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The in-plane optical anisotropy (IPOA) in (001)-grown GaAs/AlGaAs quantum wells (QWs) with different well widths varying from 2 nm to 8 nm has been studied by reflectance difference spectroscopy. Ultra-thin InAs layers with thickness ranging from 0.5 monolayer (ML) to 1.5 ML have been inserted at GaAs/AlGaAs interfaces to tune the asymmetry in the QWs. It is demonstrated that the IPOA can be accurately tailored by the thickness of the inserted ultra-thin InAs layer at the interfaces. Strain-induced IPOA has also been extracted by using a stress apparatus. We find that the intensity of the strain-induced IPOA decreases with the thickness of the inserted InAs layer, while that of the interface-induced IPOA increases with the thickness of the InAs layer. Theoretical calculations based on 6 band k · p theory have been carried out, and good agreements with experimental results are obtained. Our results demonstrate that, the IPOA of the QWs can be greatly and effectively tuned by inserting an ultra-thin InAs layer with different thicknesses at the interfaces of QWs, which does not significantly influence the transition energies and the transition probability of QWs. [ABSTRACT FROM AUTHOR]

To understand the structure and magnetocaloric effect (MCE) of the crystallized Gd-Co-Al bulk metallic glasses, investigations were performed on the unknown phase of the crystallization product. As a result, the new ternary phases with composition of Gd57.5Co20Al22.5 have been found in the Gd-Co-Al alloy system. The as-cast alloy adopts the orthorhombic crystal system with the space group of Pbam. The alloy preserves the single phase structure during annealing but experiences structural phase transition to crystallize in a different structure. The as-cast alloy orders antiferromagnetically at 59 K and continuous field-induced metamagnetic transition can be observed. The annealed one orders ferromagnetically at 101 K. The magnetization measurements suggest that the antiferromagnetic and ferromagnetic interactions coexist in both the as-cast and the annealed samples and they have complex magnetic structure. MCE of the two samples are far lower than that of the Gd-Co-Al bulk metallic glasses. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect and refrigeration capacity (RC) of Gd55Co20Al25 and Gd55Ni25Al20 bulk metallic glasses (BMGs) have been investigated. Large magnetic entropy changes ΔSM of 11.2 and 10.8 J kg-1 K-1 and large RC values of 846 and 920 J kg-1 are obtained for Gd55Co20Al25 and Gd55Ni25Al20, respectively, at a field change of 7 T. The RC value (640 J kg-1 at 5 T or 920 J kg-1 at 7 T) of Gd55Ni25Al20 BMG is larger than that reported for all magnetocaloric materials, including crystalline and amorphous materials measured under the same conditions. The large RC value is due to the broad ΔSM peak (more than 100 K), which is caused by the disordered structure of an amorphous material. The large ΔSM and RC values make these Gd-based ternary BMGs attractive candidates for magnetic refrigeration applications. [ABSTRACT FROM AUTHOR]

To date, high compressive ductility and energy absorption have been achieved in amorphous metal foams based on high-toughness Pd- and Zr-based metallic glasses and are known to result from two extrinsic toughening mechanisms: bending of struts and shear band arrest by pores. We study here a syntactic amorphous metallic foam produced by infiltration of a bed of hollow crystalline iron spheres with a low-toughness Mg-based metallic glass (Mg60Cu21Ag7Gd12). After quenching to vitrify the matrix, this foam exhibits much higher compressive failure strain and energy absorption than the monolithic metallic glass, an improvement which is assigned to an intrinsic mechanism, i.e., composite toughening by the network of hollow ductile iron spheres. [ABSTRACT FROM AUTHOR]

The cluster model studies of electronic and magnetic properties LaCo13 and La(Fe(x)Al(1-x))13, based on density-Al concentration on the electronic structure and magnetic properties. Reduction of the total binding energy gives equilibrium structures for embedded and isolated clusters. Experiments and theoretical data verify these structures. The icosoahedral structural units offer and explanation for the electronic structure and stability of NaZn(13)-type alloys.

By micromagnetic simulation, we investigated a double 360° domain walls system in two parallel nanowires. Two domain walls are coupled to each other via magnetostatic interaction. When a spin-polarized current is applied to only one nanowire or both nanowires with the same direction, the two domain walls propagate along nanowires together. The critical velocity of such system is obviously higher than that of a single 360° domain wall. The interaction between the two domain walls can be modeled as two bodies that connected by a spring, and we analyzed the coupling characteritics of the double 360° domain walls at last. [ABSTRACT FROM AUTHOR]

The electronic structure of heavy fermion superconductor CeMIn[SUB] (M=Co,Rh,Ir) is studied by density functional theory. Our results indicate that the Min[SUB2] layer plays an important role for stabilizing the layered crystal structure and determining the antiferromagnetic or paramagnetic ground state in this series. When the strong correlation effects of 4 f electrons beyond the local density approximation (LDA) are taken into account by the LDA+U approach, the calculated total (magnetic moment and band structure of CeRhIn[SUB5] yield a good agreement with the experiment. The LDA+U calculation shows that the 4 f electrons in this series are located on the border between localization and itineracy. [ABSTRACT FROM AUTHOR]

The electronic structures and magnetic properties of manganites Nd[sub 0.5]Ca[sub 0.5]MnO[sub 3] with a charge-exchange-type antiferromagnetic ordering are studied by a modified linear combination of the atomic orbital (LCAO) band method within and beyond the local spin density approximation (LSDA and LSDA+U). The known crystal structure with Jahn-Teller distortion is modeled by a large supercell consisting of 80 atoms. Orbital-ordered states like those observed experimentally are obtained in both the LSDA and LSDA+U approaches. However, the LSDA fails in getting the experimentally confirmed charge-ordered insulating ground state. Although the inclusion of the Coulomb interaction, U, in the LSDA+U approach does reduce significantly the density of states of Mn ions around the Fermi level, it does not lead to the formation of an insulating gap. The LSDA+U calculation also shows that with the inclusion of U, the 4f of Nd ions become the majority component of the residual density of states near the Fermi level. In addition, the calculation shows that both the electronic states and magnetic moments of Mn ions are sensitive to many body effects. [ABSTRACT FROM AUTHOR]

The effects on the electronic structure and magnetic property of the Ni site substitution in nonoxide perovskite superconductor MgCNi[sub 3] are studied by using density functional calculations. A sharp high peak of Ni d density of states just lies below the Fermi energy in pure MgCNi[sub 3]. Co-doping results in the onset of ferromagnetism at χ = 0.083. However, the little energy gain as well as small magnetic moment per atom indicate the weak itinerant ferromagnetism. The strong ferromagnetic spin fluctuation in MgCNi[sub 3-χ] Co[sub χ] leads to quench bulk superconductivity, while the Mn atom forms a local magnetic moment of 1.06 µ[sub B] at χ = 0.042 which suppresses superconductivity more seriously than Co does in the low doping case. Cu doping can be well accounted for by the rigid band model, which reduces the density of states at the Fermi level and the T[sub c]. [ABSTRACT FROM AUTHOR]

A systematic study on the ground state electronic structure and magnetic properties of Ni[sub n] (n=2-39 and 55) clusters are performed using the density functional calculation with the local spin-density approximation. The binding energy per atom increases monotonically. The occupation numbers do not change significantly for n>8, which helps us to understand the experimental observation of the photoelectron spectroscopy. The obtained average magnetic moment per atom is larger than the bulk value, and the evolvement of these moments towards the bulk is in good agreement with the experimental trend. However, the average moments of "core" atoms are comparable to or even larger than that of surface atoms, which indicates that the usual conclusion of surface enhancement on magnetism in transition metal clusters may be improper for these Ni[sub n] (n=14-39) clusters. © 2001 American Institute of Physics. A systematic study on the ground state electronic structure and ma! gnetic properties of Ni[sub n] (n=2-39 and 55) clusters are performed using the density functional calculation with the local spin-density approximation. The binding energy per atom increases monotonically. The occupation numbers do not change significantly for n>8, which helps us to understand the experimental observation of the photoelectron spectroscopy. The obtained average magnetic moment per atom is larger than the bulk value, and the evolvement of these moments towards the bulk is in good agreement with the experimental trend. However, the average moments of "core" atoms are comparable to or even larger than that of surface atoms, which indicates that the usual conclusion of surface enhancement on magnetism in transition metal clusters may be improper for these Ni[sub n] (n=14-39) clusters. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Proposes that the composite polaron mechanism for colossal magnetoresistance, is responsible for some unusual physical properties in perovskite manganites. Observation of huge resistance change under magnetic field found in ferromagnetic perovskite manganites; Transport properties of composite polarons; Information on specific heat of composite palorons.

Focuses on a study which examined the band structure and magnetic properties of RFe[sub11]TiN[subx] rare-earth iron intermetallic compounds. Review of related literature; Computational approach considered; Results and discussion.