Investigation of the Upper Critical Magnetic Field and Activation Energy in MgB2 Thin Film

Abstract

MgB2 film with a thickness of about 600 nm was deposited on the MgO (100) single crystal substrate using a “two-step” synthesis technique. First, deposition of boron thin film was carried out by rf magnetron sputtering on MgO substrates and followed by a post deposition annealing at 850 °C in magnesium vapor. The upper critical field Hc2 has been estimated from temperature dependences of resistivity curves in both directions of the magnetic fields perpendicular and parallel to the c-axis. Resistivity measurements of the film were performed using a standard fourprobe method under different magnetic fields up to 70 kOe in zero fields cooling regime. The upper critical magnetic field Hc2(0) at T = 0 K for 90 % of Rn was calculated by the extrapolation Hc2(T ) to the temperature T = 0 K. The results showed that Hc2 || ab(0) and Hc2 || c(0) was found to be around 22 T and 18 T, respectively. Using extracted data, the zero-temperature coherence lengths and field anisotropy ratio were calculated. In order to determine the activation energy of thermally activated flux flow of the film, Arrhenius law was taken into account.