Magnetoresistance of Carbon Nanotube with the Kane Dispersion Law

Abstract

Considering the nanotube as effective conducting media the magnetoresistance is calculated. For an electron motion along nanotube axis the spin–orbital interaction is considered as perturbation and the Dirac equation is solved for longitudinal wave functions. It is shown that in this case a magnetic field can be considered as perturbation for energy spectrum and density matrix diagonal components for each spin orientation are needed to calculate the nanotube conductivity. For narrow gap nanotube the magnetoresistance depends linearly on a weak magnetic field. Our results show that in nanotubes the negative magnetoresistance (NMR) can be described without theory of weak localization.     

Abnormal electric transport property and magnetoresistance stability of La–Sr–K–Mn–O system

The perovskite samples La1-x (Sr1-yKy )xMnO3 (y = 0.0, 0.2, 04, 0.6, 0.8) were prepared by the solid-state reaction method with comparatively low sintering temperature and with comparatively short sintering time, and the electric transport property and temperature stability of MR of this system were studied. The q-T curves show the abnormal phenomenon that with the increase of K doping amount, resistivity increases, and the insulator-metal transition temperature decreases, which is because the influence of the occupation disorder degree of A-site ions σ2 on the electric transport property of perovskite manganites is larger than that of the radius of A-site ions. In the temperature range below 225 K, MR increases continuously with the decrease of temperature, which is the characteristic of low-field magnetoresistance; in the comparatively wide temperature range near 250 K, the MR-T curves of all the samples are comparatively flat, and the value of MR almost does not change with temperature, which shows the temperature stability of magnetoresistance, and can be explained by the competition between the low-field magnetoresistance induced by spin-dependent tunneling of surface phase and the intrinsic magnetoresistance of grain phase. The magnetoresistance value of the sample with y = 0.8 keeps at (7.92 ± 0.36) % in the very wide temperature range of 225-275 K, and this is a good reference for the preparation of this kind of sample with practical application value in the future.     

Effect of electrode configuration and mode of deposition on magnetoresistance in electrodeposited Co/Cu multilayers on n-Si by a fully electrochemical method

Electrodeposition of metallic multilayers on Si is normally preceded by the vapour deposition of a metallic layer. Since vapour deposition produces an additional step in the production process, direct electrodeposition of multilayers on Si is desirable. However, direct electrodeposition on Si has resulted in low magnetoresistance (MR) - of the order of 1% - at room temperature. With the use of (i) electroless plated copper back contact, (ii) composite potentiostatic pulses, (iii) horizontal electrode configuration and (iv) non-continuous mode of deposition, a room temperature MR of 5.8% has been achieved.     

Strong correlation between structural, magnetic and transport properties of non-stoichiometric Sr2FexMo2−xO6 (0.8 ≤ x ≤ 1.5) double perovskites

Sr₂Fe_xMo_2−xO₆ (x = 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5 wt.%) (SFMO) double perovskite oxides of different compositions have been prepared by sol-gel method. These materials were subjected to X-ray diffraction and found that crystal structure changes from tetragonal to cubic around x = 1.2 wt.%. Lattice parameters and unit cell volume have been calculated using X-ray diffraction data. Magnetization studies have been carried out using Vibrating Sample Magnetometer ranging from −15 kOe to +15 kOe and saturation magnetization (M_s) has been determined. Electrical resistivity and magnetoresistance studies have been carried out in the magnetic field range of −40 kOe to +40 kOe keeping the temperature constant at 5, 150 and 300 K using standard four-probe method. Resistivity studies have also been carried out in the temperature ranging from 5 to 300 K keeping the magnetic field constant at 0, 10, 20 and 40 kOe. Maximum degree of Fe/Mo ordering (η_max) of SFMO has been calculated and compared with magnetic and transport properties. It has been found that there is a strong correlation between 3 parameters η_max, M_s and MR (%), i.e. all of them show a maximum at x = 1.0 wt.% and decreases as x deviates from 1.0 in SFMO. It has been also found that there is a different resistivity behavior between x ≤ 1.2 wt.% and x > 1.2 wt.% samples of SFMO. Semiconductor metal transition temperature was found to be maximum at x = 1.0 wt.%.     

Hexavalent chromium synthesized polyaniline nanostructures: Magnetoresistance and electrochemical energy storage behaviors

In this work, the oxidant Cr(VI) dose was observed to have influenced the polyaniline (PANI) nanostructures as well as the crystallization structure. The temperature dependent resistivity study revealed a quasi 3-dimensional variable range hopping (VRH) electrical conduction mechanism. The permittivity was found to be affected by the PANI nanostructures. The observed positive MR at room temperature in the synthesized PANI samples was analyzed by the wave-function shrinkage model. The electrochemical energy storage was investigated using the cyclic voltammetry (CV) and galvanostatic charge–discharge measurements. The highest gravimetric capacitance of 298.5 F g⁻¹ was obtained in the prepared PANI sample using 3 mmol K₂Cr₂O₇ derived from the CV at a scan rate of 5 mV s⁻¹ and the maximum value of gravimetric capacitance of 330.2 F g⁻¹ was achieved in the galvanostatic charge–discharge measurements at a current density of 0.5 A g⁻¹. After applying an external magnetic field, the capacitance decreased due to the observed positive magnetoresistance phenomenon. The cyclic stability studies revealed that the synthesized PANI samples exhibited good durability and retained around 80% of the capacitance even after 1000 charge–discharge galvanostatic cycles.     

Magnetotransport in the CeIrIn5 System: The Influence of Antiferromagnetic Fluctuations

We present an overview of magnetotransport measurements on the heavy-fermion superconductor CeIrIn₅. Sensitive measurements of the Hall effect and magnetoresistance are used to elucidate the low-temperature phase diagram of this system. The normal-state magnetotransport is highly anomalous, and experimental signatures of a pseudogap-like precursor state to superconductivity, as well as evidence for two distinct scattering times governing the Hall effect and the MR, are observed. Our observations point out the influence of antiferromagnetic fluctuations on the magnetotransport in this class of materials. The implications of these findings, both in the context of unconventional superconductivity in heavy-fermion systems and in relation to the high-temperature superconducting cuprates, are discussed.     

Dependence of Magnetization on Temperature, Magnetoresistance Effect and Magnetic Phase Diagram for the Layered Gd5Ge4 Compound

The dependence of dc magnetization and electrical transport on temperature were systemically studied for the layered Gd₅Ge₄ compound. A complex coexistence behavior of ferromagnetism (FM) with antiferromagnetism (AFM) phase and significant magnetoresistance effect were found under the inducement by the applied magnetic field. The results show an unusual magnetoresistance (MR) effect with opposite behavior at the high and low temperatures, which is positive at high temperature region and negative at low temperature region for the layered Gd₅Ge₄ alloy. And its MR maximum is close to 50%, which can be a very large numerical value e.g. for giant magnetoresistance (GMR) materials. From the magnetization loop under different temperatures, also a magnetization step behavior was found below ∼6.2 K. The results proved an existence of reentrance AFM phase at low temperature. From experimental data, also the magnetic phase diagram is obtained. This kind of complex magnetization is analyzed and discussed in the frame of phase separation. The experimental results opened also the possibility of application of the layered Gd₅Ge₄ compound in the fields of information record and sensor technique.      

磁性金属基体上非磁性涂层厚度的无损检测方法

论述了磁性金属基体上非磁性涂层厚度的无损测量方法,介绍了机械法和磁阻法两种涂层厚度测量仪的测量原理,以及国内市场上几种涂层测量仪的技术特性。     

RE－TM磁光记录薄膜的磁场电效应研究

研究了磁性薄膜磁场电效应的测试方法，ＲＥ－ＴＭ磁光薄膜的测试样品制备、样品的磁场电效应（霍尔效应和磁阻效应）及其温度特性。实验结果表明，制备的ＴｂＦｅＣＯ薄膜的补偿点约为─３８℃。