8,325 research outputs found
Comment on "Critical and slow dynamics in a bulk metallic glass exhibiting strong random magnetic anisotropy" [Appl. Phys. Lett. 92, 011923 (2008)]
In this comment, by using Monte Carlo simulation, we show that the
perpendicular shift of hysteresis loops reported in the commented work is
nothing special but simply due to the fact that the range of field does not
surpass the reversible field beyond which the two branches of the loop merge.
If the reversible field is exceeded, the shift is no longer observed. Moreover,
we point out that even using a small range of field, the shift will not be
observed if the observation time is long enough for the reversible field to
drop within the range.Comment: 2 pages, 2 figures, accepted for publication in Applied Physics
Letters Volume 94, Issue 15, Issue date 13 April 200
Differential Amplify-and-Forward Relaying in Time-Varying Rayleigh Fading Channels
This paper considers the performance of differential amplify-and-forward
(D-AF) relaying over time-varying Rayleigh fading channels. Using the
auto-regressive time-series model to characterize the time-varying nature of
the wireless channels, new weights for the maximum ratio combining (MRC) of the
received signals at the destination are proposed. Expression for the pair-wise
error probability (PEP) is provided and used to obtain an approximation of the
total average bit error probability (BEP). The obtained BEP approximation
clearly shows how the system performance depends on the auto-correlation of the
direct and the cascaded channels and an irreducible error floor exists at high
signal-to-noise ratio (SNR). Simulation results also demonstrate that, for
fast-fading channels, the new MRC weights lead to a better performance when
compared to the classical combining scheme. Our analysis is verified with
simulation results in different fading scenarios
An ac field probe for the magnetic ordering of magnets with random anisotropy
A Monte Carlo simulation is carried out to investigate the magnetic ordering
in magnets with random anisotropy (RA). Our results show peculiar similarities
to recent experiments that the real part of ac susceptibility presents two
peaks for weak RA and only one for strong RA regardless of glassy critical
dynamics manifested for them. We demonstrate that the thermodynamic nature of
the low-temperature peak is a ferromagnetic-like dynamic phase transition to
quasi-long range order (QLRO) for the former. Our simulation, therefore, is
able to be incorporated with the experiments to help clarify the existence of
the QLRO theoretically predicted so far.Comment: 10 pages, 4 figures, to appear in Appl. Phys. Lett. volume 95, Issue
22, Isue date: 30 November 200
Mangetic phase transition for three-dimensional Heisenberg weak random anisotropy model: Monte Carlo study
Magnetic phase transition (MPT) to magnetic quasi-long-range order (QLRO)
phase in a three-dimensional Heisenberg weak (D/J=4) random anisotropy (RA)
model is investigated by Monte Carlo simulation. The isotropic and cubic
distributions of RA axes are considered for simple-cubic-lattice systems.
Finite-size scaling analysis shows that the critical couplings for the former
and latter are K_c= 0.70435(2) and K_c=0.70998(4), respectively. While the
critical exponent 1/\nu =1.40824(0) is the same for both cases. A second-order
MPT to the QLRO phase is therefore evidenced to be possible in favor with the
existence of the QLRO predicted by recent functional renormalization group
theories.Comment: 9 pages, 3 figures. to be appeared in Journal of Applied Physics
Volume 105 Issue 7 on April 1, 200
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