5,429 research outputs found
Dependence of nonlocal Gilbert damping on the ferromagnetic layer type in FM/Cu/Pt heterostructures
We have measured the size effect in nonlocal Gilbert relaxation rate in
FM(t) / Cu (5nm) [/ Pt (2nm)] / Al(2nm) heterostructures, FM = \{
NiFe, CoFeB, pure Co\}. Common behavior is
observed for three FM layers, where the additional relaxation obeys both a
strict inverse power law dependence ,
and a similar magnitude
. As the tested FM layers
span an order of magnitude in spin diffusion length , the
results are in support of spin diffusion, rather than nonlocal resistivity, as
the origin of the effect
Rationalisation of Profiles of Abstract Argumentation Frameworks
International audienceDifferent agents may have different points of view. This can be modelled using different abstract argumentation frameworks , each consisting of a set of arguments and a binary attack-relation between them. A question arising in this context is whether the diversity of views observed in such a profile of argumentation frameworks is consistent with the assumption that every individual argumentation framework is induced by a combination of, first, some basic factual attack-relation between the arguments and, second, the personal preferences of the agent concerned. We treat this question of rationalisability of a profile as an algorithmic problem and identify tractable and intractable cases. This is useful for understanding what types of profiles can reasonably be expected to come up in a multiagent system
Diagonal Ladders: A New Class of Models for Strongly Coupled Electron Systems
We introduce a class of models defined on ladders with a diagonal structure
generated by plaquettes. The case corresponds to the necklace
ladder and has remarkable properties which are studied using DMRG and recurrent
variational ansatzes. The AF Heisenberg model on this ladder is equivalent to
the alternating spin-1/spin-1/2 AFH chain which is known to have a
ferrimagnetic ground state (GS). For doping 1/3 the GS is a fully doped (1,1)
stripe with the holes located mostly along the principal diagonal while the
minor diagonals are occupied by spin singlets. This state can be seen as a Mott
insulator of localized Cooper pairs on the plaquettes. A physical picture of
our results is provided by a model of plaquettes coupled diagonally
with a hopping parameter . In the limit we recover the
original model on the necklace ladder while for weak hopping parameter
the model is easily solvable. The GS in the strong hopping regime is
essentially an "on link" Gutzwiller projection of the weak hopping GS. We
generalize the model to diagonal ladders with and the 2D
square lattice. We use in our construction concepts familiar in Statistical
Mechanics as medial graphs and Bratelli diagrams.Comment: REVTEX file, 22 pages (twocolumn), 35 figures inserted in text. 12
Table
Variational and Potential Formulation for Stochastic Partial Differential Equations
There is recent interest in finding a potential formulation for Stochastic
Partial Differential Equations (SPDEs). The rationale behind this idea lies in
obtaining all the dynamical information of the system under study from one
single expression. In this Letter we formally provide a general Lagrangian
formalism for SPDEs using the Hojman et al. method. We show that it is possible
to write the corresponding effective potential starting from an s-equivalent
Lagrangean, and that this potential is able to reproduce all the dynamics of
the system, once a special differential operator has been applied. This
procedure can be used to study the complete time evolution and spatial
inhomogeneities of the system under consideration, and is also suitable for the
statistical mechanics description of the problem. Keywords: stochastic partial
differential equations, variational formulation, effective potential. PACS:
45.20.Jj; 02.50.-r; 02.50.Ey.Comment: Letter, 4 pages, no figures; v2: references added, minor change
Minimal lepton flavor violating realizations of minimal seesaw models
We study the implications of the global U(1)R symmetry present in minimal
lepton flavor violating implementations of the seesaw mechanism for neutrino
masses. In the context of minimal type I seesaw scenarios with a slightly
broken U(1)R, we show that, depending on the R-charge assignments, two classes
of generic models can be identified. Models where the right-handed neutrino
masses and the lepton number breaking scale are decoupled, and models where the
parameters that slightly break the U(1)R induce a suppression in the light
neutrino mass matrix. We show that within the first class of models,
contributions of right-handed neutrinos to charged lepton flavor violating
processes are severely suppressed. Within the second class of models we study
the charged lepton flavor violating phenomenology in detail, focusing on mu to
e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable
contributions to these processes are naturally obtained for right-handed
neutrino masses at the TeV scale. We then discuss the interplay with the
effects of the right-handed neutrino interactions on primordial B - L
asymmetries, finding that sizable right-handed neutrino contributions to
charged lepton flavor violating processes are incompatible with the requirement
of generating (or even preserving preexisting) B - L asymmetries consistent
with the observed baryon asymmetry of the Universe.Comment: 21 pages, 4 figures; version 2: Discussion on possible generic models
extended, typos corrected, references added. Version matches publication in
JHE
Application of Uniform Matrix Product State to Quantum Phase Transition with a Periodicity Change
As a method beyond the mean-field analysis, a matrix product state (MPS) with
incommensurate periodicity is applied to detect phase transitions accompanied
with periodicity change, where the incommensurate MPS is generated by acting
local-spin-rotation operators with the incommensurate periodicity on a uniform
MPS. As a commensurate/commensurate change, we calculate the partial ferro --
perfect ferro phase transition in the Heisenberg model and its critical
exponent of the magnetization curve. As a commensurate/incommensurate change,
we calculate the S=1 Heisenberg model with bilinear and biquadratic
interactions which has periodicity change in the spin-spin correlation
function.Comment: 4 pages, 3 figures, Supplement (Proc. TOKIMEKI2011) Program
No.25-P-3
A Monte Carlo Study of Correlations in Quantum Spin Ladders
We study antiferromagnetic spin--1/2 Heisenberg ladders, comprised of
chains () with ratio of inter-- to
intra--chain couplings. From measurements of the correlation function we deduce
the correlation length . For even , the static structure factor
exhibits a peak at a temperature below the corresponding spin gap. Results for
isotropically coupled ladders () are compared to those for
the single chain and the square lattice. For , the
correlation function of the two--chain ladder is in excellent agreement with
analytic results from conformal field theory, and exhibits simple
scaling behavior.Comment: 4 pages, 5 EPS figures, submitted to Phys. Rev. Let
Temperature dependence of the emission linewidth in MgO-based spin torque nano-oscillators
Spin transfer driven excitations in magnetic nanostructures are characterized
by a relatively large microwave emission linewidth (10 -100 MHz). Here we
investigate the role of thermal fluctuations as well as of the non-linear
amplitude-phase coupling parameter and the amplitude relaxation rate to explain
the linewidth broadening of in-plane precession modes induced in planar
nanostructures. Experiments on the linewidth broadening performed on MgO based
magnetic tunnel junctions are compared to the linewidth obtained from macrospin
simulations and from evaluation of the phase variance. In all cases we find
that the linewidth varies linearly with temperature when the amplitude
relaxation rate is of the same order as the linewidth and when the
amplitude-phase coupling parameter is relatively small. The small
amplitude-phase coupling parameter means that the linewidth is dominated by
direct phase fluctuations and not by amplitude fluctuations, explaining thus
its linear dependence as a function of temperature
Composite modelling of the interactions between beaches and structures
An overview of Composite Modelling (CM) is presented, as elaborated in the EU/HYDRALAB joint research project Composite Modelling of the Interactions Between Beaches and Structures. An ntroduction and are view of the main literature on CM in the hydraulic community are given. In Section 3, the case studies of CM of the seven partners participating in this project are discussed. The focus is on the methodologies used and their impact on the modeling approach, rather than the results of the experiment sperse. A further section presents reflections on key elements in CM, as they emerged in the various case studies. The related subject of Good Modelling Practice is summarized in Section5. Then guidelines are given on how to decide if CM may be beneficial, and how to set up a CM experiment. It is concluded that CM in the hydraulic community is still in its infancy but involves challenging research with significant potential
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