Magnetotransport behavior of YBa2Cu3O7-δ –Sm0.55Sr0.45MnO3 superconducting-ferromagnetic composite thin films

Abstract

Abstract We report a detailed study on the magnetotransport behavior of YBa2Cu3O7-δ -Sm0.55Sr0.45MnO3 (YBCO-SSMO) superconducting-ferromagnetic composite thin films (thickness ∼80 nm) of nominal compositions (YBCO)1-x(SSMO)x (x = 0, 0.08, and 0.14). Films are grown by pulsed laser deposition of the pure and composite targets on (001)-SrTiO3 substrates, and all are single crystalline with the c-axis normal to the plane of the substrate. The Tc(R = 0) of the pure YBCO film is ≈87 K and decreases to ≈75 K and ≈44 K with the incorporation and increase of the ferromagnetic fraction in the superconducting matrix. Successive decrease in the slope of the normal state R-T curves maps the incorporation of the high resistance channels of the SSMO. In an external magnetic field (H), the rate of decrement in the Tc(R = 0) is found to be dTc(R = 0)/dH ∼1.8 K T−1, ∼4.7 K T−1, and ∼2.8 K T−1, respectively for x = 0, 0.08, and 0.14. The upper critical field and the irreversibility field are appreciably depressed in the composite samples and suggest a broadening of the mixed-phase vortex regime. The application of the thermally activated flux flow (TAFF) model shows that the activation energy decreases sharply from U0 = 4314 (910) meV, 498 (130) meV, and 253 (66) meV for YS00, YS08, and YS14, respectively, at H = 0 T (6 T). The analysis of the field-dependent activation energy in terms of U 0 ∼ H − α and U 0 ≈ − U log H dependence suggests decoupling of the 2D vortices due to the ferromagnetic phase. The hysteresis in the current-voltage characteristics is seen to decrease with an increase in the SSMO content.