FeCuNbSiB纳米晶合金磁性电阻与结构的研究

本文系统地研究了FeCuNbSiB(Mo)系列合金的磁性与退火工艺的关系,并研究了合金元素Cu、Nb、Mo等含量对非晶及纳米晶合金磁性的影响,探讨了纳米晶电阻率与温度的关系,实验结果表明,可以获得高性能纳米晶的途径。

在离子束混合下磁性多层膜的磁电阻与感生磁各向异性现象

本实验表明在磁场中进行离子束(Au+)混合处理的AuFe多层膜,超顺磁和非超顺磁的磁矩都对磁电阻有贡献,并且表现出对于磁场的不对称性。这与在磁场下离子束混合造成的感生磁各向异性有关。并且离子束混合可以使磁阻增加5倍左右。本实验同时发现不均匀的微结构对磁阻有重要贡献。

强磁性金属薄膜磁敏电阻在自动控制系统中的应用

本文提出了强磁性金属薄膜磁敏电阻RCM0 1在几种典型应用中的解决方法。

2004年～2005年磁性功能材料及其应用研究新进展

本综述性论文开始写于1996年,其后每年撰写。本年综述的内容包含:(1)磁光记录和磁记录材料;(2)纳米铁氧体材料;(3)新的磁测量器;(4)磁电阻材料;(5)稀土磁性材料。

INVESTIGATION ON MAGNETISM OF THE NANOMETER GRANULAR FILMS

The quantum phenomenological model has been proposed to investigate the magnetic property of nanometer magnetic granular film in an applied magnetic field.The magnetoresistance of the granular films with two distinct magnetic phases has been calculated by using Born approximation.The results show that the average scattering cross section of the magnetic cluster decreases with the increasing number n of the atom.The origin of the giant magnetoresistance comes from the spin dependent scattering between conduction electrons and magnetic granules and the field dependence of magnetoresistance and the quadratic relation of magnetoresistance on the rate of magnetic moment are in good agreement with the experiments reported.

First Principles Study of the Electronic and Magnetic Properties of Ce Doped SrMnO3

The electronic and magnetic properties of Ce doped SrMnO3 have been investigated us- ing the pseudo-potential plane wave method within the generalized gradient approximation method by first principles. The different Mn-O bond lengths indicate that there is a strong Jahn-Teller distortion of the MnO6 octahedron, which associates with a structural phase transition from cubic symmetry （Pm3m） to tetragonal symmetry （I4/mcm）, and the Jahn- Teller ordering stabilizes a chain like （C-type） antiferromagnetie ground state. The electronic structures indicate that SrMnO3 and Sr1-xCexMnO3 （z=0.125 and 0.25） are semiconductor and metallic, respectively. The doping of SrMnO3 with cerium induces simultaneously a decrease in the electrical resistivity, which can be attributed to the formation of Mn3＋ as a result of charge compensation. The density of states and charge density map present that hybridization exists between some of O bands with those of Mn and Ce bands, the bonding between Sr and O is mainly ionic. Density of states and magnetic moment calculations show that the formal valence state of the Ce ion is trivalence.

Substrate temperature dependence of chemical state and magnetoresistance characteristics of Co–TiO2 nanocomposite films

Co−TiO2 nanocomposite films were prepared via magnetron sputtering at various substrate temperatures.The films comprise Co particles dispersed in an amorphous TiO2 matrix and exhibit coexisting ferromagnetic and superparamagnetic properties.When the substrate temperature increases from room temperature to 400℃,Co particles gradually grow,and the degree of Co oxidation significantly decreases.Consequently,the saturation magnetization increases from 0.13 to 0.43 T at the same Co content by increasing the substrate temperature from room temperature to 400℃.At a high substrate temperature,conductive pathways form among some of the clustered Co particles.Thus,resistivity rapidly declines from 1600 to 76μΩ·m.The magnetoresistive characteristic of Co−TiO2 films is achieved even at resistivity of as low as 76μΩ·m.These results reveal that the obtained nanocomposite films have low Co oxidation,high magnetization and magnetoresistance at room temperature.

Effect of sub-layer thickness on magnetic and giant magnetoresistance properties of Ni–Fe/Cu/Co/Cu multilayered nanowire arrays

Ni-Fe/Cu/Co/Cu multilayered nanowire arrays were electrodeposited into anodic aluminum oxide template by using dual-bath method at room temperature. Scanning electron microscopy and transmission electron microscopy were used to characterize the morphology and structure of the multilayered nanowire arrays. Vibrating sample magnetometer and physical property measurement system were used to measure their magnetic and giant magnetoresistance （GMR） properties. The effect of sub-layer thickness on the magnetic and GMR properties was investigated. The results indicate that magnetic properties of electmdeposited nanowires are not affected obviously by Cu layer thickness, while magnetic layers （Ni-Fe and Co layers） have significant influence. In addition, GMR ratio presents an oscillatory behavior as Cu layer thickness changes. The magnetic and GMR properties of the multilayered nanowire arrays are optimum at room temperature for the material structure of Ni-Fe （25 nm）/Cu （15 nm）/Co （25 nm）/Cu （15 nm） with 30 deposition cycles.

Study on switched reluctance generator

The linear and non-linear math models of the switched reluctance generator (SRG) in generator mode were established in this work. The phase current and energy conversion process during generator operation were simulated by the linear math model. The non-linear math model was used to analyze the characteristics of the SRG operation in self-excitation mode and in separately-excitation mode. Some important findings on how the SRG is operated and controlled were obtained in this study, which provides theoretical basis for further design and experimental study.

Quantum Analytical Theory for Giant Magnetoresistance in Magnetic Multilayered Cylindrical Systems

Taking into account the quantum size effects and considering three types of scattering from bulk impurities,rough surface and rough interfaces, we use quantum-statistical Green's function approach and Kubo theory to calculate the electronic conductivity and the giant magnetoresistance in magnetic multilayered cylindrical systems. It is found that in the limit of weakly scattering from impurities surface and interfaces, the total conductivity is given by a sum of conductivities of all the subbands and two spin-channels. For each subband and each spin-channel the scattering rate due to the impurities, surface and interfaces is added up.

Application of generalized impedance boundary conditions to sommerfeld half-space problem

Generalized impedance boundary conditions are employed to simplify the solution of the Sommerfeld half-space problem. An analytical expression is derived for the Hertz potential of a vertical electric dipole over the earth’s surface, in which the earth is assumed to be a layered media or homogeneous dissipative half-space. A Sommerfeld type integral in the potential function is expressed as the sum of two parts: a zeroth order Hankel function and an absolutely convergent series of Bessel functions. In addition, two expressions in closed form are obtained as the far-field and near-field approximation of the present result.

Single carrier frequency domain equalization and diversity combining for cooperative systems

A low-complexity single carrier frequency-domain equalizer （SC/FDE） and diversity combining method for cooperative systems with demodulate-and-forward relaying over frequency-selective channels is proposed. At the relay nodes, linear SC/FDE is adopted and normalized correlation coefficlent is mtrodueed to derive an equivalent source-to-relay-destination （S-R-D） channel that is highlighted in this study. At the destination, a joint SC/FDE and diversity combining receiver is proposed by utilizing the equivalent S-R-D channel. Simulation results demonstrate the superiority of the proposed SC/FDE scheme over the straightforward SC/FDE which ignores the decisions errors at the intermediate relay nodes.

Magnetic iron oxide nanoparticles carrying PTEN gene to reverse cisplatin-resistance of A549/CDDP cell lines

To evaluate the feasibility of using magnetic iron oxide nanoparticle as wild PTEN gene carrier for transfection in vitro to reverse cisplatin-resistance of A549/CDDP cells, A549/CDDP cells were transfected with the wild PTEN gene expression plasmid (pGFP-PTEN) by magnetic iron nanoparticle and lipo2000. The transfection efficiency was detected by fluorescence microscope and flow cytometer. The expression levels of PTEN mRNA and protein were detected by reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemistry analysis. The effect of PTEN transfection on cell cycle enhances the sensitivity of A549/CDDP to cisplatin and nanoparticle-mediated transfection has a higher efficiency than that of the liposome-mediated group. The apoptosis level was up-regulated in PTEN transfection group. The magnetic iron oxide nanoparticle could be used as one of the ideal gene carriers for PTEN gene delivery in vitro. PTEN can be an effective target for reversing cisplatin-resistance in lung cancer.

A Hierarchy of Resolution Systems with Restricted Substitution Rules

The proof system, based on resolution method, has become quite popular in automatic theorem proving, because this method is simple to implement. At present many kinds of extensions for resolution method are known： Resolution with restricted number of variables in disjuncts, resolution over Linear Equations, Cutting planes, etc. For Classical, Intuitionistic and Minimal （Johansson＇s） propositional logics, the authors introduce the family of resolution systems with full substitution rule （SRC, SRI and SRM） and with e-restricted substitution rule （SeRC, SeRf and SeRM）, where the number of substituted formula connectives is bounded by . The authors show that for each of mentioned logic the SR-type system （in tree form） is polynomially equivalent to Frege systems by size, but for every ~＇ 〉 0, Se＋lR-type has exponential speed-up over the SeR-type （in tree form）.

Study of doping effect,phase separation and heterojunction in CMR manganites

Mixed-valence manganites have attracted considerable research focus in recent years not only because of the potential application of colossal magnetoresistance(CMR) in magnetic devices,but also because of many intriguing physical properties observed in these materials.Doping elements at A-site can alter the filling of 3d Mn band and the tolerance factor.Therefore the hole-and electron-doped CMR manganites exhibit a rich phase diagram.In addition,more theoretical and experimental results suggest that phase separation is a critical factor for the understanding of CMR phenomena.Recently,there is an increasing interest in the fabrication and investigation on manganite-based heterojunction,which demonstrated excellent rectifying property,large MR,and photovoltaic effect.

Multiferroics and magnetoelectric effects in charge ordered compounds

The coexistence of magnetic ordering and ferroelectricity, ing on the origin of ferroelectricity, multiferroic materials known as multiferroics, has drawn a lot of research effort. Depend can be classified into different groups. In this paper, we review re cent progress in the field of multiferroics induced by different forms of charge ordering. In addition to a general description of charge order and electronic ferroelectricity, we focus on two specific systems： （1） charge order with frustration in RFe2O4 （R=Lu, Yb） system; （2） charge ordered perovskite manganites of the type （R1-xCax）MnO3 （R=La, Pr）. The charge ordering can be tuned by external electric fields, which results in pronounced magnetoelectric effects and strong dielectric tunability. Other materials and possible candidates with charge order induced multiferroics are also briefly summarized.

Large and controllable tunneling magnetoresistance in ferromagnetic/magnetic-semiconductor/ferromagnetic trilayers

In this work, we selected a magnetic-semiconductor as an interlayer and investigated the electronic transport properties in the ferromagnetic/ferromagnetic-semiconductor/ferromagnetic (FM/FS/FM) trilayers. The results indicate that the large TMR comparable to that in ferromagnetic/metal oxide/ferromagnetic sandwich can be obtained in the FM/FS/FM multilayers with considering the spin filter effect in the magnetic semiconductor layer. Moreover, the transmission coefficient and TMR can be tuned through thickness, Rashba spin-orbit coupling strength and molecular field of the magnetic semiconductor. Our calculations could provide a way to design the semiconductor spintronic devices with excellent and controllable properties.

Large and anisotropic linear magnetoresistance in bulk stoichiometric Cd_3As_2 crystals

Cd3As2 was recently identified as a novel three-dimensional （3D） topological semimetal hosting the long-pursuing 3D Dirac Fermion. Crystals of Cd3As2 grown preferentially along the [100] and [112] directions were obtained through the modified chemical vapor transfer growth method, thus allowing the examination of transport anisotropy. The resistivity and magnetore- sistance （MR） are basically linear with respect to magnetic field （H） in the measured temperature range of 2-300 K irrespective of the directions. The linear resistivity and MR are significantly anisotropic not only along [100] and [112] directions but also with respect to tilt angle between the growth directions and H, thus providing transport signatures of the 3D Dirac Fermion as well as the possible linear and anisotropic change of Weyl Fermi surface in H. Very large MR along the [100] direction is observed, even approaching 3100% at 2 K and 14 kOe （10e = 79.5775 A m^-l）. The results would be helpful in renewing interest in studying emergent phenomena arising from bulk 3D Dirac Fermion as well as in paving the way for Cd3As2 to be used in magnetoelectronic sensors.

Research Progress on Colossal Anisotropic Magnetoresistive Effect

Perovskite manganites show exotic functionalities due to the coupling between spin, charge, orbital and lattice, such as metal-insulator transition, colossal magnetoresistance （ CMR ） , charge-orbital order and phase separation. Recently, an extraordinary anisotropic magnetoresistance （ AMR ） has been observed in perovskite manganite single crystals. The AMR value is about 2 orders larger than that of the conventional 3E transition metals and alloys, which is attributed to tunable metal-insulator transition temperature modulated by the magnetic field. This result provides a new route for exploring novel AMR materials and their applications.

Transport properties in La_(0.7-x)Gd_xSr_(0.3)MnO_3 system

The influence of Gd doping at La-site on the electrical transport properties and the colossal magnetoresistance of La0.7-xGdxSr0.3MnO3 (x = 0.00, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, and 0.70) is studied. The experimental results indicate that the transport properties exhibit abnormal behavior under high doping condition. For x = 0.50, we find that a transition from metal to insulator occurs after the occurrence of insulator-metal transition near Tc, which seldom occurs in ABO3 structure. For samples x = 0.60 and 0.70, it exhibits insulator behavior far above Tc. These abnormal behaviors are attributed to different magnetic background, i.e. the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order.