162 research outputs found
Magnetic Properties of a Quantum Ferrimagnet: NiCu(pba)(D_2O)_3 . 2D_2O
We report the results of magnetic measurements on a powder sample of
NiCu(pba)(D_2O)_3 \cdot 2D_2OS\chi\chi TT\chi TJ/k_B=121
K^{2+}^{2+}g_{Ni}g_{Cu}\chi T$ at low temperatures
is reproduced fairly well by the calculation for the same ferrimagnetic model.Comment: 7pages, 4 postscript figures, usues REVTEX. appear in J. Phys. Soc.
Jpn vol 67 No.7 (1998
Magnetic Properties of Quantum Ferrimagnetic Spin Chains
Magnetic susceptibilities of spin- ferrimagnetic Heisenberg chains are
numerically investigated. It is argued how the ferromagnetic and
antiferromagnetic features of quantum ferrimagnets are exhibited as functions
of . Spin- ferrimagnetic chains behave like combinations of
spin- ferromagnetic and spin- antiferromagnetic chains provided
.Comment: 4 pages, 7 PS figures, to appear in Phys. Rev. B: Rapid Commu
Low-energy structure of the intertwining double-chain ferrimagnets A_3_Cu_3_(PO_4_)_4_ (A=Ca,Sr,Pb)
Motivated by the homometallic intertwining double-chain ferrimagnets
A_3_Cu_3_(PO_4_)_4_ (A=Ca,Sr,Pb), we investigate the low-energy structure of
their model Hamiltonian H=\sum_n_[J_1_(S_{n :1}_+S_{n :3}_)
+J_2_(S_{n+1:1}+S_{n-1:3}_)]\cdotS_{n:2}_, where S_{n:l}_ stands for the
Cu^{2+}^ ion spin labeled l in the nth trimer unit, with particular emphasis on
the range of bond alternation 0<J_2/J_1<1. Although the spin-wave theory,
whether up to O(S^1^) or up to O(S^0^), claims that there exists a flat band in
the excitation spectrum regardless of bond alternation, a perturbational
treatment as well as the exact diagonalization of the Hamiltonian reveals its
weak but nonvanishing momentum dispersion unless J_2_=J_1_ or J_2_=0. Quantum
Monte Carlo calculations of the static structure factor further convince us of
the low-lying excitation mechanism, elucidating similarities and differences
between the present system and alternating-spin linear-chain ferrimagnets.Comment: 8 pages, 6 figure
Magnetic properties of M2P4O12 ( M = Ni, Co, Cu)
We have discussed thermodynamic properties from susceptibilities and specific heat mesurements of isostructural one-dimensional M2P4O12 system. The compounds show different magnetic behaviours, varied from ferromagnetic to antiferromagnetic ordering.We have discussed thermodynamic properties from susceptibilities and specific heat mesurements of isostructural one-dimensional M2P4O12 system. The compounds show different magnetic behaviours, varied from ferromagnetic to antiferromagnetic ordering
Nuclear Spin-Lattice Relaxation in One-Dimensional Heisenberg Ferrimagnets: Three-Magnon versus Raman Processes
Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
studied by means of a modified spin-wave theory. We consider the second-order
process, where a nuclear spin flip induces virtual spin waves which are then
scattered thermally via the four-magnon exchange interaction, as well as the
first-order process, where a nuclear spin directly interacts with spin waves
via the hyperfine interaction. We point out a possibility of the three-magnon
relaxation process predominating over the Raman one and suggest model
experiments.Comment: to be published in J. Phys. Soc. Jpn. 73, No. 6 (2004
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
Whipple's disease diagnosed during biological treatment for joint disease
Objectives
Increased susceptibility to infections is among the main safety concerns raised by biological agents. We describe five cases of Whipple\u27s disease diagnosed during treatment with biological agents.
Methods
We retrospectively identified five cases of Whipple\u27s disease diagnosed between 2003 and 2009 in patients treated with TNFα antagonists in five French hospitals.
Results
Five patients (four male; mean age: 50.4 years; range: 38â67) underwent biological therapy according to prior diagnoses of rheumatoid arthritis (n = 2), ankylosing spondylitis (n = 2), or spondyloarthropathy (n = 1). Biological therapy failed to control the disease, which responded to appropriate antibiotics for Whipple\u27s disease. Retrospectively, clinical symptoms before biological therapy were consistent with Whipple\u27s disease. All five patients had favorable outcomes (mean follow-up, 29 months [13â71]).
Conclusions
Biological therapy probably worsened preexisting Whipple\u27s disease, triggering the visceral disorders. Whipple\u27s disease must be ruled out in patients with joint disease, as patients with this spontaneously fatal condition should not receive immunosuppressive agents
Simulated nuclear spin-lattice relaxation in Heisenberg ferrimagnets: Indirect observation of quadratic dispersion relations
In response to recent proton spin relaxation-time measurements on
NiCu(pba)(HO)2HO with ,
which is an excellent one-dimensional ferrimagnetic Heisenberg model system of
spin-, we study the Raman relaxation process in spin- quantum
ferrimagnets on the assumption of predominantly dipolar hyperfine interactions
between protons and magnetic ions. The relaxation time is formulated
within the spin-wave theory and is estimated as a function of temperature and
an applied field by a quantum Monte Carlo method. The low-temperature
behavior of the relaxation rate qualitatively varies with ,
while is almost proportional to due to the characteristic
dispersion relations.Comment: 5 pages, 3 figures embedded, to appear in Phys. Rev. B Rapid Commu
Magnetic properties of the distorted diamond chain at T=0
We explore, at T=0, the magnetic properties of the antiferromagnetic
distorted diamond chain described by the Hamiltonian {\cal H}
= \sum_{j=1}^{N/3}{J_1 ({\bi S}_{3j-1} \cdot {\bi S}_{3j}
+ {\bi S}_{3j} \cdot {\bi S}_{3j+1})
+ J_2 {\bi S}_{3j+1} \cdot {\bi S}_{3j+2}
+ J_3 ({\bi S}_{3j-2} \cdot {\bi S}_{3j}
+ {\bi S}_{3j} \cdot {\bi S}_{3j+2})}
\allowbreak - H \sum_{l=1}^{N} S_l^z with , which well
models with , and azurite . We employ the physical
consideration, the degenerate perturbation theory, the level spectroscopy
analysis of the numerical diagonalization data obtained by the Lanczos method
and also the density matrix renormalization group (DMRG) method. We investigate
the mechanisms of the magnetization plateaux at and , and
also show the precise phase diagrams on the plane
concerning with these magnetization plateaux, where
and is the saturation magnetization. We also calculate the magnetization
curves and the magnetization phase diagrams by means of the DMRG method.Comment: 21 pages, 29 figure
Multi-plateau magnetization curves of one-dimensional Heisenberg ferrimagnets
Ground-state magnetization curves of ferrimagnetic Heisenberg chains of
alternating spins and are numerically investigated. Calculating several
cases of , we conclude that the spin- chain generally exhibits
magnetization plateaux even at the most symmetric point. In the double- or
more-plateau structure, the initial plateau is generated on a classical basis,
whereas the higher ones are based on a quantum mechanism.Comment: 6 pages, 6 figures embedded, to appear in Phys. Rev. B 01 August 200
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