Electric-field and current-induced metastability and resistivity relaxation in La_0.8Ca_0.2MnO₃ at low temperatures

Transport, magnetic, and thermal properties of phase-separated La _0.8Ca_0.2MnO₃ crystal were studied in a wide temperature range down to 10 K. At low temperatures below the Curie point T _c=184 K, the sample resistance is characterized by spontaneous transitions to higher resistivity metastable states. Metastability becomes more pronounced when enforced by the application of current pulses at low temperatures. Metastable states are characterized by long-term memory surviving even thermal cycling to room temperatures. Only heating to T>T _e≈ 350 K erases the previously imprinted state of the system. At temperatures close to the low temperature resistivity maximum, a slow relaxation of the resistance has been observed following changes in the bias current. Ac susceptibility, low-field magnetization, and specific heat data indicate that there is a spin-cluster glass-like transition at temperatures corresponding to the maximum of the relaxation time. Phase : separation and coexistence of metallic and insulating ferromagnetic phases with different orbital order at a wide temperature range are claimed to be responsible for the observed electric-field and current effects. The disappearance of the resistance memory, effects at temperatures above T_e may be considered an indirect proof for the existence of one more temperature scale in disordered manganites.