The Influence of Layer Thickness-Ratio on Magnetoresistance in La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/La$_{1/3}$Ca$_{2/3}$MnO$_{3}$ Exchange Biased System

Isothermal magnetic field dependence of the resistance in La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ (F-LCMO)/ La$_{1/3}$Ca$_{2/3}$MnO$_{3}$(AF-LCMO) bilayer and AF-LCMO/F-LCMO/AF-LCMO trilayer at temperatures below N\'{e}el temperature of the antiferromagnetic layer were carried out to study the thickness layers influence on magneto transport properties. We grew multilayers using a high oxygen pressure sputtering technique. We systematically varied the thickness of the F-LCMO layer, t$_{F}$, maintaining constant the thickness of the AF-LCMO layer, t$_{AF}$. We studied the influence of the thickness ratio t$_{F}$/t$_{AF}$ on the ZFC and FC magnetoresistance (MR) loops. H$_{FC}$ was varied from 100 Oe to 400 Oe. We found that MR has hysteretic behavior as observed in [La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/La$_{1/3}$Ca$_{2/3}$MnO$_{3}$]$_{N}$ superlattices, where MR increases with the increasing field from H=0 to a maximum and then it decreases continuously. The position and magnitude of the maximum is not symmetric with respect to the axis H=0 for both FC and ZFC loops. We found that magnetoresistance behavior of the bilayer and trilayer is thickness-ratio dependent for both ZFC and FC loops.