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51.
The author of the comment objects to the characterization and the interpretation of magnetoresistance (MR) effects observed by us in La1−xCaxMnO3 (0≤x<0.4) samples. In this reply, arguments are used to show that the samples' characterization and explanation of the MR by considering the role of the short-charge ordering (CO) regions and magnetic domains are reasonable and acceptable. 相似文献
52.
Transmission resonances in magnetic-barrier structures 总被引：1，自引：0，他引：1
Y. Guo Z.-Q. Li B.-L. Gu Q. Sun J.-Z. Yu Y. Kawazoe 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):263-270
Quantum transport properties of electrons in simple magnetic-barrier (MB) structures and in finite MB superlattices are investigated
in detail. It is shown that there exists a transition of transmission resonances, i.e., from incomplete transmission resonances in simple MB structures consisting of unidentical blocks, to complete transmission
resonances in comparatively complex MB structures (, n is the number of barriers). In simple unidentical block arrangements in double- and triple-MB structures we can also obtain
complete transmission by properly adjusting parameters of the building blocks according to ky-value (ky is the wave vector in y direction). Strong suppression of the transmission and of the conductance is found in MB superlattices which are periodic
arrangements of two different blocks. The resonance splitting effect in finite MB superlattices is examined. It is confirmed
that the rule (i.e., for n-barrier tunneling the splitting would be (n-1)-fold) obtained in periodic electric superlattices can be extended to periodically arranged MB superlattices of identical
blocks through which electrons with tunnel, and it is no longer proper for electrons with k
y
<0 to tunnel.
Received: 18 August 1997 / Revised: 20 September 1997 / Accepted: 13 October 1997 相似文献
53.
The substitution of small contents of trivalent cations for manganese in the oxides Ln0.57Ca0.43Mn1−xMxO3 (Ln=Pr, Na) has been explored for M=Al, Ga, Fe, Cr, Sc, In. It is shown that similarly to Ba-doping, the M-doped Pr-manganites exhibit a great predisposition to ferromagnetism in a low magnetic field of 0.25 T, reaching ferromagnetic (FM) fractions of 85% for M=Ga and 100% for m=Cr, whereas in contrast only small FM fractions (∼8%) can be reached for the M-doped Nd-manganites. The great ability of both Pr and Nd manganites to exhibit ultrasharp steps at 2.5 K, at increasing magnetic field is also demonstrated. The different behaviors of the so-doped manganites are interpreted in terms of geometric effects (size of the A-sites cations and of the doping elements) and of electronic configurations and magnetic properties of the dopants. 相似文献
54.
W. Pfeiffer F. Sattler S. Vogler G. Gerber J.-Y. Grand R. Möller 《Applied physics. B, Lasers and optics》1997,64(2):265-268
Direct illumination of the tunneling gap in an ultrahigh vacuum scanning tunneling microscope with ultrashort pump-probe laser
pulses may offer ultimate spatial and temporal resolution in surface experiments. The electronic bandwidth of the tunneling
gap ( 1 THz) does not limit the time resolution. Our experiments show that multiphoton photoelectron emission from the sample limits
the application of this detection scheme at high laser fluence. However, a substrate specific pump-probe effect in the photoelectron
yield with femtosecond transients is observed on Tantalum and on GaAs(110) surfaces.
Received: 5 November 1996 相似文献
55.
Oxides have become a key ingredient for new concepts of electronic devices. To a large extent, this is due to the profusion of new physics and novel functionalities arising from ultrathin oxide films and at oxide interfaces. We present here a perspective on selected topics within this vast field and focus on two main issues. The first part of this review is dedicated to the use of ultrathin films of insulating oxides as barriers for tunnel junctions. In addition to dielectric non-magnetic epitaxial barriers, which can produce tunneling magnetoresistances in excess of a few hundred percent, we pay special attention to the possibility of exploiting the multifunctional character of some oxides in order to realize ‘active’ tunnel barriers. In these, the conductance across the barrier is not only controlled by the bias voltage and/or the electrodes magnetic state, but also depends on the barrier ferroic state. Some examples include spin-filtering effects using ferro- and ferrimagnetic oxides, and the possibility of realizing hysteretic, multi-state junctions using ferroelectric barriers. The second part of this review is devoted to novel states appearing at oxide interfaces. Often completely different from those of the corresponding bulk materials, they bring about novel functionalities to be exploited in spintronics and electronics architectures. We review the main mechanisms responsible for these new properties (such as magnetic coupling, charge transfer and proximity effects) and summarize some of the most paradigmatic phenomena. These include the formation of high-mobility two-dimensional electron gases at the interface between insulators, the emergence of superconductivity (or ferromagnetism) at the interface between non-superconducting (or non-ferromagnetic) materials, the observation of magnetoelectric effects at magnetic/ferroelectric interfaces or the effects of the interplay and competing interactions at all-oxide ferromagnetic/superconducting interfaces. Finally, we link up the two reviewed research fields and emphasize that the tunneling geometry is particularly suited to probe novel interface effects at oxide barrier/electrode interfaces. We close by giving some directions toward tunneling devices exploiting novel oxide interfacial phenomena. 相似文献
56.
Z. C. Xia F. R. Zeng M. T. Hu B. Dong G. Liu Y. Wang X. N. Feng L. Liu C. Q. Tang S. L. Yuan 《physica status solidi (a)》2006,203(2):366-371
The temperature dependence of the resistance and magnetization of Bi3+‐doped (La0.83Bi0.17)0.67Ca0.33MnO3 is investigated, for which both thermal and magnetic hysteresis phenomena are observed. In a lower applied magnetic field range of 0 < H < 0.5 T and a temperature range of 110 < T < 200 K, a two‐step magnetization behavior with an enhanced magnetoresistance effect is observed. According to the experimental results, it is surmised that the hysteresis behavior results mainly from the coexistence of charge ordered (CO) and ferromagnetic (FM) domains, for which the CO domains have relaxation and pinning effects on the growth and rotation of FM domains. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
57.
We present an analytical device model for a graphene field‐effect transistor (GFET) on a highly conducting substrate, playing the role of the back gate, with relatively short top gate which controls the source–drain current The equations of the GFET device model include the Poisson equation in the weak nonlocality approximation. Using this model, we find explicit analytical formulae for the spatial distributions of the electric potential along the channel and for the voltage dependences of the thermionic and tunneling currents. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
58.
Oxynitride has been used to decrease leakage current of thin film SiO2. Combining with the band structures obtained from first‐principles simulations, tunneling currents through SiO2/silicon oxynitride stacks were calculated. SiO2/silicon oxynitride stacks can reduce leakage current at low oxide field but will fail at higher field. The threshold oxide field, which means that SiO2/silicon oxynitride stacks can not reduce the tunneling current when oxide field is higher than it, decreases with increased nitrogen concentration while the effective oxide thickness remains constant. Direct tunneling and defect‐assisted tunneling will be dominant for lower and higher nitrogen atom concentrations, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
59.
We present a detailed study of the nonlinear dynamic susceptibility of the polycrystalline perovskite manganites La1–x Cax MnO3 (0.30 ≤ x ≤ 0.66), below and above the transition temperature as functions of frequency and temperature. Near to x = 0.5 the system changes from ferromagnetic and conducting to antiferromagnetic and insulating with a large hysteretic behavior in M (T ) and ρ (T ). The Curie temperatures determined from dynamic susceptibility analysis were compared to the data obtained previously by electrical and static magnetic measurements, and a new phase diagram was drawn. The data suggest the presence of correlated magnetic clusters near to the magnetic transition. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
60.
Zhi‐qi Kou Xiao Ma Nai‐li Di Qing‐an Li Zhao‐hua Cheng 《physica status solidi b》2005,242(14):2930-2937