4,152 research outputs found
Magnetic excitation in a new spin gap compound CuScGeO: Comparison to CuFeGeO
The compound \CuScGeO is presented as a new member of the family of weakly
coupled spin chain and dimer compounds \CuMGeO. Magnetic susceptibility, heat
capacity, and neutron inelastic scattering measurements reveal that the
compound has the same spin dimer component as \CuFeGeO. The observed narrow
band excitation in bulk measurements is consistent with spin gap behavior. The
energy scale of the weakly coupled dimers in the Sc compound is perfectly
coincident with that in the Fe compound.Comment: 5 page
Nature and Properties of the Soils of the Red and Black Complex of the Hawaiian Islands
A study was made of the mineralogical constitution of the soils of the red and black complex of the Hawaiian Islands. The application of differential thermal analysis established kaolin as the dominant mineral in the red soils and montmorillonite as the dominant mineral in the black soils. To aid in the understanding and interpretation of the experimental data a discussion of the differential thermal apparatus and the clay minerals was given. Four major variations in the soils of the red and black complex, differing in modes of formation, were recognized. The first type consists of black soils forming under low rainfall at low elevations adjacent to red soils forming under higher rainfall on upper elevations. Type II black soils may form under heavier rainfall than type I, but are stabilized by seepage waters from adjacent red soils. Type III comprises a number of black soils developing under restricted drainage, as a result of a high water table, near red soils having better internal drainage. Type IV consists of several profiles of alluvial and ash material, where a red top soil rests upon a black subsoil. In every case, except in a red and black profile from Molokai, kaolin was found to be the dominant clay mineral in the red soil and montmorillonite in the black soil, with a kaolin montmorillonite mixture in the transitionary zones. Under intense leaching and oxidation, kaolin formation was favored. In situations where retention of bases and silica was favored, montmorillonite formation occurred. The cause for the soil colors was reviewed. Hematite and goethite were listed as the main cause for the color in the red soils. Investigation of black soils low in organic carbon from Kunia road supports the view that the black color need not necessarily be associated with organic matter
Correlation between magnetic and transport properties of phase separated LaCaMnO
The effect of low magnetic fields on the magnetic and electrical transport
properties of polycrystalline samples of the phase separated compound
LaCaMnO is studied. The results are interpreted in the
framework of the field induced ferromagnetic fraction enlargement mechanism. A
fraction expansion coefficient af, which relates the ferromagnetic fraction f
with the applied field H, was obtained. A phenomenological model to understand
the enlargement mechanism is worked out.Comment: 3 pages, 3 figures, presented at the Fifth LAW-MMM, to appear in
Physica B, Minor change
CYTOPLASMIC FILAMENTS IN DEVELOPING AND ADULT VERTEBRATE SMOOTH MUSCLE
An extensive study of adult and developing smooth muscle has revealed the widespread occurrence of a distinct filament with an average diameter of about 100 A (termed the 100 A filament). Unlike that of myofilaments, their appearance in longitudinal section is uniform, but in transverse section they have a round profile, occasionally exhibiting a less electron-opaque core. The 100 A filaments are almost invariably preserved under a variety of fixation procedures, whereas myofilaments, particularly the thicker filaments, are preserved inconsistently. The 100 A filaments appear to be randomly oriented throughout the cytoplasm, either singly or in small groups, although they are sometimes concentrated in the juxtanuclear region of the smooth muscle cells. The intimate association of 100 A filaments with dark bodies, in both developing and adult smooth muscle cells, may indicate that these filaments either play a role in dark body formation or, at least, constitute a part of the dark body. The 100 A filaments are conspicuous in developing smooth muscle cells and occasionally form networks or clusters; they appear to decrease in relative number as maturation proceeds, but considerable numbers are still present in adult tissue
Al-Substitution Effects on Physical Properties of the Colossal Magnetoresistance Compouns La0.67ca0.33mno3
We present a detailed study of the polycrystalline perovskite manganites
La0.67Ca0.33AlxMn1-xO3 (x = 0, 0.1, 0.15, 0.5) at low temperatures and high
magnetic fields, including electrical resistance, magnetization, ac
susceptibility. The static magnetic susceptibility was also measured up to 1000
K. All the samples show colossal magnetoresistance behavior and the Curie
temperatures decrease with Al doping. The data suggest the presence of
correlated magnetic clusters near by the ferromagnetic transition. This appears
to be a consequence of the structural and magnetic disorder created by the
random distribution of Al atoms.Comment: 13 pages including 5 figure
Low temperature irreversibility induced by thermal cycles on two prototypical phase separated manganites
We have studied the effect of irreversibility induced by repeated thermal
cycles on the electric transport and magnetization of polycrystalline samples
of La0.5Ca0.5MnO3 and La0.325Pr0.3Ca0.375MnO3. An increase of the resistivity
and a decrease of the magnetization at different temperature ranges after
cycling is obtained in the temperature range between 300 K and 30 K. Both
compounds are known to exhibit intrinsic submicrometric coexistence of phases
and undergo a sequence of phase transitions related to structural changes.
Changes induced by thermal cycling can be partially inhibited by applying
magnetic field and hydrostatic pressure.
Our results suggest that the growth and coexistence of phases with different
structures gives rise to microstructural tracks and strain accommodation,
producing the observed irreversibility. Irrespective of the actual ground state
of each compound, the effect of thermal cycling is towards an increase of the
amount of the insulating phase in both compounds.Comment: to appear in Journal of Alloys and Compounds (2003
Equilibrium tuned by a magnetic field in phase separated manganite
We present magnetic and transport measurements on La5/8-yPryCa3/8MnO3 with y
= 0.3, a manganite compound exhibiting intrinsic multiphase coexistence of
sub-micrometric ferromagnetic and antiferromagnetic charge ordered regions.
Time relaxation effects between 60 and 120K, and the obtained magnetic and
resistive viscosities, unveils the dynamic nature of the phase separated state.
An experimental procedure based on the derivative of the time relaxation after
the application and removal of a magnetic field enables the determination of
the otherwise unreachable equilibrium state of the phase separated system. With
this procedure the equilibrium phase fraction for zero field as a function of
temperature is obtained. The presented results allow a correlation between the
distance of the system to the equilibrium state and its relaxation behavior.Comment: 13 pages, 5 figures. Submited to Journal of Physics: Condensed Matte
Effects of Fe doping in La1/2Ca1/2MnO3
The effect of Fe doping in the Mn site on the magnetic, transport and
structural properties of polycrystalline La1/2Ca1/2MnO3 was studied. Doping
with low Fe concentration (< 10%) strongly affects electrical transport and
magnetization. Long range charge order is disrupted even for the lowest doping
level studied (~2%). For Fe concentration up to 5% a ferromagnetic state
develops at low temperature with metallic like conduction and thermal
hysteresis. In this range, the Curie temperature decreases monotonously as a
function of Fe doping. Insulating behavior and a sudden depression of the
ferromagnetic state is observed by further Fe doping.Comment: 2 pages, presented at ICM2000, to appear in JMM
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