1,124 research outputs found
Kondo Screening and Magnetic Ordering in Frustrated UNi4B
UNi4B exhibits unusual properties and, in particular, a unique
antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the
low temperature behavior of this compound, we propose that the remaining 1/3 U
sites are nonmagnetic due to the Kondo effect. We derive a model in which the
coexistence of magnetic and nonmagnetic U sites is the consequence of the
competition between frustration of the crystallographic structure and
instability of the 5f moments.Comment: 4 pages, 2 figure
Second Low Temperature Phase Transition in Frustrated UNi_4B
Hexagonal UNi_4B is magnetically frustrated, yet it orders
antiferromagnetically at T_N = 20 K. However, one third of the U-spins remain
paramagnetic below this temperature. In order to track these spins to lower
temperature, we measured the specific heat C of \unib between 100 mK and 2 K,
and in applied fields up to 9 T. For zero field there is a sharp kink in C at
330 mK, which we interpret as an indication of a second phase
transition involving paramagnetic U. The rise in between 7 K and
330 mK and the absence of a large entropy liberated at may be due to a
combination of Kondo screening effects and frustration that strongly modifies
the low T transition.Comment: 4 pages, 4 figure
Laser-driven quantum magnonics and THz dynamics of the order parameter in antiferromagnets
The impulsive generation of two-magnon modes in antiferromagnets by
femtosecond optical pulses, so-called femto-nanomagnons, leads to coherent
longitudinal oscillations of the antiferromagnetic order parameter that cannot
be described by a thermodynamic Landau-Lifshitz approach. We argue that this
dynamics is triggered as a result of a laser-induced modification of the
exchange interaction. In order to describe the oscillations we have formulated
a quantum mechanical description in terms of magnon pair operators and coherent
states. Such an approach allowed us to} derive an effective macroscopic
equation of motion for the temporal evolution of the antiferromagnetic order
parameter. An implication of the latter is that the photo-induced spin dynamics
represents a macroscopic entanglement of pairs of magnons with femtosecond
period and nanometer wavelength. By performing magneto-optical pump-probe
experiments with 10 femtosecond resolution in the cubic KNiF and the
uniaxial KNiF collinear Heisenberg antiferromagnets, we observed
coherent oscillations at the frequency of 22 THz and 16 THz, respectively. The
detected frequencies as a function of the temperature ideally fit the
two-magnon excitation up to the N\'eel point. The experimental signals are
described as dynamics of magnetic linear dichroism due to longitudinal
oscillations of the antiferromagnetic vector.Comment: 25 pages, 10 figure
A compartive study of the retentive capability of the Sydney mini-screw with 6mm orthodontic anchorage miniscrews in the tibia and femur of New Zealand rabbits by removal torque test
Aim: To investigate the retentive capability of the Sydney Mini-screw with injectable bone cement by removal torque. Method: 16 New Zealand White rabbits were divided evenly into 2 groups, T1 0 week to assess primary stability and T2 8 weeks to test secondary stability. Three groups of miniscrews Sydney Mini-screw with Cement (SMSC) N=12, Sydney Miniscrew without cement (SMS) N=10 and control Aarhus (CA) 6mm screw N=10 were placed randomly and evenly between the right and left tibial and femoral sites. The SMSC and SMS required predrilling of a pilot hole and the SMSC had injectable bone cement PRODENSE. Removal torque was measured and Friedman's Test and two-sample t-test were used for statistical analysis, where appropriate. Results: Removal torque values at T1 for CA, SMS, SMSC were not significantly different (p=0.072) but were significantly different at T2 (p=0.012). Only SMS (p=0.006) showed statistically significant difference between T1 and T2. The different surgical locations at T2 did not statistically differ from each other either (p=0.948). Conclusion: Sydney Miniscrew with and without cement had significantly higher secondary stability and had a trend towards increased primary compared to a normal control miniscrew. More research is required with an increased sample size
Magnetic phase diagram and transport properties of FeGe_2
We have used resistivity measurements to study the magnetic phase diagram of
the itinerant antiferromagnet FeGe_2 in the temperature range from 0.3->300 K
in magnetic fields up to 16 T. In contrast to theoretical predictions, the
incommensurate spin density wave phase is found to be stable at least up to 16
T, with an estimated critical field \mu _0H_c of ~ 30 T. We have also studied
the low temperature magnetoresistance in the [100], [110], and [001]
directions. The transverse magnetoresistance is well described by a power law
for magnetic fields above 1 T with no saturation observed at high fields. We
discuss our results in terms of the magnetic structure and the calculated
electronic bandstructure of FeGe_2. We have also observed, for the first time
in this compound, Shubnikov-de Haas oscillations in the transverse
magnetoresistance with a frequency of 190 +- 10 T for a magnetic field along
[001].Comment: 13 pages, RevTeX, 7 postscript figures, to appear in Journal of
Physics: Condensed Matte
Specific Heat of URuSi in Fields to 42 T: Clues to the 'Hidden Order'
The large C observed at 17.5 K in URuSi is inconsistent
with the small, 0.04 moment measured for the antiferromagnetism
observed starting (perhaps coincidentally) at the same temperature. We report
measurements of this specific heat transition, thought to be due to some
'hidden order', in magnetic fields between 24 and 42 T, i. e. through the field
region where three metamagnetic transtions are known to occur at 35.8, 37.3,
and 39.4 T. The response of C in single crystal URuSi to
magnetic field, which includes a change to C being possibly associated
with a first order phase transition for high fields, is analyzed to shed
further light on the possible explanations of this unknown ordering process. At
fields above 35 T, a new high field phase comes into being; the connection
between this high field phase revealed by the specific heat and earlier
magnetization data is discussed
Field Reentrance of the Hidden Order State of URu2Si2 under Pressure
Combination of neutron scattering and thermal expansion measurements under
pressure shows that the so-called hidden order phase of URu2Si2 reenters in
magnetic field when antiferromagnetism (AF) collapses at H_AF (T). Macroscopic
pressure studies of the HO-AF boundaries were realized at different pressures
via thermal expansion measurements under magnetic field using a strain gauge.
Microscopic proof at a given pressure is the reappearance of the resonance at
Q_0=(1,0,0) under field which is correlated with the collapse of the AF Bragg
reflections at Q_0.Comment: 5 pages, 6 figures, accepted for publication in J. Phys. Soc. Jp
Induced-Moment Weak Antiferromagnetism and Orbital Order on the Itinerant-Localized Duality Model with Nested Fermi Surface: A Possible Origin of Exotic Magnetism in URuSi
The weak antiferromagnetism of URuSi is discussed on the
basis of a duality model which takes into account salient features of both
itinerant fermions and "localized" component of spin degrees of freedom. The
problem is analyzed in the framework of induced-moment mechanism by taking a
singlet-singlet crystal field scheme together with the nesting property of
partial Fermi surface of itinerant fermions . It is shown that the extremely
small ordered moment of () can be
compatible with the large specific-heat jump at the transition temperature
. Analysis performed in the presence of external magnetic field shows
that the field dependence of in the limit T\to 0 and T_{N}$ do not scale
except very near the critical field B which is consistent with a recent
observation by Mentink. It is also shown that the antiferromagnetic magnetic
order gives rise to a tiny amount of antiferromagnetic orbital order of
f-electrons.Comment: 14 pages, 2 figure PS file, accepted J. Phys. Soc. Jp
Oil Body Formation in Marchantia polymorpha Is Controlled by MpC1HDZ and Serves as a Defense against Arthropod Herbivores
Magnetic state in URu2Si2, UPd2Al3 and UNi2Al3 probed by point contacts
The antiferromagnetic (AFM) state has been investigated in the three
heavy-fermion compounds URu2Si2, UPd2Al3, and UNi2Al3 by measuring dV/dI(V)
curves of point contacts at different temperatures (1.5-20 K) and magnetic
fields (0-28 T). The zero-bias maximum in dV/dI(V) for URu2Si2 points to a
partially gapped Fermi-surface related to the itinerant nature of the AFM state
contrary to UPd2Al3 where analogous features have not been found. The AFM state
in UNi2Al3 has more similarities with URu2Si2. For URu2Si2, the same critical
field of about 40 T along the easy c axis is found for all features in dV/dI(V)
corresponding to the Neel temperature, the gap in the electronic density of
states, and presumably the ordered moments.Comment: 10 pages incl. 5 figures, LaTex 2
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