Trapping of positive muons by vacancies in thermal equilibrium

The trapping of positive muons by vacancies in crystals is by now well established. Nevertheless, so far almost all attempts to study vacancies in thermal equilibrium by μSR have failed. The only interaction sufficiently strong to permit μSR studies of vacancies in thermal equilibrium is that between the magnetic moments of muons and electrons in magnetically ordered materials. This requires high magnetic ordering temperatures Tsub(c), since the vacancy concentration decreases exponentially with decreasing temperature and since the number of sites visited by thermalized muons is limited by their lifetime. The only metals to which this method is applicable are thus α-Fe (Tsub(c) = 1043 K) and β-Co (Tsub(c) = 1390 K). A pilot study on α-Fe and on preliminary experiments on β-Co are reported. (Auth.)