Optical measurements of field-induced phenomena of the magnetic phase transition in quasi 2D MnS layers grown by MBE

We used a sensitive optical method to study the magnetic phase transition of antiferromagnetic MnS layers. The method is applicable for very small numbers of spins, e.g., thin single layers. We studied the optical and magnetic properties of MnS layers using the internal optical transition of the manganese 3d-shell. The temperature dependence of the Mn-emission exhibits a pronounced minimum revealing the para- to anti-ferromagnetic phase transition. The MnS layers were grown by molecular beam epitaxy, embedded between diamagnetic ZnSe cladding layers on a (100)-GaAs substrate. It was found that the Neel-temperature itself is influenced by the biaxial strain and can be changed in an external magnetic field in case of quasi 2D MnS-layers. The phase diagram reveals a weak Ising like anisotropic contribution in case of a 1.8 nm thin layer, whereas a 8.6 nm thick layer behaves still like an ideal isotropic Heisenberg system.