2,347 research outputs found
Magnetization steps in Zn_(1-x)Mn_xO: Four largest exchange constants and single-ion anisotropy
Magnetization steps (MST's) from Mn pairs in several single crystals of
Zn_(1-x)Mn_xO (0.0056<=x<=0.030, and in one powder (x=0.029), were observed.
The largest two exchange constants, J1/kB=-18.2+/-0.5K and J1'/kB=-24.3+/-0.6K,
were obtained from large peaks in the differential susceptibility, dM/dH,
measured in pulsed magnetic fields, H, up to 500 kOe. These two largest J's are
associated with the two inequivalent classes of nearest neighbors (NN's) in the
wurtzite structure. The 29% difference between J1 and J1' is substantially
larger than 13% in CdS:Mn, and 15% in CdSe:Mn. The pulsed-field data also
indicate that, despite the direct contact between the samples and a
superfluid-helium bath, substantial departures from thermal equilibrium
occurred during the 7.4 ms pulse. The third- and fourth-largest J's were
determined from the magnetization M at 20 mK, measured in dc magnetic fields H
up to 90 kOe. Both field orientations H||c and H||[10-10] were studied. (The
[10-10] direction is perpendicular to the c-axis, [0001].) By definition,
neighbors which are not NN's are distant neighbors (DN's). The largest DN
exchange constant (third-largest overall), has the value J/kB=-0.543+/-0.005K,
and is associated with the DN at r=c. Because this is not the closest DN, this
result implies that the J's do not decrease monotonically with the distance r.
The second-largest DN exchange constant (fourth-largest overall), has the value
J/kB=-0.080 K. It is associated with one of the two classes of neighbors that
have a coordination number z=12, but the evidence is insufficient for a
definite unique choice. The dependence of M on the direction of H gives
D/kB=-0.039+/-0.008K, in fair agreement with -0.031 K from earlier EPR work.Comment: 12 pages, 10 figures. Submitted to PR
Magnetization steps in a diluted Heisenberg antiferromagnetic chain: Theory and experiments on TMMC:Cd
A theory for the equilibrium low-temperature magnetization M of a diluted
Heisenberg antiferromagnetic chain is presented. The magnetization curve, M
versus B, is calculated using the exact contributions of finite chains with 1
to 5 spins, and the "rise and ramp approximation" for longer chains. Some
non-equilibrium effects that occur in a rapidly changing B, are also
considered. Specific non-equilibrium models based on earlier treatments of the
phonon bottleneck, and of spin flips associated with cross relaxation and with
level crossings, are discussed. Magnetization data on powders of TMMC diluted
with cadmium [i.e., (CH_3)_4NMn_xCd_(1-x)Cl_3, with 0.16<=x<=0.50 were measured
at 0.55 K in 18 T superconducting magnets. The field B_1 at the first MST from
pairs is used to determine the NN exchange constant, J, which changes from -5.9
K to -6.5 K as x increases from 0.16 to 0.50. The magnetization curves obtained
in the superconducting magnets are compared with simulations based on the
equilibrium theory. Data for the differential susceptibility, dM/dB, were taken
in pulsed magnetic fields (7.4 ms duration) up to 50 T, with the powder samples
in a 1.5 K liquid-helium bath. Non-equilibrium effects, which became more
severe as x decreased, were observed. The non-equilibrium effects are
tentatively interpreted using the "Inadequate Heat Flow Scenario," or to
cross-relaxation, and crossings of energy levels, including those of excited
states.Comment: 16 pages, 14 figure
Reduction of Soil-Borne Plant Pathogens Using Lime and Ammonia Evolved from Broiler Litter
In laboratory and micro-plots simulations and in a commercial greenhouse, soil ammonia (NH3) and pH were manipulated as means to control soil-borne fungal pathogens and nematodes. Soil ammonification capacity was increased by applying low C/N ratio broiler litter at 1–8% (w/w). Soil pH was increased using lime at 0.5–1% (w/w). This reduced fungi (Fusarium oxysporum f. sp. dianthi and Sclerotium rolfsii) and root-knot nematode (Meloidogyne javanica) in lab tests below detection. In a commercial greenhouse, broiler litter (25 Mg ha−1) and lime (12.5 Mg ha−1) addition to soil in combination with solarization significantly reduced M. javanica induced root galling of tomato test plants from 47% in the control plots (solarization only) to 7% in treated plots. Root galling index of pepper plants, measured 178 days after planting in the treated and control plots, were 0.8 and 1.5, respectively, which was statistically significantly different. However, the numbers of nematode juveniles in the root zone soil counted 83 and 127 days after pepper planting were not significantly different between treatments. Pepper fruit yield was not different between treatments. Soil disinfection and curing was completed within one month, and by the time of bell-pepper planting the pH and ammonia values were normal
Susceptibility Amplitude Ratios Near a Lifshitz Point
The susceptibility amplitude ratio in the neighborhood of a uniaxial Lifshitz
point is calculated at one-loop level using field-theoretic and
-expansion methods. We use the Schwinger parametrization of the
propagator in order to split the quadratic and quartic part of the momenta, as
well as a new special symmetry point suitable for renormalization purposes. For
a cubic lattice (d = 3), we find the result .Comment: 7 pages, late
Estimation of Site Effects in the Israel Seacoast Area by Ambient Noise Records for Microzonation
Owing to the proximity to seismically active faults as well as the population density in the band of Israel Seacoast between the towns of Ashqelon and Haifa, this region may be considered a high seismic risk zone. For quantitative assessment of seismic response in terms of horizontal-to-vertical (H/V) spectral ratios the ambient noise survey was carried out at 190 sites. Results derived from H/V analysis indicate site amplifications ranging from 1 to 8 within the frequency band 1.0-6.0 Hz. The soil profiles at the investigated sites were very different. Some sites have simple profiles in the uppermost surface layer and clear seismic impedance between the soft soil layer and the bedrock. Other sites had complicated surface soil layers and a less distinct contrast between the surface soil and underlying bedrock. In many cases our attempts to estimate depth to the hardrock reflector from borehole data failed. Only when the distribution maps of the predominant frequency and the distribution of maximum amplification were constructed was the strong correlation between geological features and measurement results revealed. The observed resonance frequencies and their amplifications were correlated with analytical functions that correspond to the 1-D subsurface model. Collection of available geological, geotechnical and geophysical data relevant to local geology and combination of the theoretical and experimental response functions provided reliable estimations of analytical site effects
Dynamics of Stock Market Correlations
We present a novel approach to the study the dynamics of stock market correlations. This is achieved through an innovative visualization tool that allows an investigation of the structure and dynamics of the market, through the study of correlations. This is based on the Stock Market Holography (SMH) method recently introduced. This qualitative measure is complemented by the use of the eigenvalue entropy measure, to quantify how the information in the market changes in time. Using this innovative approach, we analyzed data from the New York Stock Exchange (NYSE), and the Tel Aviv Stock Exchange (TASE), for daily trading data for the time period of 2000–2009. This paper covers these new concepts for the study of financial markets in terms of structure and information as reflected by the changes in correlations over time.Correlation, Stock Market Holography, eigenvalue entropy, sliding window
Magnetization Process of Nanoscale Iron Cluster
Low-temperature magnetization process of the nanoscale iron cluster in
linearly sweeped fields is investigated by a numerical analysis of
time-dependent Schrdinger equation and the quantum master
equation. We introduce an effective basis method extracting important states,
by which we can obtain the magnetization process effectively. We investigate
the structure of the field derivative of the magnetization. We find out that
the antisymmetric interaction determined from the lattice structure reproduces
well the experimental results of the iron magnets and that this interaction
plays an important role in the iron cluster. Deviations from the adiabatic
process are also studied. In the fast sweeping case, our calculations indicate
that the nonadiabatic transition dominantly occurs at the level crossing for
the lowest field. In slow sweeping case, due to the influence of the thermal
environment to the spin system, the field derivative of the magnetization shows
an asymmetric behavior, the magnetic Fhn effect, which explains
the substructure of the experimental results in the pulsed field.Comment: 5 pages of text and 2 pages of 6 figures. To appear in J. Phys. Soc.
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