69,548 research outputs found
Large magnetic heat transport in a Haldane chain material Ni(C$_3H_{10}N_2)_2NO_2ClO_4
We report a study on the heat transport of an S = 1 Haldane chain compound
Ni(C_3H_{10}N_2)_2NO_2ClO_4 at low temperatures and in magnetic fields. The
zero-field thermal conductivities show a remarkable anisotropy for the heat
current along the spin-chain direction (\kappa_b) and the vertical direction
(\kappa_c), implying a magnetic contribution to the heat transport along the
spin-chain direction. The magnetic-field-induced change of the spin spectrum
has obviously opposite impacts on \kappa_b and \kappa_c. In particular,
\kappa_b(H) and \kappa_c(H) curves show peak-like increases and dip-like
decreases, respectively, at \sim 9 T, which is the critical field that
minimizes the spin gap. These results indicate a large magnetic thermal
transport in this material.Comment: 3 pages, 2 figures, accepted for publication in J. Appl. Phys.
(Proceedings of the 12th Joint MMM/Intermag Conference
Low-temperature thermal conductivity of antiferromagnetic S = 1/2 chain material CuCl_22((CH_3)_2SO)
We study the heat transport of S = 1/2 chain compound
CuCl_22((CH_3)_2SO) along the b axis (vertical to the chain direction)
at very low temperatures. The zero-field thermal conductivity (\kappa) shows a
distinct kink at about 0.9 K, which is related to the long-range
antiferromagnetic (AF) transition. With applying magnetic field along the c
axis, \kappa(H) curves also show distinct changes at the phase boundaries
between the AF and the high-field disordered states. These results indicate a
strong spin-phonon interaction and the magnetic excitations play a role in the
b-axis heat transport as phonon scatterers.Comment: 3 pages, 3 figures, accepted for publication in J. Appl. Phys.
(Proceedings of the 58th MMM Conference
Low-temperature heat transport of CuFeGaO ( 0--0.12) single crystals
We report a study on the thermal conductivity of CuFeGaO ( 0--0.12) single crystals at temperatures down to 0.3 K and in magnetic
fields up to 14 T. CuFeO is a well-known geometrically frustrated
triangular lattice antiferromagnet and can be made to display multiferroicity
either by applying magnetic field along the axis or by doping nonmagnetic
impurities, accompanied with rich behaviors of magnetic phase transitions. The
main experimental findings of this work are: (i) the thermal conductivities
( and ) show drastic anomalies at temperature- or
field-induced magnetic transitions; (ii) the low- isotherms
exhibit irreversibility in a broad region of magnetic fields; (iii) there are
phonon scattering effect caused by magnetic fluctuations at very low
temperatures. These results demonstrate strong spin-phonon coupling in this
material and reveal the non-negligible magnetic fluctuations in the "ground
state" of pure and Ga-doped samples.Comment: 11 pages, 12 figures, accepted for publication in Phys. Rev.
Magnetization, specific heat, and thermal conductivity of hexagonal ErMnO single crystals
We report a study of magnetism and magnetic transitions of hexagonal
ErMnO single crystals by magnetization, specific heat and heat transport
measurements. Magnetization data show that the -axis magnetic field induces
three magnetic transitions at 0.8, 12 and 28 T. The specific heat shows a peak
at 2.2 K, which is due to a magnetic transition of Er moments. For
low- thermal conductivity (), a clear dip-like feature appears in
isotherm at 1--1.25 T for ; while in the case of , a step-like increase is observed at 0.5--0.8 T. The transition
fields in are in good agreement with those obtained from
magnetization, and the anomaly of can be understood by a spin-phonon
scattering scenario. The natures of magnetic structures and corresponding
field-induced transitions at low temperatures are discussed.Comment: 11 pages, 14 figures, accepted for publication in Phys. Rev.
Low-temperature heat transport of the geometrically frustrated antiferromagnets R_2Ti_2O_7 (R = Gd and Er)
We report a systematic study on the low-temperature thermal conductivity
(\kappa) of R_2Ti_2O_7 (R = Gd and Er) single crystals with different
directions of magnetic field and heat current. It is found that the magnetic
excitations mainly act as phonon scatterers rather than heat carriers, although
these two materials have long-range magnetic orders at low temperatures. The
low-T \kappa(H) isotherms of both compounds show rather complicated behaviors
and have good correspondences with the magnetic transitions, where the
\kappa(H) curves show drastic dip- or step-like changes. In comparison, the
field dependencies of \kappa are more complicated in Gd_2Ti_2O_7, due to the
complexity of its low-T phase diagram and field-induced magnetic transitions.
These results demonstrate the significant coupling between spins and phonons in
these materials and the ability of heat-transport properties probing the
magnetic transitions.Comment: 9 pages, 6 figures, accepted for publication in Phys. Rev.
Ground state and magnetic phase transitions of orthoferrite DyFeO_3
Low-temperature thermal conductivity (\kappa), as well as magnetization (M)
and electric polarization (P), of multiferroic orthoferrite DyFeO_3 single
crystals are studied with H \parallel c. When the crystal is cooled in zero
field, M, P, and \kappa all consistently exhibit irreversible magnetic-field
dependencies. In particular, with 500 mK < T \le 2 K, all these properties show
two transitions at the first run of increasing field but only the higher-field
transition is present in the subsequent field sweepings. Moreover, the
ultra-low-T (T < 500 mK) \kappa(H) shows a different irreversibility and there
is only one transition when the field is swept both up and down. All the
results indicate a complex low-T H-T phase diagram involving successive
magnetic phase transitions of the Fe^{3+} spins. In particular, the ground
state, obtained with cooling to subKelvin temperatures in zero field, is found
to be an unexplored phase.Comment: 9 pages, 7 figures, accepted for publication in Phys. Rev.
Low-temperature heat transport and magnetic-structure transition of the hexagonal TmMnO_3 single crystals
We study the low-temperature heat transport, as well as the magnetization and
the specific heat, of TmMnO_3 single crystals to probe the transitions of
magnetic structure induced by magnetic field. It is found that the low-T
thermal conductivity (\kappa) shows strong magnetic-field dependence and the
overall behaviors can be understood in the scenario of magnetic scattering on
phonons. In addition, a strong "dip"-like feature shows up in \kappa(H)
isotherms at 3.5--4 T for H \parallel c, which is related to a known spin
re-orientation of Mn^{3+} moments. The absence of this phenomenon for H
\parallel a indicates that the magnetic-structure transition of TmMnO_3 cannot
be driven by the in-plane field. In comparison, the magnetothermal conductivity
of TmMnO_3 is much larger than that of YMnO_3 but smaller than that of HoMnO_3,
indicating that the magnetisms of rare-earth ions are playing the key role in
the spin-phonon coupling of the hexagonal manganites.Comment: 7 pages, 6 figures, accepted for publication in Phys. Rev.
Quantum optomechanics with a mixture of ultracold atoms
We study cavity optomechanics of a mixture of ultracold atoms with tunable
nonlinear collisions. We show that atomic collisions provide linear couplings
between fictitious condensate oscillators, leading to possibilities of
achieving a globally coupled quantum optomechanical network with an integrated
atom chip. Potential applications range from simulating collective
nonequilibrium dynamics in fields well past physics to probing unique
properties of quantum mixtures.Comment: 4 pages, 3 figure
An irreversible magnetic-field dependence of low-temperature heat transport of spin-ice compound Dy_2Ti_2O_7 in a [111] field
We study the low-temperature thermal conductivity (\kappa) of Dy_2Ti_2O_7
along and perpendicular to the (111) plane and under the magnetic field along
the [111] direction. Besides the step-like decreases of \kappa at the
field-induced transitions from the spin-ice state to the kagom\'e-ice state and
then to the polarized state, an abnormal phenomenon is that the \kappa(H)
isotherms show a clear irreversibility at very low temperatures upon sweeping
magnetic field up and down. This phenomenon surprisingly has no correspondence
with the well-known magnetization hysteresis. Possible origins for this
irreversibility are discussed; in particular, a pinning effect of magnetic
monopoles in spin ice compound by the weak disorders is proposed.Comment: 7 pages, 5 figures, Submitted at 02Jul2012; resubmitted to Phys. Rev.
B at 11Sep201
Magnetically originated phonon-glass-like behavior in Tb_2Ti_2O_7 single crystal
We report a study on the thermal conductivity (\kappa) of Tb_2Ti_2O_7 single
crystals at low temperatures. It is found that in zero field this material has
an extremely low phonon thermal conductivity in a broad temperature range. The
mean free path of phonons is even smaller than that of amorphous materials and
is 3--4 orders of magnitude smaller than the sample size at 0.3 K. The strong
spin fluctuation of the spin-liquid state is discussed to be the reason of the
strong phonon scattering. The magnetic-field dependence of \kappa and
comparison with Y_2Ti_2O_7 and TbYTi_2O_7 confirm the magnetic origin of this
phonon-glass-like behavior.Comment: 7 pages, 4 figures, accepted for publication in Phys. Rev.
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