Superconductivity of MgB₂ sputtered thin films with aluminium nitride buffer layers

MgB₂ thin films were deposited, at low temperature substrates, in situ, on a polished c-cut sapphire substrates, with the aluminium nitride (AlN) buffer layers, using the multiple-target sputtering system. The magnetoresistivities were measured using dc-4 terminal method in applied magnetic field up to 9 Tesla. The upper critical field anisotropy, H_c2(T) and irreversibility field H_irr(T) versus temperature were determinated. The Hall density of charge are slightly temperature dependence and positive in normal state. The critical temperature of 30-32 K and critical current density of 10⁶-10⁷ A/cm² at 4, 2 K were obtained. Using extracted data, the coherence length ξ₀, anisotropic coefficient γ and penetration depth λ_L were calculated.