354 research outputs found
Non-equilibrium dynamics in an interacting nanoparticle system
Non-equilibrium dynamics in an interacting Fe-C nanoparticle sample,
exhibiting a low temperature spin glass like phase, has been studied by low
frequency ac-susceptibility and magnetic relaxation experiments. The
non-equilibrium behavior shows characteristic spin glass features, but some
qualitative differences exist. The nature of these differences is discussed.Comment: 7 pages, 11 figure
Magnetic ejection of diamagnetic sub-millimeter grains observed by a chamber-type μG generator orientated to identify material of a single particle
Soft x-ray magnetic circular dichroism study of weakly ferromagnetic ZnVO thin film
We performed a soft x-ray magnetic circular dichroism (XMCD) study of a
ZnVO thin film which showed small ferromagnetic moment. Field and
temperature dependences of V 2 XMCD signals indicated the coexistence of
Curie-Weiss paramagnetic, antiferromagnetic, and possibly ferromagnetic V ions,
quantitatively consistent with the magnetization measurements. We attribute the
paramagnetic signal to V ions substituting Zn sites which are somewhat
elongated along the c-axis
Two Cases of Primary Malignant Fibrous Histiocytoma of the Liver: Immunohistochemical Expression of Ezrin and Its Relationship with Prognosis
Malignant fibrous histiocytoma (MFH) as soft tissue sarcoma would not be especially noteworthy, but primary hepatic MFH reports are extremely rare. Herein, we report ezrin expression in tumor tissues from two primary hepatic MFH cases with different prognoses. Cases 1 and 2 were both women, ages 45 and 70 years, respectively. Case 1 had an 11×10 cm liver tumor in segment (S) 3, and case 2 had two liver tumors, 12×8 cm in S5 and 10×7 cm in S8. Neither had any other systemic tumors. Cases 1 and 2 survived for two year and ten months and for eight and a half months, respectively, after the initial tumor resection. Microscopically, the tumors of these two cases were similar and showed proliferation of atypical cells, including spindle, pleomorphic and multi-nucleated giant cells arranged in storiform, sheet and/or fascicle patterns, with scattered foci of inflammatory cells, indicating MFH. Ezrin expression in tumor tissue from case 1 was sparse, whereas that of case 2 showed strong ezrin expression in many tumor cells. The present results indicate ezrin immunoreactivity in primary hepatic MFH to correlate possible with prognosis, which is consistent with reports on some other types of malignancies
Metal-insulator Crossover Behavior at the Surface of NiS_2
We have performed a detailed high-resolution electron spectroscopic
investigation of NiS and related Se-substituted compounds
NiSSe, which are known to be gapped insulators in the bulk at all
temperatures. A large spectral weight at the Fermi energy of the room
temperature spectrum, in conjunction with the extreme surface sensitivity of
the experimental probe, however, suggests that the surface layer is metallic at
300 K. Interestingly, the evolution of the spectral function with decreasing
temperature is characterized by a continuous depletion of the single-particle
spectral weight at the Fermi energy and the development of a gap-like structure
below a characteristic temperature, providing evidence for a metal-insulator
crossover behavior at the surfaces of NiS and of related compounds. These
results provide a consistent description of the unusual transport properties
observed in these systems.Comment: 12 pages, 3 figure
Spin-Peierls phases in pyrochlore antiferromagnets
In the highly frustrated pyrochlore magnet spins form a lattice of corner
sharing tetrahedra. We show that the tetrahedral ``molecule'' at the heart of
this structure undergoes a Jahn-Teller distortion when lattice motion is
coupled to the antiferromagnetism. We extend this analysis to the full
pyrochlore lattice by means of Landau theory and argue that it should exhibit
spin-Peierls phases with bond order but no spin order. We find a range of Neel
phases, with collinear, coplanar and noncoplanar order. While collinear Neel
phases are easiest to generate microscopically, we also exhibit an interaction
that gives rise to a coplanar state instead.Comment: REVTeX 4, 14 pages, 12 figures (best viewed in color
Scaling behavior of the dipole coupling energy in two-dimensional disordered magnetic nanostructures
Numerical calculations of the average dipole-coupling energy in two-dimensional disordered magnetic nanostructures are
performed as function of the particle coverage . We observe that scales as with an
unusually small exponent --1.0 for coverages
. This behavior is shown to be primarly given by the
contributions of particle pairs at short distances, which is intrinsically
related to the presence of an appreciable degree of disorder. The value of
is found to be sensitive to the magnetic arrangement within the
nanostructure and to the degree of disorder. For large coverages
we obtain with , in agreement
with the straighforward scaling of the dipole coupling as in a periodic
particle setup. Taking into account the effect of single-particle anisotropies,
we show that the scaling exponent can be used as a criterion to distinguish
between weakly interacting () and strongly interacting
() particle ensembles as function of coverage.Comment: accepted for publication in Phys.Rev.
Clustering transitions in vibro-fluidized magnetized granular materials
We study the effects of long range interactions on the phases observed in
cohesive granular materials. At high vibration amplitudes, a gas of magnetized
particles is observed with velocity distributions similar to non-magnetized
particles. Below a transition temperature compact clusters are observed to form
and coexist with single particles. The cluster growth rate is consistent with a
classical nucleation process. However, the temperature of the particles in the
clusters is significantly lower than the surrounding gas, indicating a
breakdown of equipartition. If the system is quenched to low temperatures, a
meta-stable network of connected chains self-assemble due to the anisotropic
nature of magnetic interactions between particles.Comment: 4 pages, 5 figure
Magnetic Coupling between 3He and 19F at Low Temperatures
Measurements of relaxation phenomena between liquid 3He and 19F nuclei in small fluorocarbon particles are reported. Magnetic cross relaxation between the 19F in the substrate and the liquid is observed in measurements between 1 K and 0.6 mK. The spin temperatures remain strongly coupled in magnetic fields up to 125 mT. Moreover it is observed that there is a decrease in magnetic relaxation time at the onset of superfluidity in the liquid 3He and that the thermal relaxation times are remarkably short at all temperatures
Phase Separation and the Low-Field Bulk Magnetic Properties of Pr0.7Ca0.3MnO3
We present a detailed magnetic study of the perovskite manganite
Pr0.7Ca0.3MnO3 at low temperatures including magnetization and a.c.
susceptibility measurements. The data appear to exclude a conventional spin
glass phase at low fields, suggesting instead the presence of correlated
ferromagnetic clusters embedded in a charge-ordered matrix. We examine the
growth of the ferromagnetic clusters with increasing magnetic field as they
expand to occupy almost the entire sample at H ~ 0.5 T. Since this is well
below the field required to induce a metallic state, our results point to the
existence of a field-induced ferromagnetic insulating state in this material.Comment: 15 pages with figures, submitted to Physical Review
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