Examination of the Scaling Behavior of Critical Properties in MgB2/SiC/Si Thin Films

Abstract

Abstract Scaling behaviors of critical current densities in MgB2 thin films are investigated with different film thickness. MgB2 films were grown on SiC buffered Si substrate by sequential evaporation of boron and magnesium. The amount of supplied boron was controlled so as to result in MgB2 film thickness of 50 nm or 10 nm with excess magnesium. The critical current density J c and irreversibility field H irr were estimated from magnetic field dependence of DC magnetization hystereses. Variation of J c is analyzed against temperature at each value of constant magnetic field. For the 50 nm film J c could scale with [1 − ( T / T c)2] m’ with critical exponents m’ from 4 to 8. However, variation of m’ is interpreted as only in appearance and as due to low-field approximation assumed in this simplified scaling. More comprehensive scaling formula for reduced critical current density has been applied in wide range of temperature and field, and good fitting to our experimental data has been obtained over 10 orders of magnitude. On the other hand, for the 10 nm film, experimental data of the reduced current density indicated a kink in the middle temperature and field range, and fitting with the formula was poor, inferring weak pinning. Various scaling behaviors of J c and H irr are examined in relation to film quality, pinning strength and nature of superconductivity.