  Hybrid superconductor-semiconductor heterostructures are promising platforms
for realizing topological superconductors and exploring Majorana bound states
physics. Motivated by recent experimental progress, we theoretically study how
magnetic insulators offer an alternative to the use of external magnetic fields
for reaching the topological regime. We consider different setups, where: (1)
the magnetic insulator induces an exchange field in the superconductor, which
leads to a splitting in the semiconductor by proximity effect, and (2) the
magnetic insulator acts as a spin-filter tunnel barrier between the
superconductor and the semiconductor. We show that the spin splitting in the
superconductor alone cannot induce a topological transition in the
semiconductor. To overcome this limitation, we propose to use a spin-filter
barrier that enhances the magnetic exchange and provides a mechanism for a
topological phase transition. Moreover, the spin-dependent tunneling introduces
a strong dependence on the band alignment, which can be crucial in
quantum-confined systems. This mechanism opens up a route towards networks of
topological wires with fewer constraints on device geometry compared to
previous devices that require external magnetic fields.
