6,851 research outputs found
Magnetic anisotropy, first-order-like metamagnetic transitions and large negative magnetoresistance in the single crystal of GdPdSi
Electrical resistivity (), magnetoresistance (MR), magnetization,
thermopower and Hall effect measurements on the single crystal
GdPdSi, crystallizing in an AlB-derived hexagonal structure are
reported. The well-defined minimum in at a temperature above N\'eel
temperature (T= 21 K) and large negative MR below 3T, reported
earlier for the polycrystals, are reproducible even in single crystals. Such
features are generally uncharacteristic of Gd alloys. In addition, we also
found interesting features in other data, e.g., two-step first-order-like
metamagnetic transitions for the magnetic field along [0001] direction. The
alloy exhibits anisotropy in all these properties, though Gd is a S-state ion.Comment: RevTeX, 5 pages, 6 encapsulated postscript figures; scheduled to be
published in Phy. Rev. B (01 November 1999, B1
Magnetic behaviour of Eu_2CuSi_3: Large negative magnetoresistance above Curie temperature
We report here the results of magnetic susceptibility,
electrical-resistivity, magnetoresistance (MR), heat-capacity and ^{151}Eu
Mossbauer effect measurements on the compound, Eu_2CuSi_3, crystallizing in an
AlB_2-derived hexagonal structure. The results establish that Eu ions are
divalent, undergoing long-range ferromagnetic-ordering below (T_C=) 37 K. An
interesting observation is that the sign of MR is negative even at temperatures
close to 3T_C, with increasing magnitude with decreasing temperature exhibiting
a peak at T_C. This observation, being made for a Cu containing magnetic
rare-earth compound for the first time, is of relevance to the field of
collosal magnetoresistance.Comment: To appear in PRB, RevTex, 4 pages text + 6 psFigs. Related to our
earlier work on Gd systems (see cond-mat/9811382, cond-mat/9811387,
cond-mat/9812069, cond-mat/9812365
Observation of a temperature dependent electrical resistance minimum above the magnetic ordering temperature in GdPdSi
Results on electrical resistivity, magnetoresistance, magnetic Results on
electrical resistivity, magnetoresistance, magnetic susceptibility, heat
capacity and Gd Mossbauer measurements on a Gd-based intermetallic compound,
GdPdSi are reported. A finding of interest is that the resistivity
unexpectedly shows a well-defined minimum at about 45 K, well above the long
range magnetic ordering temperature (21 K), a feature which gets suppressed by
the application of a magnetic field. This observation in a Gd alloy presents an
interesting scenario. On the basis of our results, we propose electron
localization induced by s-f (or d-f) exchange interaction prior to long range
magnetic order as a mechanism for the electrical resistance minimum.Comment: 4 pages, 4 figure
Large Low Temperature Magnetoresistance and Magnetic Anomalies in TbPdSi and DyPdSi
The results of heat-capacity, magnetic susceptibility, electrical resistivity
and magnetoresistance measurements on the compounds
TbPdSi and DyPdSi, are reported. The results establish that
these compounds undergo long-range magnetic ordering (presumably with a complex
magnetic structure) below (Tc=) 23 and 8 K respectively. The is negative in the vicinity of Tc and the magnitude grows as Tc is approached
from higher temperature as in the case of well-known giant magnetoresistance
systems (La manganite based perovskites); this is attributed to the formation
of some kind of magnetic polarons. The magnitude of magnetoresistance at low
temperatures is quite large, for instance, about 30% in the presence of 60 kOe
field at 5 K in the Dy sample.Comment: 4 pages, 3 figures, RevTe
Pion parameters in nuclear medium from chiral perturbation theory and virial expansion
We consider two methods to find the effective parameters of the pion
traversing a nuclear medium. One is the first order chiral perturbation
theoretic evaluation of the pion pole contribution to the two-point function of
the axial-vector current. The other is the exact, first order virial expansion
of the pion self-energy. We find that, although the results of chiral
perturbation theory are not valid at normal nuclear density, those from the
virial expansion may be reliable at such density. The latter predicts both the
mass-shift and the in-medium decay width of the pion to be small, of about a
few MeV.Comment: 9 Pages RevTex, 3 eps figure
Controlled Release of Drug to the Intestine from pH-responsive Chitosan-Poly (vinyl alcohol) Interpenetrating Network Hydrogels
Hydrogels are polymeric networks with three-dimensional configuration capable of imbibing high amounts of water or biological fluids. A truly amazing class of hydrogels that has found potential use for a wide variety of applications is the class of “smart” or “intelligent” hydrogels. Among all, pH-sensitive smart hydrogels have garnered special interest. Chitosan, a polycationic bioplomer, has received a great deal of attention in the fabrication of pH-responsive hydrogels. The interest in chitosan as intestinal drug delivery carriers arises from the fact that it is degraded by the microflora of the colon and is not digested in the upper gastrointestinal tract. Chitosan hydrogels, however, suffer from certain limitations such as poor mechanical strength, high porosity and tendency to absorb moisture. One of the most common methods to alleviate this problem is to incorporate chitosan into another polymeric network by the formation of an interpenetrating network. The focus of the present project is to synthesize pH-responsive chitosan- poly (vinyl alcohol) interpenetrating network hydrogels for controlled delivery of drug to the intestine
The structural and electrical properties of thermally grown TiO2 thin films
We studied the structural and electrical properties of TiO2 thin films grown by thermal oxidation of e-beam evaporated Ti layers on Si substrates. Time of flight secondary ion mass spectroscopy (TOF-SIMS) was used to analyse the interfacial and chemical composition of the TiO2 thin films. Metal oxide semiconductor (MOS) capacitors with Pt or Al as the top electrode were fabricated to analyse electrical properties of the TiO2 thin films. We show that the reactivity of the Al top contact affects electrical properties of the oxide layers. The current transport mechanism in the TiO2 thin films is shown to be Poole–Frenkel (P–F) emission at room temperature. At 84 K, Fowler– Nordheim (F–N) tunnelling and trap-assisted tunnelling are observed. By comparing the electrical characteristics of thermally grown TiO2 thin films with the properties of those grown by other techniques reported in the literature, we suggest that, irrespective of the deposition technique, annealing of as-deposited TiO2 in O2 is a similar process to thermal oxidation of Ti thin films
La substitution induced linear temperature dependence of electrical resistivity and Kondo behavior in the alloys, Ce_{2-x}La_{x}CoSi_{3}
The results of electrical resistivity, heat capacity and magnetic
susceptibility behavior of new class of alloys, Ce_{2-x}La_{x}CoSi_{3}, are
reported. The x= 0.0 alloy is mixed valent and La substitution for Ce (x= 0.25)
induces linear temperature dependence of resistivity at low temperatures, an
observation of relevance to the topic of non-Fermi liquid behavior. The
modifications of Kondo effect for all the alloys are also presented.Comment: Accepted for publication in Solid State Communication
Magnetic behavior of single crystalline HoPdSi
The magnetic behavior of single-crystal HoPdSi, crystallizing in an
AlB-derived hexagonal structure, is investigated by magnetic susceptibility
() and electrical resistivity () measurements along two directions.
There is no dramatic anisotropy in the high temperature Curie-Weiss parameter
or in the and isothermal magnetization data, though there is a
noticeable anisotropy in the magnitude of between two perpendicular
orientations. The degree of anisotropy is overall less prominent than in the Gd
(which is an S-state ion!) and Tb analogues. A point of emphasis is that this
compound undergoes long range magnetic ordering below 8 K as in the case of
analogous Gd and Dy compounds. Considering this fact for these compounds with
well-localised f-orbital, the spin glass freezing noted for isomorphous U
compounds in the recent literature could be attributed to the role of the
f-ligand hybridization, rather than just Pd-Si disorder.Comment: Physical Review B, in pres
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