The ALICE experiment at the LHC

A free-energy function is constructed, which couples strain and magnetic moments in ferromagnetic shape memory alloys. The associated Gibbs function is used to calculate time-dependent transition probabilities between martensite variants in a magnetic field under applied stress. By keeping track of the variant fractions, the evolution of strain and magnetization is determined. The simulation model is built in a finite element program for structural analysis, in order to simulate magnetic field-dependent strain and magnetization characteristics of a test actuator. The influence of material parameters and sample geometry is discussed.     

Fabrication,Microstructure, and Properties of Nanoporous Pd,Ni, and Their Alloys by Dealloying

Nanoporous metals can be fabricated by dealloying, which is one of the reactions that occur during the corrosion of alloys. Nanoporous gold has been widely investigated for several decades, and it has recently been found that other metals, such as platinum, palladium, nickel, and copper, can form nanoporous structures through the dealloying of binary alloys. This article mainly shows fabrication and properties of nanoporous palladium and nickel after introduction of nanoporous metals by referring to nanoporous gold as an example. It is necessary to select binary alloys with suitable elements, in which the dissolution of the less noble element and the aggregation of the nobler element at the solid/electrolyte interface are simultaneously allowed. Postprocessing by thermal or acid treatment alters the nanoporous structure. Various properties of nanoporous metals (including mechanical, catalytic, piezoelectric, hydrogenation, and magnetic ones) are different from those of bulk and nanocrystalline materials and nanoparticles because of their specific three-dimensional network structures consisting of nanosized pores and ligaments. Hydrogenation and magnetic properties are reviewed in terms of lattice strain at curved surfaces. These new metallic nanomaterials are now being investigated from the viewpoint of functional applications, and provide much room for study in various fields.     

Preparation and magnetic properties of ultrafine particles of Fe---Ni alloys

Ultrafine particles (UFP) of six kinds of Fe---Ni alloys were synthesized by the method of hydrogen plasma reaction. The prepared UFP samples were examined by X-ray diffraction, electron transmission microscopy and magnetic measurement. The spherical Fe---Ni UFP alloys with a mean particle size less than 35 nm can be prepared with a production rate much higher than by conventional methods. The phase constitution of UFP alloys is different from the equilibrium phase diagram owing to rapid condensation of evaporated metal gases. Although the magnetization for the UFP alloys has almost the same temperature dependence as that of the bulk alloys, the saturation magnetization remarkably decreases as the bulk alloys change into the UFP alloys.     

Preparation and magnetic properties of ultrafine particles of FeNi alloys

Ultrafine particles (UFP) of six kinds of FeNi alloys were synthesized by the method of hydrogen plasma reaction. The prepared UFP samples were examined by X-ray diffraction, electron transmission microscopy and magnetic measurement. The spherical FeNi UFP alloys with a mean particle size less than 35 nm can be prepared with a production rate much higher than by conventional methods. The phase constitution of UFP alloys is different from the equilibrium phase diagram owing to rapid condensation of evaporated metal gases. Although the magnetization for the UFP alloys has almost the same temperature dependence as that of the bulk alloys, the saturation magnetization remarkably decreases as the bulk alloys change into the UFP alloys.     

The concentration dependence of the electronic specific heat of nearly and weakly ferromagnetic transition metal alloys

An explanation of the asymmetric peak in the electronic specific heat coefficient at the critical concentration for the onset of ferromagnetism in transition metal alloys is provided in terms of the critical fluctuations of magnetization.     

Development of a magnetic measurement device for thin ribbon samples

This paper presents a magnetic measurement device for thin ribbon samples, which are produced by rapid cooling technique. This device enables us to measure magnetic properties easily by only inserting a ribbon sample into a sample holder. The sample holder was made by bakelite to fix any width sample. A long solenoid coil was used to generate a uniform magnetic field and the sample holder was placed at the mid part of the solenoid. The magnetic field strength was measured using a shunt resistor and the magnetic flux density and magnetization in sample ribbons were evaluated by using search coils. The accuracy of measurement was verified with an amorphous metal ribbon sample. Next, we have measured magnetic properties of some magnetic shape memory alloys, which have different compositions. The measured results are compared and we clarified the effect of Sm contents on the magnetic properties.     

热磁预处理对Ni-Mn-Ga单晶磁学和力学性能的影响

研究了预先热磁处理对Ni_503Mn_287Ga₂₁单晶的磁学和力学性能的影响.首先将样品加热到居里温度之上让其冷却,冷却方式分为两种：一种是施加一定大小的磁场从高于居里温度冷却至室温,另一种是在样品经历顺磁-铁磁相变后但还未发生奥氏体-马氏体相变前施加相同大小和方向的磁场并冷却至室温.室温时的拉伸-压缩实验结果表明单晶样品在经历前一种处理后,其可逆应变、磁化强度的变化 （ΔM）比后一种处理的相应值要小很多.在后一种热磁处理的样品中,顺磁-铁磁相变发生后形成了自发磁畴,但这种磁畴不具有择优取向.在顺磁-铁磁相变结束后施加磁场,容易导致择优的马氏体准单畴出现,从而表现出大的可逆应变和ΔM.但对于前者,我们认为样品从居里温度降到室温过程中,其中的磁畴在相同的磁场作用下获得择优生长,形成大磁畴,导致磁诱导的强各向异性.这种择优取向的大磁畴在随后马氏体相变期间影响着马氏体的自发排列方式,不利于马氏体准单畴的出现,结果导致较小的可逆应变和ΔM. 关键词： 磁和力学锻炼 Ni-Mn-Ga单晶 铁磁和马氏体相变     

Surface effects on saturation magnetization in nanoporous Ni

Nanoporous Ni specimens with ligament lengths of 10–210 nm and specific surface areas of 0.03–0.58 nm^?1 were fabricated by the dealloying of Ni_0.25Mn_0.75 alloy and annealing at 473–873 K, and saturation magnetization investigated in terms of their size dependence. Saturation magnetization decreased with decreasing ligament length or increasing specific surface area. This trend is the same as that for nanoparticle Ni. However, the saturation magnetization of nanoporous Ni tends to be lower than that of the nanoparticle Ni when their specific surface areas are the same. It is suggested, therefore, that the surface effect due to a noncollinear arrangement is enhanced by the surface defects in the nanoporous Ni.     

Quantitative model of large magnetostrain effect in ferromagnetic shapell memory alloys

A quantitative model describing the large magnetostrain effect observed in several ferromagnetic shape memory alloys such as Ni₂MnGa is briefly reported.The paper contains an exact thermodynamic consideration of the mechanical and magnetic properties of similar types of materials. As a result, the basic mechanical state equation including magnetic field effect is directly derived from a general Maxwell relation. It is shown that the magnetic field induced deformation effect is directly connected with the strain dependence of magnetization. A simple model of magnetization and its dependence on the strain is considered and applied to explain the results of experimental study of large magnetostrain effects in Ni₂MnGa. Received 29 September 1999     

Study of the magnetic interaction in nanocrystalline Pr-Fe-Co-Nb-B permanent magnets

The magnetic properties of an isotropic, epoxy resin bonded magnets made from Pr-Fe-Co-Nb-B powder were investigated. The magnetization reversal process and magnetic parameters were examined by measurements of the initial magnetization curve, major and minor hysteresis loops and sets of recoil curves. From the initial magnetization curve and the field dependencies of the reversible and irreversible magnetization components derived from the recoil loops it was found that the magnetization reversal process is the combination of the nucleation of reversed domains and pinning of domain walls at the grain boundaries and the reversible rotation of magnetization vector in single domain grains. The interactions between grains were studied by means of δM plots. The nonlinear behavior of δM curve approve that the short range intergrain exchange coupling interactions are dominant in a field up to the sample coercivity.The interaction domains and fine magnetic structure were revealed as the evidence of exchange coupling between soft α-Fe and hard magnetic Nd₂Fe₁₄B grains.     

Comparison of the electrochemical behaviour of SnO2 and PbO2 negative electrodes for lithium ion batteries

In this paper we report our structural and electrochemical investigations of tin dioxide and lead dioxide electrodes in order to highlight the difference observed between them. The electrochemical reactions of these two oxides are known: the reduction of the metal oxide and the reversible formation/decomposition of the lithium-metal alloys. The reversible capacity of these systems is based on the alloy formation. The first reaction is supposedly irreversible (formation of Li₂O), but the X-ray diffraction analysis and especially¹¹⁹Sn Mössbauer spectrometry show a possible re-oxidation of the metal particles in the case of tin dioxide electrodes. However, this reaction is not fully reversible and occurs at a high potential vs. Li. For lead dioxide electrodes, the re-oxidation of the metal particles seems more difficult in spite of the similar structure of both oxides.     

Reentrant magnetism - a low field study

We report low field dc magnetization measurements on (Fe_xMn_1?x)₇₅P₁₆B₆Al₃ alloys at 4 ? T ? 300 K. Reentrant magnetic behavior is observed for x = 0.65, 0.7 and 0.8. By comparing field cooled and zero-field cooled states at low T we separate out the reversible and irreversible contributions to the magnetization M and identify the (field-dependent) temperature for the onset of irreversibility. It is shown that the reversible part of the magnetization can be described by the usual scaling laws for critical behavior in magnetic systems not only at the transition from the paramagnetic to the ferromagnetic phase but also when the latter transforms to a spin glass. We identify the irreversible part of M with a spin glass order parameter.     

磁性材料进展

磁性材料大体上分为两类 :其一为铁磁有序的金属磁性材料 ;其二绝大多数为亚铁磁有序、具有半导体导电性质的非金属磁性材料 .5 0年代以前 ,金属磁性材料占绝对优势 ;5 0年代以后 ,非金属磁性材料发展成为磁性材料的主流 ,除电力工业用的高饱和磁化强度FeSi合金外 ,铁氧体几乎应用于各个领域 .历史似乎按螺旋形的方式发展 ,90年代后 ,金属磁性材料又以新的面貌出现 ,3d (4f,4d ,5d ,5f… )合金与化合物、非晶、纳米微晶磁性材料重领风骚 ,其性能远超越铁氧体 .纳米磁性材料将成为新的功能材料 .文章重点介绍了永磁材料与软磁材料 ,其他如磁记录材料、磁致冷材料、磁致伸缩材料等将作简单介绍 .     

Fabrication of Ni nanodots templated by nanoporous polysulfone membrane: Structural and Magnetic properties

Two-dimensional nickel nanodots were prepared using a simple polymer based lithography process on silicon substrates. The nanoporous polysulfone membranes were fabricated using a phase inversion polymerization process. Nickel nanodots were then grown using the polysulfone membrane as a mask. The structures were written by depositing a certain thickness of nickel using electron beam evaporation. After lift off, the structural properties of the samples were studied using atomic force microscopy and grazing incidence X-ray diffractometry. The dots were found to have diameters in the range of 75–120 nm and heights of 3–5 nm. The magnetization and magnetic domain arrangement of the Ni nanodots were analyzed using vibrating sample magnetometer and magnetic force microscopy respectively. The nanodots were found to exhibit excellent soft ferromagnetic properties with a preferred easy axis of magnetization.     

Perpendicular surface magnetic anisotropy in an amorphous ferromagnet induced by adsorption occurring through the mechanism of the formation of hydrogen bonds

It has been found that the domain structures of amorphous magnetically soft iron-based ferromagnetic ribbons in an atmosphere of water vapor and methyl alcohol are significantly different. In the former case, several domains separated by domain walls oriented at an angle of 30°–40° to the long side of the sample are observed. In the latter case, two domains separated by one wall located in the middle of the sample in parallel to its long side are observed. In the former case, the normal component of the magnetization on the sample surface has been detected using the polar magnetooptical Kerr effect. In the latter case, the normal component of the magnetization is almost absent. The observed effects are reversible. The normal component of the magnetization is induced by the desorption of water and methyl alcohol molecules, which are absorbed through the mechanism of the formation of hydrogen bonds, from the sample surface. According to the performed estimate, the effective field of the perpendicular magnetic anisotropy reaches a value of 1.6 kA/m.     

A structural, magnetostrictive and M(o)ssbauer study of Tb0.3Dy0.7(Fe0.9T0.1)1.95 alloys

The effect of ⅢA metal and transition metal T substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe0.9T0.1)1.95 (T = Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb0.3Dy0.7(Fe0.9T0.1)1.95 alloys is the MgCu2-type cubic Laves phase structure for different substitution. The magnetostriction λs decrases greatly for the substitution of IIIA metal B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb0.3Dy0.7(Fe0.9T0.1)1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostriction λs. It was also found that the effect of different substitutions on the spontaneous magnetostriction λ111 is distinct. The analysis of the Mossbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.     

Magnetic clusters in amorphous metal alloys

The effect of thermal treatment in combination with an external magnetic field and/or elastic stress on the magnetic characteristics of amorphous metal alloys of the 2NSR type is studied. The complex behavior of the magnetization and coercivity values in dependence on the length of annealing at temperatures below crystallization is described. It is assumed that the observed changes in the macroscopic magnetic characteristics are associated with the formation of clusters with different degrees of exchange interaction.     

Properties of Heusler-type materials Fe2TSi and FeCo2Si

A number of 3d, 4d and 5d elements are substituted into Fe₃Si in an attempt to form Heusler-like alloys. It is found that with the heat treatment followed, only the 3d elements V, Mn and Co form Heusler alloys. Substitution of the other elements produces polyphase materials. For such elements the limits of solubility in Fe₃Si are determined. For the Heusler alloys the data on degrees of disorder, hyperfine fields and magnetization are presented. These studies, in addition, test the already known site preferences of the transition metal impurities in Fe₃Si at high impurity concentrations.     

Inverted near-surface hysteresis loops in heterogeneous (nanocrystalline/amorphous) Fe<Subscript>81</Subscript>Nb<Subscript>7</Subscript>B<Subscript>12</Subscript> alloys

Inverted hysteresis loops were observed for the first time in the near-surface layers of heterogeneous (nanocrystalline/amorphous) Fe₈₁Nb₇B₁₂ alloys. In particular, a negative residual magnetization is observed when a positive magnetic field applied in the sample plane is decreased to zero. The inverted hysteresis is qualitatively explained within the framework of a two-phase model, according to which the heterogeneous alloys contain two dissimilar phases exhibiting uniaxial magnetic anisotropy and featuring antiferromagnetic exchange interaction.