1,427 research outputs found
Training Induced Positive Exchange Bias in NiFe/IrMn Bilayers
Positive exchange bias has been observed in the
NiFe/IrMn bilayer system via soft x-ray resonant
magnetic scattering. After field cooling of the system through the blocking
temperature of the antiferromagnet, an initial conventional negative exchange
bias is removed after training i. e. successive magnetization reversals,
resulting in a positive exchange bias for a temperature range down to 30 K
below the blocking temperature (450 K). This new manifestation of magnetic
training is discussed in terms of metastable magnetic disorder at the
magnetically frustrated interface during magnetization reversal.Comment: 4 pages, 3 figure
Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization
We follow for the first time the evolution of the spin and orbital angular
momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray
magnetic circular dichroism. Both components decrease with a 130 +/- 40 fs time
constant upon excitation with a femtosecond laser pulse. Additional x-ray
absorption measurements reveal an increase in the spin-orbit interaction by 6
+/- 2 % during this process. This is the experimental demonstration quantifying
the importance of spin-orbit mediated processes during the demagnetization
Manifestation of fundamental quantum complementarities in time-domain interference experiments with quantum dots: A theoretical analysis
A theoretical analysis is presented showing that fundamental complementarity
between the particle-like properties of an exciton confined in a semiconductor
quantum dot and the ability of the same system to show interference may be
studied in a time domain interference experiment, similar to those currently
performed. The feasibility of such an experiment, including required pulse
parameters and the dephasing effect of the environment, is studied.Comment: Final, considerably extended version; 8 pages, 3 figure
Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers
We present a comprehensive study of the exchange bias effect in a model
system. Through numerical analysis of the exchange bias and coercive fields as
a function of the antiferromagnetic layer thickness we deduce the absolute
value of the averaged anisotropy constant of the antiferromagnet. We show that
the anisotropy of IrMn exhibits a finite size effect as a function of
thickness. The interfacial spin disorder involved in the data analysis is
further supported by the observation of the dual behavior of the interfacial
uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we
have observed that the antiferromagnetic uncompensated spins are dominantly
frozen with nearly no rotating spins due to the chemical intermixing, which
correlates to the inferred mechanism for the exchange bias.Comment: 4 pages, 3 figure
Effective non-Markovian description of a system interacting with a bath
We study a harmonic system coupled to chain of first neighbor interacting
oscillators. After deriving the exact dynamics of the system, we prove that one
can effectively describe the exact dynamics by considering a suitable shorter
chain. We provide the explicit expression for such an effective dynamics and we
provide an upper bound on the error one makes considering it instead of the
dynamics of the full chain. We eventually prove how error, timescale and number
of modes in the truncated chain are related
Time Evolution of the External Field Problem in QED
We construct the time-evolution for the second quantized Dirac equation
subject to a smooth, compactly supported, time dependent electromagnetic
potential and identify the degrees of freedom involved. Earlier works on this
(e.g. Ruijsenaars) observed the Shale-Stinespring condition and showed that the
one-particle time-evolution can be lifted to Fock space if and only if the
external field had zero magnetic components. We scrutinize the idea, observed
earlier by Fierz and Scharf, that the time-evolution can be implemented between
time varying Fock spaces. In order to define these Fock spaces we are led to
consider classes of reference vacua and polarizations. We show that this
implementation is up to a phase independent of the chosen reference vacuum or
polarization and that all induced transition probabilities are well-defined and
unique.Comment: 60 pages, 1 figure, revised introduction, summary of results added,
typos correcte
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