Vacancy formation in thermal equilibrium in ferromagnetic iron and cobalt studied by the spin rotation of positive muons

The transverse spin relaxation of positive muons has been measured in non-magnetized polycrystalline Fe and Co between 300 K and the Curie temperatures. From the trapping of muons by vacancies in thermal equilibrium observed in ferromagnetic Fe lower and upper limits to the monovacancy formation enthalpy (1.59 eV < HF1V < 1.73 eV) and a lower limit for the binding enthalpy of the positive muon in a vacancy (εFe1V > 1.3 eV) are deduced. Preliminary Co data are in accordance with positron-annihilation measurements under the assumption that the muon-vacancy binding enthalpy εCo1V is about 1.1 eV. (author) 30 refs., 1 fig