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1.
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
2.
Quoc Thanh Phung Van Khai Vu An Bang Ngac Huy Sinh Nguyen Nam Nhat Hoang 《Journal of magnetism and magnetic materials》2012
The magnetic and transport properties of the perovskites La0.67Ca0.33Mn1-xTMxO3 were found to be sufficiently changed with the substitution of Mn-sites by other 3d transition-metal cations (TM=Cu,Zn; x=0.15). The values of TC, TM−I, and TCMR were surveyed when Mn was replaced by Cu and Zn. The magnetic field induced resistivity and magnetic entropy change of these samples showed abrupt changes near TC (194.2 and 201.5 K for Cu and Zn-doped case respectively) and attained the highest values among the doped cases (up to 20% Cu). The maximum values (obtained at H=4 kOe) of magnetoresistance ratio (CMR) were 27.8%, and 24.5% and of magnetic entropy change (−ΔSM) were 3.9 and 3.2 J/kg K for Cu and Zn-doped, respectively. 相似文献
3.
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
4.
The effect of Ni2+ doping on the magnetic and magnetocaloric properties of La0.7Ca0.3MnO3 manganites synthesized via the auto-combustion method is reported. The aim of studying Ni2+-substituted La0.7Ca0.3Mn1 ? xNixO3 (, and 0.1) manganites was to explore the possibility of increasing the operating temperature range for the magnetocaloric effect through tuning of the magnetic transition temperature. X-ray diffraction analysis confirmed the phase purity of the synthesized samples. The substitution of Mn3+ ions by Ni2+ ions in the La0.7Ca0.3MnO3 lattice was also corroborated through this technique. The dependence of the magnetization on the temperature reveals that all the compositions exhibit a well-defined ferromagnetic to paramagnetic transition near the Curie temperature. A systematic decrease in the values of the Curie temperature is clearly observed upon Ni2+ doping. Probably the replacement of Mn3+ by Ni2+ ions in the La0.7Ca0.3MnO3 lattice weakens the Mn3+–O–Mn4+ double exchange interaction, which leads to a decrease in the transition temperature and the magnetic moment in the samples. By using Arrott plots, it was found that the phase transition from ferromagnetic to paramagnetic is second order. The maximum magnetic entropy changes observed for the , and 0.1 composites was 0.85, 0.77, 0.63, and 0.59 J/kg?K, respectively, under a magnetic field of 1.5 T. In general, it was verified that the magnetic entropy change achieved for La0.7Ca0.3Mn1 ? xNixO3 manganites synthesized via the auto-combustion method is higher than those reported for other manganites with comparable Ni2+-doping levels synthesized via standard solid state reaction. The addition of Ni2+ increases the value of the relative cooling power as compared to that of the parent compound. The highest value of this parameter (~60 J/kg) is found for a Ni-doping level of 2% around 230 K in a field of 1.5 T. 相似文献
5.
A. Rostamnejadi M. VenkatesanP. Kameli H. SalamatiJ.M.D. Coey 《Journal of magnetism and magnetic materials》2011,323(16):2214-2218
The La0.67Sr0.33MnO3 composition prepared by sol-gel synthesis was studied by dc magnetization measurements. A large magnetocaloric effect was inferred over a wide range of temperature around the second-order paramagnetic-ferromagnetic transition. The change of magnetic entropy increases monotonically with increasing magnetic field and reaches the value of 5.15 J/kg K at 370 K for Δμ0H=5 T. The corresponding adiabatic temperature change is 3.3 K. The changes in magnetic entropy and the adiabatic temperature are also significant at moderate magnetic fields. The magnetic field induced change of the specific heat varies with temperature and has maximum variation near the paramagnetic-ferromagnetic transition. The obtained results show that La0.67Sr0.33MnO3 could be considered as a potential candidate for magnetic refrigeration applications above room temperature. 相似文献
6.
Magnetocaloric effect (MCE) in fine-grained perovskite manganites of the type La0.67Ba0.33Mn1−xSnxO3 (x=0.05, 0.1 and 0.15) were prepared by the solid-state method. The prepared samples remain single phase and exhibit paramagnetic to ferromagnetic phase transition (TC) at 340, 325 and 288 K for x=0.05, 0.1 and 0.15, respectively. From the measured magnetization data of La0.67Ba0.33Mn1−xSnxO3 compounds as a function of field (2 T), the associated magnetic entropy change close to their respective Curie temperatures and the relative cooling power (RCP) have been determined. Large MCE has been obtained in all samples and |ΔSM|max reached the highest value of 2.49 J/kg K at TC (288 K) for the sample x=0.15, with H=2 T. 相似文献
7.
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
8.
Shyam Surthi Sushma Kotru R.K. PandeyPatrick Fournier 《Solid State Communications》2003,125(2):107-110
Polycrystalline samples of La0.67Ca0.33MnO3 were prepared by solid-state reactions by varying the pelletization force and the sintering temperature. Lowering the sintering temperature gave rise to smaller grains and increased the overall resistivity of the ceramic. Partial melting was observed in the ceramics sintered at higher temperatures (1400-1500 °C). Additionally, these ceramics showed two distinct resistivity peaks. The resistivity peak near the magnetic transition (TC) was sharp, whereas the second peak was a broad one observed below TC. 相似文献
9.
Sonia Ben Abdelkhalek Nabil Kallel Sami Kallel Octavio Peña Mohamed Oumezzine 《Journal of magnetism and magnetic materials》2012
Critical behavior in the La0.6Sr0.4Mn0.8Fe0.1Cr0.1O3 ceramics was studied using magnetization methods. Results show that the paramagnetic–ferromagnetic transition is of second order. Based on the critical behavior analysis using the Banerjee criterion and the Kouvel–Fisher method, we find the critical exponents: β=0.395±0.010, γ=1.402±0.010, and δ=5.208±0.007, for which the magnetic interaction is satisfied within the three-dimensional Heisenberg model. Results indicate the presence of short-range interactions. The magnetic entropy change (−ΔSM) reached maximum values of 1.75, 1.45, 1.15, 0.8 and 0.43 J Kg−1 K−1 under a magnetic field variation of 5, 4, 3, 2 and 1 T, respectively. Nevertheless, these (−ΔSM) values are much low for any potential application at this moment. The nature of this phenomenon is discussed in relation to the characteristics of the magnetic phase transition and critical exponents. 相似文献
10.
The perovskite bilayers La0.67Ca0.33MnO3 (LCMO) (100 nm) / La0.67Sr0.33MnO3(LSMO) (100 nm) and LSMO (100 nm) / LCMO (100 nm) are fabricated by a facing-target sputtering technique. Their transport and magnetic properties are investigated. It is found that the transport properties between them are different obviously due to distinguishable structures, and the different lattice strains in both films result in the difference of metal-to-insulator transition. Only single-step magnetization loop appears in our bilayers from 5K to 320K, and the coercive force of LSMO/LCMO varies irregularly with a minimum ~ 2387A/m which is lower than that of LCMO and LSMO single layer films. The behaviour is explained by some magnetic coupling. 相似文献
11.
Wei Ning 《Journal of magnetism and magnetic materials》2009,321(9):1159-1162
Electron spin resonance (ESR) study was carried out on La0.67Ca0.33Mn1−xFexO3 (x=0.0, 0.04) samples. The temperature dependence of the ESR spectra indicates the presence of phase separation above and below TC in x=0.0 and 0.04 sample, respectively. The increase of the g-value in the high-temperature region indicates the existence of local spin correlations even in the paramagnetic state. The activation energy obtained from both the temperature dependence of the ESR intensity and linewidth exhibits a smaller value in the Fe-doped sample. Our study suggests that the ferromagnetic spin correlations would be significantly weakened by a slight doping of Fe ions on Mn sites. 相似文献
12.
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
13.
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
14.
Manganite film electrodes were integrated with a spacer layer of strontium titanate to produce an epitaxial La0.67Ca0.33MnO3/(1000 nm)SrTiO3/La0.67Ca0.33MnO3 (LCMO/STO/LCMO) heterostructure by laser ablation. At T = 300 K, the mechanical stresses in the STO layer relaxed to a considerable extent, while the LCMO electrodes were found
to be under biaxial lateral tensile strain, with the lattice unit cell of the top electrode distorted considerably stronger
(a
∥/a
⊥ ≈ 1.026) than that of the bottom electrode (≈1.008) (a
∥ and a
⊥ are the unit cell parameters in the substrate plane and along the normal to its surface, respectively). The reciprocal of
the capacitance C of the plane-parallel LCMO/STO/LCMO film capacitors thus formed increased almost linearly with increasing temperature T in the range 50–250 K. At T < 100 K, the capacitance C decreased by approximately 50% in an electric field E = 40 kV/cm. After the electric field E was varied as 0 → + 100 kV/cm → 0, the capacitance C decreased by approximately 3% and the maximum in the C(E, T > 200 K) dependence shifted by approximately 9 kV/cm with respect to the point E = 0. 相似文献
15.
Brajendra Singh Ranjan K. Sahu S. Sundar Manoharan K. Drr K. -H. Müller 《Journal of magnetism and magnetic materials》2004,270(3):358-363
The substitutional effect of Ru on the magnetic and transport properties of double exchange ferromagnets, La0.7Sr0.3MnO3 and La0.5Sr0.5CoO3 has been investigated. It is found that substitution of 10% Ru at the Mn site of La0.7Sr0.3MnO3 decreases the Curie temperature by 20 K than that of the parent compound. However, a large decrease in the Curie temperature, ΔTc80 K and the system undergoes a transition from metallic state to insulating state is observed when 10% Ru is doped in La0.5Sr0.5CoO3. The marginal effect of Ru in the Mn–O–Mn sublattice in comparison to the Co–O–Co sublattice could be due to the magnetic exchange interaction between Mn and Ru by virtue of the fact that Ru exhibits variable valence states, Ru+4/Ru+5. The eg and t2g parentage of Ru+5 is similar to Mn+4 and therefore, Ru+5 ion appears to participate in the double exchange mediated ferromagnetic (FM) interaction. On the other hand, Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co+3: t2g5eg1), forcing a double exchange FM state to anti-FM state. 相似文献
16.
Z.C. Xia S.L. YuanW. Feng L.J. ZhangG.H. Zhang J. TangL. Cheng Q.H. ZhengL. Liu S. LiuC.Q. Tang 《Solid State Communications》2003,126(10):567-571
The influence of Fe3O4 contents on the electrical transport properties (resistivity and ac susceptibility) of a series of composite samples of La0.67Ca0.33MnO3/Fe3O4 is studied. Results show that the Fe3O4 phase not only shifts the intrinsic insulator-metal (I-M) transition temperature TP1 to a lower temperature, but also causes a new I-M transition at a lower temperature TP2 (TP2<TP1). On the basis of an analysis by scanning electron microscopy and X-ray diffraction, we suggest that the decrease of the I-M transition temperature and the formation of the new I-M transition are caused by the segregation of a new phases related to the Fe3O4 at grain boundaries or surfaces of the La0.67Ca0.33MnO3 grains. 相似文献
17.
Juan Zhao 《Journal of magnetism and magnetic materials》2009,321(19):2977-2980
In this paper, magnetic property and magnetocaloric effect (MCE) in nanoparticles perovskite manganites of the type (La0.67−xGdx)Sr0.33MnO3 (x=0.10, 0.15, 0.20) synthesized by using an amorphous molecular alloy as precursor have been reported. From the magnetic measurements as function of temperature and magnetic applied field, we have discovered that the Curie temperature (TC) of the prepared samples is found to be strongly dependent on Gd content. The Curie temperature of samples is 358.4, 343.2, and 285.9 K for x=0.1, 0.15, and 0.2, respectively. A large magnetocaloric effect close to TC has been observed with a maximum of magnetoentropy change in all the samples, ∣ΔSM∣max of 1.96 and 4.90 J/kg K at 2 and 5 T, respectively, for a substitution rate of 0.15. In addition, the maximum magnetic entropy change observed for samples with different concentration of Gd, exhibits a linear dependence with the applied high magnetic field. These results suggest that (La0.67−x Gdx)Sr0.33MnO3 (x=0.10, 0.15, 0.20) compounds could be a suitable candidate as working substance in magnetic refrigeration near room temperature. 相似文献
18.
Junji Awaka Norihito Kijima Shoichi Nagata 《Journal of Physics and Chemistry of Solids》2008,69(7):1740-1746
High-purity powder specimens of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 have been successfully synthesized by solid-state chemical reaction. The Rietveld refinements from X-ray powder diffraction data verified that these compounds have the garnet-type structure (space group , No. 230) with the lattice constant of a=12.596(2) Å for AgCa2Mn2V3O12 and a=12.876(2) Å for NaPb2Mn2V3O12. Calculation of the bond valence sum supported that Mn is divalent and V is pentavalent in these garnets. Estimation of the quadratic elongation and the bond angle variance showed that the distortions of the MnO6 octahedra and the VO4 tetrahedra are significantly suppressed. Our new results of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 are compared to those of AgCa2M2V3O12 and NaPb2M2V3O12 (M=Mg, Co, Ni, Zn). 相似文献
19.
Zhao Juan 《Journal of magnetism and magnetic materials》2009,321(1):43-46
In this paper, nanosized particles of (La0.47Gd0.2)Sr0.33MnO3 perovskite-type oxides were successfully synthesized at a relatively low calcinated temperature at 800 °C for 10 h using amorphous molecular alloy as precursor. X-ray diffraction (XRD) and electron diffraction (ED) revealed that the resulting product is of pure single-phase rhombohedral structure. The Curie temperature TC and magnetic entropy change (MCE) in (La0.47Gd0.2)Sr0.33MnO3 polycrystalline nanoparticles are determined and compared to those of similar systems prepared by the conventional solid-state reaction method. The Curie temperature TC is shifted to 298 k, and a relatively large MCE with a broad peak around Curie temperature is observed in (La0.47Gd0.2)Sr0.33MnO3 polycrystalline particles. These results suggested that this material is a suitable candidate as working substance in magnetic refrigeration near room temperature. 相似文献
20.
The influences of boron addition on the phase formation, Curie temperature and magnetic entropy change of the NaZn13-type La(Fe0.9Si0.1)13 compound have been investigated. Eight boron containing La(Fe0.9Si0.1)13Bx samples were prepared with x=0, 0.03, 0.06, 0.1, 0.2, 0.3, 0.5 and 0.6, respectively. Experimental results show that a small amount of B addition in La(Fe0.9Si0.1)13 forms the solid solution NaZn13-type structure phase by substituting B for Si or doping B into interstitial position of the lattice, preserves its giant magnetocaloric effects due to their first-order structural/magnetic transition, as well as increase its Curie temperature Tc slightly. The maximum magnetic entropy changes in the magnetic field change of 0–1.6 T are around 20 J kg–1 K–1 for the samples with Boron addition less than 0.3, while improving the Curie temperatures by 2 K. 相似文献