86 research outputs found
Magnetic-field dependence of antiferromagnetic structure in CeRh1-xCoxIn5
We investigated effects of magnetic field H on antiferromagnetic (AF)
structures in CeRh_{1-x}Co_xIn_5 by performing the elastic neutron scattering
measurements. By applying H along the [1,-1,0] direction, the incommensurate AF
state with the propagation vector of q_{h1}=(1/2,1/2,0.297) observed at H=0 is
replaced by the commensurate AF state with the q_{c2} = (1/2, 1/2, 1/4)
modulation above 2 T for x=0.23, while the AF states with the
q_{c1}=(1/2,1/2,1/2) and q_{h2}=(1/2,1/2,0.42) modulations seen at H=0 change
into a single q_{c1}-AF state above ~1.6 T for x=0.7. These results suggest the
different types of AF correlation for Co concentrations of 0.23 and 0.7 in an
applied magnetic field H.Comment: 4 pages, 2 figures, to appear in the proceedings of ICM2009
(Karlsruhe, Germany
Pressure-temperature phase diagram of the heavy-electron superconductor URu2Si2
The pressure-temperature phase diagram of the heavy-electron superconductor
URu2Si2 has been reinvestigated by ac-susceptibility and elastic
neutron-scattering (NS) measurements performed on a small single-crystalline
rod (2 mm in diameter, 6 mm in length) in a Cu-Be clamp-type high-pressure cell
(P < 1.1 GPa). At ambient pressure, this sample shows the weakest
antiferromagnetic (AF) Bragg reflections reported so far, corresponding to the
volume-averaged staggered moment of mord ~ 0.011 mB/U. Under applied pressure,
the AF scattering intensity exhibits a sharp increase at P ~ 0.7 GPa at low
temperatures. The saturation value of the AF scattering intensity above 0.7 GPa
corresponds to mord ~ 0.41 mB/U, which is in good agreement with that (~ 0.39
mB/U) observed above 1.5 GPa in our previous NS measurements. The
superconductivity is dramatically suppressed by the evolution of AF phase,
indicating that the superconducting state coexists only with the hidden order
phase. The presence of parasitic ferro- and/or antiferromagnetic phases with
transition temperatures T1star =120(5) K, T2star = 36(3) K and T3star = 16.5(5)
K and their relationship to the low-T ordered phases are also discussed.Comment: 6 pages, 7 figures, submitted to J. Magn. Magn. Mater. (ICM2006
Intrinsic Pinning in the High Field C-Phase of UPt_3
We report on the a.c. magnetic response of superconducting UPt_3 in a d.c.
magnetic field. At low fields (H < H^*), the in-phase susceptibility shows a
sharp drop at followed by a gradual decrease with decreasing temperature,
while the out-of-phase component shows a large peak at T_c followed by an
unusual broad peak. As the B-C phase line is crossed (H>H^*), however, both the
in-phase and out-of-phase susceptibilities resemble the zero-field Meissner
curves. We interpret these results in terms of a vortex pinning force which,
while comparatively small in the A/B-phases, becomes large enough to
effectively prevent vortex motion in the C-phase.Comment: Modified discussion, slight changes to figures, accepted in PRB Rapid
Communications. RevTex file, 5 figure
Tuning Heavy Fermion Systems into Quantum Criticality by Magnetic Field
We discuss a series of thermodynamic, magnetic and electrical transport
experiments on the two heavy fermion compounds CeNi2Ge2 and YbRh2Si2 in which
magnetic fields, B, are used to tune the systems from a Non-Fermi liquid (NFL)
into a field-induced FL state. Upon approaching the quantum-critical points
from the FL side by reducing B we analyze the heavy quasiparticle (QP) mass and
QP-QP scattering cross sections. For CeNi2Ge2 the observed behavior agrees well
with the predictions of the spin-density wave (SDW) scenario for
three-dimensional (3D) critical spin-fluctuations. By contrast, the observed
singularity in YbRh2Si2 cannot be explained by the itinerant SDW theory for
neither 3D nor 2D critical spinfluctuations. Furthermore, we investigate the
magnetization M(B) at high magnetic fields. For CeNi2Ge2 a metamagnetic
transition is observed at 43 T, whereas for YbRh2Si2 a kink-like anomaly occurs
at 10 T in M vs B (applied along the easy basal plane) above which the heavy
fermion state is completely suppressed.Comment: 15 pages, 8 figures, submitted to Journal of Low Temperature Physics,
special Series on "High Magnetic Field Facilities
Low-temperature specific heat for ferromagnetic and antiferromagnetic orders in CaRu1-xMnxO3
Low-temperature specific heat of CaRu1-xMnxO3 was measured to clarify the
role of d electrons in ferromagnetic and antiferromagnetic orders observed
above x=0.2. Specific heat divided by temperature C_p/T is found to roughly
follow a T^2 function, and relatively large magnitudes of electronic specific
heat coefficient gamma were obtained in wide x range. In particular, gamma is
unchanged from the value at x=0 (84 mJ/K^2 mol) in the paramagnetic state for
x<=0.1, but linearly reduced with increasing x above x= 0.2. These features of
gamma strongly suggest that itinerant d electrons are tightly coupled with the
evolution of magnetic orders in small and intermediate Mn concentrations.Comment: 4 pages, 2 figures, to be published in J. Phys.: Conf. Ser. (SCES
2011, Cambridge, UK
Competition between hidden order and antiferromagnetism in URu_2Si_2 under uniaxial stress studied by neutron scattering
We have performed elastic neutron scattering experiments under uniaxial
stress sigma applied along the tetragonal [100], [110] and [001] directions for
the heavy electron compound URu2Si2. We found that antiferromagnetic (AF) order
with large moment is developed with sigma along the [100] and [110] directions.
If the order is assumed to be homogeneous, the staggered ordered moment mu_o
continuously increases from 0.02 mu_B (sigma=0) to 0.22 mu_B (0.25 GPa). The
rate of increase partial mu_o/partial sigma is ~ 1.0 mu_B/GPa, which is four
times larger than that for the hydrostatic pressure (partial mu_o/partial P sim
0.25 mu_B/GPa). Above 0.25 GPa, mu_o shows a tendency to saturate, similar to
the hydrostatic pressure behavior. For sigma||[001], mu_o shows only a slight
increase to 0.028 mu_B (sigma = 0.46 GPa) with a rate of ~ 0.02 mu_B/GPa,
indicating that the development of the AF state highly depends on the direction
of sigma. We have also found a clear hysteresis loop in the isothermal
mu_o(sigma) curve obtained for sigma||[110] under the zero-stress-cooled
condition at 1.4 K. This strongly suggests that the sigma-induced AF phase is
metastable, and separated from the "hidden order" phase by a first-order phase
transition. We discuss these experimental results on the basis of crystalline
strain effects and elastic energy calculations, and show that the c/a ratio
plays a key role in the competition between these two phases.Comment: 9 pages, 7 figures, to appear in Physical Review
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