  Antiferromagnets (AFMs) with anomalous quantum responses have lead to new
progress for the understanding of their magnetic and electronic structures from
symmetry and topology points of view. Two typical topological states are the
collinear antiferromagnetic Weyl semimetal (WSM) and Weyl nodal loop semimetal
(WNLSM). In comparison with the counterparts in ferromagnets and non-collinear
AFMs, the WSMs and WNLSMs in collinear AFMs are still waiting for experimental
verification. In this work, we theoretically predicted the coexistence of Weyl
points (WPs) and Weyl nodal loops (WNLs) in transition metal oxide RuO2. Owing
to the small magnetocrystalline anisotropy energy, the WPs and WNLs can
transform to each other via tuning the Neel vector. Moreover, since the WPs are
very close to Fermi level and the WNLs are even crossing Fermi level, the
topological states in RuO2 can be easily probed by photoemission and STM
methods. Our result provides a promising material platform for the study of WSM
and WNLSM states in collinear AFMs.
