Effect of Nonmagnetic Localized States in Al Films with EnhancedTc

Abstract

Mixtures of Al with 10 wt% ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ and various concentrations of transition-metal elements (Cr, Mn, Fe) were sputtered at 77 °K and their transition temperature ($T_c$) was measured without warming above 77 °K. The transition temperature ($T_{\mathrm{co}}$) of the reference Al-10-wt%-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ mixture is approximately 3 °K. In agreement with Kaiser's theory, $T_c$ depends exponentially on the transition-metal concentration. The excellent agreement between film data and bulk data provides further proof that many electronic properties, in particular the density of states, of the aluminum with enhanced $T_c$ are very close to bulk values.