„« CONSOLUTE CRITICAL POINT OF MAGNETIC PHASE MIXTURE IN MANGANITES

C. ACHA, G. GARBARINO AND P. LEVY

Ischia, Italia

Workshop; XIII International Workshop on Oxide Electronics; 2006

WOE

If a  binary solution exhibits a consolute critical point, then for temperatures above  a critical temperature (T*), the system is homogeneous and single phase, while closer to T*, droplets of each phase are formed, which sizes varies temporally and spatially, diverging in size at T*. In these conditions, the system should be described by critical laws that  can be universal and found in a wide variety of systems [1]. Here we present DC and pulsed electric field measurements of the resistance of La0.625-yPryCa0.375MnO3 (y=0.4) single crystals as a function of temperature. The low temperature regime of the resistivity is highly current and voltage dependent. An irreversible transition from high (HR) to a low resistivity (LR) is obtained upon the increase of the electric field up to a temperature dependent critical value (Vc). By performing simultaneous magnetic and transport experiments we reveal the 1D nature of the percolation path established upon the application of Vc, which may produce an increase of conductivity of more than four orders or magnitude. We also show that the low resistance (LR) conducting regime obtained in this way is dominated by multistep tunneling processes [2], as pointed out by the study of the I-V characteristics. Analyzing the critical behavior of Vc in a defined temperature region, we determine the existence of a critical solution temperature or a consolute point. As far as we know, this link for the phase separation scenario is demonstrated here for the first time. This common behavior between magnetic phases in manganites and liquid mixtures sheds light on one of the possible mechanisms of magnetic phase separation on manganites. The critical behavior near the consolute point can be at the origin of static and dynamic anomalies of some properties like the recently reported peak in the magnetic viscosity [3].     [1] P Heller, Rep. Prog. Phys. 30 (1967) 731-826    [2] J. Klein, C. Höfener, S. Uhlenbruck, L. Alff, B. Büchner and R. Gross, Europhys. Lett.        47 (1999) 371. [3] L. Ghivelder and F. Parisi, Phys. Rev. B 71 (2005) 184425.