Hall effect, magnetoresistivity and magnetic properties of MgB₂ thin films with AlN buffer layers

MgB₂ thin films were deposited at low temperature substrates, in situ, on c-plane sapphire substrates, with the aluminium nitride (AlN) buffer layers, using the multiple-target sputtering system. The magnetoresistivities were measured using dc-five probe 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 determined. The Hall coefficients R(H) are slightly temperature dependent and positive in the normal state. The critical temperature of 30-32 K and critical current density of 10⁶-10⁷A/cm² at 4.2 K were obtained. Using extracted data, the coherence length ξ_o, anisotropic coefficient γ and penetration depth λ_L were calculated.