Instability of metal-insulator transition against thermal cycling in phaseseparated Cr-doped manganites - art. no. 064424

Pr0.5Ca0.5Mn1-xCrxO3 (x=0.015-0.05) undergoes an insulator-metal (I-M) tran sition below a temperature T-p driven by percolation of ferromagnetic metal lic clusters in a charge ordered insulating matrix. Surprisingly, the I-M t ransition in these compounds is unstable against thermal cycling: T-p decre ases and the resistivity at T-p increases upon temperature cycling between a starting temperature T-S and a final temperature T-F and changes are larg er for smaller x. The resistivity transition to the low temperature metalli c state in x=0.015 can be completely destroyed by thermal cycling in absenc e of magnetic field as well asunder H=2 T. Magnetization measurements sugge st that the ferromagnetic phase fraction decreases with increasing thermal cycling. Contrary to the thermal cycling induced effect, isothermal aging c auses a slow decrease of resistivity as a function of time. We suggest that increase of strains in the ferromagnetic-charge ordered interface during t hermal cycling could be a possible origin of the observed effect.