333 research outputs found
Sporulation of Pyricularia spp. in culture. effect of some aromatic compounds
The effect of L-tyrosine, DL-phenylalanine, shikimic acid and chlorogenic acid on sporulation was studied with six isolates of Pyricularia from different gramineous hosts. In general, the isolates from cultivated gramineae sporulated better than the isolates from the wild grasses. The effect of the compounds on sporulation varied with the isolate. Possible genetic differences among the isolates are invoked to explain the results
Resistive relaxation in field-induced insulator-metal transition of a (LaPr)SrMnO bilayer manganite single crystal
We have investigated the resistive relaxation of a
(LaPr)SrMnO single crystal, in
order to examine the slow dynamics of the field-induced insulator to metal
transition of bilayered manganites. The temporal profiles observed in remanent
resistance follow a stretched exponential function accompanied by a slow
relaxation similar to that obtained in magnetization and magnetostriction data.
We demonstrate that the remanent relaxation in magnetotransport has a close
relationship with magnetic relaxation that can be understood in the framework
of an effective medium approximation by assuming that the first order parameter
is proportional to the second order one.Comment: 6 pages,5 figure
Does EELS haunt your photoemission measurements?
It has been argued in a recent paper by R. Joynt (R. Joynt, Science 284, p
777 (1999)) that in the case of poorly conducting solids the photoemission
spectrum close to the Fermi Energy may be strongly influenced by extrinsic loss
processes similar to those occurring in High Resolution Electron Energy Loss
Spectroscopy (HR-EELS), thereby obscuring information concerning the density of
states or one electron Green's function sought for. In this paper we present a
number of arguments, both theoretical and experimental, that demonstrate that
energy loss processes occurring once the electron is outside the solid,
contribute only weakly to the spectrum and can in most cases be either
neglected or treated as a weak structureless background.Comment: 6 pages, figures included. Submitted to PR
Manifestation of geometric frustration on magnetic and thermodynamic properties of pyrochlores (X=Ti, Zr)
We present here magnetization, specific heat and Raman studies on
single-crystalline specimens of the first pyrochlore member of
the rare-earth titanate series. Its analogous compound in the
rare-earth zirconate series is also investigated in the polycrystalline form.
The Sm spins in remain unordered down to at least T = 0.5 K. The
absence of magnetic ordering is attributed to very small values of exchange
() and dipolar interaction ()
between the spins in this pyrochlore. In contrast, the pyrochlore
is characterized by a relatively large value of Sm-Sm spin
exchange (); however, long-range ordering of the
spins is not established at least down to T = 0.67 K, due to
frustration of the spins on the pyrochlore lattice. The ground state
of ions in both pyrochlores is a well-isolated Kramer's doublet. The
higher-lying crystal field excitations are observed in the low-frequency region
of the Raman spectra of the two compounds recorded at T = 10 K. At higher
temperatures, the magnetic susceptibility of shows a broad
maximum at T = 140 K while that of changes monotonically. Whereas
is a promising candidate for investigating spin-fluctuations on a
frustrated lattice as indicated by our data, the properties of
seem to conform to a conventional scenario where geometrical frustration of the
spin exclude their long-range ordering.Comment: 24 pages, 6 figures, Accepted for publication in Phys. Rev.
Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite(LaPr)SrMnO
We report a significant decrease in the low-temperature resistance induced by
the application of an electric current on the -plane in the paramagnetic
insulating (PMI) state of
(LaPr)SrMnO. A colossal
electroresistance effect attaining -95% is observed at lower temperatures. A
colossal magnetoresistive step appears near 5T at low temperatures below 10K,
accompanied by an ultrasharp width of the insulator-metal transition. Injection
of higher currents to the crystal causes a disappearance of the steplike
transition. These findings have a close relationship with the presence of the
short-range charge-ordered clusters pinned within the PMI matrix of the crystal
studied.Comment: 4 pages 3 figure
Anomalous pressure effect on the remanent lattice striction of a (La,Pr)SrMnO bilayered manganite single crystal
We have studied the pressure effect on magnetostriction, both in the
-plane and along the c-axis, of a (La,Pr)SrMnO
bilayered manganite single crystal over the temperature region where the
field-induced ferromagnetic metal (FMM) transition takes place. For comparison,
we have also examined the pressure dependence of magnetization curves at the
corresponding temperatures. The applied pressure reduces the critical field of
the FMM transition and it enhances the remanent magnetostriction. An anomalous
pressure effect on the remanent lattice relaxation is observed and is similar
to the pressure effect on the remanent magnetization along the c-axis. These
findings are understood from the view point that the double-exchange
interaction driven FMM state is strengthened by application of pressure.Comment: 7 pages,7 figure
Steplike Lattice Deformation of Single Crystalline (LaPr)SrMnO Bilayered Manganite
We report a steplike lattice transformation of single crystalline
(LaPr)SrMnObilayered manganite
accompanied by both magnetization and magnetoresistive jumps, and examine the
ultrasharp nature of the field-induced first-order transition from a
paramagnetic insulator to a ferromagnetic metal phase accompanied by a huge
decrease in resistance. Our findings support that the abrupt magnetostriction
is closely related to an orbital frustration existing in the inhomogeneous
paramagnetic insulating phase rather than a martensitic scenario between
competing two phases.Comment: 5 pages,4figures, v4: figures are changed, in press in Phys.Rev.Let
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