Search

The structural, electronic, and magnetic properties of CoFeCrX (X=Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L21 structure with small disorder. The cubic phase of CoFeCrSi was found to be highly stable against heat treatment, but CoFeCrGe disintegrated into other new compounds when the temperature reached 402°C (675K). Although the first-principle calculation predicted the possibility of tetragonal phase in CoFeCrGe, the tetragonal phase could not be stabilized experimentally. Both CoFeCrSi and CoFeCrGe compounds showed ferrimagnetic spin order at room temperature and have Curie temperatures (TC) significantly above room temperature. The measured TC for CoFeCrSi is 790K but that of CoFeCrGe could not be measured due to its dissociation into new compounds at 675K. The saturation magnetizations of CoFeCrSi and CoFeCrGe are 2.82μB/f.u. and 2.78μB/f.u., respectively, which are close to the theoretically predicted value of 3μB/f.u. for their half-metallic phases. The calculated band gaps for CoFeCrSi and CoFeCrGe are, respectively, 1eV and 0.5eV. These materials have potential for spintronic device applications, as they exhibit half-metallic electronic structures with large band gaps, and Curie temperatures significantly above room temperature. [ABSTRACT FROM AUTHOR]

This paper describes a progressive image transmission (PIT) scheme using a variable block size coding technique in conjunction with a variety of quantization schemes in the transform domain. The proposed scheme uses a region growing technique to partition the images so that regions of different sizes can be addressed using a small amount of side information. This segmentation divides the image into five different regions that vary in size based on the details within the image. High-detail blocks are classified into four different categories based on the energy distribution followed by vector quantization (VQ), and low-detail blocks are encoded with scalar quantization (SQ). Progressive refinement is achieved by proper masking of the information in the transform domain. Simulation results show that the reconstructed images preserve fine and pleasant qualities based on both subjective and mean square error criteria. Also, the receiver reconstructs more details in each stage so that the observer can recognize the image quickly.

Mn1.5X0.5Sn (X = Cr, Mn, Fe, Co) nanomaterials in the hexagonal Ni2In-type crystal structure have been prepared using arc-melting and melt spinning. All the rapidly quenched Mn1.5X0.5Sn alloys show moderate saturation magnetizations with the highest value of 458 emu/cm3 for Mn1.5Fe0.5Sn, but their Curie temperatures are less than 300K. All samples except the Cr containing one show spin-glass-like behavior at low temperature. The magnetic anisotropy constants calculated from the high-field magnetization curves at 100K are on the order of 1 Merg/cm3. The vacuum annealing of the ribbons at 550 °C significantly improved their magnetic properties with the Curie temperature increasing from 206K to 273K for Mn1.5Fe0.5Sn. [ABSTRACT FROM AUTHOR]

The Co-substituted Mn2RuSn nanomaterials, namely, Mn2Ru0.5Co0.5Sn and Mn2Ru0.35Co0.65Sn have been synthesized and investigated. The presence of Co in the Mn2RuSn (a = 6.21 Å) decreased the lattice parameter, where a = 6.14 Å and 6.12 Å for the as prepared Mn2Ru0.5Co0.5Sn and Mn2Ru0.35Co0.65Sn, respectively. The samples show a ferrimagnetic spin order with relatively small coercivities, similar to those of soft magnetic materials. There is a substantial increase in the Curie temperature (Tc = 448 K for Mn2Ru0.5Co0.5Sn and 506 K for Mn2Ru0.35Co0.65Sn) of Mn2RuSn (Tc = 272.1 K) due to Co substitution, which is a result of strengthening of the positive exchange interaction in this material. These materials are highly stable against heat treatment of up to 450 °C. The first-principles calculations are consistent with our experimentally observed structural and magnetic properties. They also provide insight on how the magnetic and electronic structures change when Ru is replaced with Co in Mn2RuSn. [ABSTRACT FROM AUTHOR]

Vertical type probe is made by microelectromechanical system (MEMS) process in microscale for high degree of integration and performance. To design reliable probe before manufacturing, mechanical properties in microscale is needed. Also, manufactured probe is heat-treated to release residual stress. In this paper, to understand mechanical properties and heat treatment effect in microscale, tensile tests for Ni–Co alloy thin film is performed using specimen with heat-treated under air. The Ni–Co thin film has some enhanced mechanical properties by heat effect and becomes brittle. The changes of grain size distribution and grain direction are observed through electron back-scattered diffraction (EBSD). [ABSTRACT FROM AUTHOR]

Racemic fluids of chiral calamitic molecules are investigated with molecular dynamics simulations. In particular, the phase behavior as a function of density is examined for eight racemates. The relationship between chiral discrimination and orientational order in the phase is explored. We find that the transition from the isotropic phase to a liquid crystal phase is accompanied by an increase in chiral discrimination, as measured by differences in radial distributions. Among ordered phases, discrimination is largest for smectic phases with a significant preference for heterochiral contact within the layers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structural, magnetic, and electron-transport properties of Mn3-xPtxSn (x=0, 0.5, 1) nanomaterials prepared by arc-melting, melt-spinning, and annealing were investigated. It was found that the hexagonal structure is the most stable structure for Mn3Sn and the samples show an antiferromagnetic spin order at room temperature. The Pt-containing samples are mainly tetragonal but contain a small amount of other impurity phases, including hexagonal Mn3Sn and Mn2Sn. At room temperature, the Pt-containing samples show ferri- or ferromagnetic spin order with a Curie temperature of about 370 K. The measured high-field magnetization and anisotropy constant for Mn2PtSn are 405 emu/cm3 and 2.6 Mergs/cm3, respectively. The samples are all highly conducting with metallic electron transport and show a substantial negative magnetoresistance. [ABSTRACT FROM AUTHOR]

The magnetic and magnetocaloric properties of iron-substituted Co2VGa alloys, Co2-xFexVGa (x = 0, 0.1, 0.15, 0.2, 0.3), were investigated. The Fe-substituted samples, prepared by arc melting, melt spinning, and annealing, crystallized in the L21 Heusler structure, without any secondary phases. The Curie temperature and high-field magnetization at 50 K decreased from 345 K and 44 emu/g (1.90 μB/f.u.) for Co2VGa to 275 K and 39 emu/g (1.66 μB/f.u.) for Co1.7Fe0.3VGa, respectively, but the maximum entropy change remained almost insensitive to Fe concentration for x ≤ 0.2, the highest value being 3.3 J/kgK at 7 T for Co1.85Fe0.15VGa. First-principle calculations show that Co2VGa retains its half-metallic band structure until at least 30% of the cobalt atoms are replaced by Fe atoms. The wide operating temperature window near room temperature and the lack of thermal and magnetic hysteresis are the interesting features of these materials for application in room-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]