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1.
The influence of SiO2 on the electrical transport properties of LCMO/SiO2 composites with different SiO2 contents x is investigated, where LCMO represents La2/3Ca1/3MnO3. Results show that the SiO2 phase not only shifts the metal–insulator transition temperature (Tp) to a high temperature range, but also has an effect on the magnetoresistance (MR) of the composites. The temperature dependence of resistivity indicates that the Tp of the composites is obviously higher than that of pure LCMO, and that the peak resistivity ρmax of the composites is lower than that of pure LCMO. In the SiO2 content x∼0.02, the TP is the highest and ρmax becomes the lowest. The experimental observation is discussed on the basis of the analysis of scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns. Compared with pure LCMO, a possible interpretation is presented by considering the influence of SiO2 on the coupling between ferromagnetic (FM) domains of LCMO. 相似文献
2.
The effect of Te-doping at La-site on structural, magnetic and transport properties in the manganites La0.7Sr0.3−xTexMnO3 (0≤x≤0.15) has been investigated. All samples show a rhombohedral structure with the space group . It shows that the Mn-O-Mn bond angle decreases and the Mn-O bond length increases with the increase of Te content. The Curie temperature TC decreases with increasing Te-doping level, in contrast, the magnetization magnitude of Te-doping samples at low temperatures increase with increasing x as x≤0.05 and then decrease with further increasing x to 0.15. The results are discussed in terms of the combined effects of the opening of the new double exchange (DE) channel between Mn2+-O-Mn3+ due to the introduction of Mn2+ ions because of the substitution of Te4+ for Sr2+ and the reduction of the transfer integral b due to the decrease of the Mn-O-Mn bond angle. 相似文献
3.
The evolution of magnetic and electrical phases in La0.8−δCa0.2MnO3 was investigated in terms of La deficiency. We found that the increase of the La deficiency tends to raise the Curie temperature (TC) in La0.8−δCa0.2MnO3. The FM clusters formed in compounds with large La deficiency provide percolation paths above TC. With increasing the La defect, the transport property changes from insulating to metallic state, which is in association with the crossover from a second order to a first order magnetic phase transition in the vicinity of TC. 相似文献
4.
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
5.
Asish K. Kundu 《Solid State Communications》2005,134(5):307-311
Magnetic and electrical properties of Ln0.5Ba0.5CoO3−δ with Ln=Dy and Er have been investigated to examine the effects of large cation size-disorder. While the Dy compound shows the small magnetic anomaly around 290 K just as the Gd derivative, the Er compound is essentially paramagnetic due to the large cation size-disorder. Compositions with the same average A-site cation radii as Dy0.5Ba0.5CoO2.91 and Er0.5Ba0.5CoO2.9, but with smaller size-disorder, show progressive evolution of ferromagnetism and metallic properties with decreasing disorder. 相似文献
6.
The influence of dc current on the resistivity ρ and the Young's modulus E of La0.5Ca0.5MnO3 compound has been investigated by means of an in situ measuring method. At low temperatures, both the resistivity ρ and the relative modulus ΔE increase with the current. A relaxation behavior of ρ to the higher resistive state is observed at a fixed temperature and a constant current. After storing the sample for a few days, ρ decreases with the current, accompanying a slight drop of ΔE at low temperatures. Current-induced effects on ρ and ΔE are interpreted according to the current-induced interwinning of Mn3+O6 octahedral distortion modes between Q2- and Q3-types, which is suggested to contribute to the variation of the resistivity. 相似文献
7.
J. Yang Y.Q. Ma R.L. Zhang B.C. Zhao R. Ang W.H. Song Y.P. Sun 《Solid State Communications》2005,136(5):268-272
The magnetism and transport properties of the samples LaMn1−xTixO3 (0≤x≤0.2) were investigated. All samples show a rhombohedral structure () at room temperature. The sample with x=0 undergoes the paramagnetic-ferromagnetic (PM-FM) transition accompanied by an insulator-metal (I-M) transition due to the oxygen excess. The doped samples show ferromagnetism and cluster behavior at low temperatures. Though no I-M transition associated with the PM-FM transition appears, the magnetoresistance (MR) effect was observed especially at low temperatures under the applied fields of 0.5 T. Due to the fact that the oxygen content in the Ti-doped samples is nearly stochiometry (3.01) and the Hall resistivity at room temperature is negative, the ferromagnetism in LaMn1−xTixO3 (0.05≤x≤0.2) is believed to be consistent with the Mn2+-O-Mn3+ double exchange (DE) mechanism. These results suggest that DE can be obtained by direct Mn-site doping. 相似文献
8.
The effect of Al substitution for Mn site in layered manganese oxides La1.3Sr1.7Mn2−xAlxO7 on the magnetic and electrical properties has been investigated. It is interesting that all the samples undergo a similar and complex transition with lowing temperature; they transform from the two-dimensional short-range ferromagnetic order at T*, then enter the three-dimensional long-range ferromagnetic state at TC, at last they display the canted antiferromagnetic state below TN. T*, TC and TN are all reduced with Al content. Resistivity increases sharply with increasing Al concentration, and the metal-insulator transition disappears when x reaches 10%. Additionally, magnetoresistance (MR) effect is weakened. Al substitution dilutes the magnetic active Mn-O-Mn network and weakens the double exchange interaction, and further suppresses FM ordering and metallic conduction. Owing to the anisotropic interaction in the layered perovskite, the magnetic and electrical properties are more sensitive to Al doping level than those in ABO3-type perovskite. 相似文献
9.
Z.C. Xia S.L. YuanW. Feng L.J. ZhangG.H. Zhang J. TangL. Liu S. LiuG. Peng D.W. NiuL. Chen Q.H. ZhengZ.H. Fang C.Q. Tang 《Solid State Communications》2003,128(8):291-294
The temperature dependence of the resistivity for composite samples of (1−x)La0.67Ba0.33MnO3+xYSZ(LBMO/YSZ) with different YSZ doping level of x has been investigated in a magnetic field range of 0-7000 Oe, where the YSZ represents yttria-stabilized zirconia (8 mol% Y2O3+92 mol% ZrO2). With increasing YSZ doping level, the range of 0-10%, the metal-insulator transition temperature (TP) decreases. However, the resistivity, specially the low temperature resistivity, increases. Results also show that the YSZ doping level has an important effect on a low field magnetoresistance (LFMR). In the magnetic field of 7000 Oe, a room temperature magnetoresistance value of 20% was observed for the composite with a YSZ doping level of 2%, which is encouraging for potential application of CMR materials at room temperature and low field. 相似文献
10.
The effect of Te-doping at La-site on structural, magnetic and transport properties in the manganites La0.7Ca0.3−xTexMnO3 (0≤x≤0.15) has been investigated. All samples show an orthorhombic structure (O′-Pbnm) at room temperature. It shows that the Mn-O-Mn bond angle decreases and the Mn-O bond length increases with the increase in the Te content. All samples exhibit an insulator-metal (I-M) transition and the resistivity increases with the increase in the Te-doping level. Additionally, the Curie temperature Tc decreases and the transition becomes broader with increasing Te-doping level, in contrast, the magnetization of Te-doping samples at low temperatures decrease with increasing x as x≤0.10 and then increase with further increasing x to 0.15. The results are discussed in terms of Jahn-Teller (JT) vibrational anisotropy Q3/Q2 and the opening of the new DE channel between Mn2+-O-Mn3+ due to the introduction of Mn2+ ions because of the substitution of Te4+ ions for Ca2+ ions. 相似文献
11.
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
12.
Z.C. Xia S.L. Yuan W. FengL.J. Zhang G.H. ZhangJ. Tang L. LiuD.W. Liu Q.H. ZhengL. Chen Z.H. FangS. Liu C.Q. Tang 《Solid State Communications》2003,127(8):567-572
An enhanced magnetoresistance and a two-fold effect result from impurity dopant were observed in composites of La0.67Ca0.33MnO3/YSZ and La0.67Ca0.33MnO3/Fe3O4. Where YSZ represents yttria-stabilized zirconia and the doping level of both YSZ and Fe3O4 is 1 mol%. Different electrical and magnetic transport properties, in particular a lower field magnetization behavior, were observed between pure La0.67Ca0.33MnO3 and the impurity doped La0.67Ca0.33MnO3 composites. Compared with pure La0.67Ca0.33MnO3, a possible interpretation is presented by considering the influences of YSZ and Fe3O4 on the structure of grain boundaries and/or surfaces of La0.67Ca0.33MnO3grains. 相似文献
13.
The structure, transport and magnetic properties of (La0.8Sr0.2)1−xMnO3 (0≤x≤0.30) polycrystalline perovskite manganites have been investigated. For all the samples the Curie temperatures, Tc, remain nearly unchanged (329±3 K). Resistivity versus temperature curves for the samples show a double-peak behavior. A significant magnetoresistance (MR) effect and different temperature dependences of the MR ratios of the samples are observed. The shapes of the MR-T curves of the samples can be adjusted by changing x. For the x=0.30 sample, a nearly constant MR ratio of (9.5±0.5)% is obtained over the temperature range from 205 to 328 K. 相似文献
14.
Effect of Fe3O4 segregation at grain boundaries on the electrical transport and magnetic properties of La0.67Ca0.33MnO3 is investigated. The experimental results show that the Fe3O4 segregation not only shifts the paramagnetic-ferromagnetic transition temperature of La0.6TCa0.33MnO3 to a lower temperature region but also induces a new transition in a lower temperature region. Meanwhile, the transition processes observed in both the resistivity and magnetization curves are obviously widened. Compared to pure La0.67Ca0.33MnO3, we assume that the Fe3O4 segregation level at the grain boundaries can modify the electrical transport and magnetic properties of La0.67Ca0.33MnO3. 相似文献
15.
Yimin Cui Liuwan Zhang Chunchang Wang Kai shi Bisong Cao 《Journal of magnetism and magnetic materials》2006
Upon annealing polycrystalline La0.67Ba0.33MnO3 bulk samples in flowing 95%Ar:5%H2 mixed gas at 700 °C for different time, the insulator–metal transition temperature, TP and the amplitude of AC magnetic susceptibility were decreased first, then increased, finally decreased again. While the resistivity was increased monotonically. This anomalous behavior was explained by the combinational effects of oxygen loss and Ba ion vacancies caused by the segregation of Ba ion related impurity phase. 相似文献
16.
I. Pallecchi L. Pellegrino E. Bellingeri A.S. Siri D. Marré G.C. Gazzadi 《Journal of magnetism and magnetic materials》2008
In this work we analyse systematically how morphological and magnetotransport properties of manganite thin films are affected by the damage induced by focused ion beam (FIB) irradiation. We irradiate different areas of the same sample with doses ranging from 5×1012 to 3×1017 ions/cm2 and we find that the film becomes swollen for doses up to 1016 ions/cm2 and is eventually eroded by ion milling for further irradiation. On the other hand, transport properties are much more sensitive to FIB irradiation: the metal–insulator transition temperature is found to decrease monotonically with increasing doses up to 1.8×1013 ions/cm2. At doses higher than 5.6×1013 ions/cm2 the metallic state is completely suppressed and likely, also ferromagnetism. 相似文献
17.
18.
Effects of doping Na on the structure, electrical and magnetic properties of La2/3Ca1/3MnO3 are investigated. A structural phase transition from orthorhombic to rhombohedral structure takes place at y=0.375. All samples show metal-insulator (M-I) transition at the transition temperature and undergo the transition from paramagnetism to ferromagnetism at the Curie temperature TC. and TC increase monotonically with increasing Na content. However the Na-doped samples have a shoulder in their electrical transport curves found below and shows a widened magnetic transition process. On the other hand, intrinsic colossal magnetoresistance (CMR) peaks are observed in all the samples, but samples with y around 0.25 show two MR peaks which can be attributed to magnetic inhomogeneity induced by the doped Na+ ions. Here we propose a method to broaden the CMR peak of perovskite manganite, which is beneficial for practical applications. 相似文献
19.
We report magnetic and photomagnetic studies on polycrystalline Nd0.7Sr0.3CoO3. Strong irreversibility in field cooled and zero field cooled data is observed. The hysteresis plot exhibits a very high coercivity at low temperatures. On photon irradiation, a decrease in the coercivity and an irreversible magnetization enhancement are observed. The analysis of all these data suggest that microscopic phase separation of competing ferromagnetism and antiferromagnetism and/or light-induced spin conversion processes among low, intermediate and high spin states of cobalt ions are responsible for all the properties. 相似文献
20.
Polycrystalline Sm1.4Sr1.2Ca0.4Mn2O7 has been successfully synthesized and investigated with respect to its magnetic and electrical properties. It is found that the sample shows a metal insulator (M-I) transition at 88 K. The maxima of the magnetoresistance (MR) ratio are 95.38% and 98.55% under applied fields of 2 T and 5 T, respectively. At 10 K, the MR attains ∼75% at 5 T. The large MR at low temperature can be attributed to the effects of nearly fully spin-polarized carriers tunneling through the insulating (Sm, Sr, Ca)2O2 layers between the adjacent MnO2 bi-layers. The magnetization data indicates the existence of ferromagnetic clusters. 相似文献