An adaptive algorithm for n-body field expansions
Weinberg, Martin D.
1998-05-28
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11 records were found.
We have performed tunneling spectroscopy measurements down to 4.2 K on single crystals of La0.75Sr0.25MnO3 and La0.7Ca0.3MnO3, which show the colossal magnetoresistive behavior in the ferromagnetic metallic phase. The tunneling spectroscopy measurements give information on the density of states (DOS) at and close to the Fermi level EF. The observed energy dependence of the DOS is similar to that seen in correlated oxides with disorder, which is an important observation since it raises fundamental questions regarding the nature of the metallic state in these oxides. Measurements at low temperatures reveal that the DOS in these compounds show a depletion close to EF, |E–EF|< 15 meV; unlike that in conventional metals. The normalized DOS, close to EF shows an energy dependence alpha |E–EF|2 at low temperatures but remains finite as E - EF...
Colossal electroresistance and current induced resistivity switching have been measured in the ferromagnetic insulating (FMI) state of single crystal manganite La0.82Ca0.18MnO3. The sample has a Curie transition temperature TC = 165 K and the FMI state is realized for temperatures T<100 K. The electroresistance (ER), arising from a strong nonlinear resistivity, attains a large value ( ≈ 100%) in the FMI state. However, this is accompanied by a collapse of the magnetoresistance (MR) to a small value even in magnetic field (H) of 10 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled.
Comment: 4 pages, 5 figures
Comment: 4 pages, 5 figures
Comment: 4 pages, 4 eps figures, to be published in Phys. Rev. Lett
We describe the evolution of the static and dynamic spin correlations of
La$_{1-x}$Ca$_x$MnO$_3$, for x=0.1, 0.125 and 0.2, where the system evolves
from the canted magnetic state towards the insulating ferromagnetic state,
approaching the metallic transition (x=0.22).
In the x=0.1 sample, the observation of two spin wave branches typical of two
distinct types of magnetic coupling, and of a modulation in the elastic diffuse
scattering characteristic of ferromagnetic inhomogeneities, confirms the static
and dynamic inhomogeneous features previously observed at x$<$0.1. The
anisotropic q-dependence of the intensity of the low-energy spin wave suggests
a bidimensionnal character for the static inhomogeneities. At x=0.125, which
corresponds to the occurence of a ferromagnetic and insulating state, the two
spin wave branches reduce to a ...
The ferromagnetic and insulating state observed in La$_{1-x}$Ca$_{x}$MnO$_3$,
0.125$<$x$<$0.2, is characterized by structural and magnetic anomalies below
T$_C$, similar to those observed in the x$_{Sr}$$\approx$1/8. A neutron
scattering study of the superlattice {\bf Q$_0$}= (0,0,1+/4)$_{cub}$ peak, and
of the magnetic excitations are reported in the x$_{Ca}$=0.2 sample. The
occurrence of this superstructure is associated with the observation of a gap
in the spin dynamics, at a {\bf q$_0$} wave-vector ({\bf q$_0$}={\bf
Q$_0$}-$\tau$) with the same modulus $|${\bf q$_0$}$|$ in all directions, which
divides the dispersion into two regimes. For $|${\bf q}$|$$<$$|${\bf q$_0$}$|$
the dispersion is splitted into two or three curves. For $|${\bf
q}$|$$>$$|${\bf q$_0$}$|$, magnetic excitations lock on acoustic and optic
phonon energies, rev...
The effect of resistive switching in doped manganites being in the
ferromagnetic state has been studied using resistive and magneto-optic methods.
The visualization of magnetic structure of La0.75Sr0.25MnO3-x single crystals,
and its transformation under electric current proposed local superheating of
the material above the Curie temperature, which was supported by numerical
calculation. The obtained results suggest a significant role of
micrometer-scale inhomogeneity of manganites in phase separation, magnetic and
transport properties of the material.
Comment: 11 pages, 7 figures, submitted to Phys. Rev. B
Comment: 4 pages (RevTex), 3 figures (encapsulated postscript)
