Hypergiant spin polarons photogenerated in ferromagnetic europium chalcogenides

We find that in the ferromagnetic semiconductor EuS, near its Curie temperature, a single band-edge photon generates a spin polaron (SP), whose magnetic moment approaches 20,000 Bohr magnetons. This is much larger than the supergiant photoinduced SPs in antiferromagnetic europium chalcogenides, reported previously. The larger SP in ferromagnetic EuS, and still larger expected for EuO, is explained by a larger Bohr radius of the photoexcited electron state, which encircles and polarizes a greater number of lattice spins. However, because the wave function of the photoexcited electron spreads over a greater volume, the photoexcited electron exchange interaction with individual lattice spins weakens, which makes the SP more easily quenched thermally.