  MoS2 atomic layers have recently attracted much interest because of their
two-dimensional structure as well as tunable optical, electrical, and
mechanical properties for next generation electronic and electro-optical
devices. Here we have achieved facile fabrication of MoS2 thin films on CdS
nanowires by cation exchange in solution at room temperature and importantly
observed their extraordinary magnetic properties. We establish the atomic
structure of the MoS2/CdS heterostructure by taking atomic images of the
MoS2/CdS interface as well as performing first-principles density functional
geometry optimizations and STEM-ADF image simulations. Furthermore, our first
principles density functional calculations for the MoS2/CdS heterostructure
reveal that the magnetism in the MoS2/CdS heterostructure stems from the
ferromagnetic MoS2 monolayer next to the MoS2/CdS interface. The ferromagnetism
is attributed to the partial occupation of the Mo dx2-y2/dxy conduction band in
the interfacial MoS2 monolayer caused by the mixed covalent-ionic bonding among
the MoS2 and CdS monolayers near the MoS2/CdS interface. The present findings
of the ferromagnetic MoS2 monolayer with large spin polarization at the
MoS2-semiconductor interface suggest a new route for fabrication of the
transition metal dichalcogenide-based magnetic semiconductor multilayers for
applications in spintronic devices.
