Above room temperature T
c, magnetism
is becoming viable in diluted magnetic semiconductors, which show
different magnetic orders, depending on the dopant type and their
fabrication method. However, how the defects can influence the magnetic
properties remains unclear at the atomic level. In this article, by
taking the Co-doped tetragonal MO2 (t-MO2, M
= Ti, Sn, Hf, and Zr) as an example, the density functional theory-based
investigations show that the magnetic order is mainly decided by the
defect clustering effect, following a “defect-distance-based”
defect correlation principle. It is found that the distance between
two defects (Co–Co) leads to an alteration of magnetic order,
where SnO2 and ZrO2 show antiferromagnetic (AFM)
behavior when the nearest Co–Co distance lies within one octahedron,
while a larger distance gives rise to the ferromagnetic (FM) state.
In contrast, TiO2 exhibits an AFM state at the neighboring
Co–Co configuration with the nearest Co–Co distance
larger than one octahedra, while HfO2 showed an opposite
trend as that of TiO2. Furthermore, the position of oxygen
vacancies mainly affects the magnitude of magnetization instead of
magnetic order. We believe this work would significantly advances
the understanding of defect chemistry and condensed matter physics
related to diluted FM-AFM systems.