123 research outputs found
Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field
Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2
antiferromagnetic chain with alternating -tensor and Dzyaloshinskii-Moriya
interactions that exhibits a field-induced spin gap, are probed by means of
pulsed-field electron spin resonance spectroscopy. In particular, we report on
a minimum of the gap in the vicinity of the saturation field T
associated with a transition from the sine-Gordon region (with soliton-breather
elementary excitations) to a spin-polarized state (with magnon excitations).
This interpretation is fully confirmed by the quantitative agreement over the
entire field range of the experimental data with the DMRG investigation of the
spin-1/2 Heisenberg chain with a staggered transverse field
Optical sorting and detection of sub-micron objects in a motional standing wave
An extended interference pattern close to surface may result in both a
transmissive or evanescent surface fields for large area manipulation of
trapped particles. The affinity of differing particle sizes to a moving
standing wave light pattern allows us to hold and deliver them in a
bi-directional manner and importantly demonstrate experimentally particle
sorting in the sub-micron region. This is performed without the need of fluid
flow (static sorting). Theoretical calculations experimentally confirm that
certain sizes of colloidal particles thermally hop more easily between
neighboring traps. A new generic method is also presented for particle position
detection in an extended periodic light pattern and applied to characterization
of optical traps and particle behaviorComment: 5 pages, 6 figures, Optical Trapping pape
Photoinduced Magnetization in a Thin Fe-CN-Co Film
The magnetization of a thin Fe-Co cyanide film has been investigated from 5 K
to 300 K and in fields up to 500 G. Upon illumination with visible light, the
magnetization of the film rapidly increases. The original cluster glass
behavior is further developed in the photoinduced state and shows substantial
changes in critical temperature and freezing temperature.Comment: 2 pages, 2 figures, 1 table, International Conference on Magnetism
200
Recommended from our members
Observing distant objects with a multimode fiber-based holographic endoscope
Holographic wavefront manipulation enables converting hair-thin multimode optical fibers into minimally invasive lensless imaging instruments conveying much higher information densities than conventional endoscopes. Their most prominent applications focus on accessing delicate environments, including deep brain compartments, and recording micrometer-scale resolution images of structures in close proximity to the distal end of the instrument. Here, we introduce an alternative "far-field"endoscope capable of imaging macroscopic objects across a large depth of field. The endoscope shaft with dimensions of 0.2 × 0.4 mm2 consists of two parallel optical fibers: one for illumination and the other for signal collection. The system is optimized for speed, power efficiency, and signal quality, taking into account specific features of light transport through step-index multimode fibers. The characteristics of imaging quality are studied at distances between 20 mm and 400 mm. As a proof-of-concept, we provide imaging inside the cavities of a sweet pepper commonly used as a phantom for biomedically relevant conditions. Furthermore, we test the performance on a functioning mechanical clock, thus verifying its applicability in dynamically changing environments. With the performance reaching the standard definition of video endoscopes, this work paves the way toward the exploitation of minimally invasive holographic micro-endoscopes in clinical and diagnostics applications. © 2021 Author(s)
Observing distant objects with a multimode fibre-based holographic endoscope
Holographic wavefront manipulation enables converting hair-thin multimode
optical fibres into minimally invasive lensless imaging instruments conveying
much higher information densities than conventional endoscopes. Their most
prominent applications focus on accessing delicate environments, including deep
brain compartments, and recording micrometre-scale resolution images of
structures in close proximity to the distal end of the instrument. Here, we
introduce an alternative 'farfield' endoscope, capable of imaging macroscopic
objects across a large depth of field. The endoscope shaft with dimensions of
0.20.4 mm consists of two parallel optical fibres, one for
illumination and the second for signal collection. The system is optimized for
speed, power efficiency and signal quality, taking into account specific
features of light transport through step-index multimode fibres. The
characteristics of imaging quality are studied at distances between 20 and 400
mm. As a proof-of-concept, we provide imaging inside the cavities of a sweet
pepper commonly used as a phantom for biomedically relevant conditions.
Further, we test the performance on a functioning mechanical clock, thus
verifying its applicability in dynamically changing environments. With
performance reaching the standard definition of video endoscopes, this work
paves the way towards the exploitation of minimally-invasive holographic
micro-endoscopes in clinical and diagnostics applications.Comment: 9+6 pages, 4+5 figure
Origin of magnetic moments in defective TiO2 single crystals
In this paper we show that ferromagnetism can be induced in pure TiO2 single
crystals by oxygen ion irradiation. By combining x-ray diffraction,
Raman-scattering, and electron spin resonance spectroscopy, a defect complex,
\emph{i.e.} Ti ions on the substitutional sites accompanied by oxygen
vacancies, has been identified in irradiated TiO2. This kind of defect complex
results in a local (TiO) stretching Raman mode. We elucidate that
Ti ions with one unpaired 3d electron provide the local magnetic
moments.Comment: 4 pages, 4 figures, to be published at Phys. Rev.
Magnetocaloric Study of Spin Relaxation in `Frozen' Dipolar Spin Ice Dy2Ti2O7
The magnetocaloric effect of polycrystalline samples of pure and Y-doped
dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K
to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic
interest, it is proposed that the magnetocaloric effect may be used as an
appropriate tool for the qualitative study of slow relaxation processes in the
spin ice regime. In the high temperature regime the temperature change on
adiabatic demagnetization was found to be consistent with previously published
entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by
adiabatic demagnetization was followed by an irreversible rise in temperature
that persisted after the removal of the applied field. The relaxation time
derived from this temperature rise was found to increase rapidly down to 0.3 K.
The data near to 0.3 K indicated a transition into a metastable state with much
slower relaxation, supporting recent neutron scattering results. In addition,
magnetic dilution of 50 % concentration was found to significantly prolong the
dynamical response in the milikelvin temperature range, in contrast with
results reported for higher temperatures at which the spin correlations are
suppressed. These observations are discussed in terms of defects and loop
correlations in the spin ice state.Comment: 9 figures, submitted to Phys. Rev.
Electron Spin Resonance in a Spin-1/2 Heisenberg Strong-rung Ladder
Cu(CHN)Cl, a strong-rung spin-1/2 Heisenberg ladder compound,
is probed by means of electron spin resonance (ESR) spectroscopy in the
field-induced gapless phase above . The temperature dependence of the
ESR linewidth is analyzed in the quantum field theory framework, suggesting
that the anisotropy of magnetic interactions plays a crucial role, determining
the peculiar low-temperature ESR linewidth behavior. In particular, it is
argued that the uniform Dzyaloshinskii-Moriya interaction (which is allowed on
the bonds along the ladder legs) can be the source of this behavior in
Cu(CHN)Cl
Spin Dynamics in Chains with Next-Nearest-Neighbor Exchange Interactions
Low-energy magnetic excitations in the spin-1/2 chain compound
(CHN)CuCl [known as (6MAP)CuCl] are probed by means of
tunable-frequency electron spin resonance. Two modes with asymmetric (with
respect to the line) frequency-field dependences are resolved,
illuminating the striking incompatibility with a simple uniform
Heisenberg chain model. The unusual ESR spectrum is explained in terms of the
recently developed theory for spin-1/2 chains, suggesting the important role of
next-nearest-neighbor interactions in this compound. Our conclusion is
supported by model calculations for the magnetic susceptibility of
(6MAP)CuCl, revealing a good qualitative agreement with experiment
Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6
We report on high-field magnetization, specific-heat and electron spin
resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg
antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes
below TN = 4.38 K is described in the frame of the meanfield theory, confirming
a collinear magnetic structure with an easy-plane anisotropy. The obtained
results allowed us to determine the anisotropy/exchange interaction ratio, A/J
= 0.003, and the upper limit for the inter/intra-plane exchange-interaction
ratio, J'/J = 1/16. It is argued that despite the onset of 3D long-range
magnetic ordering the magnetic properties of this material (including
high-magnetic-field magnetization and non-monotonic field dependence of the
Neel temperature) are strongly affected by two-dimensional spin correlations.Comment: 5 pages, 7 figure
- …