426 research outputs found
Inducing ferromagnetism and Kondo effect in platinum by paramagnetic ionic gating
Electrically controllable magnetism, which requires the field-effect
manipulation of both charge and spin degrees of freedom, has attracted growing
interests since the emergence of spintronics. In this work, we report the
reversible electrical switching of ferromagnetic (FM) states in platinum (Pt)
thin films by introducing paramagnetic ionic liquid (PIL) as the gating media.
The paramagnetic ionic gating controls the movement of ions with magnetic
moments, which induces itinerant ferromagnetism on the surface of Pt films with
large coercivity and perpendicular anisotropy mimicking the ideal
two-dimensional Ising-type FM state. The electrical transport of the induced FM
state shows Kondo effect at low temperature suggesting spatially separated
coexistence of Kondo scattering beneath the FM interface. The tunable FM state
indicates that paramagnetic ionic gating could serve as a versatile method to
induce rich transport phenomena combining field effect and magnetism at
PIL-gated interfaces.Comment: 17 pages, 4 figure
Effect of band filling in the Kondo lattice: A mean-field approach
The usual Kondo-lattice, including an antiferromagnetic exchange interaction
between nearest-neighboring localized spins, is treated here in a mean-field
scheme that introduces two mean-field parameters: one associated with the local
Kondo effect, and the other related to the magnetic correlations between
localized spins. Phases with short-range magnetic correlations or coexistence
between those and the Kondo effect are obtained. By varying the number of
electrons in the conduction band, we notice that the Kondo effect tends to be
suppressed away from half filling, while magnetic correlations can survive if
the Heisenberg coupling is strong enough. An enhanced linear coefficient of the
specific heat is obtained at low temperatures in the metallic state.Comment: 7 pages, ReVTeX two-column, 7 figure
Mechanism of thermally activated c-axis dissipation in layered High-T superconductors at high fields
We propose a simple model which explains experimental behavior of -axis
resistivity in layered High-T superconductors at high fields in a limited
temperature range. It is generally accepted that the in-plane dissipation at
low temperatures is caused by small concentration of mobile pancake vortices
whose diffusive motion is thermally activated. We demonstrate that in such
situation a finite conductivity appears also in -direction due to the phase
slips between the planes caused by the mobile pancakes. The model gives
universal relation between the components of conductivity which is in good
agreement with experimental data.Comment: RevTeX, 4 pages, 2 Postscript figure
Magnetic field dependence of vortex activation energy: a comparison between MgB2, NbSe2 and Bi2Sr2Ca2Cu3O10 superconductors
The dissipative mechanism at low current density is compared in three
different classes of superconductors. This is achieved by measurement of
resistance as a function of temperature and magnetic field in clean
polycrystalline samples of NbSe2, MgB2 and Bi2Sr2Ca2Cu3O10 superconductors.
Thermally activated flux flow behavior is clearly identified in bulk MgB2.
While the activation energy at low fields for MgB2 is comparable to
Bi2Sr2Ca2Cu3O10, its field dependence follows a parabolic behavior unlike a
power law dependence seen in Bi2Sr2Ca2Cu3O10. We analyze our results based on
the Kramer's scaling for grain boundary pinning in MgB2and NbSe2
Experimental evidence for an intermediate phase in the multiferroic YMnO3
We have studied YMnO by high-temperature synchrotron X-ray powder
diffraction, and have carried out differential thermal analysis and dilatometry
on a single crystal sample. These experiments show two phase transitions at
about 1100K and 1350K, respectively. This demonstrates the existence of an
intermediate phase between the room temperature ferroelectric and the high
temperature centrosymmetric phase. This study identifies for the first time the
different high-temperature phase transitions in YMnO.Comment: 10 pages 5 figures. New version, Additional data, Journal of Physics:
Condensed Matter, in Pres
Single domain transport measurements of C60 films
Thin films of potassium doped C60, an organic semiconductor, have been grown
on silicon. The films were grown in ultra-high vacuum by thermal evaporation of
C60 onto oxide-terminated silicon as well as reconstructed Si(111). The
substrate termination had a drastic influence on the C60 growth mode which is
directly reflected in the electrical properties of the films. Measured on the
single domain length scale, these films revealed resistivities comparable to
bulk single crystals. In situ electrical transport properties were correlated
to the morphology of the film determined by scanning tunneling microscopy. The
observed excess conductivity above the superconducting transition can be
attributed to two-dimensional fluctuations.Comment: 4 pages, 4 figure
Magnetic Exciton Mediated Superconductivity in the Hidden-Order Phase of URu2Si2
We propose the magnetic exciton mediated superconductivity occurring in the
enigmatic hidden-order phase of URu2Si2. The characteristic of the massive
collective excitation observed only in the hidden-order phase is well
reproduced by the antiferro hexadecapole ordering model as the trace of the
dispersive crystalline-electric-field excitation. The disappearance of the
superconductivity in the high-pressure antiferro magnetic phase can naturally
be understood by the sudden suppression of the magnetic-exciton intensity. The
analysis of the momentum dependence of the magnetic-exciton mode leads to the
exotic chiral d-wave singlet pairing in the Eg symmetry. The Ising-like
magnetic-field response of the mode yields the strong anisotropy observed in
the upper critical field even for the rather isotropic 3-dimensional Fermi
surfaces of this compound.Comment: 5 pages, 4 figure
Induced-Moment Weak Antiferromagnetism and Orbital Order on the Itinerant-Localized Duality Model with Nested Fermi Surface: A Possible Origin of Exotic Magnetism in URuSi
The weak antiferromagnetism of URuSi is discussed on the
basis of a duality model which takes into account salient features of both
itinerant fermions and "localized" component of spin degrees of freedom. The
problem is analyzed in the framework of induced-moment mechanism by taking a
singlet-singlet crystal field scheme together with the nesting property of
partial Fermi surface of itinerant fermions . It is shown that the extremely
small ordered moment of () can be
compatible with the large specific-heat jump at the transition temperature
. Analysis performed in the presence of external magnetic field shows
that the field dependence of in the limit T\to 0 and T_{N}$ do not scale
except very near the critical field B which is consistent with a recent
observation by Mentink. It is also shown that the antiferromagnetic magnetic
order gives rise to a tiny amount of antiferromagnetic orbital order of
f-electrons.Comment: 14 pages, 2 figure PS file, accepted J. Phys. Soc. Jp
What Does The Korringa Ratio Measure?
We present an analysis of the Korringa ratio in a dirty metal, emphasizing
the case where a Stoner enhancement of the uniform susceptibilty is present. We
find that the relaxation rates are significantly enhanced by disorder, and that
the inverse problem of determining the bare density of states from a study of
the change of the Knight shift and relaxation rates with some parameter, such
as pressure, has rather constrained solutions, with the disorder playing an
important role. Some preliminary applications to the case of chemical
substitution in the RbKC family of superconductors is
presented and some other relevant systems are mentioned.Comment: 849, Piscataway, New Jersey 08855 24 June 199
Magnetoelectric coupling in the cubic ferrimagnet Cu2OSeO3
We have investigated the magnetoelectric coupling in the lone pair containing
piezoelectric ferrimagnet Cu2OSeO3. Significant magnetocapacitance develops in
the magnetically ordered state (TC = 60 K). We find critical behavior near TC
and a divergence near the metamagnetic transition at 500 Oe. High-resolution
X-ray and neutron powder diffraction measurements show that Cu2OSeO3 is
metrically cubic down to 10 K but that the ferrimagnetic ordering reduces the
symmetry to rhombohedral R3. The metric cubic lattice dimensions exclude a
magnetoelectric coupling mechanism involving spontaneous lattice strain, and
this is unique among magnetoelectric and multiferroic materials.Comment: accepted for publication in PR
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