High-density magnetic-vacancy inclusion in Co2MnGa single crystal probed by spin-polarized positron annihilation spectroscopy.

Co2MnGa is a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. Using spin-polarized positron annihilation spectroscopy, we examined a Bridgman-grown Co2MnGa single crystal with a nearly perfectL21-ordered structure and a reference Co2MnAl polycrystal with a Mn-Al-disorderedB2 structure. We found that a large amount of magnetic vacancies (more than 100 ppm) were included in the Co2MnGa crystal but not the Co2MnAl crystal. We discuss possible reasons for the inclusion of vacancies, the role of vacancies in the development of the ordered structure, and the electronic states associated with the vacancies. Toward the development of Co2MnGa-based devices, the manners for reducing vacancies as well as the influence of vacancies on the electrical transport properties should be considered.