1,245 research outputs found
Thickness dependent magnetotransport in ultra-thin manganite films
To understand the near-interface magnetism in manganites, uniform, ultra-thin
films of La_{0.67}Sr_{0.33}MnO_3 were grown epitaxially on single crystal (001)
LaAlO_3 and (110) NdGaO_3 substrates. The temperature and magnetic field
dependent film resistance is used to probe the film's structural and magnetic
properties. A surface and/or interface related dead-layer is inferred from the
thickness dependent resistance and magnetoresistance. The total thickness of
the dead layer is estimated to be for films on NdGaO_3 and for films on LaAlO_3.Comment: 11 pages, 4 figure
Coexistence of superconductivity and ferromagnetism in two dimensions
Ferromagnetism is usually considered to be incompatible with conventional
superconductivity, as it destroys the singlet correlations responsible for the
pairing interaction. Superconductivity and ferromagnetism are known to coexist
in only a few bulk rare-earth materials. Here we report evidence for their
coexistence in a two-dimensional system: the interface between two bulk
insulators, LaAlO (LAO) and SrTiO (STO), a system that has been studied
intensively recently. Magnetoresistance, Hall and electric-field dependence
measurements suggest that there are two distinct bands of charge carriers that
contribute to the interface conductivity. The sensitivity of properties of the
interface to an electric field make this a fascinating system for the study of
the interplay between superconductivity and magnetism.Comment: 4 pages, 4 figure
Positive exchange bias in ferromagnetic La0.67Sr0.33MnO3 / SrRuO3 bilayers
Epitaxial La0.67Sr0.33MnO3 (LSMO)/ SrRuO3 (SRO) ferromagnetic bilayers have
been grown on (001) SrTiO3 (STO) substrates by pulsed laser deposition with
atomic layer control. We observe a shift in the magnetic hysteresis loop of the
LSMO layer in the same direction as the applied biasing field (positive
exchange bias). The effect is not present above the Curie temperature of the
SRO layer (), and its magnitude increases rapidly as the temperature is lowered
below . The direction of the shift is consistent with an antiferromagnetic
exchange coupling between the ferromagnetic LSMO layer and the ferromagnetic
SRO layer. We propose that atomic layer charge transfer modifies the electronic
state at the interface, resulting in the observed antiferromagnetic interfacial
exchange coupling.Comment: accepted to Applied Physics Letter
Localization of Two-dimensional Electron Gas in LaAlO3/SrTiO3 Heterostructures
We report strong localization of 2D electron gas in LaAlO3 / SrTiO3 epitaxial
thin-film heterostructures grown on (LaAlO3)0.3-(Sr2AlTaO3)0.7 substrates by
using pulsed laser deposition with in-situ reflection high-energy electron
diffraction. Using longitudinal and transverse magnetotransport measurements,
we have determined that disorder at the interface influences the conduction
behavior, and that increasing the carrier concentration by growing at lower
oxygen partial pressure changes the conduction from strongly localized at low
carrier concentration to metallic at higher carrier concentration, with
indications of weak localization. We interpret this behavior in terms of a
changing occupation of Ti 3d bands near the interface, each with a different
spatial extent and susceptibility to localization by disorder, and differences
in carrier confinement due to misfit strain and point defects.Comment: 12 pages, 4 figure
The Electronic and Superconducting Properties of Oxygen-Ordered MgB2 compounds of the form Mg2B3Ox
Possible candidates for the Mg2B3Ox nanostructures observed in bulk of
polycrystalline MgB2 (Ref.1) have been studied using a combination of
Z-contrast imaging, electron energy loss spectroscopy (EELS) and
first-principles calculations. The electronic structures, phonon modes, and
electron phonon coupling parameters are calculated for two oxygen-ordered MgB2
compounds of composition Mg2B3O and Mg2B3O2, and compared with those of MgB2.
We find that the density of states for both Mg2B3Ox structures show very good
agreement with EELS, indicating that they are excellent candidates to explain
the observed coherent oxygen precipitates. Incorporation of oxygen reduces the
transition temperature and gives calculated TC values of 18.3 K and 1.6 K for
Mg2B3O and Mg2B3O2, respectively.Comment: Submitted to PR
Nonlinear Meissner Effect in Nb\u3csub\u3e3\u3c/sub\u3eSn Coplanar Resonators
We investigated the nonlinear Meissner effect (NLME) in Nb3Sn thin-film coplanar resonators by measuring the resonance frequency as a function of a parallel magnetic field at different temperatures. We used low rf power probing in films thinner than the London penetration depth λ(B) to significantly increase the field onset of vortex penetration and measure the NLME under equilibrium conditions. Contrary to the conventional quadratic increase of λ(B) with B expected in s-wave superconductors, we observed a nearly linear increase of the penetration depth with B. We concluded that this behavior of λ(B) is due to weak linked grain boundaries in our polycrystalline Nb3Sn films, which can mimic the NLME expected in a clean d-wave superconductor
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