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51.
H. R. Salva P. Monceau A. Ghilarducci S. Seiro M. Saint-Paul P. Lejay 《Physica B: Condensed Matter》2002,320(1-4):97-99
In previous works (Jornadas SAM 2000; J. Magn. Magn. Mater. 226–230 (2001) 988) the low-frequency anelastic effects of two manganite perovskites of La2/3Sr1/3MnO3 and La2/3Ca1/3MnO3 were studied at 1 Hz and temperatures above those of the metal–insulator transition. An important internal friction peak (P1) appears at 414 and 419 K, respectively, with a modulus variation and no appreciable contribution to electrical resistivity. Another compound Pr1/2Ca1/2MnO3 of the same family has been studied by anelastic mechanical spectroscopy in order to add new data which could elucidate the (P1) peak mechanism. The measurements were made in a sub-resonant forced pendulum (0.1–20 Hz) and in a vibrating reed equipment (kHz range). A stable (P1) peak has been detected at 410 K (1 Hz), with a corresponding modulus step. The appearance of this relaxation peak in the Pr1/2Ca1/2MnO3 compound, and its high activation energy value, similar to the other compounds measured, indicates that the microscopic origin of this relaxation does not correspond to an oxygen jump (characteristic activation energy0.8–0.9 eV). 相似文献
52.
53.
This article gives a quantum‐trajectory demonstration of the observed electric, magnetic, and thermal effects on a quantum dot with circular or elliptic shape. By applying quantum trajectory method to a quantum dot, we reveal the quantum‐mechanical meanings of the classical concepts of backscattering and commensurability, which were used in the literature to explain the peak locations of the magnetoresistance curve. Under the quantum commensurability condition, electronic quantum trajectories in a circular quantum dot are shown to be stationary like a standing wave, whose presence increases the electrical resistance. A hidden quantum effect called magnetic stagnation is discovered and shown to be the main cause of the observed jumps of the magnetoresistance curve. Quantum trajectories in an elliptic quantum dot are found to be chaotic and an index of chaos called Lyapunov exponent is proposed to measure the irregularity of the various quantum trajectories. It is shown that the response of the Lyapunov exponent to the applied magnetic field captures the main features of the experimental magnetoresistance curve. © 2014 Wiley Periodicals, Inc. 相似文献
54.
Using a previous qualitative explanation to describe the transport properties of polycrystalline La2/3Ca1/3MnO3 thick films, we achieved a good fit of the temperature dependence of the resistance R(T). Depending on the sample, we have observed different metal–insulator (MI) transitions while the magnetic behavior is always similar. Small regions of depleted Tc adjacent to the grain boundary could have an important resistance contribution without affecting the magnetic properties in an appreciable manner. In this work, we achieve a quantitative explanation for the different transport behaviors that we have observed experimentally. 相似文献
55.
Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film
La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics
are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial
magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears
at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic
conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese
atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance
with the increase in temperature is due to enhanced spin-flip scattering process. 相似文献
56.
Structural, magnetic and magnetotransport properties of La0.7−x
Ce
x
Ba0.3MnO3 (x = 0–0.4) have been investigated although some unreacted secondary phases of CeO2 were present. The rhombohedral structure (R-3c) forx = 0 transforms to orthorhombic with the space groupImma forx = 0.3. All samples showed ferromagnetic transition above 300 K and a negative magnetoresistance. For x>0.1, magnetization
data measured at 1 T showed a decrease at low temperatures (T < 50 K) due to antiferro-magnetic coupling between Ce-local moments and Mn-moments. Forx = 0.4, the resistivity showed a maximum around 200 K which corresponds to ordering temperature of cerium. Since these results
are similar to that observed in the Sr-containing La0.5−x
Ce
x
Sr0.5MnO3 (x = 0–0.4) system, we suggest that the cerium ions are in the trivalent state and the anomalous behaviour has been attributed
to a Kondo-like effect.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
57.
58.
59.
The mechanism of GMR effects in La(Mn1–x
Fe
x
)O3 (x=0, 0.01, 0.03) oxides has been investigated by means of magnetic measurements, resistivity measurements in magnetic field and Mössbauer spectroscopy. For the x=0.01 sample, the GMR behavior is similar to that of the conventional (La, A)MnO3 (A: divalent cations) oxides. For the x=0.03 sample, even though the temperature dependence of the Mössbauer spectra was similar to that of the x=0.01 sample, the mechanism for the occurrence of the GMR effect seems to be different. The x=0 sample shows a similar behavior to the x=0.03 sample. A thermal stabilization of spin fluctuation is proposed for the x=0 and x=0.03 sample. 相似文献
60.
通过实验研究了La07-xDyxSr03MnO3(x=000,030,040,050,060,070)体系的M_T曲线,M_H曲线,ρ_T曲线和MR_T曲线. 实验结果表明:随着Dy掺杂的增加,体系从长程铁磁有序向自旋团簇玻璃态、反铁磁及 亚铁磁状态转变. x=030样品的M_T曲线上在TN附近出现磁化强度尖峰, x=040时尖峰消失. 对x=050样品,ZFC的M_T曲线随温度增加出现一个谷,随 后在TN处出现峰;而FC的M_T曲线在低温下呈现负磁矩. 对x=060和070 样品,不论FC还是ZFC的M_T曲线都类似于x=050的ZFC的M_T曲线. 高掺杂时的输 运性质在其磁背景下发生异常. 这些奇异现象用Nel的双格子模型并联合M_H回滞曲线 给予很好地解释.
关键词:
磁结构
输运行为
庞磁电阻效应 相似文献