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We have studied low frequency resistance fluctuations (noise) in a single crystal of the rare earth perovskite manganite Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ which shows a charge ordering transition at a temperature $T_{CO}$ ~ 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 $S_V(f)$ contains two components - one broad band 1/f part that exists for all frequency and temperature ranges and a single frequency Lorentzian of frequency $f_c$ which is strongly temperature dependent. The Lorentzian in $S_V(f)$ 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 $T_{CO}$ where it makes the dominating contribution to the fluctuation. When the applied dc bias is increased beyond a certain threshold current density $J_{th}$, 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 ($\approx 30nm$) and the kinetics being controlled by an activation barrier $E_{a} ~ 0.45eV. The 1/f noise is low for $T>>T_{CO}$ but increases by nearly two orders in a narrow temperature range as $T_{CO}$ 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 figures

We present the results of a study of specific heat on a single crystal of Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ 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 $\approx$ 1.8 J/mol K at 0T, decreases to $\sim$ 1.5 J/mol K in presence of 8T magnetic field. Our measurements enable us to estimate the latent heat $L_{CO}$ $\approx$ 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. B

We report observation of substantial thermal relaxation in single crystal of charge ordered system Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ 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 $T_{MH}

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 Pr$_{0.63}$Ca$_{0.37}$MnO$_{3}$ and simultanously measuring the magnetization of the current carrying conductor using a high T$_c$ 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 figures

Non-linear conduction in a single crystal of charge-ordered Pr$_{0.63}$Ca$_{0.37}$MnO$_{3}$ has been investigated in an applied magnetic field. In zero field, the non-linear conduction, which starts at T$<$T$_{CO}$ can give rise to a region of negative differential resistance (NDR) which shows up below the N\'eel temperature. Application of a magnetic field inhibits the appearance of NDR and makes the non-linear conduction strongly hysteritic on cycling of the bias current. This is most severe in the temperature range where the charge ordered state melts in an applied magnetic field. Our experiment strongly suggests that application of a magnetic field in the CO regime causes a coexistance two phases., Comment: 4 pages TeX; 5 eps figures; Submitted to Phys. Rev. B

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 figures