481 research outputs found
Critical Phenomena at the Antiferromagnetic Phase Transition of Azurite
We report on high-resolution acoustic, specific-heat and thermal expansion
measurements in the vicinity of the antiferromagnetic phase transition at T_N =
1.88 K on a high-quality single crystal of the natural mineral azurite. A
detailed investigation of the critical contribution to the various quantities
at T_N is presented. The set of critical exponents and amplitude ratios of the
singular contributions above and below the transition indicate that the system
can be reasonably well described by a three-dimensional Heisenberg
antiferromagnet.Comment: 9 pages, 3 figures, proceedings of ICM 2012, JKP
Interplay of Spin and Lattice Degrees of Freedom in the Frustrated Antiferromagnet CdCr_2O_4: High-field and Temperature Induced Anomalies of the Elastic Constants
Temperature and magnetic field studies of the elastic constants of the
chromium spinel CdCr_2O_4 show pronounced anomalies related to strong
spin-phonon coupling in this frustrated antiferromagnet. A detailed comparison
of the longitudinal acoustic mode propagating along the [111] direction with
theory based on an exchange-striction mechanism leads to an estimate of the
strength of the magneto-elastic interaction. The derived spin-phonon coupling
constant is in good agreement with previous determinations based on infrared
absorption. Further insight is gained from intermediate and high magnetic field
experiments in the field regime of the magnetization plateau. The role of the
antisymmetric Dzyaloshinskii-Moriya interaction discussed and we compare the
spin-phonon coupling in CdCr_2O_4 in both the ordered and disordered states.Comment: 12 pages, 8 figures; Appendix added,To appear in Phys Rev.
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The Beagle 2 microscope
The Beagle 2 microscope provides optical images of the Martian surface at a resolution 5x higher than any other experiment currently planned. By using a novel illumination system it images in three colors and can also detect fluorescent materials
Elastic Properties and Magnetic Phase Diagrams of Dense Kondo Compound Ce0.75La0.25B6
We have investigated the elastic properties of the cubic dense Kondo compound
Ce0.75La0.25B6 by means of ultrasonic measurements. We have obtained magnetic
fields vs temperatures (H-T) phase diagrams under magnetic fields along the
crystallographic [001], [110] and [111] axes. An ordered phase IV showing the
elastic softening of c44 locates in low temperature region between 1.6 and 1.1
K below 0.7 T in all field directions. The phase IV shows an isotropic nature
with regard to the field directions, while the antiferro-magnetic phase III
shows an anisotropic character. A remarkable softening of c44 and a spontaneous
trigonal distortion εyz+εzx+εxy recently reported by Akatsu et
al. [J. Phys. Soc. Jpn. 72 (2003) 205] in the phase IV favor a ferro-quadrupole
(FQ) moment of Oyz+Ozx+Oxy induced by an octupole ordering.Comment: 9 figures, Strongly Correlated Electron
Magnetic edge states of impenetrable stripe
The electron motion in a strong perpendicular magnetic field close to the
impenetrable stripe is considered by making use of the singular integral
equation technique. The energy spectrum is calculated and compared with the
energy spectrum of the round antidot.Comment: REVTeX4 format, 9 pages with 9 figures (*.eps
Magnetic phase transitions in Gd64Sc36 studied using non-contact ultrasonics
The speed and attenuation of ultrasound propagation can be used to determine material properties and identify phase transitions. Standard ultrasonic contact techniques are not always convenient due to the necessity of using couplant; however, recently reliable non-contact ultrasonic techniques involving electromagnetic generation and detection of ultrasound with electromagnetic acoustic transducers (EMATs) have been developed for use on electrically conducting and/or magnetic materials. We present a detailed study of magnetic phase transitions in a single crystal sample of Gd64Sc36 magnetic alloy using contact and non-contact ultrasonic techniques for two orientations of external magnetic field. Phase diagrams are constructed based on measurements of elastic constant C33, the attenuation and the efficiency of generation when using an EMAT. The EMATs are shown to provide additional information related to the magnetic phase transitions in the studied sample, and results identify a conical helix phase in Gd64Sc36 in the magnetic field orientation
Continuous mode cooling and phonon routers for phononic quantum networks
We study the implementation of quantum state transfer protocols in phonon
networks, where in analogy to optical networks, quantum information is
transmitted through propagating phonons in extended mechanical resonator arrays
or phonon waveguides. We describe how the problem of a non-vanishing thermal
occupation of the phononic quantum channel can be overcome by implementing
optomechanical multi- and continuous mode cooling schemes to create a 'cold'
frequency window for transmitting quantum states. In addition, we discuss the
implementation of phonon circulators and switchable phonon routers, which rely
on strong coherent optomechanical interactions only, and do not require strong
magnetic fields or specific materials. Both techniques can be applied and
adapted to various physical implementations, where phonons coupled to spin or
charge based qubits are used for on-chip networking applications.Comment: 33 pages, 8 figures. Final version, a few minor changes and updated
reference
Frequency-dependent magnetotransport and particle dynamics in magnetic modulation systems
We analyze the dynamics of a charged particle moving in the presence of
spatially-modulated magnetic fields. From Poincare surfaces of section and
Liapunov exponents for characteristic trajectories we find that the fraction of
pinned and runaway quasiperiodic orbits {\em vs}. chaotic orbits depends
strongly on the ratio of cyclotron radius to the structure parameters, as well
as on the amplitude of the modulated field. We present a complete
characterization of the dynamical behavior of such structures, and investigate
the contribution to the magnetoconductivity from all different orbits using a
classical Kubo formula. Although the DC conductivity of the system depends
strongly on the pinned and runaway trajectories, the frequency response
reflects the topology of all different orbits, and even their unusual temporal
behavior.Comment: Submitted to PRB - 14 figure files - REVTEX tex
Geometrical quadrupolar frustration in DyB
Physical properties of DyB have been studied by magnetization, specific
heat, and ultrasonic measurements. The magnetic entropy change and the
ultrasonic properties in the intermediate phase II indicate that the degeneracy
of internal degrees of freedom is not fully lifted in spite of the formation of
magnetic order. The ultrasonic attenuation and the huge softening of
in phase II suggests existence of electric-quadrupolar (orbital) fluctuations
of the 4-electron. These unusual properties originate from the geometrical
quadrupolar frustration.Comment: 4 pages, 4 figures, accepted for publication in Journal of the
Physical Society of Japa
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