Different behavior in transport measurements on planar-type YBa2Cu3O7−δ/La1/3Ca2/3MnO3/La2/3Ca1/3MnO3 heterostructures

YBa2Cu3O7−δ(YBCO)/La1/3Ca2/3MnO3(LCMO-AF)/La2/3Ca1/3MnO3(LCMO-F) junctions with nominal layer thicknesses of 100, 7, and 80 nm, respectively, were fabricated using a dc sputtering technique. The junctions were structured to transistor dimensions by standard UV-photolithography and chemical etching process. Electrical measurements were carried out both on the superconducting micro-bridges and the antiferromagnetic (AF) barriers. The AF barriers displayed different electrical behavior for the same nominal barrier thickness. Thus, for junctions with a barrier resistance of around 60 Ω (V = 0), a clear superconducting gap-like structure was observed. On the contrary, junctions with a barrier resistance of around 30 Ω (V = 0) featured a pronounced, temperature dependent zero-bias conductance peak G(V = 0). The value of G(V = 0) decreased as the temperature was increased, which was an indication of metallic-like behavior associated to the presence of pin-holes in the junction area. On the other hand, spin-polarized carrier injection from the ferromagnetic layer into the strip-like YBa2Cu3O7−δ film provoked a strong reduction of IC with an efficiency K(K = ΔIC/ΔIg) as large as 1.4 at 15 K.