Effect of long processing time on microstructure and transport properties of Fe1.1Se alloy produced by chemical vapor transport (CVT) technique

In this work we present physical, electrical and magnetic properties of beta-Fe1.1Se single crystalline alloys produced by chemical vapor transport technique using short (120 h) and long (700 h) heating processes. The best T (c) was obtained from the long time processed samples. Magnetization results showed that samples are typical type-II superconductor. Calculated critical current density values, at zero field, were found to be 1.1 x 10(6) Acm(-2) for long time processed samples at 2 K and indicates strong pinning mechanism and bulk superconducting nature. The zero temperature value of higher upper critical field was calculated to be H (c2)(0) = 244 kOe. Calculated values of coherence length were found between 3.65 and 3.67 nm. Pauli paramagnetic limit, H (P) (0) = 1.84T (c) , is exceeded for both series of samples. Results obtained suggested that the spin-paramagnetic effect possibly the dominant pair-breaking mechanism for both series of samples.