Positive and Negative Magnetoresistance of a-C:Fe/Si Heterojunctions

The transition between positive and negative magnetoresistance (MR) is observed for Fe-doped amorphous carbon film/n-silicon (a-C:Fe/Si) heterojunctions. The sign of the MR changes as the applied bias voltage and temperature are changing. The MR transition voltage decreases from 0.2 to 0.06 V when temperature increases from 220 to 280 K. The transition from positive MR to negative MR is found to be accompanied by a decrease in slope of log(I) ~ log(V) plot. This phenomenon may be related to holes and electrons having different magnetic field responses.     

Fe3Si formation in Fe–Si diffusion couples

Two different types of bulk diffusion couples for the Fe–Si system, i.e. Fe/Si and Fe/Fe3Si, have been studied, with emphasis placed on the formation and growth of Fe3Si. Results indicate that Fe3 Si forms initially in Fe/Si couples, followed by FeSi and then FeSi2. Fe3Si has a wide range of stoichiometry, from 10–25 at% Si; however, only stoichiometric Fe3Si appeared in Fe3Si diffusion layers of Fe/Si couples. Off-stoichiometric Fe3Si formed in Fe3Si/Fe couples. The free energy of Fe3Si and Fe–Si affinity are used to explain Fe3Si formation behaviour and the atomic diffusion mechanism in the Fe3Si lattice. © 1998 Kluwer Academic Publishers     

Magnetoresistance and electroresistance effects in Fe3O4 nanoparticle system

Nearly monodisperse spherical magnetite (Fe₃O₄) nanoparticles are prepared by colloidal chemistry route. Magnetic and electronic transport properties of the annealed pellets of these nanoparticles are reported. Effect of external magnetic and electric fields on the magnetic and transport properties of the material are studied as a function of temperature. We find that the highest resistance state of the ferromagnetic system occurs at a magnetic field which is approximately equal to its magnetic coercivity; this establishes the magnetoresistance (MR) in this system to be of the conventional tunnelling type MR as against the spin-valve type MR found more recently in some ferromagnetic oxide systems. The material also shows electroresistance (ER) property with its low-temperature resistance being strongly dependent on the excitation current that is used for the measurement. This ER effect is concluded to be intrinsic to the material and is attributed to the electric field-induced melting of the charge-order state in magnetite.     

Fe3Si基合金的织构研究

采用两次温轧工艺制备出Ｆｅ３Ｓｉ基合金薄板，分别经过去应力退 完全再结晶退火后进行织构研究。结果表明，首次发现Ｆｅ３Ｓｉ基合金轧制后存在单一组分的「１１０」「１１０」形变织构。基本上不存在再结晶织构，即有序的Ｆｅ３Ｓｉ金属间化合物存在着再结晶织构弱化现象。     

金属间化合物Fe3Si的制备方法

文章综述了金属间化合物Fe3Si制备方法的研究现状,详细介绍了Fe3Si的几种常用制备方法,如分子束外延（MBE）、脉冲激光沉积（PLD）、物理气相沉积（PVD）、化学气相沉积（CVD）和机械合金化（MA）,最后归纳了金属间化合物Fe3Si研究面临的主要问题,展望了今后的发展趋势。     

Magnetoresistance of UPt3

We have performed measurements of the temperature dependence of the magnetoresistance up to 9 T in bulk single crystals of UPt₃ with the magnetic field along the b-axis, the easy magnetization axis. We have confirmed previous results for transverse magnetoresistance with the current along the c-axis, and report measurements of the longitudinal magnetoresistance with the current along the b-axis. The presence of a linear term in both cases indicates broken orientational symmetry associated with magnetic order. With the current along the c-axis the linear term appears near 5 K, increasing rapidly with decreasing temperature. For current along the b-axis the linear contribution is negative.     

金属间化合物Fe3Si的研究进展

文章简要介绍了金属间化合物Fe3Si的基本性质、常用的制备方法,以及在软磁性能等方面的应用,并对存在的一些问题以及未来可能的研究方向做了简要探讨。     

Magnetoresistance Intensification of Fe3O4/BaTiO3 Nanoparticle-Composite-Sinter Produced by Low Temperature Heat Treatment

We have presented the study on the magnetoresistance intensification of (Fe₃O₄)_1?X /(BaTiO₃) _X nanoparticle-composite-sinter (NPCS) produced by low temperature heat treatment. The average sizes of ??-Fe₂O₃ and BaTiO₃ nanoparticles are 30?nm and 40?nm, respectively. They were homogeneously mixed together and were sintered at 500?°C for 3?hours in the atmosphere of Ar(90%)/H₂(10%). X?of (Fe₃O₄)_1?X /(BaTiO₃) _X NPCS was varied between 0 and 0.75. With increasing?X, the electrical resistivity (ER) increases and shows the Mott??s variable-range-hopping (VRH) conduction behavior in a wide temperature region. The negative differential magnetoresistivity (ND-MR) is observed for all samples in a moderately high magnetic field region. In a low magnetic field region, the MR shows a large hysteresis. As X increases, the variation of the MR is intensified. We consider that the total number of network channels of the electrical conduction is reduced and the spin scattering is consequently intensified.     

Fe3Si薄膜的制备和性能研究

介绍了Fe3Si的一些基本特性及Fe3Si薄膜的几种主要制备方法,重点介绍了分子束外延法中不同类型衬底、温度对Fe3Si薄膜形成的影响,并且分析了各种制备方法中的一些重要参数对薄膜结构及性质的影响。随着Fe3Si薄膜制备工艺的不断完善,Fe3Si薄膜将会成为一种性能优秀的自旋电子器件。     

Fe3Si基合金的制备及应用研究进展

Ｆｅ３Ｓｉ基合金具有优异的软磁性能,不仅有希望硅钢片（在高频信息领域）,而且还广泛用作音几视频磁头材料和卡片阅读器用磁头材料。本文综述了Ｆｅ３Ｓｉ基合金的制备工艺及应用,并结合我们的研究工作,分析了其研究现状,简要论述了其发展前景。     

Low-rate sputter-deposited Fe3Si thin films on Si substrates: structural and ferromagnetic properties

Fe3Si thin films were sputter-deposited on Si(001) substrates. Structural investigations show that Fe3Si was deposited poly-crystalline with a Si-containing layer at the Fe3Si/Si interface. The formation of the layer was attributed to the influence of low deposition rates used in this study on the grain nucleation in Fe3Si. This layer helps to stabilize the ferromagnetic properties of the subsequent annealed films at 350 degrees C with 5 Oe obtained for coercive field H(c), approximately 920 emu/cm3 for saturation magnetization M(s) and approximately 0.9M(s) for remnant magnetization M(r).     

High-temperature creep and structure investigation of nearly stoichiometric Fe3Si

Single crystals of nearly stoichiometric Fe₃Si were creep-deformed at temperatureT = 450 to 850° C and applied stress=40 to 250 MPa. While the temperature dependence of the steady-state creep rate of crystals with less than 25 at% Si can be described by an exponential function exp (–H _exp/kT), the Fe-26 at% Si samples show an exponential dependence only below 500° C and above 600° C. At intermediate temperatures the dependence is weak. It is suggested that in this intermediate range two phases exist. The experimental results are consistent with the assumption that the phase boundaries do not hinder dislocation movement, and that the disocation velocity in the two phases is different.     

High-temperature creep and structure investigation of nearly stoichiometric Fe3Si

X-ray diffraction measurements were carried out on powdered single crystals of nearly stoichiometric Fe₃Si. The experimental data obtained in the temperature range from room temperature up to 750‡ C in terms of long-range order, thermal expansion, phase transition and Debye temperature (together with values of the Curie temperature) support the existence of two modifications of the DO₃ structure for Fe-26 at% Si alloys and a phase transition in the DO₃ structure field at 595‡ C. The high-temperature modification has a smaller thermal expansion coefficient, a higher Curie temperature and a higher Debye temperature.     

微量Si在W－7Ni－3Fe重合金中的行为

研究了掺到原料Ｗ粉中微量Ｓｉ（４００ｐｐｍ）在Ｗ－７Ｎｉ－３Ｆｅ重合金中的分布及在液相烧结过程中的行为．结果表明，Ｓｉ主要以固溶形式分布在Ｗ晶粒中．Ｘ射线光电子能谱（ＸＰＳ）分析发现，在掺杂Ｓｉ的Ｗ－Ｗ及Ｗ－基体相界面富集ＳｉＯ２和Ｎａ２ＳｉＯ３在未掺杂试样的断口表面发现了较弱的ＷＯ２的ＸＰＳ谱，而在掺杂合金中未发现ＷＯ２．     

微量Si在W—7Ni—3Fe重合金中的行为

研究了掺到原料Ｗ粉中微量Ｓｉ（４００ｐｐｍ）在Ｗ－７Ｎｉ－３Ｆｅ重合金中的分布及在液相烧结过程中的行为。结果表明，Ｓｉ主要以固溶形式分布在Ｗ晶粒中。Ｘ射线光电子能谱（ＸＰＳ）分析发现，在掺杂Ｓｉ的Ｗ－Ｗ及Ｗ－基体相界面富集ＳｉＯ２和Ｎａ２ＳｉＯ３在未掺杂试样的断口表面发现了较弱的ＷＯ２的ＸＰＳ谱，而在掺杂合金中未发现ＷＯ２。     

高能球磨法制备Fe_3Si合金粉末

采用高能球磨法研究了原子配比Fe75Si25的混合粉末在不同的球磨条件下的机械合金化,用X射线衍射(XRD)仪、扫描电子显微镜(SEM)表征样品的物相、晶体结构、晶粒尺寸和点阵常数,分析了Fe75Si25粉末的机械合金化机理。研究表明,球磨时间、球料比和球磨机转速对机械合金化(MA)进程有重要影响。MA 55h后可达到完全合金化,Si溶入Fe中形成α-Fe(Si)饱和固溶体,晶粒尺寸减小至7～8nm。     

Peculiarities of Magnetoresistance of [Fe/SiO]n Discontinuous Multilayers

Journal of Superconductivity and Novel Magnetism - The influence of the magnetic and insulator layer thickness on the crystal structure and magnetoresistive properties of [Fe/SiO]n discontinuous...     

超薄Ni81Fe19薄膜的各向异性磁电阻及磁性能

利用磁控溅射方法制备了一系列超薄Ta(5nm)/Ni81Fe19(20nm)/Ta(3nm)磁性薄膜。着重研究了基片温度、缓冲层厚度对Ni81Fe19薄膜各相异性磁电阻(AMR)及磁性能的影响。利用X射线衍射仪分析了薄膜结构、晶粒取向;用四探针技术测量了薄膜的电阻率和各向异性磁电阻;用FD-SMOKE-A表面磁光克尔效应试验系统测量了薄膜的磁滞回线。结果表明:在基片温度为400℃时制备的Ni81Fe19薄膜具有较大的各向异性磁电阻效应和较低的磁化饱和场,薄膜最大各向异性磁电阻为3.5%,最低磁化饱和场为739.67A/m。基片温度为500℃制备的薄膜,饱和磁化强度Ms值最大。随着缓冲层厚度x的增加,坡莫合金薄膜的AMR值先变大后减小,在x=5nm时达到最大值。     

真空热压烧结制备Fe_3Si基金属间化合物

采用真空热压烧结工艺直接烧结Fe、Si混合粉末,制备了Fe3Si金属间化合物。研究了热压烧结时间对烧结产物微观结构、硬度及致密度的影响。结果表明,经950℃、22MPa热压烧结0.5～4h均可得到高度有序的Fe3Si块体,且随烧结时间的延长,烧结产物中Fe3Si的含量有所增加,但当烧结时间长于2h,Fe3Si的有序度有所降低。同时烧结产物的硬度和密度也有同样的变化规律,其中烧结时间2h时烧结产物具有最佳硬度和密度,分别为90.7HRC和4.62g/m3。     

Crystallization of amorphous Fe73.5Si13.5B9Nb3Cu1

A study is reported on the devitrification behaviour of the amorphous alloy Fe73.5Si13.5B9Nb3Cu1. Samples of the studied glass underwent isothermal and non-isothermal heat treatments in a thermal analysis apparatus. In addition some samples were very rapidly heated to very high temperatures by means of a laser beam. In this way a large temperature range was explored and information was obtained on the overall thermal evolution of the studied amorphous alloy. The experimental results suggest that, as recently proposed in the literature, nanocrystallization can be linked to a rate limiting Nb diffusion stage in the crystal growth process. However topological short range ordering (TSRO) and chemical short range ordering (CSRO) also affect the devitrification behaviour. In the case of the studied alloy, three temperature ranges can be defined. At low temperature only TSRO occurs. Above a temperature that lies approximately in the range 450–500°C, glass in glass phase separation occurs up to a temperature that lies approximately in the range 700–750°C, above which it appears to be very limited. The occurrence of glass in glass phase separation appears to be necessary to obtain a fine microstructure, because Nb concentrates in the boron depleted, iron rich glassy phase. The occurrence of TSRO prior to demixing should be avoided if nanocrystallization is desired. All this appears to be satisfied by isothermally treating the sample at a temperature of 555°C. This revised version was published online in November 2006 with corrections to the Cover Date.