Mechanical Behavior of Cohesive Soil under Repeated Loading

A new triaxial apparatus which can control the stress condition automatically in a constant mean principal stress under repeated loading was developed, Mechanical behavior of cohesive soils under repeated loading was investigated. Excess pore water pressure generated in loading cycles was measured and the experimental results were interpreted in terms of effective stress by using elasto-plastic models

Observation of the spin-charge thermal isolation of ferromagnetic Ga_{0.94}Mn_{0.06}As by time-resolved magneto-optical measurement

The dynamics of magnetization under femtosecond optical excitation is studied in a ferromagnetic semiconductor Ga_{0.94}Mn_{0.06}As with a time-resolved magneto-optical Kerr effect measurement with two color probe beams. The transient reflectivity change indicates the rapid rise of the carrier temperature and relaxation to a quasi-thermal equilibrium within 1 ps, while a very slow rise of the spin temperature of the order of 500ps is observed. This anomalous behavior originates from the thermal isolation between the charge and spin systems due to the spin polarization of carriers (holes) contributing to ferromagnetism. This constitutes experimental proof of the half-metallic nature of ferromagnetic Ga_{0.94}Mn_{0.06}As arising from double exchange type mechanism originates from the d-band character of holes

Alkali-halogen metasomatism of the CM carbonaceous chondrites

Meteorite Hills (MET) 01075 is unique among the CM carbonaceous chondrites in containing the feldspathoid mineral sodalite, and hence it may provide valuable evidence for a nebular or parent body process that has not been previously recorded by this meteorite group. MET 01075 is composed of aqueously altered chondrules and calcium‐ and aluminum‐rich inclusions (CAIs) in a matrix that is predominantly made of serpentine‐ and tochilinite‐rich particles. The chondrules have been impact flattened and define a foliation petrofabric. Sodalite occurs in a 0.6 mm size CAI that also contains spinel, perovskite, and diopside together with Fe‐rich phyllosilicate and calcite. By analogy with feldspathoid‐bearing CAIs in the CV and CO carbonaceous chondrites, the sodalite is interpreted to have formed by replacement of melilite or anorthite during alkali‐halogen metasomatism in a parent body environment. While it is possible that the CAI was metasomatized in a precursor parent body, then excavated and incorporated into the MET 01075 parent body, in situ metasomatism is the favored model. The brief episode of relatively high temperature water–rock interaction was driven by radiogenic or impact heating, and most of the evidence for metasomatism was erased by subsequent lower temperature aqueous alteration. MET 01075 is very unusual in sampling a CM parent body region that underwent early alkali‐halogen metasomatism and has retained one of its products

Electronic structures of doped anatase TiO2\rm TiO_{2}: Ti1−xMxO2\rm Ti_{1-x}M_{x}O_{2} (M=Co, Mn, Fe, Ni)

We have investigated electronic structures of a room temperature diluted magnetic semiconductor : Co-doped anatase $\rm TiO_{2}$. We have obtained the half-metallic ground state in the local-spin-density approximation(LSDA) but the insulating ground state in the LSDA+$U$+SO incorporating the spin-orbit interaction. In the stoichiometric case, the low spin state of Co is realized with the substantially large orbital moment. However, in the presence of oxygen vacancies near Co, the spin state of Co becomes intermediate. The ferromagnetisms in the metallic and insulating phases are accounted for by the double-exchange-like and the superexchange mechanism, respectively. Further, the magnetic ground states are obtained for Mn and Fe doped $\rm TiO_{2}$, while the paramagnetic ground state for Ni-doped $\rm TiO_{2}$.Comment: 5 pages, 4 figure

Half-metallic Antiferromagnet BaCrFeAs2

First-principles calculations and a tight-binding analysis predict that the iron-pnictide BaCrFeAs2 is a promising candidate for half-metallic material with fully-compensated magnetization. The transition-metal ions Cr and Fe prefer the three-dimensional intervening lattice, which yields the antiferromagnetic order of spin orientations. Due to the difference between Cr and Fe in the electronegativity, a band gap is opened at the Fermi level in the spin channel in which Fe provides the majority carriers. The selective hybridization between 3d orbitals of Cr and As:4p states due to the peculiar lattice structure of the iron-pnictide is shown to be crucial for the novel properties.Comment: added reference

Ferromagnetism in laser deposited anatase Ti1−x_{1-x}Cox_{x}O_{2-\delta} films

Pulsed laser deposited films of Co doped anatase TiO2 are examined for Co substitutionality, ferromagnetism, transport, magnetotransport and optical properties. Our results show limited solubility (up to ~ 2 %) of Co in the as-grown films and formation of Co clusters thereafter. For Ti0.93Co0.07O2-d sample, which exhibits a Curie temperature (Tc) over 1180 K, we find the presence of 20-50 nm Co clusters as well as a small concentration of Co incorporated into the remaining matrix. After being subjected to the high temperature anneal during the first magnetization measurement, the very same sample shows a Tc ~ 650 K and almost full matrix incorporation of Co. This Tc is close to that of as-grown Ti0.99Co0.01O2-d sample (~ 700 K). The transport, magnetotransport and optical studies also reveal interesting effects of the matrix incorporation of Co. These results are indicative of an intrinsic Ti1-xCoxO2-d diluted magnetic semiconductor with Tc of about 650-700 K.Comment: 14 pages + 9 figure

Surface Half-Metallicity of CrAs in the Zinc-Blende Structure

The development of new techniques such as the molecular beam epitaxy have enabled the growth of thin films of materials presenting novel properties. Recently it was made possible to grow a CrAs thin-film in the zinc-blende structure. In this contribution, the full-potential screened KKR method is used to study the electronic and magnetic properties of bulk CrAs in this novel phase as well as the Cr and As terminated (001) surfaces. Bulk CrAs is found to be half-ferromagnetic for all three GaAs, AlAs and InAs experimental lattice constants with a total spin magnetic moment of 3 $\mu_B$. The Cr-terminated surface retains the half-ferromagnetic character of the bulk, while in the case of the As-termination the surface states destroy the gap in the minority-spin band.Comment: 4 pages, 2 figures, new text, new titl

Exchange interactions and Curie temperature in (GaMn)As

We use supercell and frozen-magnon approaches to study the dependence of the magnetic interactions in (Ga,Mn)As on the Mn concentration. We report the parameters of the exchange interaction between Mn spins and the estimates of the Curie temperature within the mean-field and random-phase approximations. In agreement with experiment we obtain a nonmonotonous dependence of the Curie temperature on the Mn concentration. We estimate the dependence of the Curie temperature on the concentration of the carries in the system and show that the decrease of the number of holes in the valence band leads to fast decrease of the Curie temperature. We show that the hole states of the valence band are more efficient in mediating the exchange interaction between Mn spins than the electron states of the conduction band

Polaron percolation in diluted magnetic semiconductors

We theoretically study the development of spontaneous magnetization in diluted magnetic semiconductors as arising from a percolation of bound magnetic polarons. Within the framework of a generalized percolation theory we derive analytic expressions for the Curie temperature and the magnetization, obtaining excellent quantitative agreement with Monte Carlo simulation results and good qualitative agreement with experimental results.Comment: 5 page