  We propose a universal practical approach to realize magnetic second-order
topological insulator (SOTI) materials, based on properly breaking the time
reversal symmetry in conventional (first-order) topological insulators. The
approach works for both three dimensions (3D) and two dimensions (2D), and is
particularly suitable for 2D, where it can be achieved by coupling a quantum
spin Hall insulator with a magnetic substrate. Using first-principles
calculations, we predict bismuthene on EuO(111) surface as the first realistic
system for a 2D magnetic SOTI. We explicitly demonstrate the existence of the
protected corner states. Benefited from the large spin-orbit coupling and
sizable magnetic proximity effect, these corner states are located in a
boundary gap $\sim 83$ meV, hence can be readily probed in experiment. By
controlling the magnetic phase transition, a topological phase transition
between a first-order TI and a SOTI can be simultaneously achieved in the
system. The effect of symmetry breaking, the connection with filling anomaly,
and the experimental detection are discussed.
