Vacancy induced magnetism in WO3

The possibility to obtain ferromagnetic (FM) phase from native defects in WO3 is investigated by theoretically analyzing six different crystalline structures. The local magnetic moment from vacancies is calculated using the projector augmented wave method in combination with the local spin density approximation including a Coulomb correction (LSDA + U) of the W d-states. We find that tungsten vacancies V-W can induce a magnetic phase of similar to 3.5 mu(B)/V-W with a local magnetic moment on the oxygen atoms of at most similar to 1 mu(B)/V-W, whereas corresponding oxygen vacancies V-O have no impact on the magnetic coupling. Intriguingly, although the six crystalline structures have very comparable bonds, the magnetic moment generated by the cation vacancies is different, showing higher local magnetic moments for WO3 structures with low crystalline symmetry. The results indicate that WO3:V-W cannot induce a hole-mediated FM phase, and instead V-W in WO3 induces a local magnetic moment on the unpaired states at surrounding O atoms.