共查询到20条相似文献,搜索用时 125 毫秒
1.
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
2.
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
3.
S.K. BarikC. Krishnamoorthi R. Mahendiran 《Journal of magnetism and magnetic materials》2011,323(7):1015-1021
We have studied the effect of Fe substitution on magnetic and magnetocaloric properties in La0.7Sr0.3Mn1−xFexO3 (x=0.05, 0.07, 0.10, 0.15, and 0.20) over a wide temperature range (T=10-400 K). It is shown that substitution by Fe gradually decreases the ferromagnetic Curie temperature (TC) and saturation magnetization up to x=0.15 but a dramatic change occurs for x=0.2. The x=0.2 sample can be considered as a phase separated compound in which both short-range ordered ferromagnetic and antiferromagnetic phases coexist. The magnetic entropy change (−ΔSm) was estimated from isothermal magnetization curves and it decreases with increase of Fe content from 4.4 J kg−1 K−1 at 343 K (x=0.05) to 1.3 J kg−1 K−1 at 105 K (x=0.2), under ΔH=5 T. The La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating temperature range over 60 K around room temperature with refrigerant capacity of 225 J kg−1, and magnetic entropy of 4 J kg−1 K−1 which will be an interesting compound for application in room temperature refrigeration. 相似文献
4.
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
5.
G. LalithaP. Venugopal Reddy 《Physica B: Condensed Matter》2011,406(19):3568-3575
With a view to understand the elastic behaviour of a material system, La0.67Sr0.33−xBaxMnO3 (where x=0, 0.1, 0.2, and 0.33) especially in the vicinity of their magnetic transition temperature TC, a systematic investigation of ultrasonic velocity over a temperature range 300-400 K has been carried out. The materials prepared by citrate gel route, were characterized structurally by XRD and on analyzing the XRD patterns, it has been concluded that all the samples are having rhombohedral structure with space group of R3?c. The magnetic (TC) transition temperatures determined by AC susceptibility measurements are found to decrease continuously with increasing barium concentration. Finally, the ultrasonic longitudinal velocities of all the samples are found to exhibit considerable softening in the vicinity of their magnetic transition temperatures, TC and the observed behaviour is explained using mean field theory and Jahn-Teller theorem. 相似文献
6.
Single-phase polycrystalline samples of La0.67Ca0.33Mn1−xO3 (x=0.00, 0.02, 0.04, 0.06) have been prepared using the sol-gel method. The structure, magnetocaloric properties and the Curie temperature of the samples with different Mn vacancy concentrations have been investigated. The experimental results show that vacancy doping at the Mn-sites has a significant influence on the magnetic properties of La0.67Ca0.33Mn1−xO3. The Curie temperature decreases monotonically with increasing the Mn-site vacancy concentration x. A remarkable enhancement of the magnetic entropy change has been obtained in the La0.67Ca0.33Mn0.98O3 sample. The entropy change reaches |ΔSM|=3.10 J kg−1 K−1 at its Curie temperature (264 K) under an applied magnetic field H=10 kOe, which is almost the same value as that of pure Gd. 相似文献
7.
The magnetic properties and the Griffiths singularity were investigated in Mn-site doped manganites of La0.45Sr0.55Mn1−xCoxO3 (x=0, 0.05, 0.10 and 0.15) in this work. The parent sample La0.45Sr0.55MnO3 undergoes a paramagnetic-ferromagnetic transition at TC=290 K and a ferromagnetic-antiferromagnetic transition at TN=191 K. The doping of Co ions enhances the ferromagnetism and suppresses the antiferromagnetism. The enhanced ferromagnetism results from the fact that the Co doping enhances the Mn3+-Mn4+ double-exchange interaction and induces the Co2+-Mn4+ ferromagnetic superexchange interaction. Detailed investigation on the magnetic behavior above TC exhibits that the Griffiths singularity takes place in this series of Mn-site doped compounds. The correlated disorder induced by the Co ionic doping, together with the phase competition from the ferromagnetic and the antiferromagnetic interactions among Mn ions, is responsible for the Griffiths singularity. 相似文献
8.
Jun Shen Yang-Xian Li Ji-Rong Sun 《Journal of magnetism and magnetic materials》2009,321(15):2336-2339
Magnetic entropy change ΔSm, hysteresis loss and refrigerant capacity of NaZn13-type La0.7Pr0.3Fe13−xSix (1.5?x?2.0) compounds have been investigated. The Curie temperature TC increases linearly with the increase of silicon concentration. Although the maximum value of ΔSm under a field change of 0−5 T decreases from 30.5 to 11.4 J/kg K as x increases from 1.5 to 2.0, the hysteresis loss at TC reduces remarkably from 89.2 J/kg for x=1.5 to zero for x=2.0 because the increase of Si content can weaken the itinerant electron metamagnetic transition. The effective refrigerant capacity RCeff is maintained at high values of 362−439 J/kg for a field change of 0−5 T. This implies that a large ΔSm and a high RCeff can be achieved simultaneously in the La0.7Pr0.3Fe13−xSix compounds. 相似文献
9.
G.V. Lashkarev V.I. Sichkovskyi V.E. Slynko T. Story W. Knoff 《Journal of magnetism and magnetic materials》2009,321(11):1782-1784
It is expected that joint existence of ferromagnetic properties and ferroelectric structural phase transition in diluted magnetic semiconductors IV-VI leads to new possibilities of these materials. Temperature of ferroelectric transition for such crystals can be tuned by the change of Sn/Ge ratio. Magnetic susceptibility, Hall effect, resistivity and thermoelectric power of Ge1−x−ySnxMnyTe single crystals grown by Bridgeman method (x=0.083-0.115; y=0.025-0.124) were investigated within 4.2-300 K. An existence of FM ordering at TC∼50 K probably due to indirect exchange interaction between Mn ions via degenerated hole gas was revealed. A divergence of magnetic moment temperature dependences at T?TC in field-cooled and zero-field-cooled regimes is obliged to magnetic clusters which are responsible for superparamagnetism at T>TC≈Tf (freezing temperature) and become ferromagnetic at TC arranging spin glass state at T<Tf≈TC. Phase transition of ferroelectric type at T≈46 K was revealed. Anomalous Hall effect which allows to determine magnetic moment was observed. 相似文献
10.
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
11.
P. NishaS. Savitha Pillai K.G. SureshManoj Raama Varma 《Journal of magnetism and magnetic materials》2012,324(1):37-43
The influence of partial substitution of La by Dy on the magnetocaloric response of (La1−xDyx)0.67Ca0.33Mn0.9V0.1O3, where x=0.03, 0.15 and 0.25 is studied. Rietveld refinement of X-ray diffraction pattern using GSAS method shows that the compounds adopt the orthorhombic structure with Pnma space group. The systematic change in lattice parameters and magnetic phase transition indicates the substitution effect of Dy. From the magnetization isotherms at different temperatures, magnetic entropy change close to their respective transition temperatures (TC) has been evaluated. The maximum value of entropy change near TC is found to be about 4.8 J/kg K at 187.5 K for LCMVDy0.03, 2.45 J/kg K at 107.5 K for LCMVDy0.15 and 2.15 J/kg K at 92.5 K for LCMVDy0.25 at 4 T. Dy addition produces a reduction in TC and in magnitude of the magnetic entropy change. Even though the entropy change decreases with increasing Dy substitution the refrigerant temperature range, ΔT, is found to be 10 K for LCMVDy0.03, 31 K for LCMVDy0.15 and 35 K for LCMVDy0.25 compounds [90%] at 4 T. The field dependence of the magnetic entropy change is also analyzed showing the power law dependence, ΔSM∞Hn where n=0.75(2) for LCMVDy0.03, n=0.80(4) for LCMVDy0.15 and n=0.92(8) for LCMVDy0.25 compounds at their respective transition temperatures. The relative cooling power and its field dependance are also analyzed. 相似文献
12.
Effects of Ag addition on electrical transport and magnetic properties of La0.67Ba0.33Mn0.88Cr0.12O3
Xiao-Bo Yuan Yi-Hua LiuNa Yin Cheng-Jian WangLiang-Mo Mei 《Journal of magnetism and magnetic materials》2006
We have prepared a series of polycrystalline manganites with the nominal compositions, La0.67Ba0.33Mn0.88Cr0.12O3/Agx (LBMCO/Agx) (x is the mole fraction) with x=0, 0.05, 0.1, 0.15, 0.2, 0.23, 0.27, 0.3, 0.35. The X-ray diffraction patterns show that the samples with x>0.05 are two-phase composites. The Ag addition in LBMCO improves the properties of grain surfaces/boundaries and reduces the resistivity of the composites. For x=0.30 sample, a minimum resistivity is obtained and a maximum room temperature magnetoresistance up to −54.5% was observed at 288 K, 1 T field. The room temperature TC and the reduced resistivity are responsible for the enhancement of room temperature MR. 相似文献
13.
Sushil K. Misra Sergey I. Andronenko Saket Asthana 《Journal of magnetism and magnetic materials》2010,322(19):2902-16348
Four manganite samples of the series, (La1/3Sm2/3)2/3SrxBa0.33−xMnO3, with x=0.0, 0.1, 0.2 and 0.33, were investigated by X-band (∼9.5 GHz) electron paramagnetic resonance (EPR) in the temperature range 4-300 K. The temperature dependences of EPR lines and linewidths of the samples with x=0.0, 0.1 and 0.2, containing Ba2+ ions, exhibit similar behavior, all characterized by the transition temperatures (TC) to ferromagnetic states in the 110-150 K range. However, the sample with x=0.33 (containing no Ba2+ ions) is characterized by a much higher TC=205 K. This is due to significant structural changes effected by the substitution of Ba2+ ions by Sr2+ ions. There is an evidence of exchange narrowing of EPR lines near Tmin, where the linewidth exhibits the minimum. Further, a correlation between the temperature dependence of the EPR linewidth and conductivity is observed in all samples, ascribed to the influence of small-polaron hopping conductivity in the paramagnetic state. The peak-to-peak EPR linewidth was fitted to ΔBpp(T)=ΔBpp,min+A/Texp(−Ea/kBT), with Ea=0.09 eV for x=0.0, 0.1 and 0.2 and Ea=0.25 eV for x=0.33. From the published resistivity data, fitted here to σ(T)∝1/T exp(−Eσ/kBT), the value of Eσ, the activation energy, was found to be Eσ=0.18 eV for samples with x=0.0, 0.1 and 0.2 and Eσ=0.25 eV for the sample with x=0.33. The differences in the values of Ea and Eσ in the samples with x= 0.0, 0.1and 0.2 and x=0.33 has been ascribed to the differences in the flip-flop and spin-hopping rates. The presence of Griffiths phase for the samples with x=0.1 and 0.2 is indicated; it is characterized by coexistence of ferromagnetic nanostructures (ferrons) and paramagnetic phase, attributed to electronic phase separation. 相似文献
14.
Min Zhou Hong-Ye WuHong-jin Wang Lin ZhengJian-Jun Zhao Ru XingYi Lu 《Physica B: Condensed Matter》2012,407(12):2219-2222
The physical properties of Tb3+ ions substitution at A-site are investigated in the layered manganite La1.2Sr1.8Mn2O7. A series of La1.2−xTbxSr1.8Mn2O7 (x=0, 0.05, 0.15, and 0.20) shows that doping with a Tb ion of smaller radius in La1.2Sr1.8Mn2O7 caused diffraction peaks to shift to high angle. Some samples have an impure diffraction at about 30°, but all samples form single-phase. Samples can be well indexed on a Sr3Ti2O7-type tetragonal structure with the space group I4/mmm. According to the M-T curves, when x≤0.05, the series of samples shows ferromagnetism at low temperatures. With increasing temperature, they have two magnetic transitions at different temperatures. When x≥0.15, the magnetizations dramatically decrease. The ρ–T curves of samples show the metal–insulator transition for x=0, 0.05, and the maximum MR values in magnetic field 5 T are 74% at about 73 K and 94% at about 86 K. When x≥0.15, the samples remain in the insulator state in the whole observed temperature range, and the maximum MR values of 86% and 69% appeared at 74 K and 42 K. 相似文献
15.
Younghun Hwang Sunglae ChoHyekyeong Kim Youngho Um 《Journal of magnetism and magnetic materials》2006
We have investigated the magnetic and electrical transport properties of Si1−xMnx single crystals grown by the vertical Bridgman method. The alloys with Mn concentrations up to x=0.64 have weak ferromagnetic ordering around TC∼30 K. However, Si0.25Mn0.75 alloys show weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, which is confirmed by magnetization and electrical transport studies. 相似文献
16.
Ajay Kaushal 《Physica B: Condensed Matter》2009,404(20):3732-3738
Sn1−xMnxO2 (x=0.01-0.05) thin films were synthesized on quartz substrate using an inexpensive ultrasonic spray pyrolysis technique. The influence of doping concentration and substrate temperature on structural and magnetic properties of Sn1−xMnxO2 thin films was systematically investigated. X-ray diffraction (XRD) studies of these films reflect that the Mn3+ ions have substituted Sn4+ ions without changing the tetragonal rutile structure of pure SnO2. A linear increase in c-axis lattice constant has been observed with corresponding increase in Mn concentration. No impurity phase was detected in XRD patterns even after doping 5 at% of Mn. A systematic change in magnetic behavior from ferromagnetic to paramagnetic was observed with increase in substrate temperature from 500 to 700 °C for Sn1−xMnxO2 (x=0.01) films. Magnetic studies reveal room-temperature ferromagnetism (RTFM) with 3.61×10−4 emu saturation magnetization and 92 Oe coercivity in case of Sn1−xMnxO2 (x=0.01) films deposited at 500 °C. However, paramagnetic behavior was observed for the films deposited at a higher substrate temperature of 700 °C. The presence of room-temperature ferromagnetism in these films was observed to have an intrinsic origin and could be obtained by controlling the substrate temperature and Mn doping concentration. 相似文献
17.
B. Munirathinam M. Krishnaiah M. Manivel Raja 《Journal of Physics and Chemistry of Solids》2010,71(12):1763-1767
Lanthanum based mixed valence manganite system La1−xCax−0.08Sr0.04Ba0.04MnO3 (LCSBMO; x=0.15, 0.24 and 0.33) synthesized through the sol-gel route is systematically investigated in this paper. The electronic transport and magnetic susceptibility properties are analyzed and compared, apart from the study of unit cell structure, microstructure and composition. Second order phase transition is observed in all the samples and significant difference is observed between the insulator to metal transition temperature (TMI) and paramagnetic (PM) to ferromagnetic (FM) transition temperature (TC). In contrast to the insulating FM behaviour usually observed in La1−xCaxMnO3 (LCMO) for x=0.15, a clear insulator to metal transition is observed for LCSBMO for the same percentage of lanthanum. The temperature dependent resistivity of polycrystalline pellets, when obeying the well studied law ρ=ρo+ρ2T2 for T<TMI, is observed to differ significantly in the values of ρo and ρ2, with the electrical conductivity increasing with x. The variable range hopping model has been found to fit resistivity data better than the small polaron model for T>TMI. AC magnetic susceptibility study of the polycrystalline powders of the manganite system shows the highest PM to FM transition of 285 K for x=0.33. 相似文献
18.
We synthesized the Mn-doped Mg(In2−xMnx)O4 oxides with 0.03?x?0.55 using a solid-state reaction method. The X-ray diffraction patterns of the samples were in a good agreement with that of a distorted orthorhombic spinel phase. Their lattice parameters and unit-cell volumes decrease with x due to the substitution of the smaller Mn3+ ions to the larger In3+ ions. The undoped MgIn2O4 oxide presents diamagnetic signals for 5 K?T?300 K. The M(H) at T=300 K reveals a fairly negative-sloped linear relationship. Neither magnetic hysteresis nor saturation behavior was observed in this parent sample. For the Mn-doped samples, however, positive magnetization were observed between 5 and 300 K even if the x value is as low as 0.03. The mass susceptibility enhances with Mn content and it reaches the highest value of 1.4×10−3 emu/g Oe (at T=300 K) at x=0.45. Furthermore, the Mn-doped oxides with x=0.06 and 0.2, respectively, exhibit nonlinear magnetization curves and small hysteretic loops in low magnetic fields. Susceptibilities of the Mn-doped samples are much higher than those of MnO2, Mn2O3 oxides, and Mn metals. These results show that the oxides have potential to be magnetic semiconductors. 相似文献
19.
B.S. Wang W.J. LuS. Lin J.C. LinP. Tong B.C. ZhaoW.H. Song Y.P. Sun 《Journal of magnetism and magnetic materials》2012,324(5):773-781
The effects of Mn substitutions on the crystal structure, magnetic properties, and magnetocaloric effect (MCE) of antiperovskite Sn1−xCMn3+x (0≤x≤0.40) have been investigated detailedly. Both the Curie temperature (TC) and the magnetizations at 40 kOe decrease with increasing x firstly for x≤0.10, and then increase with increasing x further. The type of magnetic transition changes from first-order to second-order around x=0.10 with increasing x. Chemical composition-dependent MCE is also studied around TC. With increasing x, the maximal magnetic entropy changes decrease and the magnetic phase transitions broaden. Accordingly, the relative cooling power (RCP) increases with increasing x, reaching the largest values of ∼0.56 J/cm3 (∼75 J/kg) and ∼1.66 J/cm3 (∼221 J/kg) with the magnetic changes of 20 kOe and 48 kOe, respectively. Considering the large RCP, inexpensive, and innoxious raw materials, these serial samples Sn1−xCMn3+x are suggested to be potential room-temperature magnetic refrigerant materials. 相似文献
20.
Y. Hirobe Y. Kubo K. Kouyama H. Kunugita K. Ema H. Kuwahara 《Solid State Communications》2005,133(7):449-453
Photoinduced effects in a single crystal of bilayered manganites, La2−2xSr1+2xMn2O7 (x=0.38), were investigated in a wide range of temperatures by pump-probe measurement at a photon energy of 1.6 eV. In a ferromagnetic metallic state, significant enhancement of positive rise in differential reflectivity with a slow relaxing time of 100 ps was observed just below TC=127 K, indicating that the reflectivity change with the slow relaxation time constant is induced by laser heating. We have also observed an unconventional fast relaxing component that has a time constant of the order of 10 ps. This fast relaxing component, whose absolute value has an asymmetric peak at TC, is presumably due to short-range correlation of Jahn-Teller distortion. 相似文献