Simple One-Step Synthesis and Superconducting Properties of SmFeAsO_1-xF_x

The recent discovery of superconductivity in REFeAsO (RE, rare-earth metal) has generated enormous interest because these materials are the first non-copper oxide superconductors with critical temperatures T_c exceeding 50K as well as upper critical fields well above 100T. However, for these new superconductors, very complicated synthesis routes, such as the complex two-step synthesis or high-pressure sintering, are required. Furthermore, there is the toxicity and volatility of arsenic to consider, sometimes a sealed quartz tube of arsenic exploded during annealing. We present a new method for producing high-temperature SmFeAsO_1-xF_x superconductors by using a one-step sintering process. Superconducting transition with the onset temperature of 54.6K and high critical fields H_c2(0)≥200T were confirmed in SmFeAsO_0.7F_0.3. At 5K and at self field, critical current densities J_c estimated from the magnetization hysteresis using the whole sample size and the average particle size have reached 8.5×10³ and 1.2×10⁶A/cm², respectively. Moreover, J_c exhibited a very weak dependence on magnetic field. This simple and safe one-step synthesis technique should be effective in other rare earth derivatives of iron-based superconductors.