Superconductivity of Mg–B layers prepared by a multi-energy implantation of boron into magnesium and magnesium into boron bulk substrates followed by the furnace and pulsed plasma annealing

Abstract

B ions into Mg and Mg ions into B substrates were implanted in triple mode, i.e. each sample was sequentially implanted at three different energies starting from the highest one (80–150 keV range) to the lowest one (40–70 keV range). The energies and fluencies in each particular batch were simulated to yield a possibly large region in which the Mg:B ratio corresponds to stoichiometric MgB 2 compound. These structures were next annealed using high intensity hydrogen plasma pulses of energy densities between 1.5 and 4.0 J/cm 2, or furnace annealed at 350–600 °C in a stream of flowing Ar-4%H 2 mixture. The simulated profiles were in fair agreement with those derived from the RBS measurements. Magnetically modulated microwave absorption (MMMA), magnetization and resistance measurements showed that the superconducting transition onset temperature T c onset shifted from about 13 K in the best magnesium sample implanted with single-energy B ions, to 22–28 K for multi-energy implantation treatments. Respective shift in Mg-implanted boron samples was from about 33.3 K to 36.5 K. However, broadening of the transition to the superconducting state is observed for the multi-energy treatment in both cases. Possible reasons for these effects and proposed means to improve the method are discussed.