Effect of disorder and vacancy defects on electrical transport properties of Co2MnGa thin films grown by magnetron sputtering

Co2MnGa is known as a Weyl semimetal exhibiting giant anomalous Hall and Nernst effects. However, the performance of Co2MnGa thin films grown on MgO(001) by the magnetron sputtering method is somewhat lower than that of the bulk crystals. Here, we attempted to improve the electrical transport properties by post-growth annealing at temperatures from 573 to 773 K. X-ray diffraction analysis indicated that the degree of long-range order changed from A2 to B2 plus L21 upon annealing at 673 K or above. Positron annihilation spectroscopy revealed the presence of high-density (≳100 ppm) divacancies, which were absent in the bulk crystal, and their partial improvement near the Co2MnGa/MgO interface on annealing at 673 K or above. Accompanying these structural changes, the longitudinal and anomalous Hall conductivities increased considerably and the anomalous Hall angle reached a maximum value of 11.8%. These findings imply that the post-growth annealing improved the electrical transport properties of Co2MnGa films through the development of long-range crystal order and reduction of divacancies. However, the electrical performance achieved by thermal annealing was still insufficient in comparison with the bulk crystals, and hence for further improvement, alternative approaches may need to be considered.