Magnetotransport Properties in Epitaxial Exchange-Biased La_2/3Ca_1/3MnO₃/La_1/3Ca_2/3MnO₃ Superlattices

Superlattices of ferromagnetic (F) and antiferromagnetic (AF) oxide materials have attracted increased attention given the exchange bias or exchange anisotropy phenomenon. Research on magnetic oxide superlattices has focused toward the technological goals of increasing magnetoresistance in lower applied magnetic fields and more useful temperature ranges for various applications. Superlattices of F-LCMO and AF-LCMO layers were grown on (001)-oriented SrTiO₃substrates. We studied the temperature dependence of magnetotransport properties for a series of [AF-LCMO (7.6 nm)/F-LCMO (t_F)]nsuperlattices as a function of the ferromagnetically doped layer thickness, t_F, while the antiferromagnetic (AF) layer thickness, taf, was kept constant. Magnetotransport measurements at different temperatures were done on a series of [AF(7.6 nm)/F(t_F)]_N superlattices. The ZFC resistance has a maximum at negative fields, for all multilayers, with descending fields (from 1 to — 1 kOe). In all samples a shift along the field axis of the FC loop with respect to that of the ZFC loop is observed. The H_exvalues determined from these displacements of the FC loops of the magnetoresistance loops increase when temperature decreases and its magnitude also depends on the ferromagnetic layer thickness.