252 research outputs found
Low temperature resistivity in a nearly half-metallic ferromagnet
We consider electron transport in a nearly half-metallic ferromagnet, in
which the minority spin electrons close to the band edge at the Fermi energy
are Anderson-localized due to disorder. For the case of spin-flip scattering of
the conduction electrons due to the absorption and emission of magnons, the
Boltzmann equation is exactly soluble to the linear order. From this solution
we calculate the temperature dependence of the resistivity due to single magnon
processes at sufficiently low temperature, namely , where is
the Anderson localization length and is the magnon stiffness. And depending
on the details of the minority spin density of states at the Fermi level, we
find a or scaling behavior for resistivity. Relevance to the
doped perovskite manganite systems is discussed
Magnetoresistance of metallic perovskite oxide LaNiO
We report a study of the magnetoresistance (MR) of the metallic perovskite
oxide LaNiO as a function of the oxygen stoichiometry
( 0.14), magnetic field (H ) and temperature (1.5K T 25K). We find a strong dependence of the nature of MR on the oxygen
stoichiometry. The MR at low temperatures change from positive to negative as
the sample becomes more oxygen deficient (i.e, increases). Some of the
samples which are more resistive, show a resistivity minima at
20K. We find that in these samples the MR is positive at T >
and negative for T < . We conclude that in the absence of
strong magnetic interaction, the negative MR in these oxides can arise from
weak localisation effects.Comment: 10 pages in REVTeX format, 4 eps fig
Self Injection length in La0.7 Ca0.3 Mno3-YBa 2Cu3O7-d ferromagnet- superconductor multi layer thin films
We have carried out extensive studies on the self-injection problem in
barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-d
(YBCO). The heterojunctions were grown in situ by sequentially growing LCMO and
YBCO films on LaAlO3 (LAO) substrate using a pulsed laser deposition
(PLD) system. YBCO micro-bridges with 64 microns width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, Ic, was
measured at 77K on both the control side as well as the LCMO side for different
YBCO film thickness. It was observed that while the control side showed a Jc of
~2 x 10E6 A/ cm2 the LCMO side showed about half the value for the same
thickness (1800 A). The difference in Jc indicates that a certain thickness of
YBCO has become 'effectively' normal due to self-injection. From the
measurement of Jc at two different thickness' (1800 A and 1500 A) of YBCO both
on the LAO as well as the LCMO side, the value of self-injection length (at
77K) was estimated to be ~900 A self-injection length has been quantified. A
control experiment carried out with LaNiO3 deposited by PLD on YBCO did not
show any evidence of self-injection.Comment: 6 pages, one figure in .ps forma
Electronic structure, magnetism and superconductivity of MgCNi
The electronic structure of the newly discovered superconducting perovskite
MgCNi is calculated using the LMTO and KKR methods. The states near the
Fermi energy are found to be dominated by Ni-d. The Stoner factor is low while
the electron-phonon coupling constant is estimated to be about 0.7, which
suggests that the material is a conventional type of superconductor where T
is not affected by magnetic interactions. However, the proximity of the Fermi
energy to a large peak in the density of states in conjunction with the
reported non-stoichiometry of the compound, has consequences for the stability
of the results.Comment: 3 pages, 4 figure
Magnetic and transport properties of Mo substituted La0.67Ba0.33Mn1-xMoxO3 perovskite system
The effect of doping Mo for Mn on the magnetic and transport properties of
the colossal magnetoresistance material, La0.67Ba0.33MnO3, has been studied.
Compounds of the series La0.67Ba0.33Mn1-xMoxO3 (x=0.0 to 0.1) have been
prepared and found to crystallize in the orthorhombic structure (space group
Pbnm). Energy Dispersive X-ray Analysis (EDAX) measurements confirm the
stoichiometry of all the samples. Magnetotransport and magnetization
measurements reveal that the metal-insulator transition temperature (Tp)
decreases from 330K for x=0 to 255K for x=0.1. The change in Tp on Mo
substitution is relatively much smaller than the corresponding change observed
on substitution by other transition elements, such as Ti, Fe, Co, Ni, etc.
Further, the ferromagnetic transition temperature (TC) is nearly unchanged by
Mo substitution. This is in striking contrast to the large decrease in TC
observed with substitution of above-mentioned 3d elements. These unusual
magnetic and transport properties of La0.67Ba0.33Mn1-xMoxO3 may be either due
to the formation of magnetic pair between Mn and Mo or due to strong
Mo(4d)-O(2p) overlap, which in turn, may affect the Mn-Mn interaction via the
oxygen atomsComment: 25 pages, 5 figure
Optical Spectra in the Ferromagnetic States near the Charge Ordering
The optical conductivity is studied numerically for the ferromagnetic
metallic state close to the charge ordering observed in perovskite manganites.Comment: 11 pages, Latex, 6 ps figure
Room temperature magnetic entropy change and magnetoresistance in La_{0.70}(Ca_{0.30-x}Sr_x)MnO_3:Ag 10% (x = 0.0-0.10)
The magnetic and magnetocaloric properties of polycrystalline
La0.70(Ca0.30-xSrx)MnO3:Ag 10% manganite have been investigated. All the
compositions are crystallized in single phase orthorhombic Pbnm space group.
Both, the Insulator-Metal transition temperature (TIM) and Curie temperature
(Tc) are observed at 298 K for x = 0.10 composition. Though both TIM and Tc are
nearly unchanged with Ag addition, the MR is slightly improved. The MR at 300 K
is found to be as large as 31% with magnetic field change of 1Tesla, whereas it
reaches up to 49% at magnetic field of 3Tesla for La0.70Ca0.20Sr0.10MnO3:Ag0.10
sample. The maximum entropy change (\DeltaSMmax) is 7.6 J.Kg-1.K-1 upon the
magnetic field change of 5Tesla, near its Tc (300.5 K). The
La0.70Ca0.20Sr0.10MnO3:Ag0.10 sample having good MR (31%1Tesla, 49%3Tesla) and
reasonable change in magnetic entropy (7.6 J.Kg-1.K-1, 5 Tesla) at 300 K can be
a potential magnetic refrigerant material at ambient temperatures.Comment: 11 pages text + Figs comments/suggestions
([email protected]
Ferromagnetic transition in a double-exchange system
We study ferromagnetic transition in three-dimensional double-exchange model.
The influence of strong spin fluctuations on conduction electrons is described
in coherent potential approximation. In the framework of thermodynamic approach
we construct for the system "electrons (in a disordered spin configuration) +
spins" the Landau functional, from the analysis of which critical temperature
of ferromagnetic transition is calculated.Comment: 4 pages, 1 eps figure, LaTeX2e, RevTeX. References added, text
change
Exchange Field Induced Magnetoresistance in Colossal Magnetoresistance Manganites
The effect of an exchange field on electrical transport in thin films of
metallic ferromagnetic manganites has been investigated. The exchange field was
induced both by direct exchange coupling in a ferromagnet/antiferromagnet
multilayer and by indirect exchange interaction in a ferromagnet/paramagnet
superlattice. The electrical resistance of the manganite layers was found to be
determined by the absolute value of the vector sum of the effective exchange
field and the external magnetic field.Comment: 5 pages, 4 figure
Spin Excitation Spectrum of LaMnO
As an effective model to describe perovskite-type manganates (La,)MnO,
the double-exchange model on a cubic lattice is investigated. Spin excitation
spectrum of the model in the ground state is studied using the spin wave
approximation. Spin wave dispersion relation observed in the inelastic neutron
scattering experiment of LaPbMnO is reproduced. Effective
values for the electron bandwidth as well as Hund's coupling is estimated from
the data.Comment: 10 pages LaTeX including 4 PS figure
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