Magnetic Field Dependence of Magnetotransport Properties of MgB2/CrO2 Bilayer Thin Films

In this work, we comparatively investigated two MgB2 films: one (F1) was typically fabricated using the PLD method, while the other (F2) was fabricated using the same method but on top of a 100-nm-thick CrO2 layer. Both films had a thickness of 300 nm and were annealed ex situ at 700 °C for 30 min before being investigated under an external magnetic field of up to ± 7 T. The activation energy (Uo), upper critical field (HC2), irreversibility field (Hirr), magnetoresistance (MR), and I-V characteristics for the two films were studied in detail, and the results were compared with theoretical models. XRD analysis showed that both films are c-axis-oriented, while the RRR values for the films were found to be 1.6 and 1.89, respectively. Experimental data showed a broadening of the R-T transitions for an increasing magnetic field, with such broadening observed to be wider for F2 due to surface superconductivity. The activation energy under magnetic fields ranging from 0 to 7 T was calculated using our data and compared with a theoretical model. In both films, Uo followed a parabolic curve but was higher for F2 up to 6 T before sharply decreasing, while it continued to follow the same trend for F1 up to 7 T. The theoretical model was in good agreement with F1 for the full span of magnetic fields used. HC2 and Hirr were estimated and fitted using Ginzburg–Landau theory, but although the fitting was very good for F1, some modification in fitting parameters was required to obtain the same fitting for F2. Magnetoresistance and I-V characteristics confirm that the CrO2 layer in F2 leads to faster damage to the superconductivity property for high magnetic fields and temperatures.