thermodynamic Maxwell’s relation. The magnetocaloric study exposes a quite large value of the magnetic entropy change, which decreases when increasing Er concentration. For an applied magnetic field of 5 T,the values of (– ΔS _Max) peak are about 10.8 and 9.8 J kg ^?1 K ^?1 for Co₄₅Er₅₅ and Co₃₅Er₆₅, respectively. From the field dependence of the magnetic entropy ΔS _M (ΔS _M α H ⁿ ) and the relative cooling power (RCP) (RCP α H ^1+1/δ), it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method.     

Magnetically Recyclable Spinel Mn x Ni1−x Fe2 O 4 (x= 0.0–0.5) Nano-photocatalysts: Structural,Morphological and Opto-magnetic Properties

Manganese doped nickel ferrite (Mn _x Ni_1?x Fe₂ O ₄: x = 0.0–0.5) spinel nanoparticles (NPs) were successfully prepared by a facile microwave combustion method (MCM) using urea as the fuel. The prepared samples were characterized by different techniques. Powder X-ray diffraction (XRD) analysis was confirmed the formation of a single-phase NiFe₂ O ₄ spinel structure. The average crystallite sizes of the samples were in the range of 11.49 to 17.24 nm, which was confirmed by Sherrer’s formula. The morphology of the samples showed a nanoparticle-like structure with smaller agglomeration, which was confirmed by high-resolution scanning electron microscopy (HR-SEM). The particle size diameter ranges from 15 to 20 nm, which was confirmed by high-resolution transmission electron microscopy (HR-TEM). Energy dispersive X-ray (EDX) analysis confirmed the elemental composition, which was also evidence for the formation of single pure phase. Selected area electron diffraction (SAED) analysis showed well crystalline nature. UV-visible diffuse reflectance spectra (DRS) and photoluminescence (PL) spectrum analysis was used to calculate the optical band gap, and the values are slightly increased (2.02 to 2.42 eV) with increasing the Mn-dopant, due to the decreasing of particle size, which may be due to the quantum confinement effect. Magnetic properties of the samples were analyzed by vibrating sample magnetometer (VSM) technique, which showed the magnetization (M _s ) value of the samples are increased with increasing Mn content and reach a maximum value of 67.82 emu/g for Mn_0.5Ni_0.5Fe₂ O ₄ sample. Photo-catalytic activity of the samples was measured and showed the photocatalytic degradation (PCD) of methylene blue dye with good results. The catalyst was magnetically recycled and reused five consecutive cycles and showed good reproducibility without change of catalytic activity.     

Effective Electron Correlation and Spin Density Fluctuation in Iron-Based Fluorides SrFe1?x Co x AsF (x=0,0.125)

Using first-principles calculation, we study effective electron correlation and spin density fluctuation in iron-based fluorides SrFe_1?x Co _x AsF (x=0, 0.125). We obtain the observed magnetic moment of Fe atom with a strongly attractive electron correction. Whereas, different from the parent compound, the density of state of superconducting SrFe_1?x Co _x AsF (x=0.125) near to the Fermi energy is reduced for both signs of effective electron correlation, and suggests strong instability there. In addition, spin density fluctuation resulted from the effective correlation exists in Co-doped compound, may propagate in the form of collective excitation and manifest as spin fluctuation with specific q-vector in momentum space.