38 research outputs found
Low frequency random telegraphic noise (RTN) and 1/f noise in the rare-earth manganite PrCaMnO near the charge-ordering transition
We have studied low frequency resistance fluctuations (noise) in a single
crystal of the rare earth perovskite manganite PrCaMnO
which shows a charge ordering transition at a temperature ~ 245K. The
noise measurements were made using an ac bias with and without a dc bias
current imposed on it. We find that the spectral power contains two
components - one broad band 1/f part that exists for all frequency and
temperature ranges and a single frequency Lorentzian of frequency which
is strongly temperature dependent. The Lorentzian in which appears due
to Random telegraphic noise (RTN) as seen in the time series of the
fluctuation, is seen in a very narrow temperature window around where
it makes the dominating contribution to the fluctuation. When the applied dc
bias is increased beyond a certain threshold current density , the
electrical conduction becomes non-linear and one sees appearance of a
significant Lorentzian contribution in the spectral power due to RTN. We
explain the appearance of the RTN as due to coexisting Charge ordered (CO) and
reverse orbitally ordered (ROO) phases which are in dynamical equilibrium over
a mesoscopic length scale () and the kinetics being controlled by
an activation barrier T>>T_{CO}T_{CO}$ is
approached from above and the probability distribution function (PDF) deviates
strongly from a Gaussian. We explain this behavior as due to approach of charge
localization with correlated fluctuators which make the PDF non-Gaussian.Comment: 23 pages, 14 figure
Thermal relaxation in charge ordered Pr Ca MnO in presence of a magnetic field
We report observation of substantial thermal relaxation in single crystal of
charge ordered system PrCaMnO in an applied magnetic
field of H = 8T. The relaxation is observed when the temperature is scanned in
presence of a magnetic field in the temperature interval
where is the charge ordering temperature and is charge
melting temperature in a field. In this temperature range the system has
coexisting charged ordered insulator (COI) and ferromagnetic metallic (FMM)
phases. No such relaxation is observed in the COI state in H = 0T or in the FMM
phase at in presence of a magnetic field. We conclude that the
thermal relaxation is due to two coexisting phases with nearly same free
energies but separated by a potential barrier. This barrier makes the
transformation from one phase to the other time-dependent in the scale of the
specific heat experiment and gives rise to the thermal relaxation.Comment: 4 pages LaTEX, 3 eps figure
Magnetic Field resulting from non-linear electrical transport in single crystals of charge-ordered Pr Ca MnO}
In this letter we report that the current induced destabilization of the
charge ordered (CO) state in a rare-earth manganite gives rise to regions with
ferromagnetic correlation. We did this experiment by measurement of the I-V
curves in single crystal of the CO system
PrCaMnO and simultanously measuring the magnetization
of the current carrying conductor using a high T SQUID working at T = 77K.
We have found that the current induced destabilization of the CO state leads to
a regime of negative differential resistance which leads to a small enhancement
of the magnetization of the sample, indicating ferromagnetically aligned
moments.Comment: 4 pages LateX, 4 eps figure
Non-linear electrical conduction and broadband noise in charge-ordered rare earth manganate Nd_0.5Ca_0.5MnO_3
Measurements of the dc transport properties and the low-frequency
conductivity noise in films of charge ordered Nd_0.5Ca_0.5MnO_3 grown on Si
subtrate reveal the existence of a threshold field in the charge ordered regime
beyond which strong non linear conduction sets in along with a large broad band
conductivity noise. Threshold-dependent conduction disappears as T -> T_{CO},
the charge ordering temperature. This observation suggests that the charge
ordered state gets depinned at the onset of the non-linear conduction.Comment: 3 pages of two-column text and 4 eps figure
Specific heat study of single crystalline Pr Ca MnO in presence of a magnetic field
We present the results of a study of specific heat on a single crystal of
PrCaMnO performed over a temperature range 3K-300K in
presence of 0 and 8T magnetic fields. An estimate of the entropy and latent
heat in a magnetic field at the first order charge ordering (CO) transition is
presented. The total entropy change at the CO transition which is 1.8
J/mol K at 0T, decreases to 1.5 J/mol K in presence of 8T magnetic
field. Our measurements enable us to estimate the latent heat
235 J/mol involved in the CO transition. Since the entropy of the
ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered
insulating (COI) state, a subtle change in entropy stabilises either of these
two states. Our low temperature specific heat measurements reveal that the
linear term is absent in 0T and surprisingly not seen even in the metallic FMM
state.Comment: 8 pages (in RevTEX format), 12 figures (in postscript format)
Submitted to Phys. Rev.
A Chemical Genomics Approach to Drug Reprofiling in Oncology: Antipsychotic Drug Risperidone as a Potential Adenocarcinoma Treatment
Drug reprofiling is emerging as an effective paradigm for discovery of cancer treatments. Herein, an antipsychotic drug is immobilised using the Magic Tag® chemical genomics tool and screened against a T7 bacteriophage displayed library of polypeptides from Drosophila melanogaster, as a whole genome model, to uncover an interaction with a section of 17-β-HSD10, a proposed prostate cancer target. A computational study and enzyme inhibition assay with full length human 17-β-HSD10 identifies risperidone as a drug reprofiling candidate. When formulated with rumenic acid, risperidone slows proliferation of PC3 prostate cancer cells in vitro and retards PC3 prostate cancer tumour growth in vivo in xenografts in mice, presenting an opportunity to reprofile risperidone as a cancer treatment