44 research outputs found
Intrinsic double-peak structure of the specific heat in low-dimensional quantum ferrimagnets
Motivated by recent magnetic measurements on A3Cu3(PO4)4 (A=Ca,Sr) and
Cu(3-Clpy)2(N3)2 (3-Clpy=3-Chloropyridine), both of which behave like
one-dimensional ferrimagnets, we extensively investigate the ferrimagnetic
specific heat with particular emphasis on its double-peak structure. Developing
a modified spin-wave theory, we reveal that ferromagnetic and antiferromagnetic
dual features of ferrimagnets may potentially induce an extra low-temperature
peak as well as a Schottky-type peak at mid temperatures in the specific heat.Comment: 5 pages, 6 figures embedded, Phys. Rev. B 65, 214418 (2002
Low-Temperature Properties of Quasi-One-Dimensional Molecule-Based Ferromagnets
Quantum and thermal behaviors of low-dimensional mixed-spin systems are
investigated with particular emphasis on the design of molecule-based
ferromagnets. One can obtain a molecular ferromagnet by assembling molecular
bricks so as to construct a low-dimensional system with a magnetic ground state
and then coupling the chains or the layers again in a ferromagnetic fashion.
Two of thus-constructed quasi-one-dimensional bimetallic compounds are
qualitatively viewed within the spin-wave treatment, one of which successfully
grows into a bulk magnet, while the other of which ends in a singlet ground
state. Then, concentrating on the ferrimagnetic arrangement on a two-leg ladder
which is well indicative of general coupled-chain ferrimagnets, we develop the
spin-wave theory and fully reveal its low-energy structure. We inquire further
into the ferromagnetic aspect of the ferrimagnetic ladder numerically
calculating the sublattice magnetization and the magnetic susceptibility. There
exists a moderate coupling strength between the chains in order to obtain the
most ferromagnetic ferrimagnet.Comment: 10 pages, 7 figures embedded, to be published in J. Phys. Soc. Jpn.
Vol.70, No.5 (2001
Hole Dynamics in the Orthogonal-Dimer Spin System
The dynamics of a doped hole in the orthogonal-dimer spin system is
investigated systematically in one, two and three dimensions. By combining the
bond-operator method with the self-consistent
Born approximation, we argue that a dispersive quasi-particle state in the
dimer phase is well defined even for quasi-two-dimensional systems. On the
other hand, a doped hole in the plaquette-singlet phase hardly itinerates,
forming an almost localized mode. We further clarify that although the
quasi-particle weight in the dimer phase is decreased in the presence of the
interchain coupling, it is not suppressed but even enhanced upon the
introduction of the interlayer coupling.Comment: 8 pages, 10 figure
Spin-Wave Description of Haldane-gap antiferromagnets
Modifying the conventional antiferromagnetic spin-wave theory which is
plagued by the difficulty of the zero-field sublattice magnetizations diverging
in one dimension, we describe magnetic properties of Haldane-gap
antiferromagnets. The modified spin waves, constituting a grand canonical
bosonic ensemble so as to recover the sublattice symmetry, not only depict well
the ground-state correlations but also give useful information on the
finite-temperature properties.Comment: to be published in J. Phys. Soc. Jpn. Vol. 72, No. 4 (2003
Bosonic representation of one-dimensional Heisenberg ferrimagnets
The energy structure and the thermodynamics of ferrimagnetic Heisenberg
chains of alternating spins S and s are described in terms of the Schwinger
bosons and modified spin waves. In the Schwinger representation, we average the
local constraints on the bosons and diagonalize the Hamiltonian at the
Hartree-Fock level. In the Holstein-Primakoff representation, we optimize the
free energy in two different ways introducing an additional constraint on the
staggered magnetization. A new modified spin-wave scheme, which employs a
Lagrange multiplier keeping the native energy structure free from temperature
and thus differs from the original Takahashi Scheme, is particularly stressed
as an excellent language to interpret one-dimensional quantum ferrimagnetism.
Other types of one-dimensional ferrimagnets and the antiferromagnetic limit S=s
are also mentioned.Comment: to be published in Phys. Rev. B 69, No. 6, 0644XX (2004
Nuclear Magnetic Relaxation in the Haldane-Gap Antiferromagnet Ni(C_2_H_8_N_2_)_2_NO_2_(ClO_4_)
A new theory is proposed to interpret nuclear spin-lattice relaxation-time
(T_1_) measurements on the spin-1 quasi-one-dimensional Heisenberg
antiferromagnet Ni(C_2_H_8_N_2_)_2_NO_2_(ClO_4_) (NENP). While Sagi and Affleck
pioneeringly discussed this subject in terms of field-theoretical languages,
there is no theoretical attempt yet to explicitly simulate the novel
observations of 1/T_1_ reported by Fujiwara et al.. By means of modified spin
waves, we solve the minimum of 1/T_1_ as a function of an applied field,
pending for the past decade.Comment: to be published in J. Phys. Soc. Jpn. 73, No. 4 (2004
Frustrated 3-Dimensional Quantum Spin Liquid in CuHpCl
Inelastic neutron scattering measurements are reported for the quantum
antiferromagnetic material Cu_2(C_5H_12N_2)_2Cl_4 (CuHpCl). The magnetic
excitation spectrum forms a band extending from 0.9 meV to 1.4 meV. The
spectrum contains two modes that disperse throughout the a-c plane of the
monoclinic unit cell with less dispersion along the unique b-axis. Simple
arguments based on the measured dispersion relations and the crystal structure
show that a spin ladder model is inappropriate for describing CuHpCl. Instead,
it is proposed that hydrogen bond mediated exchange interactions between the
bi-nuclear molecular units yield a three-dimensional interacting spin system
with a recurrent triangular motif similar to the Shastry-Sutherland Model
(SSM). Model independent analysis based on the first moment sum rule shows that
at least four distinct spin pairs are strongly correlated and that two of
these, including the dimer bond of the corresponding SSM, are magnetically
frustrated. These results show that CuHpCl should be classified as a
frustration induced three dimensional quantum spin liquid.Comment: 13 pages, 17 figures (Color) ReSubmitted to Phys. Rev. B 9/21/2001
resubmission has new content email comments to [email protected] or
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Mandibular reconstruction with vascularised bone flaps: a systematic review over 25 years
To explore the techniques for mandibular reconstruction with composite free flaps and their outcomes, we systematically reviewed reports published between 1990 and 2015. A total of 9499 mandibular defects were reconstructed with 6178 fibular, 1380 iliac crest, 1127 composite radial, 709 scapular, 63 serratus anterior and rib, 32 metatarsal, and 10 lateral arm flaps including humerus. The failure rate was higher for the iliac crest (6.2%, 66/1059) than for fibular, radial, and scapular flaps combined (3.4%, 202/6018) (p<0.001). We evaluated rates of osteotomy, non-union, and fistulas. Implant-retained prostheses were used most often for rehabilitation after reconstruction with iliac crest (44%, 100/229 compared with 26%, 605/2295 if another flap was used) (p<0.001). There were no apparent changes in the choice of flap or in the complications reported. Although we were able to show some significant differences relating to the types of flap used, we were disappointed to find that fundamental outcomes such as the need for osteotomy, and rates of non-union and fistulas were under-reported. This review shows the need for more comprehensive and consistent reporting of outcomes to enable the comparison of different techniques for similar defects