576 research outputs found
Evidence for short-range antiferromagnetic fluctuations in Kondo-insulating YbB12
The spin dynamics of mixed-valence YbB12 has been studied by inelastic
neutron scattering on a high-quality single crystal. In the Kondo-insulating
regime realized at low temperature, the spectra exhibit a spin-gap structure
with two sharp, dispersive, in-gap excitations at E = 14.5 and approximately 20
meV. The lower mode is shown to be associated with short-range correlations
near the antiferromagnetic wave vector q0 = (1/2, 1/2, 1/2). Its properties are
in overall agreement with those expected for a "spin exciton'' branch in an
indirect hybridization gap semiconductor.Comment: 4 pages, 4 figures ; submitted to Physical Review Letter
Structural Modification and Metamagnetic Anomaly in the Ordered State of CeOs2Al10
A caged compound CeOs2Al10, crystallizing in the orthorhombic YbFe2Al10-type
structure, undergoes a mysterious phase transition at T_0=29 K. We report the
results of electron diffraction, magnetization, and magnetoresistance for
single crystals. Superlattice reflections characterized by a wave vector q =
(0, -2/3, 2/3) observed at 15 K indicate a structural modification in the
ordered state. Activation-type behavior of the electrical resistivity along the
three principal axes below 50 K suggests gap opening in the conduction band.
The magnetic susceptibility \chi = M/B is highly anisotropic,
\chi_a>\chi_c>\chi_b, all of which sharply decrease on cooling below T_0.
Furthermore, a metamagnetic anomaly in the magnetization and a step in the
magnetoresistance occur at B=6-8 T only when the magnetic field is applied
parallel to the orthorhombic c axis. However, T_0 hardly changes under magnetic
fields up to 14 T, irrespective of the field direction. By using these data, we
present a B-T phase diagram and discuss several scenarios for the mysterious
transition.Comment: 6 pages, 7 figures, accepted for publication in Phys. Rev.
Direct observation of Fe spin reorientation in single crystalline YbFe6Ge6
We have grown single crystals of YbFe6Ge6 and LuFe6Ge6 and characterized
their anisotropic behaviour through low field magnetic susceptibility,
field-dependent magnetization, resistivity and heat capacity measurements. The
Yb+3 valency is confirmed by LIII XANES measurements. YbFe6Ge6 crystals exhibit
a field-dependent, sudden reorientation of the Fe spins at about 63 K, a unique
effect in the RFe6Ge6 family (R = rare earths) where the Fe ions order
anti-ferromagnetically with Neel temperatures above 450 K and the R ions'
magnetism appears to behave independently. The possible origins of this unusual
behaviour of the ordered Fe moments in this compound are discussed.Comment: 12 pages, 8 figures, accepted in J. Phys.: Cond. Matte
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