共查询到20条相似文献,搜索用时 46 毫秒
1.
Mazhar Iqbal Muhammad Nasir Khan Ayaz Arif Khan Imran Zaka Amjad Mehmood Ikhtiar Ahmad 《Journal of Superconductivity and Novel Magnetism》2018,31(11):3535-3544
We present an extensive study of the magnetic properties of a novel La0.5Ba0.5MnO3 perovskite material prepared by the hydrothermal method. The explored sample was structurally studied by the x-ray diffraction (XRD) method which confirms the formation of a pure cubic phase of a perovskite structure with Pm3m space group. The magnetic properties were probed by employing temperature M (T) and external magnetic field M (μoH) dependence of magnetization measurements. A magnetic phase transition from ferromagnetic to paramagnetic phase occurs at 339 K in this sample. The maximum magnetic entropy change (\(\left | {{\Delta } S}_{M}^{\max } \right |\)) took a value of 1.4 J kg??1 K??1 at the applied magnetic field of 4.0 T for the explored sample and has also been found to occur at Curie temperature (TC). This large entropy change might be instigated from the abrupt reduction of magnetization at TC. The magnetocaloric effect (MCE) is maximum at TC as represented by M (μoH) isotherms. The relative cooling power (RCP) is 243.2 J kg??1 at μoH =?4.0 T. Moreover, the critical properties near TC have been probed from magnetic data. The critical exponents δ, β, and γ with values 3.82, 0.42, and 1.2 are close to the values predicted by the 3D Ising model. Additionally, the authenticity of the critical exponents has been confirmed by the scaling equation of state and all data fall on two separate branches, one for T < TC and the other for T > TC, signifying that the critical exponents obtained in this work are accurate. 相似文献
2.
We study the magnetic field vs. temperature (H – T) and pressure vs. temperature (P – T) phase diagrams of the T c ≈ 5.5 K superconducting phase in Pd x Bi2Te3 (x ≈ 1) using electrical resistivity versus temperature measurements at various applied magnetic fields (H) and magnetic susceptibility versus temperature measurements at various applied magnetic fields (H) and pressure (P). The H – T phase diagram has an initial upward curvature as observed in some unconventional superconductors. The critical field extrapolated to T = 0 K is H c (0) ≈ 6–10 kOe. The T c is suppressed approximately linearly with pressure at a rate d T c /d P ≈ ?0.28 K/GPa. 相似文献
3.
Intikhab A. Ansari V. P. S. Awana Rajeev Rawat M. Shahabuddin M. Husain H. Kishan A. V. Narlikar 《Journal of Materials Science》2007,42(15):6306-6309
We report fluctuation-induced conductivity (FIC) of the polycrystalline MgB2 superconductor in the presence of magnetic field. The results are described in terms of the temperature derivative of the resistivity, dρ/dT. The dρ/dT peak temperature observed for H = 0 Tesla at 39 K remains very distinct under applied fields of 6 Tesla and 8 Tesla at 22 and 20 K respectively. Aslamazov and Larkin (AL) equations are used to explain the anisotropic nature of the polycrystalline MgB2. The effective coherence length, ξ p (0) determined experimentally is 55.17 Å, which roughly matches with previously reported experimental work. 相似文献
4.
T. E. Kuzmicheva V. A. Vlasenko S. Yu. Gavrilkin S. A. Kuzmichev K. S. Pervakov I. V. Roshchina V. M. Pudalov 《Journal of Superconductivity and Novel Magnetism》2016,29(12):3059-3064
We studied nearly optimally Ni-substituted BaFe2?x Ni x As2 (BFNA) single crystals with T C ≈ 18.5 K. In irreversible magnetization measurements, we determined the field dependence of the critical current density and discuss the nature of observed strong bulk pinning. Using intrinsic multiple Andreev reflections effect (IMARE) spectroscopy, we directly determine two distinct superconducting gaps and resolve their moderate anisotropy in the momentum space. The BCS-ratio for the large gap 2Δ L /k B T C > 4.1 evidences for a strong coupling in the Δ L -bands. 相似文献
5.
Mohamed Baazaoui Sobhi Hcini Michel Boudard Sadok Zemni Mohamed Oumezzine 《Journal of Superconductivity and Novel Magnetism》2015,28(7):1887-1893
The critical behavior of perovskite manganite La0.67Ba0.33Mn0.95Fe0.05O3 at the ferromagnetic–paramagnetic has been analyzed. The results show that the sample exhibited the second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various such as modified d’Arrott plot Kouvel–Fisher method and critical magnetization M(T C, H). The critical exponents values for the La0.67Ba0.33Mn0.95Fe0.05O3 are close to those expected from the mean field model β = 0.504 ± 0.01 with T C = 275661 ± 0.447 (from the temperature dependence of the spontaneous magnetization below T C ), γ = 1.013 ± 0.017 with T C = 276132 ± 0.452 (from the temperature dependence of the inverse initial susceptibility above T C ), and δ = 3.0403 ± 0.0003. Moreover, the critical exponents also obey the single scaling equation of M(H, ε) = |ε| β f ±(H/|ε| β+γ ). 相似文献
6.
Martin Nikolo Vivien S. Zapf John Singleton Jianyi Jiang Jeremy D. Weiss Eric E. Hellstrom 《Journal of Superconductivity and Novel Magnetism》2016,29(11):2745-2752
Vortex dynamics and nonlinear ac response are studied in a Ba(Fe0.94 Ni0.06)2As2(T c = 18.5 K) bulk superconductor in magnetic fields up to 12 T via ac susceptibility measurements of the first ten harmonics. A comprehensive study of the ac magnetic susceptibility and its first ten harmonics finds shifts to higher temperatures with increasing ac measurement frequencies (10 to 10,000 Hz) for a wide range of ac (1, 5, and 10 Oe) and dc fields (0 to 12 T). The characteristic measurement time constant t 1 is extracted from the exponential fit of the data and linked to vortex relaxation. The Anderson-Kim Arrhenius law is applied to determine flux activation energy E a /k as a function dc magnetic field. The de-pinning, or irreversibility lines, were determined by a variety of methods and extensively mapped. The ac response shows surprisingly weak higher harmonic components, suggesting weak nonlinear behavior. Our data does not support the Fisher model; we do not see an abrupt vortex glass to vortex liquid transition and the resistivity does not drop to zero, although it appears to approach zero exponentially. 相似文献
7.
Jianming Zhan Lin Li Tingting Wang Jialu Wang Yihong Chen Li Zhang Jingqin Shen Peigang Li Yuke Li 《Journal of Superconductivity and Novel Magnetism》2017,30(2):305-309
Through the measurement of resistivity, magnetic susceptibility, and Hall effect, we discovered a novel BiSe2-based superconductor Ca0.5La0.5FBiSe2 with T c of 3.9 K. A strong diamagnetic signal below T c in susceptibility χ(T) is observed indicating the bulk superconductivity. The negative Hall coefficient throughout the whole temperature regime implies the dominant electron-type carriers in the sample. Different to most of BiS2-based compounds where superconductivity develops from a semiconducting-like normal state, its resistivity in the present compound exhibits a metallic behavior down to T c . Together with the enhanced T c , the metallic character of the normal state implies that the electronic structure of Ca0.5La0.5FBiSe2 may be different to those in the other BiS2-based compounds. 相似文献
8.
Geet Awana Rabia Sultana P. K. Maheshwari Reena Goyal Bhasker Gahtori Anurag Gupta V. P. S. Awana 《Journal of Superconductivity and Novel Magnetism》2017,30(4):853-856
In this letter, we report on the growth and characterization of bulk Bi 2Se 3 single crystals. The studied Bi 2Se 3 crystals are grown by the self-flux method through the solid-state reaction from high-temperature (950 °C) melt of constituent elements and slow cooling (2 ℃/h). The resultant crystals are shiny and grown in the [00l] direction, as evidenced from surface XRD. Detailed Reitveld analysis of powder X-ray diffraction (PXRD) of the crystals showed that these are crystallized in the rhombohedral crystal structure with a space group of R3m (D5), and the lattice parameters are a = 4.14 (2), b = 4.14 (2), and c = 28.7010 (7) Å. Temperature versus resistivity (ρ?T) plots revealed metallic conduction down to 2 K, with typical room temperature resistivity (ρ 300 K) of around 0.53 m Ω-cm and residual resistivity (ρ 0 K) of 0.12 m Ω-cm. Resistivity under magnetic field [ ρ(T)H] measurements exhibited large + ve magneto-resistance right from 2 to 200 K. Isothermal magneto-resistance [ ρH] measurements at 2, 100, and 200 K exhibited magneto-resistance (MR) of up to 240 %, 130 %, and 60 %, respectively, at 14 T. Further, the MR plots are nonsaturating and linear with the field at all temperatures. At 2 K, the MR plots showed clear quantum oscillations at above say 10 T applied field. Also, the Kohler plots, i.e., Δρ/ ρ oversus B/ ρ, were seen consolidating on one plot. Interestingly, the studied Bi 2Se 3 single crystal exhibited the Shubnikov-de Haas (SdH) oscillations at 2 K under different applied magnetic fields ranging from 4 to 14 T. 相似文献
9.
L. T. Denisova L. A. Irtyugo Yu. F. Kargin N. V. Belousova V. V. Beletskii V. M. Denisov 《Inorganic Materials》2018,54(4):361-365
The Dy2Ge2O7 and Ho2Ge2O7 pyrogermanates have been prepared by solid-state reactions in several sequential firing steps in the temperature range 1237–1473 K using stoichiometric mixtures of Dy2O3 (or Ho2O3) and GeO2. The heat capacity of the synthesized germanates has been determined as a function of temperature by differential scanning calorimetry in the range 350–1000 K. The experimentally determined C p (T) curves of the dysprosium and holmium germanates have no anomalies and are well represented by the Maier–Kelley equation. The experimental C p (T) data have been used to evaluate the thermodynamic functions of the Dy2Ge2O7 and Ho2Ge2O7 pyrogermanates: enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(T). 相似文献
10.
L. T. Denisova L. A. Irtyugo Yu. F. Kargin V. V. Beletskii V. M. Denisov 《Inorganic Materials》2016,52(6):584-586
Gd2Sn2O7 gadolinium stannate with the pyrochlore structure has been prepared by solid-state reaction and its high-temperature heat capacity has been determined by differential scanning calorimetry in the temperature range 350–1020 K. The Cp(T) data are shown to be well represented by the classic Maier–Kelley equation. The experimental Cp(T) data have been used to evaluate the thermodynamic functions of gadolinium stannate: enthalpy increment H°(T)–H°(339 K), entropy change S°(T)–S°(339 K), and reduced Gibbs energy Ф°(Т). 相似文献
11.
We report bulk superconductivity at 2.5 K in LaO0.5F0.5BiSe2 compound through the DC magnetic susceptibility and electrical resistivity measurements. The synthesized LaO0.5F0.5BiSe2 compound is crystallized in tetragonal structure with space group P4/nmm and Reitveld refined lattice parameters are a = 4.15(1) Å and c = 14.02(2) Å. The lower critical field of H c1 = 40 Oe, at temperature 2 K is estimated through the low field magnetization measurements. The LaO0.5F0.5BiSe2 compound showed metallic normal state electrical resistivity with residual resistivity value of 1.35 m Ω cm. The compound is a type-II superconductor, and the estimated H c2(0) value obtained by WHH formula is above 20 kOe for 90 % ρ n criteria. The superconducting transition temperature decreases with applied pressure till around 1.68 GPa and with further higher pressures a high- T c phase emerges with possible onset T c of above 5 K for 2.5 GPa. 相似文献
12.
Mohamed Hsini Sobhi Hcini Sadok Zemni 《Journal of Superconductivity and Novel Magnetism》2018,31(1):81-87
Magnetic entropy change (?ΔS M ) of Nd0.67 Ba0.33Mn0.98Fe0.02O3 perovskite have been analyzed by means of theoretical models. An excellent agreement has been found between the (ΔSM) values estimated by Landau theory and those obtained using the classical Maxwell relation. In order to estimate the spontaneous magnetization M s pont(T), we used the mean-field theory to analyses the (ΔSM) vs. M 2 data. The obtained M s pont(T) values are in good agreement with those found from the classical extrapolation from the Arrott plots(H/M vs. M 2), confirming that the magnetic entropy is a valid approach to estimate the spontaneous magnetization in our system. At a relatively low magnetic field, a phenomenological model has been used to estimate the values of the magnetic entropy change. The results are in good agreement with those obtained from the experimental data using Maxwell relation. 相似文献
13.
We report the results of magnetic, magnetocaloric properties, and critical behavior investigation of the double-layered perovskite manganite La1.4(Sr0.95Ca0.05)1.6Mn2O7. The compounds exhibits a paramagnetic (PM) to ferromagnetic (FM) transition at the Curie temperature T C = 248 K, a Neel transition at T N = 180 K, and a spin glass behavior below 150 K. To probe the magnetic interactions responsible for the magnetic transitions, we performed a critical exponent analysis in the vicinity of the FM–PM transition range. Magnetic entropy change (??S M) was estimated from isothermal magnetization data. The critical exponents β and γ, determined by analyzing the Arrott plots, are found to be T C = 248 K, β = 0.594, γ = 1.048, and δ = 2.764. These values for the critical exponents are close to the mean-field values. In order to estimate the spontaneous magnetization M S(T) at a given temperature, we use a process based on the analysis, in the mean-field theory, of the magnetic entropy change (??S M) versus the magnetization data. An excellent agreement is found between the spontaneous magnetization determined from the entropy change [(??S M) vs. M 2] and the classical extrapolation from the Arrott curves (µ0H/M vs. M 2), thus confirming that the magnetic entropy is a valid approach to estimate the spontaneous magnetization in this system and in other compounds as well. 相似文献
14.
T. Şaşmaz Kuru E. Şentürk V. Eyüpoğlu 《Journal of Superconductivity and Novel Magnetism》2017,30(3):647-655
In this work, the conduction and dielectric properties of Al0.2Cd0.8Fe2O4 ferrite nanoparticle, which was synthesized by a co-precipitation method, were investigated. Experimental data were taken from 20 Hz to 10 MHz and from 293 to 613 K. AC conductivity of the sample was analyzed within the framework of the overlapping large polaron tunneling (OLPT) mechanism. DC conductivity behavior fits the classical Arrhenius-type conductivity in the examined temperature range. Electrical properties of the material sample have been studied using an impedance spectroscopy technique. The effect of frequency and temperature on dielectric constant (ε ′), dielectric loss (tan ??), and impedance (Z′ and Z′′) has been discussed in terms of hopping of charge carriers between Fe2+ and Fe3+ ions. According to results, a relaxation process fits the Cole–Cole model. 相似文献
15.
In this paper, we report an ultralow thermal conductivity and a high-temperature phase stability of the (Nd1?x Ce x )2Zr2O7+x system over the temperature range from room temperature to 1600 °C and over a wide composition range (0.2 ≤ x ≤ 0.8), and the (Nd1?x Ce x )2Zr2O7+x system is therefore considered a strong candidate material for the fabrication of next-generation high-temperature thermal barrier coatings. The observed thermal conductivities (0.65–1.0 W/mK) are about 60–40% lower than those of undoped Nd2Zr2O7 over the same temperature range (100–700 °C) and indicate a glass-like behavior. For comparison, the variation in the thermal conductivity with the temperature of the (Gd1?x Ce x )2Zr2O7+x system with similar point defects was also measured, and the observed behavior was almost the same as that of undoped Gd2Zr2O7 and was mostly determined by phonon–phonon scattering (λ ∝ 1/T). The effect of point defect scattering and strong phonon scattering sources (rattlers) on the thermal conductivity is also discussed in this paper. The results of this study suggest that the ultralow thermal conductivity of (Nd1?x Ce x )2Zr2O7+x can be attributed to the presence of rattlers because of the large difference between the ionic radii of the Nd3+ and Ce4+ ions. 相似文献
16.
R. G. Veliev R. Z. Sadykhov E. M. Kerimova Yu. G. Asadov A. I. Dzhabbarov 《Inorganic Materials》2009,45(5):474-479
In a temperature range of 80–400 K, electrical and magnetic properties of layered compounds TlCrS2 and TlCrSe2 are investigated. It is shown that these compounds are p-type semiconductors and possess ferromagnetic ordering with T C ~90 and 105 K, respectively. 相似文献
17.
R. M. Hamad T. S. Kayed S. Kunwar K. A. Elsayed E. Abu-Ruz Kh. A. Ziq 《Journal of Superconductivity and Novel Magnetism》2018,31(6):1727-1732
We investigate the effects of iron content on the upper critical field (H c2) and the activation energy U(T) in thermally activated flux flow in Fe x Se0.5Te0.5 near the superconducting transition temperature T c . The variations in H c2(T) with temperature are analyzed using Ginzburg-Landau (GL), Werthamer-Helfand-Hohenberg (WHH) models along with the empirical relation (ER). The obtained values of H c2(0) depend strongly on the model and the criteria used to determine the transition temperature. However, the general trend is that that H c2(0) increases with the increasing Fe content. The activation energy U(T) is maximum for x =? 1 and rapidly suppressed by excess or deficiency of iron. The low values of U(T) (~10 meV) reflect the low vortex-pinning nature (due to defects, vacancies, etc.) in the Fe x Se0.5Te0.5 superconductor. 相似文献
18.
We have studied the 77-K photoluminescent properties of As2S3 semiconducting glass prepared at different temperatures (T 1 = 870 K; T 2 = 1120 K; T 3 = 1370 K) and cooling rates (v 1 = 10?2 K/s, v 2 = 1.5 K/s, v 3 = 1.5 × 102 K/s). The results demonstrate that the structural, optical, and photoluminescent properties of semiconducting chalcogenide glasses can be tuned over a considerable range by varying the preparation conditions. 相似文献
19.
The effects of Ba 2+ doping on the electrical and magnetic properties of charge-ordered Pr0.6Ca0.4MnO3 were investigated through electrical resistivity and AC susceptibility measurements. X-ray diffraction data analysis showed an increase in unit cell volume with increasing Ba 2+ content indicating the possibility of substituting Ba 2+ for the Ca-site. Electrical resistivity measurements showed insulating behavior and a resistivity anomaly at around 220 K. This anomaly is attributed to the existence of charge ordering transition temperature, \(T^{\mathrm {R}}_{\text {CO}}\) for the x = 0 sample. The Ba-substituted samples exhibited metallic to insulator transition (MI) behavior, with transition temperature, T MI, increasing from ~98 K (x = 0.1) to ~122 K (x = 0.3). AC susceptibility measurements showed ferromagnetic to paramagnetic (FM-PM) transition for Ba-substituted samples with FM-PM transition temperature, T c, increasing from ~121 K (x = 0.1) to ~170 K (x = 0.3), while for x = 0, an antiferromagnetic to paramagnetic transition behavior with transition temperature, T N, ~170 K was observed. In addition, inverse susceptibility versus T plot showed a deviation from the Curie–Weiss behavior above T c, indicating the existence of the Griffiths phase with deviation temperature, T G, increasing from 160 K (x = 0.1) to 206 K (x = 0.3). Magnetoresistance, MR, behavior indicates intrinsic MR mechanism for x = 0.1 which changed to extrinsic MR for x > 0.2 as a result of Ba substitution. The weakening of charge ordering and inducement of ferromagnetic metallic (FMM) state as well as increase in both T c and T MI are suggested to be related to the increase of tolerance factor, τ, and increase of e g ?electron bandwidth as average ionic radius at A-site, <r A> increased with Ba substitution. The substitution may have reduced MnO6 octahedral distortion and changed the Mn–O–Mn angle which, in turn, promotes itinerancy of charge carrier and enhanced double exchange mechanism. On the other hand, increase in A-site disorder, which is indicated by the increase in σ 2 is suggested to be responsible for the widening of the difference between T c and T MI. 相似文献
20.
Reena Goyal A. K. Srivastava Monu Mishra Govind Gupta Rajveer Jha V. P. S. Awana 《Journal of Superconductivity and Novel Magnetism》2018,31(4):943-949
In the present report, we investigate various properties of the Nb2PdS5 superconductor. Scanning electron microscopy displayed slabs like laminar growth of Nb2PdS5 while X-ray photoelectron spectroscopy exhibited the hybridisation of sulphur (2p) with both palladium (3d) and niobium (3d). High-field (140 kOe) magneto-transport measurements revealed that superconductivity (\(T_{c}^{\text {onset}} =?7\) K and T cρ=?0 = 6.2 K) of the studied Nb2PdS5 material is quite robust against magnetic field with the upper critical field (H c2) outside the Pauli paramagnetic limit. Thermally activated flux flow (TAFF) of the compound showed that resistivity curves follow Arrhenius behaviour. The activation energy for Nb2PdS5 is found to decrease from 15.15 meV at 10 kOe to 2.35 meV at 140 kOe. Seemingly, the single vortex pinning is dominant in low-field regions, while collective pinning is dominant in high-field region. The temperature dependence of AC susceptibility confirmed the T c at 6 K, further varying amplitude and frequency, showed well-coupled granular nature of superconductivity. The lower critical field (H c1) is extracted from DC magnetisation measurements at various T below T c. It is found that H c1(T) of Nb2PdS5 material seemingly follows the multiband nature of superconductivity. 相似文献