Thin Film Magnesium Boride Superconductor with Very High Critical Current Density and Enhanced Irreversibility Field

TLDR

MgB₂, discovered to superconduct at 39 K, offers a low‑cost, high‑performance alternative to Nb₃Sn and Nb‑Ti, with a higher critical temperature that could enable greater magnetic fields and current densities. MgB₂ thin films exhibit a steeper temperature dependence of the irreversibility field, achieving H*(4.2 K) > 14 T, and support critical current densities of 1 MA cm⁻² at 1 T and 10⁵ A cm⁻² at 10 T, underscoring their promise for high‑field superconducting applications.

Abstract

The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. With twice the critical temperature of Nb_3Sn and four times that of Nb-Ti alloy, MgB_2 has the potential to reach much higher fields and current densities than either of these technological superconductors. A vital prerequisite, strongly linked current flow, has already been demonstrated even at this early stage. One possible drawback is the observation that the field at which superconductivity is destroyed is modest. Further, the field which limits the range of practical applications, the irreversibility field H*(T), is ~7 T at liquid helium temperature (4.2 K), significantly lower than ~10 T for Nb-Ti and ~20 T for Nb_3Sn. Here we show that MgB_2 thin films can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding H*(4.2 K) above 14 T. In addition, very high critical current densities at 4.2 K, 1 MA/cm_2 at 1 T and 10_5 A/cm_2 at 10 T, are possible. These data demonstrate that MgB_2 has credible potential for high-field superconducting applications.