68 research outputs found
Tunneling and rattling in clathrate crystal
We present tunneling and rattling motions of an off-center guest atom in cage
referring to a clathrate crystal La_3Pd_{20}Ge_6. The elastic constant C_{44}
of La_3Pd_{20}Ge_6 shows a Debye-type dispersion around 20 K obeying a
relaxation time tau = tau_0exp(E/k_{B}T) with an attempt time tau_0 =
2.0*10^{-12} sec and an activation energy E = 197 K. At low temperatures below
3 K down to 20 mK, the C_{44} shows a softening of C_{44} =
C_{44}^0(T-T_C^0)/(T-Theta) with T_C^0 = -337.970 mK and Theta = -338.044 mK.
These facts are attributed to two different types of the off-center motions
with Gamma_5 symmetry in 4a-site cage of La_3Pd_{20}Ge_6, a thermally activated
rattling motion over the potential hill and a tunneling motion through the
potential hill at low temperatures.Comment: 5 pages, 4 figures, to be published Phys. Rev.
The role of hyperfine coupling in magnetic and quadrupolar ordering of Pr3Pd20Si6
We study the ternary clathrate Pr3Pd20Si6 in specific heat and
AC-susceptibility measurements on a high-quality single crystal, distinguishing
antiferromagnetic (AFM) and antiferroquadrupolar (AFQ) ordering on two
sublattices of inequivalent Pr sites. The specific heat shows the direct
involvement of nuclear spin degrees of freedom in the AFM ordering, which is
well supported by our calculation of the hyperfine level scheme without
adjustable parameters. Pr3Pd20Si6 is therefore one of the rare materials where
the nuclear moments are involved in the formation of the magnetic ground state.Comment: 5 pages, 5 figure
Magnetic-Field-Independent Ultrasonic Dispersions in the Magnetically Robust Heavy Fermion System SmOs4Sb12
Elastic properties of the filled skutterudite compound SmOsSb have
been investigated by ultrasonic measurements. The elastic constant
shows two ultrasonic dispersions at 15 K and 53 K
for frequencies between 33 and 316 MHz, which follow a Debye-type
formula with Arrhenius-type temperature-dependent relaxation times, and remain
unchanged even with applied magnetic fields up to 10 T. The corresponding
activation energies were estimated to be = 105 K and = 409 K,
respectively. The latter, , is the highest value reported so far in the
Sb-based filled skutterudites. The presence of magnetically robust ultrasonic
dispersions in SmOsSb implies a possibility that an emergence of a
magnetically insensitive heavy fermion state in this system is associated with
a novel local charge degree of freedom which causes the ultrasonic dispersion.Comment: 5 pages, 4 figure
Quadrupolar effect and rattling motion in heavy fermion superconductor PrOs_4Sb_{12}
The elastic properties of a filled skutterudite PrOs_4Sb_{12} with a heavy
Fermion superconductivity at T_C=1.85 K have been investigated. The elastic
softening of (C_{11}-C_{12})/2 and C_{44} with lowering temperature down to T_C
indicates that the quadrupolar fluctuation due to the CEF state plays a role
for the Cooper paring in superconducting phase of PrOs_4Sb_{12}. A Debye-type
dispersion in the elastic constants around 30 K revealed a thermally activated
Gamma_{23} rattling due to the off-center Pr-atom motion obeying
tau=tau_{0}exp(E/k_{B}T) with an attempt time tau_0=8.8*10^{-11} sec and an
activation energy E=168 K. It is remarkable that the charge fluctuation of the
off-center motion with Gamma_{23} symmetry may mix with the quadrupolar
fluctuation and enhance the elastic softening of (C_{11}-C_{12})/2 just above
T_C.Comment: 5 pages, 4 figures, to be published to Phys. Rev.
Magnetic phase diagram of antiferroquadrupole ordering in HoB2C2
The magnetic phase diagram for antiferro-quadrupole (AFQ) ordering in
tetragonal HoBC has been investigated by measurements of elastic
constants , and in fields along the basal -
plane as well as the principal [001]-axis. The hybrid magnet (GAMA) in Tsukuba
Magnetic Laboratory was employed for high field measurements up to 30 T. The
AFQ phase is no longer observed above 26.3 T along the principal [001] axis in
contrast to the relatively small critical field of 3.9 T in fields applied
along the basal [110] axis. The quadrupolar intersite interaction of
and/or is consistent with the anisotropy in the magnetic phase diagram
of the AFQ phase in HoBC.Comment: Phys. Rev. B. (2005) in press. approx 8 pages, 10 figure
Myelodysplastic syndrome accompanied by basophilia and eosinophilia with t(5;12)(q31;p13)
The t(5;12)(q31not, vert, similar35;p12not, vert, similar13) is rare among cytogenetically categorized myeloid diseases. Here we describe a case of myelodysplastic syndrome (MDS) with basophilia followed by leukocytosis, basophilia, and eosinophilia with t(5;12)(q31;p13).A 44-year-old man was referred to Tsukuba University Hospital in August 2005, due to severe anemia and thrombocytopenia. Peripheral blood examination showed hemoglobin 4.5 g/dL, with mean corpuscular volume 109 fL, platelets 73 × 109/L, and white blood cells 4.9 × 109/L with 23% basophils, 3% eosinophils, and 0% blasts. Bone marrow was slightly hypocellular, with trilineage dysplasia. Cytogenetic examination of the bone marrow cells revealed a normal karyotype, 46,XY. A diagnosis of myelodysplastic syndrome–refractory anemia with excess blasts type 2 (MDS-RAEB2) was made according to the WHO classification
Ferroquadrupole ordering and Gamma_5 rattling motion in clathrate compound Ce_3Pd_20Ge_6
Lattice effects in a cerium based clathrate compound Ce_3Pd_20Ge_6 with a
cubic Cr_23C_6-type structure have been investigated by ultrasonic and thermal
expansion measurements. Elastic softenings of (C_11-C_12)/2 and C_44
proportional to the reciprocal temperature 1/T above T_Q1 = 1.25 K are well
described in terms of the quadrupole susceptibility for the ground state
Gamma_8 quartet. A huge softening of 50 % in (C_11-C_12)/2 and a spontaneous
expansion DL/L = 1.9x10^-4 along the [001] direction in particular indicate the
ferroquadrupole ordering of O_2^0 below T_Q1. The elastic anomalies associated
with the antiferromagnetic ordering at T_N2 = 0.75 K and the incommensurate
antiferromagnetic ordering are also found. Notable frequency dependence of C_44
around 10 K is accounted for by the Debye-type dispersion indicating a Gamma_5
rattling motion of an off-center Ce ion along the [111] direction with eight
fractionally occupied positions around the 4a site in a cage. The thermally
activated Gamma_5 rattling motion obeying a relaxation time t = t_0exp(E/k_BT)
with an attempt time t_0 = 3.1x10^-11 sec and an activation energy E = 70 K
dies out with decreasing temperature, and then the off-center tunneling state
of Ce ion in the 4a-site cage will appear at low temperatures.Comment: 11 pages, 15 figures, to be published on Phys. Rev.
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