194 research outputs found
Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite
Coupling of spin-waves with electromagnetic cavity field is demonstrated in
an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at
0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures
were found at crossings of spin-wave resonances with Fabry-Perot cavity modes
formed in samples. The obtained spectra are explained in terms of classical
electrodynamics and a microscopic model.Comment: 3 pages, 2 figure
Cavity-mediated coupling of antiferromagnetic spin waves
Coupling of space-separated oscillators is interesting for quantum and
communication technologies. In this work, it is shown that two
antiferromagnetic oscillators placed inside an electromagnetic cavity couple
cooperatively to its terahertz modes and, in effect, hybridized
magnon-polariton modes are formed. This is supported by a systematic study of
reflection spectra from two parallel-plane slabs of hematite
(-FeO), measured as a function of their temperatures and
separation distance, and modeled theoretically. The mediating cavity was formed
by the crystals themselves and the experiment was performed in a practical
distance range of a few millimetres and above room temperature. Cavity-mediated
coupling allows for engineering of complex resonators controlled by their
geometry and by sharing properties of their components
Orbital domain state and finite size scaling in ferromagnetic insulating manganites
55Mn and 139La NMR measurements on a high quality single crystal of
ferromagnetic (FM) La0.80Ca20MnO3 demonstrate the formation of localized
Mn(3+,4+) states below 70 K, accompanied with strong anomalous increase of
certain FM neutron Bragg peaks. (55,139)(1/T1) spin-lattice relaxation rates
diverge on approaching this temperature from below, signalling a genuine phase
transition at T(tr) approx. 70 K. The increased local magnetic anisotropy of
the low temperature phase, the cooling-rate dependence of the Bragg peaks, and
the observed finite size scaling of T(tr) with Ca (hole) doping, are suggestive
of freezing into an orbital domain state, precursor to a phase transition into
an inhomogeneous orbitally ordered state embodying hole-rich walls.Comment: 4 pages, 4 figure
Ferrimagnetism of the magnetoelectric compound CuOSeO probed by Se NMR
We present a thorough Se NMR study of a single crystal of the
magnetoelectric compound CuOSeO. The temperature dependence of the
local electronic moments extracted from the NMR data is fully consistent with a
magnetic phase transition from the high-T paramagnetic phase to a low-T
ferrimagnetic state with 3/4 of the Cu ions aligned parallel and 1/4
aligned antiparallel to the applied field of 14.09 T. The transition to this
3up-1down magnetic state is not accompanied by any splitting of the NMR lines
or any abrupt modification in their broadening, hence there is no observable
reduction of the crystalline symmetry from its high-T cubic \textit{P}23
space group. These results are in agreement with high resolution x-ray
diffraction and magnetization data on powder samples reported previously by Bos
{\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean
field theory description of the problem based on a microscopic spin Hamiltonian
with one antiferromagnetic ( K) and one ferromagnetic
( K) nearest-neighbor exchange interaction
Establishing the fundamental magnetic interactions in the chiral skyrmionic Mott insulator Cu2OSeO3 by terahertz electron spin resonance
The recent discovery of skyrmions in CuOSeO has established a new
platform to create and manipulate skyrmionic spin textures. We use high-field
electron spin resonance (ESR) spectroscopy combining a terahertz free electron
laser and pulsed magnetic fields up to 64 T to probe and quantify its
microscopic spin-spin interactions. Besides providing direct access to the
long-wavelength Goldstone mode, this technique probes also the high-energy part
of the excitation spectrum which is inaccessible by standard low-frequency ESR.
Fitting the behavior of the observed modes in magnetic field to a theoretical
framework establishes experimentally that the fundamental magnetic building
blocks of this skyrmionic magnet are rigid, highly entangled and weakly coupled
tetrahedra.Comment: 5 pages, 3 Figure
Antiferromagnetic resonance in -FeO up to its N\'eel temperature
Hematite (-FeO) is an antiferromagnetic material with a very
low spin damping and high N\'eel temperature. The temperature dependence of the
antiferromagnetic resonance in a bulk single crystal of hematite was
characterized from room temperature up to the N\'eel temperature in the
frequency range of 0.19-0.5 THz. From these data, the N\'eel temperature was
estimated as 966 K
Current-induced two-level fluctuations in pseudo spin-valves (Co/Cu/Co) nanostructures
Two-level fluctuations of the magnetization state of pseudo spin-valve
pillars Co(10 nm)/Cu(10 nm)/Co(30 nm) embedded in electrodeposited nanowires
(~40 nm in diameter, 6000 nm in length) are triggered by spin-polarized
currents of 10^7 A/cm^2 at room temperature. The statistical properties of the
residence times in the parallel and antiparallel magnetization states reveal
two effects with qualitatively different dependences on current intensity. The
current appears to have the effect of a field determined as the bias field
required to equalize these times. The bias field changes sign when the current
polarity is reversed. At this field, the effect of a current density of 10^7
A/cm^2 is to lower the mean time for switching down to the microsecond range.
This effect is independent of the sign of the current and is interpreted in
terms of an effective temperature for the magnetization.Comment: 4 pages, 5 figures, revised version, to be published in Phys. Rev.
Let
Toxic effects of estradiol E2 on development in the European tree frog (Hyla arborea)
Estrogenic hormones are a major environmental threat to aquatic wildlife. Here we report chronic toxic effects of exposure to the naturally excreted estrogen, 17β-estradiol (E2), on the larval and subadult development of the European tree frog (Hyla arborea), by an experimental setting and long-term monitoring. In addition to the documented impact on sexual development and mating behavior, the general toxicity of human-released estrogens may contribute to global amphibian declines
Embodied memory: unconscious smiling modulates emotional evaluation of episodic memories.
Since Damasio introduced the somatic markers hypothesis in Damasio (1994), it has spread through the psychological community, where it is now commonly acknowledged that somatic states are a factor in producing the qualitative dimension of our experiences. Present actions are emotionally guided by those somatic states that were previously activated in similar experiences. In this model, somatic markers serve as a kind of embodied memory. Here, we test whether the manipulation of somatic markers can modulate the emotional evaluation of negative memories. Because facial feedback has been shown to be a powerful means of modifying emotional judgements, we used it to manipulate somatic markers. Participants first read a sad story in order to induce a negative emotional memory and then were asked to rate their emotions and memory about the text. Twenty-four hours later, the same participants were asked to assume a predetermined facial feedback (smiling) while reactivating their memory of the sad story. The participants were once again asked to fill in emotional and memory questionnaires about the text. Our results showed that participants who had smiled during memory reactivation later rated the text less negatively than control participants. However, the contraction of the zygomaticus muscles during memory reactivation did not have any impact on episodic memory scores. This suggests that manipulating somatic states modified emotional memory without affecting episodic memory. Thus, modulating memories through bodily states might pave the way to studying memory as an embodied function and help shape new kinds of psychotherapeutic interventions
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