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1.
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
2.
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
3.
K. Riahi I. Messaoui W. Cheikhrouhou-Koubaa S. Mercone B. Leridon M. Koubaa A. Cheikhrouhou 《Journal of Superconductivity and Novel Magnetism》2017,30(8):2081-2089
The La0.78Dy0.02Ca0.2MnO3 (LDCMO) compound prepared via high-energy ball-milling (BM) presents a ferromagnetic-to-paramagnetic transition (FM-PM) and undergoes a second-order phase transition (SOFT). Based on a phenomenological model, magnetocaloric properties of the LDCMO compound have been studied. Thanks to this model, we can predict the values of the magnetic entropy change ΔS, the full width at half-maximum δ T FWHM, the relative cooling power (RCP), and the magnetic specific heat change ΔC p for our compound. The significant results under 2 T indicate that our compound could be considered as a candidate for use in magnetic refrigeration at low temperatures. In order to further understand the FM-PM transition, the associated critical behavior has been investigated by magnetization isotherms. The critical exponents estimated by the modified Arrott plot, the Kouvel–Fisher plot, and the critical isotherm technique are very close to those corresponding to the 3D-Ising standard model (β = 0.312 ± 0.07, γ = 1.28 ± 0.02, and δ = 4.80).Those results revealed a long-range ferromagnetic interaction between spins. 相似文献
4.
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
5.
M. Mansouri H. Omrani W. Cheikhrouhou-Koubaa A. Cheikhrouhou 《Journal of Superconductivity and Novel Magnetism》2017,30(11):3039-3044
La0.45Dy0.05Ca0.5Mn0.9V0.1O3, prepared by solid-state route, was characterized using x-ray diffraction at room temperature. The Rietveld refinement shows that the sample crystallizes in orthorhombic structure with Pbnm space group. A secondary phase LaVO4 has been also detected. The temperature dependence of the magnetization was investigated to determine the characteristics of the magnetic transition. The sample exhibits a paramagnetic-ferromagnetic transition (PM-FM) at T C = 81 ± 0.7 K when temperature decreases. The study of the inverse of susceptibility reveals the presence of ferromagnetic clusters in the paramagnetic region. A metamagnetic transition was observed from the M(H) curves and the magnetic entropy change was calculated from magnetization curves at different temperatures in order to evaluate the magnetocaloric effect. 相似文献
6.
E. Yu. Anikina V. N. Verbetsky A. G. Savchenko V. P. Menushenkov I. V. Shchetinin 《Inorganic Materials》2017,53(10):1009-1012
Interaction of hydrogen with the intermetallic compound Nd2Fe17 has been studied for the first time by calorimetry using a differential heat conduction calorimeter coupled to a Sieverts apparatus. Hydrogen absorption and desorption reactions were run at 200°C, and two types of data were obtained: p–C–T and ΔH–C–T (where p is the equilibrium hydrogen pressure, C = H/Nd2Fe17, ΔH is the reaction enthalpy, and T is the measurement temperature). The p–C–T curves obtained for the hydrogen absorption and desorption processes have no plateau or two-phase region, in contrast to what is characteristic of the formation of a hydride phase. At the same time, the ΔH(C) curves have a few portions where the enthalpy of reaction between hydrogen and the intermetallic compound remains constant: 0 < C < 2.0, with ΔH abs =–85.05 ± 0.65 kJ/mol H 2; 2.0 < C < 2.7, with ΔH abs =–80.64 ± 1.00 kJ/mol H2; and 1.9 < C < 2.7, with ΔH des = 76.48 ± 0.85 kJ/mol H2. The data obtained in this study suggest that positions 9e and 18g in the intermetallic compound are occupied by hydrogen in a particular order. 相似文献
7.
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
8.
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
9.
L. T. Denisova L. A. Irtyugo Yu. F. Kargin V. V. Beletskii V. M. Denisov 《Inorganic Materials》2017,53(1):93-95
Tb2Sn2O7 has been prepared by solid-state reaction in air at 1473 K over a period of 200 h and its isobaric heat capacity has been studied experimentally in the range 350–1073 K. The C p(T) data for this compound have no extrema and are well represented by the classic Maier–Kelley equation. The experimental C p(T) data have been used to evaluate the thermodynamic properties of terbium stannate (pyrochlore structure): enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(Т). 相似文献
10.
M. R. Laouyenne Sa. Mahjoub M. Baazaoui E. K. Hlil M. Oumezzine 《Journal of Superconductivity and Novel Magnetism》2016,29(5):1151-1157
In this work, we are going to show the method based on mean-field scaling for the Nd0.6Sr0.3Ca0.1Mn0.975Fe0.025 O3 sample, where from scaling of experimental magnetization data, the mean-field exchange parameter λ and the f function of the equation of state \(M(T,H)=B_{S} [\frac {\left ({H+H_{\text {ex}}} \right )}{T}]\) are directly determined. The scaling approach allows finding the dependence of H ex on T or higher powers of M, which determine the order of the phase transition. Quantum spin number has been determined. In this study, we use \(\left | {\Delta S_{M} (T)} \right |\) obtained from isothermal magnetization measurements; we compare this result to mean-field theory fittings from a novel scaling method through the use of theoretical results S, g, and λ. The obtained results by mean-field theory are suitable and in good agreement with the classical Maxwell relation. 相似文献
11.
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
12.
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
13.
Single phase samples of Ni(Cr1?xMn x )2O4 (x = 0–0.50) were synthesized by using sol–gel route. Investigation of structural, magnetic, exchange bias and magnetization reversal properties was carried out in the bulk samples of Ni(Cr1?xMn x )2O4. Rietveld refinement of the X-ray diffraction patterns recorded at room temperature reveals the tetragonal structure for x = 0 sample with I41/amd space group and cubic structure for x ≥ 0.05 samples with \( {\text{Fd}\bar{3}\text{m}} \) space group. Magnetization measurements show that all samples exhibit ferrimagnetic behavior, and the transition temperature (TC) is found to increase from 73 K for x = 0 to 138 K for x = 0.50. Mn substitution induces magnetization reversal behavior especially for 30 at% of Mn in NiCr2O4 system with a magnetic compensation temperature of 45 K. This magnetization reversal is explained in terms of different site occupation of Mn ions and the different temperature dependence of the magnetic moments of different sublattices. Study of exchange bias behavior in x = 0.10 and 0.30 samples reveals that they exhibit negative and tunable positive and negative exchange bias behavior, respectively. The magnitudes of maximum exchange bias field of these samples are found to be 640 and 5306 Oe, respectively. Exchange bias in x = 0.10 sample originates from the anisotropic exchange interaction between the ferrimagnetic and the antiferromagnetic components of magnetic moment. The tunable exchange bias behavior in x = 0.30 sample is explained in terms of change in domination of one sublattice moment over the other as the temperature is varied. 相似文献
14.
Devina Sharma Jagdish Kumar Arpita Vajpayee Ranjan Kumar P. K. Ahluwalia V. P. S. Awana 《Journal of Superconductivity and Novel Magnetism》2011,24(6):1925-1931
In the present study, we report an intercomparison of various physical and electronic properties of MgB2 and AlB2. In particular, the results of phase formation, resistivity ρ(T), thermoelectric power S(T), magnetization M(T), heat capacity (C P ), and electronic band structure are reported. The original stretched hexagonal lattice with a=3.083 Å, and c=3.524 Å of MgB2 shrinks in c-direction for AlB2 with a=3.006 Å, and c=3.254 Å. The resistivity ρ(T), thermoelectric power S(T) and magnetization M(T) measurements exhibited superconductivity at 39 K for MgB2. Superconductivity is not observed for AlB2. Interestingly, the sign of S(T) is +ve for MgB2 the same is ?ve for AlB2. This is consistent with our band structure plots. We fitted the experimental specific heat of MgB2 to Debye–Einstein model and estimated the value of Debye temperature (Θ D) and Sommerfeld constant (γ) for electronic specific heat. Further, from γ, the electronic density of states (DOS) at Fermi level N(E F) is calculated. From the ratio of experimental N(E F) and the one being calculated from DFT, we obtained value of λ to be 1.84, thus placing MgB2 in the strong coupling BCS category. The electronic specific heat of MgB2 is also fitted below T c using α-model and found that it is a two gap superconductor. The calculated values of two gaps are in good agreement with earlier reports. Our results clearly demonstrate that the superconductivity of MgB2 is due to very large phonon contribution from its stretched lattice. The same two effects are obviously missing in AlB2, and hence it is not superconducting. DFT calculations demonstrated that for MgB2, the majority of states come from σ and π 2p states of boron on the other hand σ band at Fermi level for AlB2 is absent. This leads to a weak electron phonon coupling and also to hole deficiency as π bands are known to be of electron type, and hence obviously the AlB2 is not superconducting. The DFT calculations are consistent with the measured physical properties of the studied borides, i.e., MgB2 and AlB2. 相似文献
15.
Structural, magnetic, magnetocaloric, and electrical properties are reported for mixed-valence manganite La0.67Pb0.13Na0.2MnO3. X-ray diffraction reveals that the sample crystallizes in the rhombohedric structure with the R-3c space group. The magnetic properties of the polycrystalline La0.67Pb0.13Na0.2MnO3 compound are discussed in detail, based on the susceptibility, magnetization, and isotherm. The sample presents a ferromagnetic property with T C= 275 K and a Griffiths phase at T G= 325 K which gives the existence of ferromagnetic clusters in the paramagnetic domain. A large deviation is usually observed between field cooled (FC) and zero field cooled (ZFC). M(T) is a low temperature below the blocking temperature. At 40 K, a spin-glass or a cluster-glass state is seen to arise from a ferromagnetic state. This is caused by the competition between the antiferromagnetic and ferromagnetic interactions. The electrical properties show the presence of a metal–semiconductor transition at T M?Sc. To understand the dependence of disorder with the transport mechanism, we used the phenomenological equation for resistivity under a percolation approach, which is dependent on the phase segregation of a paramagnetic semiconductor and ferromagnetic metallic regions. 相似文献
16.
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
17.
We have developed processes for the synthesis of Ni0.75Zn0.25Fe2–xLnxO4 ferrite solid solutions with the spinel structure and investigated the effect of the rare-earth elements Nd, Gd, Yb, and Lu on the chemical composition, extent, lattice parameters, and magnetic properties of the solid solutions. The results demonstrate that rare-earth solubility in the parent spinel reaches ≈2.5 at %, which leads to changes in the magnetic characteristics of the material, in particular in its saturation magnetization Ms, TC, and coercive force Hc. 相似文献
18.
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
19.
F. Z. Rachid R. Moubah R. El Ouatib S. Derkaoui H. Lassri 《Journal of Superconductivity and Novel Magnetism》2018,31(7):2073-2077
Amorphous Co75Er17B8 ribbons were prepared by the melt spinning technique, and their magnetic properties were studied. Mean field theory was used to describe the temperature dependence of magnetization. High-field magnetization studies performed in magnetic fields up to 15 T have revealed a magnetic behavior typical of a non-collinear magnetic structure of Er and Co sublattices. The simulated magnetization curves show the existence of two critical fields at H cri1 =?9.5 T and H cri2 =?94.2 T, corresponding to collinear ferrimagnet, and collinear field-forced ferromagnetic behaviors. The high value of H cri2 highlights the strong antiferromagnetic interaction between Er and Co sublattices. From the non-collinear regime, the inter-subnetwork molecular field coefficients of the ferrimagnetic alloy were accurately evaluated. In addition, it is shown that the region of canted moments can be satisfactorily described by a phase diagram in the H-T plane. 相似文献
20.
Epitaxial Sm0.35Pr0.15Sr0.5MnO3 thin films were deposited on LaAlO3 (LAO, (001)), SrTiO3 (STO, (001)), and (La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT, (001)) single-crystalline substrates by using pulsed laser deposition technique. In order to examine the strain effect on electronic and magnetic properties, films were studied by X-ray diffraction, electrical resistivity, and dc magnetization measurements. The film grown on LAO substrate is under compressive strain, and it undergoes ferromagnetic → paramagnetic transition at Curie temperature (T C) of ~ 165 K and metal → insulator transition at ~ 107 K. The films grown on STO and LSAT substrates are under tensile strain and have T C of ~ 120 and 130 K, respectively, and show metal → insulator transition at ~ 145 and 137 K, respectively. At T < T C, the zerofield and fieldcooled magnetization curves of all the films show a huge bifurcation. In the case of films on STO and LSAT substrates, hysteresis is also observed in fieldcooled cooling and warming magnetization vs. temperature measurement protocols at low magnetic field. All the signatures of the firstorder magnetic phase transition are absent in the case of film on LAO substrate. The occurrence and absence of firstorder magnetic phase transition in films on LAO, STO, and LSAT substrates, respectively, have been well explained through the substrateinduced film lattice strain. 相似文献