7,968 research outputs found
Field sweep rate dependence of magnetic domain patterns: Numerical simulations for a simple Ising-like model
We study magnetic domain patterns in ferromagnetic thin films by numerical
simulations for a simple Ising-like model. Magnetic domain patterns after
quench demonstrate various types of patterns depending on the field sweep rate
and parameters of the model. How the domain patterns are formed is shown with
use of the number of domains, the domain area, and domain area distributions as
well as snapshots of domain patterns. Considering the proper time scale of the
system, we propose a criterion for the structure of domain patterns.Comment: 11 pages, 7 figure
Enhanced thermoelectric properties by Ir doping of PtSb2 with pyrite structure
The effects of Ir doping on the thermoelectric properties of Pt1-xIrxSb2 (x =
0, 0.01, 0.03, and 0.1) with pyrite structure were studied. Measurements of
electrical resistivity rho, Seebeck coefficient S, and thermal conductivity
kappa were conducted. The results showed an abrupt change from semiconducting
behavior without Ir (x = 0) to metallic behavior at x = 0.01. The sample with x
= 0.01 exhibited large S and low rho, resulting in a maximum power factor
(S^2/rho) of 43 muW/cmK^2 at 400 K. The peculiar "pudding mold"-type electronic
band dispersion could explain the enhanced thermoelectric properties in the
metallic state.Comment: 3 pages, 2 figure
Multi-Triplet Magnons in SrCu(BO) Studied by Thermal Conductivity Measurements in Magnetic Fields
We have measured the thermal conductivity parallel to the a-axis of the
Zn-free and 1% Zn-substituted SrCuZn(BO) in magnetic fields
up to 14 T, in order to examine the thermal conductivity due to the
multi-triplet magnons. It has been found that the thermal conductivity peak
observed in the spin gap state is suppressed by the substitution of Zn for Cu
in high magnetic fields above 6 T, while it is not changed in low magnetic
fields below 6 T. The results suggest that the thermal conductivity peak in the
spin-gap state of SrCu(BO) is composed of not only thermal
conductivity due to phonons but also that due to the multi-triplet magnons in
high fields above 6 T.Comment: 7 pages, 2 figure
Transient cosmic ray increase associated with a geomagnetic storm
On the basis of worldwide network data of cosmic ray nucleonic components, the transient cosmic ray increase due to the depression of cosmic ray cutoff rigidity during a severe geomagnetic storm was investigated in terms of the longitudinal dependence. Multiple correlation analysis among isotropic and diurnal terms of cosmic ray intensity variations and Dst term of the geomagnetic field is applied to each of various station's data. It is shown that the amplitude of the transient cosmic ray increase associated with Dst depends on the local time of the station, and that its maximum phase is found in the evening sector. This fact is consistent with the theoretical estimation based on the azimuthally asymmetric ring current model for the magnetic DS field
Periodically-driven cold atoms: the role of the phase
Numerous theoretical and experimental studies have investigated the dynamics
of cold atoms subjected to time periodic fields. Novel effects dependent on the
amplitude and frequency of the driving field, such as Coherent Destruction of
Tunneling have been identified and observed. However, in the last year or so,
three distinct types of experiments have demonstrated for the first time,
interesting behaviour associated with the driving phase: i.e. for systems
experiencing a driving field of general form ,
different types of large scale oscillations and directed motion were observed.
We investigate and explain the phenomenon of Super-Bloch Oscillations (SBOs) in
relation to the other experiments and address the role of initial phase in
general. We analyse and compare the role of in systems with homogeneous
forces (), such as cold atoms in shaken or amplitude-modulated
optical lattices, as well as non-homogeneous forces (), such
as the sloshing of atoms in driven traps, and clarify the physical origin of
the different -dependent effects.Comment: 10 pages, 1 figur
Effects of an oscillating field on pattern formation in a ferromagnetic thin film: Analysis of patterns traveling at a low velocity
Magnetic domain patterns under an oscillating field is studied theoretically
by using a simple Ising-like model. We propose two ways to investigate the
effects of the oscillating field. The first one leads to a model in which
rapidly oscillating terms are averaged out, and the model can explain the
existence of the maximum amplitude of the field for the appearance of patterns.
The second one leads to a model that includes the delay of the response to the
field, and the model suggests the existence of a traveling pattern which moves
very slowly compared with the time scale of the driving field.Comment: 9 pages, 3 figure
Burst size distributions in the digitized data of the ion chambers t Mt. Norikura and sea level stations
A practical and simple method for burst rejection is applied to the digitized data of cosmic ray ion chambers at Mt. Norikura, Tokyo and Kochi. As a result of burst rejection, the burst size frequency distributions in the digitized data at mountain altitude and sea level ion chambers is obtained. Results show that there are no significant differences between the digital and analog data processing in burst rejection
Single-crystal growth and dependences on the hole concentration and magnetic field of the magnetic ground state in the edge-sharing CuO chain system CaYCuO
We have succeeded in growing large-size single-crystals of
CaYCuO with and measured the
magnetic susceptibility, specific heat and magnetization curve, in order to
study the magnetic ground state in the edge-sharing CuO chain as a function
of hole concentration and magnetic field. In , it has been
found that an antiferromagnetically ordered phase with the magnetic easy axis
along the b-axis is stabilized and that a spin-flop transition occurs by the
application of magnetic fields parallel to the b-axis. The antiferromagnetic
transition temperature decreases with increasing and disappears around 1.4. Alternatively, a spin-glass phase appears around . At where the hole concentration is 1/3 per Cu, it appears that a
spin-gap state is formed owing to the formation of spin-singlet pairs. No sign
of the coexistence of an antiferromagnetically ordered state and a spin-gap one
suggested in CaCuO has been found in
CaYCuO.Comment: 13 pages, 12 figures, 1 tabl
Energy diffusion in frustrated quantum spin chains exhibiting Gaussian orthogonal ensemble level statistics
Frustrated quantum spin chains with the next-nearest-neighbor (NNN)
couplings are typically deterministic many-body systems exhibiting Gaussian
orthogonal ensemble (GOE) spectral statistics. We investigate energy diffusion
for these spin chains in the presence of a periodically oscillating magnetic
field. Diffusion coefficients are found to obey the power law with respect to
both the field strength and driving frequency with its power varying depending
on the linear response and non-perturbative regimes. The widths of the linear
response and the non-perturbative regimes depend on the strength of
frustrations. We have also elucidated a mechanism for oscillation of energy
diffusion in the case of weakened frustrations.Comment: 6 pages, 6 figure
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