  Frustrated magnets are one class of fascinating materials that host many
intriguing phases such as spin ice, spin liquid and complex long-range magnetic
orderings at low temperatures. In this work we use first-principles
calculations to find that in a wide range of magnetically frustrated oxides, at
zero temperature a number of non-collinear magnetic orderings are more stable
than the type-I collinear ordering that is observed at finite temperatures. The
emergence of non-collinear orderings in those complex oxides is due to
higher-order exchange interactions that originate from second-row and third-row
transition metal elements. This implies a collinear-to-noncollinear spin
transition at sufficiently low temperatures in those frustrated complex oxides.
Furthermore, we find that in a particular oxide Ba$_2$YOsO$_6$, experimentally
feasible uniaxial strain can tune the material between two different
non-collinear magnetic orderings. Our work predicts new non-collinear magnetic
orderings in frustrated complex oxides at very low temperatures and provides a
mechanical route to tuning complex non-collinear magnetic orderings in those
materials.
