Time-dependent transport effects in CoFe/Al2O3 discontinuous multilayers

Discontinuous multilayered metal-insulator Co80Fe20(t)/Al2O3(30 Angstrom) t hin films with different values of nominal thickness t of metal layer were prepared by ion beam deposition. At t < 14 Angstrom, a new phenomenon of sl ow electric relaxation was found, suggesting formation of highly nonequilib rium electronic states in the process of tunnel transport in such systems. An extension of the well-known Sheng-Abeles approach on the case of finite concentrations of charged granules is proposed. Within mean-field approxima tion, it gives a general picture of this phenomenon, though the corrections due to correlation between charges can be essential. (C) 2000 American Ins titute of Physics. [S0021-8979(00)74708-6].