Electrodeposited Co–Cu/Cu multilayered microposts

X-ray lithography and electrodeposition were combined to deposit an array of Co–Cu/Cu multilayer microposts of 500 μm tall into deep recesses for novel giant magnetoresistance (GMR) architectures. A citrate-boric acid electrolyte was used with pulsed potential. The applied potential was determined through inspection of the polarization curve from linear sweep voltammetry, and scanning electron microscopy (SEM)/transmission electron microscope (TEM) confirmed the micropost layered structure. Room temperature magnetoresistance was reported for different bilayer sizes of the micropost, and up to 4% current perpendicular-to-plane giant magnetoresistance (CPP-GMR) with saturation values less than 1 T was observed.     

Co/Cr/Pd多层膜的磁性和磁光特性的研究

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Structure and Magnetoresistance of Co–Gd and Al–Co–Gd Alloy Films

Technical Physics - Structural data and dependences of the film resistance on magnetic field strength R(H) are presented for Co–Gd and Al–Co–Gd alloy films obtained by vacuum...     

Micromagnetic simulation of Sm–Co/α-Fe/Sm–Co trilayers with various angles between easy axes and the film plane

Hysteresis loops and energy products have been calculated systematically by a three-dimensional(3D) software OOMMF for Sm–Co/α-Fe/Sm–Co trilayers with various thicknesses and β, where β is the angle between the easy axis and the field applied perpendicular to the film plane. It is found that trilayers with a perpendicular anisotropy possess considerably larger coercivities and smaller remanences and energy products compared with those with an in-plane anisotropy.Increase of β leads to a fast decrease of the maximum energy product as well as the drop of both remanence and coercivity. Such a drop is much faster than that in the single-phased hard material, which can explain the significant discrepancy between the experiment and the theoretical energy products. Some modeling techniques have been utilized with spin check procedures performed, which yield results in good agreement with the one-dimensional(1D) analytical and experimental data, justifying our calculations. Further, the calculated nucleation fields according to the 3D calculations are larger than those based on the 1D model, whereas the corresponding coercivity is smaller, leading to more square hysteresis loops and better agreement between experimental data and the theory.     

Interdiffusion and solid solution strengthening in Ni–Co–Pt and Ni–Co–Fe ternary systems

Diffusion couple experiments are conducted in Co–Ni–Pt system at 1200?°C and in Co–Ni–Fe system at 1150?°C, by coupling binary alloys with the third element. Uphill diffusion is observed for both Co and Ni in Pt rich corner of the Co–Ni–Pt system, whereas in the Co–Ni–Fe system, it is observed for Co. Main and cross interdiffusion coefficients are calculated at the composition of intersection of two independent diffusion profiles. In both the systems, the main interdiffusion coefficients are positive over the whole composition range and the cross interdiffusion coefficients show both positive and negative values at different regions. Hardness measured by performing the nanoindentations on diffusion couples of both the systems shows the higher values at intermediate compositions.     

Decagonal quasicrystal in the Al–Pd–Mn system

Abstract

A stable decagonal quasicrystal in Al₇₀Pd_30?xMn_x alloys (x = 10–20) was examined by electron diffraction and high-resolution electron microscopy. The decagonal quasicrystalline grains are formed with definite crystallographic relationships to adjacent icosahedral and Al₃Mn crystalline grains. The structure of the decagonal phase, which is formed as the main phase at near Al₇₀Pd₁₀Mn₂₀ composition, is a mixture of decagonal quasicrystalline regions with some linear phason strain and microcrystalline regions. The structures of both regions may be interpreted in terms of quasiperiodic and periodic tilings, constructed with two types of bond lengths, S (about 2 nm) and L (= τ · S, where τ is the Golden ratio), of the same atom cluster with decagonal symmetry.     

Disorder in liquid Cu–Pd alloys

The disorder in thermodynamic and microscopic structure of liquid Cu–Pd alloy at 1350?K has been studied using regular associated solution model. For this, we have calculated free energy of mixing (G_M ), activity (a), concentration fluctuation in long wavelength limit [S_CC (0)] and chemical short-range order parameter (α ₁) of liquid Cu–Pd alloy at 1350?K. The energetic and structural asymmetry of liquid Cu–Pd alloys has been successfully explained on the basis of regular associated solution model.     

Superconducting property of Zr–Co and Zr–Co–Al alloys fabricated by rapid solidification

The superconducting property of Zr_(1−x)Co_x (x = 10–50 at.%) alloys and a Zr₅₅Co₃₀Al₁₅ bulk metallic glass fabricated using techniques of rapid solidification was investigated. The Zr₅₅Co₃₀Al₁₅ alloy crystallized by heat treatment in a vacuum atmosphere exhibited superconductivity of T_c,on = 2.4 K. This was attributable to the superconducting property of a crystalline Zr–Co alloy precipitated in the Zr₅₅Co₃₀Al₁₅ alloy. The T_c,on of the crystalline Zr_(1−x)Co_x alloy was sensitive to the Co content. The increase of Co content for the Zr_(1−x)Co_x alloy led to the decrease of T_c,on. The Zr_(1−x)Co_x alloy exhibited superconductivity of a maximum T_c,on = 3.9 K for the Zr₈₀Co₂₀ alloy with superconducting nanocrystal particles embedded in the amorphous matrix.     

Magnetic transition in Co/(Gd–Co) multilayers

[Co/Gd_0.36Co_0.64]₄/Co multilayers with Co termination layer have been prepared by rf sputtering. They form macroscopic ferrimagnets with a compensation temperature (T_comp) determined by the thickness ratio of the layers. In low fields the magnetization of Co and Gd–Co layers are along the axis of the applied field. Increasing field makes the moments of both the Co and Gd–Co layers deviate from the axis of the field giving rise to a transition into a twisted state. These magnetic transitions were studied by vibrating sample magnetometer (VSM), magneto-optic Kerr effect and magnetoresistance measurements at various temperatures. The nucleation and evolution of surface- and bulk-twisted magnetic states were also observed in these multilayers.     

Elemental and phase composition analysis of hydrogen-sensitive Pd/Mg–Ni films

A magnesium–nickel (Mg–Ni) film with a palladium (Pd) overcoat is switchable between a conducting metallic state and a semiconducting state through hydridation and dehydridation processes. The Pd overcoat is added to suppress possible oxidation of the alloy layer. However, some Pd and oxygen (O) atoms are still able to diffuse into the alloy layer, such that the distributions of elemental and phase compositions along the direction of depth are quite complicated. In this work, we propose a method to obtain more detailed information on the elemental and phase compositions in a Pd/Mg–Ni film by means of analyzing Pd 3d_5/2, Pd 3p_3/2, Ni 2p_3/2, Mg 1s and O 1s photoelectron spectra. The method was applied to analyze a typical Pd/Mg–Ni film sample. Results verified that Pd can diffuse into the alloy layer. An Mg–O phase is formed near the surface. An Mg–Ni alloy phase dominates at deeper regions. The Mg–Ni phase contains 80% of the total number of atoms in the film, and is non-stoichiometric and highly disordered. Nevertheless, it can give a remarkable change of electrical resistivity during hydridation–dehydridation processes. PACS 79.60.-i; 61.05.C-; 79.60.Ht     

Ferrimagnetic properties of Co/(Gd–Co) multilayers

Co/(Gd–Co) multilayers have been prepared by rf-sputtering and investigated by means of Transverse Magnetooptic Kerr Effect (TMOKE), SQUID and VSM magnetometry. The composition of amorphous _Gd0.36Co0.64${\mathrm{Gd}}_{0.36}{\mathrm{Co}}_{0.64}$ layers was chosen so that their saturation magnetization was dominated by Gd moments in all the temperature range. Co and Gd–Co layers formed a macroscopic ferrimagnetically coupled system displaying a compensation temperature. Complete magnetic moment compensation was found at such point. An inversion of TMOKE hysteresis loops and a divergent behaviour of coercivity were also observed. By changing the layers thickness it has been possible to control the magnetic characteristics of the Co/(Gd–Co) structures, in particular the compensation takes place at different temperatures.     

Auger parameters of ternary Pd–Ni–P amorphous alloys

A series of bulk ternary amorphous alloys of Pd_{100?3 x} Ni_{2 x} P _x were prepared and their amorphicity checked by X-ray diffraction (XRD) and neutron scattering. Auger parameters of these alloys have been derived from X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectra (AES). Experiments of XPS and AES on each elemental metal and Ni₂P were also performed for comparison. The results show a clear compositional dependence for the 3d binding energies and the MNN Auger energies of Pd on alloying, while Ni 2p core levels and the Ni LMM Auger lines show a weaker variation. Analysis of the data using “excited atom” models indicates electron transfer from Pd, with P carrying negative charge, but the differences in behaviour of the two metallic species suggests that covalent bonding changes may be significant.     

[Pd/Co-Nb/Pd/Si]多层膜的结构与磁性

用高频溅射法制备了两套[Pd/Co-Nb/Pd/Si]多层膜,分别用X射线衍射和振动样品磁强计做了结构和磁性测量。随Pd层厚度增加(或Co-Nb层厚度减少),Pd层由非晶态过渡到晶态,并观察到Pd的fcc(111)双峰结构,双峰的位置逐渐从两侧向体材料Pd的fcc(111)峰的位置靠近。双峰来源于Co-Nb层与Pb层、Pd层与Si层的晶格失配度以及靠近这两种界面的Pd原子的极化不同。样品的饱和磁化强度随Pd层增厚(或Co-Nb层增厚)从小于同样成分的Co-Nb合金体材料的饱和磁化强度值单调增大到大于体材料     

Superconducting property of Zr–Co–Al–Nb metallic glasses

The superconducting property of Zr₅₅Co_(30?x)Al₁₅Nb_x (x = 0–20 at.%) metallic glasses fabricated by rapid solidification was investigated. The Zr₅₅Co_(30–x)Al₁₅Nb_x (x = 5–20 at.%) metallic glasses with a mixture structure of amorphous and nanocrystal phases exhibited superconductivity of T_c,on = 1.8–2.6 K. The maximum T_c,on = 2.6 K was obtained for the Zr₅₅Co₁₀Al₁₅Nb₂₀ metallic glass. This was attributable to the superconducting property of nanocrystalline particles contained in the Zr₅₅Co₁₀Al₁₅Nb₂₀ alloy. The increase of Nb element in the Zr₅₅Co_(30–x)Al₁₅Nb_x alloy led to the increase of T_c,on and the decrease of glass transition temperature. The glass transition temperature was between 704 and 749 K for the Zr₅₅Co_(30–x)Al₁₅Nb_x (x = 0–20 at.%) alloys. The temperature interval of supercooled liquid state was between 51 and 68 K for the Zr₅₅Co_(30–x)Al₁₅Nb_x (x = 0–20 at.%) alloys.     

Magnetic and structural properties of Pd–Mn–Sn intermetallics compounds

Magnetic and structural properties of Heusler Pd_0.5Mn_{0.5- x} Sn _x with x = 0.05, 0.10, 0.17, 0.20 and 0.25, have been studied by magnetisation and X-ray diffraction measurements at room and low temperatures. The crystal structure at room temperature is L2₁ cubic phase for x = 0.17, 0.20, 0.25 and B2 cubic phase for x = 0.10. Martensite structure 10M, was observed at room temperature for x = 0.05. X-ray measurements at low temperatures revealed a structural transformation from B2 to 14M for the x = 0.10 case. The lattice parameter of the L2₁ phase decreases linearly with the concentration, x. A ferromagnetic behaviour has been detected for L2₁ compounds, but the ferromagnetic exchange characteristic of each composition is of different strength. This gives rise to different Curie temperatures.     

Sm–Co high-temperature permanent magnet materials

Permanent magnets capable of reliably operating at high temperatures up to ~450?C are required in advanced power systems for future aircrafts, vehicles, and ships. Those operating temperatures are far beyond the capability of Nd–Fe–B magnets. Possessing high Curie temperature, Sm–Co based magnets are still very important because of their hightemperature capability, excellent thermal stability, and better corrosion resistance. The extensive research performed around the year 2000 resulted in a new class of Sm_2(Co, Fe, Cu, Zr)_(17)-type magnets capable of operating at high temperatures up to 550?C. This paper gives a systematic review of the development of Sm–Co permanent magnets, from the crystal structures and phase diagrams to the intrinsic magnetic properties. An emphasis is placed on Sm_2(Co, Fe, Cu, Zr)_(17)-type magnets for operation at temperatures from 300?C to 550?C. The thermal stability issues, including instantaneous temperature coefficients of magnetic properties, are discussed in detail. The significance of nanograin structure, nanocrystalline, and nanocomposite Sm–Co magnet materials, and prospects of future rare-earth permanent magnets are also given.     

在Pd/Cu(100)表面上外延的超薄Co膜的结构和磁性

利用脉冲激光溅射(PLD)和分子束外延(MBE)方法制备了超薄膜系统 Co/Pd/Cu(100).脉冲激 光溅射生长的单原子Pd层呈现了很好的二维生长模式.在这个Pd表面上，分子束外延生长的C o层直至12个原子层都表现了层-层生长模式.利用俄歇电子谱(AES)和低能电子衍射(LEED)研 究了该系统的表面结构.利用低温磁光克效应(MOKE)研究了系统的磁学性质.结构研究表明， Co层由于面内晶格失配应力而具有一个四方正交结构；与对比样品Co/Cu(100)的比较研究说 明Pd层的存在强烈地改善了Co膜的起始生长模式和结构.磁光克效应测量表明，Pd层的存在 改变了Co层的磁学性质. 关键词： 薄膜的磁性质 组织与形貌 界面磁性     

Influence of aluminum doping in Li–Co–Ti ferrite

The crystallographic and magnetic properties of low aluminum doped lithium cobalt titanium ferrites, Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄(0.0≤x≤0.5), in the scope of spinel structure and ferrimagnetic property were investigated. Ferrites were doped with aluminum in the range of 0.0–0.5 and were synthesized by using the conventional ceramic methods. Using X-ray diffraction and Mössbauer spectroscopy, we confirmed the formation of crystallized particles. All of the samples showed a single phase with a spinel structure, and the lattice parameters linearly decreased as the doped aluminum content was increased. The particle size of the samples also decreased as the doped aluminum content increased. Until x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄, the Mössbauer spectra could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra of Fe³⁺ with A- and B-sites. However, for x=0.5, the Mössbauer spectrum could be fitted with two Zeeman sextets and one doublet. From the variation of the Mössbauer parameters and the absorption area ratio, the cation distributions were determined. The magnetic behavior of the samples showed that an increase in the aluminum contents led to a decrease in the saturation magnetization, whereas the coercivity decreased until x=0.4 and then increased. The minimum coercivity was 52.4 Oe at x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄.     

Dislocation climb and low-temperature plasticity of an Al–Pd–Mn quasicrystal

Dislocations and phason faults have been studied by transmission electron microscopy in an Al-Pd-Mn sample deformed at 300°C under a high pressure. All dislocation movements have occurred by climb, in contrast with the usual interpretations of dislocation motion in quasicrystals. Several modes of dissociation and decomposition of dislocations have been observed, allowing for estimations of phason fault and antiphase-boundary energies. Work softening is tentatively explained in terms of a varying chemical stress.