共查询到20条相似文献,搜索用时 15 毫秒
1.
Nabil Kallel Sami Kallel Ahmed Hagaza Mohamed Oumezzine 《Physica B: Condensed Matter》2009,404(2):285-288
Single-phase polycrystalline samples of La0.7Sr0.3Mn1-xCrxO3 with nominal composition of x=0.00, 0.20, 0.40 and 0.50 were prepared by a conventional solid-state reaction method in air. Investigations of magnetization were carried out in the temperature range 5-400 K and magnetic field range 0-8 T. It was found that the Curie temperature TC decreases with increasing x and the maximum magnetic entropy change (−ΔSM) for x=0.20 is ∼1.203 and ∼2.653 J/kg K, respectively for 2 and 6 T magnetic field near the temperature of 280 K. 相似文献
2.
A.V. Kartashev I.N. Flerov N.V. Volkov K.A. Sablina 《Journal of magnetism and magnetic materials》2010,322(6):622-627
Heat capacity and intensive magnetocaloric effect (MCE) in manganites (La1−yEuy)0.7Pb0.3MnO3 [y=0.2; 0.6] (LEPM) were investigated by means of adiabatic calorimeter. The heat capacity anomaly as well as the values of both the intensive (ΔTAD) and the extensive (ΔSMCE) MCE were found to decrease upon increased replacement of La with nonmagnetic Eu. However, because of widening of the MCE peaks, the LEPM compounds show the relative cooling power, RCP/ΔH, comparable to other solid solutions of manganites. Owing to strong effect of Eu→La substitution on the Curie temperature, LEPM might have potential as the solid state refrigerants in multi-element cooling apparatus operating in a wide temperature range. 相似文献
3.
P.T. Phong N.V. Dai T.D. Thanh L.V. Hong 《Journal of magnetism and magnetic materials》2010,322(18):2737-152
The electrical transport properties and the magnetoresistance of La0.7Ca0.3MnO3/La0.7Sr0.2Ca0.1MnO3 composites are investigated as a function of sintering temperature. On the basis of an analysis by X-ray powder diffraction and scanning electron microscopy we suggest that raising the sintering temperature enhanced the interfacial reaction and creates interfacial phases at the boundaries of the La0.7Ca0.3MnO3 and La0.7Sr0.2Ca0.1MnO3. Results also show that in 3 kOe, and at the Curie temperature, the magnetoresistance value of 14% was observed for the composite sintered at 1300 °C. Based on the phenomenological equation for conductivity under a percolation approach, which depends on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions, we fitted the experimental resistivity—temperature data from 50-300 K and find that the activation barrier decreases as temperature is increased. 相似文献
4.
A.M. AlievA.G. Gamzatov A.B. BatdalovA.S. Mankevich I.E. Korsakov 《Physica B: Condensed Matter》2011,406(4):885-889
A technology of obtaining the single-phase ceramic samples of La1−xKxMnO3 manganites and the dependence of their structural parameters on the content of potassium has been described. Magnetocaloric effect (MCE) in the obtained samples has been measured by two independent methods: classical direct methodic and a method of magnetic field modulation. The values of MCE obtained by both methods substantially differ. The explanation of the observed divergences is given. The correlation between the level of doping and MCE value has been defined. The value of TC determined by the MCE maximum conforms with the literature data obtained by other methods. 相似文献
5.
Rabindra Nath Mahato K. Sethupathi V. Sankaranarayanan R. Nirmala 《Journal of magnetism and magnetic materials》2010,322(17):2537-9465
Sol-gel prepared nanocrystalline La0.7Te0.3MnO3 has rhombohedral crystal structure (space group R3¯C) at room temperature and orders ferromagnetically at ∼280 K (TC). A large magnetic entropy change of ∼12.5 J kg−1 K−1 is obtained near TC for a field change of 50 kOe. This magnetocaloric effect could be explained in terms of Landau theory. The temperature dependence of electrical resistivity shows metal-insulator transition at TC and a giant magnetoresistance of ∼52% in 50 kOe. The co-existence of giant magnetoresistance and large magnetocaloric effect near room temperature makes nanocrystalline La0.7Te0.3MnO3 a promising material for magnetic refrigeration and spintronic device applications. 相似文献
6.
Wei Tang Xuan Luo Xuebin Zhu Zhaorong Yang 《Journal of magnetism and magnetic materials》2010,322(16):2360-99
The structure, magnetic properties, and magnetocaloric effect of La0.7Ca0.3MnO3 ceramics with different particle sizes have been investigated. It is found that the Curie temperature increases first, and then decreases as particle size decreases and the type of magnetic phase transition changes from first-order to second-order, which may be attributed to surface pressure effects. The maximum magnetic entropy change and relative cooling power (RCP) show non-monotonic behaviors with decreasing the particle size. However, for the 3400 nm sample, the magnetic entropy change −ΔSM reaches the maximum values of 6.41 and 8.63 J/kg K for the field changes of 2.0 and 4.5 T, respectively. Furthermore, the estimated large RCP values under lower magnetic fields in La0.7Ca0.3MnO3 are comparable with those of typical magnetic refrigerant materials in the corresponding temperature range, suggesting those compounds might be promising candidates for magnetic refrigeration. 相似文献
7.
S.P. AltintasA. Amira A. VarilciC. Terzioglu 《Journal of magnetism and magnetic materials》2012,324(7):1331-1336
Bulk samples of gadolinium doped manganites with compositional formula La0.7−xGdxCa0.3MnO3 (x=0.0 and 0.1) were prepared by conventional solid state reaction method. After characterizing the samples by X-ray diffraction, scanning electron microscope and energy dispersive X-ray spectrometer, a systematic investigation of electrical and magneto-transport properties has been investigated. The replacement of La ion by Gd results in a decrease of the metal-insulator transition temperature TMI and the magnetoresistance as well as the resistivity are found to increase. The electrical resistivity in the entire temperature range fit well with the phenomenological percolation model, which is based upon an approach that the system consists of the phase separated ferromagnetic metallic and paramagnetic insulating regions. 相似文献
8.
N.G. Bebenin R.I. ZainullinaV.V. Ustinov Ya.M. Mukovskii 《Journal of magnetism and magnetic materials》2012,324(6):1112-1116
The effect of magnetic inhomogeneity on magnetic, magnetocaloric, and transport properties of the colossal magnetoresistance manganites with first order ferromagnetic-to-paramagnetic phase transition is studied. The experiments were performed on the single-crystalline samples of La0.6Pr0.1Ca0.3MnO3. The inhomogeneity is described by the Curie temperature distribution function, which is found from the magnetization data. The temperature dependence of the magnetic field induced change in the entropy is shown to be determined by the distribution function and the shift of the transition temperature in a magnetic field. Similarly, magnetoresistance in the transition region is determined by the resistivity at H=0 and the shift of the transition temperature. The maximum entropy change as well as maximum magnetoresistance can be achieved in the magnetic field of order δTC/BM where δTC is the transition width and BM is the rate of change of the Curie temperature with magnetic field.Our approach to analysis of the effects of inhomogeneity is general and therefore can be used for all compounds with the first order magnetic phase transition. 相似文献
9.
J.C. Debnath R. ZengJ.H. Kim S.X. Dou 《Journal of magnetism and magnetic materials》2011,323(1):138-143
The influence of first and second order magnetic phase transitions on the magnetocaloric effect (MCE) and refrigerant capacity or relative cooling power (RCP) of La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3 materials has been investigated. Large low-field-induced magnetic entropy changes are observed in La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3 materials. The La0.7Ca0.3MnO3 material experiences a large entropy change with a first-order magnetic phase transition at the Curie temperature, TC. On the other hand, La0.7Ca0.3Mn0.95Co0.05O3 displays a smaller entropy change with a second order phase transition. While a first-order magnetic transition material induces a larger MCE (7.528 J/kg K at 5 T) at TC, this is limited to a narrow temperature range, resulting in a relatively small RCP (218 J/kg), while the Co-doped second-order magnetic transition material induces a smaller MCE (7.14 J/kg K for 5 T), but it is spread over a broader temperature range, resulting in a larger RCP (308 J/kg). The maximum magnetoresistance (MR, defined as ρ(0)/ρ(H)-1) under a field of 5 T is about 206% and 333% for La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3, respectively. The refrigeration capacity (RCP) is enhanced in La0.7Ca0.3Mn0.95Co0.05O3 (by about 41%) due to small changes from Co doping. The magnetocaloric features of these materials at lower magnetic fields (MCE=3.163 for La0.7Ca0.3Mn0.95Co0.05O3 and 4.63 J/kg K for La0.7Ca0.3MnO3 at 1 T), and the high RCP and MR can provide some ideas for exploring novel magnetic refrigerants that can operate with permanent magnets rather than superconducting ones as the magnetic field source. 相似文献
10.
Polycrystalline perovskite La0.67Ca0.33MnO3 was synthesized by a sol–gel method. Its adiabatic temperature change ΔTad induced by a magnetic field change was measured directly. At 268 K, near its Curie temperature TC, ΔTad of La0.67Ca0.33MnO3 induced by a magnetic field change of 2.02 T reaches 2.4 K. The latent heat Q and magnetic entropy change −ΔSM induced by a magnetic field change were calculated from the temperature dependence of ΔTad and zero-field heat capacity Cp. The maximum values of Q and −ΔSM in La0.67Ca0.33MnO3 induced by a magnetic field change of 2.02 T are 1.85 J g−1 and 6.9 J kg−1 K−1, respectively. The former is larger than the phase transition latent heat of heating or cooling, which is about 1.70 J g−1. 相似文献
11.
We investigated magnetocaloric effect in La0.45Pr0.25Ca0.3MnO3 by direct methods (changes in temperature and latent heat) and indirect method (magnetization isotherms). This compound undergoes a first-order paramagnetic to ferromagnetic transition with TC=200 K upon cooling. The paramagnetic phase becomes unstable and it transforms into a ferromagnetic phase under the application of magnetic field, which results in a field-induced metamagnetic transition (FIMMT). The FIMMT is accompanied by release of latent heat and temperature of the sample as evidenced from differential scanning calorimetry and thermal analysis experiments. A large magnetic entropy change of ΔSm=−7.2 J kg−1 K−1 at T=212.5 K and refrigeration capacity of 228 J kg−1 are found for a field change of ΔH=5 T. It is suggested that destruction of magnetic polarons and growth of ferromagnetic phase accompanied by a lattice volume change with increasing magnetic field is responsible for the large magnetocaloric effect in this compound. 相似文献
12.
Hangfu Yang Pengyue ZhangQiong Wu Hongliang GeMinxiang Pan 《Journal of magnetism and magnetic materials》2012
The influence of monovalent doping on the magnetocaloric effect (MCE) and refrigerant capacity or relative cooling power (RCP) of Pr0.5Sr0.3M0.2MnO3 (M=Na, Li, K and Ag) materials has been investigated. A large magnetocaloric effect was inferred over a wide range of temperature around the second order paramagnetic–ferromagnetic transition. The maximum magnetic entropy changes (ΔSM) reached 1.8, 2.2, 1.6 and 2.1 J/kg K and the relative cooling power (RCP) approached 58.9, 59.3, 69.6 and 54.6 J/kg for Na, Li, K and Ag doped materials in the magnetic change of 15 kOe, respectively. According to the results determined by the Maxwell relation, the magnetic entropy change fits well with the Landau theory of phase transition above TC for Pr0.5Sr0.3Li0.2MnO3. The large magnetic entropy change induced by low magnetic field suggested that these materials are beneficial for practical applications. 相似文献
13.
Polycrystalline perovskite manganites La0.7−xEuxBa0.3MnO3(x=0.05, 0.1 and 0.15) were prepared by sol-gel method. The prepared samples remain single phase with a perovskite structure, revealed by X-ray diffraction. The structure refinement of La0.7−xEuxBa0.3MnO3(x=0.05, 0.1 and 0.15) samples was performed in the hexagonal setting of the R3¯c space group. The dependence of magnetization M on applied magnetic field H and temperature T was measured carefully near the Curie temperature TC for all the samples. With the increasing Eu content, both the unit cell volume and Curie temperature TC of 298 K has been detected with a maximum of magnetic entropy |ΔSMmax| for the La0.7−xEuxBa0.3MnO3 with x=0.15, reaching a value of 2.3 J/kg K when a magnetic field of 10 kOe was applied and the relative cooling power (RCP) is 46 J/kg. These results suggest that the material may be a suitable candidate as working substance in magnetic refrigeration near room temperature. 相似文献
14.
A. Y. Ramos C. Giacomelli E. Favre-Nicolin L. Ranno 《Physica B: Condensed Matter》2002,320(1-4):83-85
We report here on an X-ray absorption study of La0.7Sr0.3MnO3 films epitaxially grown on SrTiO3 substrate. The local organization around Mn in oriented films with 600 Å in thickness was investigated by polarized Extended X-ray Absorption Fine Structure. The angle between electric field vector and film surface was set equal to 5° and 70° to investigate almost independently the contribution of the manganese neighbors situated in and out of the film plane. The first neighboring shell oxygen is found to be the same in both geometries, but small changes in the next neighboring contribution are observed. These changes are associated with variation in the Mn–Mn bond length. A small in-plane elongation (3%) is observed in the constrained films with respect to the unconstrained case. 相似文献
15.
P.T. Phong N.V. Khiem N.V. Dai L.V. Hong 《Journal of magnetism and magnetic materials》2009,321(19):3330-3334
We report the resistivity (ρ)-temperature (T) patterns in (1-x)La0,7Ca0,3MnO3+xAl2O3 composites (0≤x≤0.05) over a temperature regime of 50-300 K. Al2O3 addition has increased the resistivity of these composites. The Curie temperature (TC) is almost independent on the Al2O3 content and is about 250 K for all the samples, while the metal-insulator transition temperature (TMI) decreases with increasing Al2O3 content. Based on the phenomenological equation for conductivity under a percolation approach, which is dependent on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions, we fitted the experimental data (ρ−T) from 50 to 300 K and find that the activation barrier increases as Al2O3 content increases. 相似文献
16.
T.D. ThanhP.T. Phong N.V. DaiD.H. Manh N.V. KhiemL.V. Hong N.X. Phuc 《Journal of magnetism and magnetic materials》2011,323(1):179-184
We report magneto-transport and magnetic properties of (1-x)La0.7Ca0.3MnO3+xAl2O3 composites synthesized through a solid-state reaction method combined with a high energy milling method. Most interestingly, the effective magnetic anisotropy is found to decrease with increase in the non-magnetic insulating Al2O3 phase fraction in the composites. In addition, we observed that the magnitude of low-field magnetoresistance arising from spin-polarized tunneling of conduction electrons, as well as that of high-field magnetoresistance, displays a Curie-Weiss law-like behavior. Finally, we found that the temperature dependence of low and high-field magnetoresistance is controlled predominantly by the nature of temperature response of surface magnetization of the particles. 相似文献
17.
We present the temperature dependence of La0.85Ag0.15MnO3 resistivity in the temperature interval between 77 and 340 K and magnetic fields up to 26 kOe. We offer a method of separating tunnel magnetoresistance from total magnetoresistance. A change in both the magnetic entropy, which is caused by the magnetocaloric effect (MCE), and the magnetoresistance are shown to be connected through a simple relationship to La0.85Ag0.15MnO3. 相似文献
18.
J. Sacanell P. Levy L. Ghivelder G. Polla F. Parisi 《Physica B: Condensed Matter》2002,320(1-4):90-93
The effect of low-magnetic fields on the magnetic and electrical transport properties of polycrystalline samples of the phase-separated compound La0.5Ca0.5MnO3 is studied. The results are interpreted in the framework of the field-induced ferromagnetic fraction enlargement mechanism. A fraction expansion coefficient f, which relates the ferromagnetic fraction f with the applied field H, was obtained. A phenomenological model to understand the enlargement mechanism is worked out. 相似文献
19.
P.T. Phong D.H. Manh N.V. Dang L.V. Hong I.J. Lee 《Physica B: Condensed Matter》2012,407(18):3774-3780
We report the structural, magentoresistance and electro-magnetic properties of ferromagnet–ferroelectric–type (1−x)La0.7Sr0.3MnO3/xBaTiO3 (with x=0.0%, 3.0%, 6.0%, 12%, 15.0% and 18.0%, in wt%) composites fabricated through a solid-state reaction method combined with a high energy milling method. The insulator–metal transition temperature shifts to a lower temperature and resistivity increases while the feromagnetic–paramagnetic transition temperature remains almost unchanged with the increase of BaTiO3 content. Magnetoresistance of the composites at an applied magnetic field H=3 kOe is enhanced in the wide temperature ranges with the introduction of BaTiO3, which could be explained by the enhanced spin polarized tunneling effect induced by the introduction of BaTiO3. The low-field magnetoresistance of the composite is analyzed in the light of a phenomenological model based on the spin polarized tunneling at the grain boundaries. Furthermore, the temperature dependence of resistivity for this series has been best-fitted by using the adiabatic small polaron and variable range hopping models. These models may be used to explain effect of BTO on the electronic transport properties on high temperature paramagnetic insulating region. 相似文献
20.
Jiyu Fan Li Pi Lei ZhangWei Tong Langsheng LingBo Hong Yangguang ShiWeichun Zhang Di LuYuheng Zhang 《Physica B: Condensed Matter》2011,406(11):2289-2292
In this paper, we have studied the magnetic and magnetocaloric properties of the perovskite manganite Pr0.55Sr0.45MnO3. It shows a sharp paramagnetic-ferromagnetic phase transition at 291 K and possesses a moderate magnetic entropy change near room temperature. In addition, a large relative cooling power (143.64 J/kg) and a wide temperature range (84 K) have been found in this material. Compare with the Landau model, we find that the itinerant electrons mainly contribute the larger magnetic entropy change at paramagnetic region. 相似文献