  In this work, we demonstrate that skyrmions can be nucleated in the free
layer of a magnetic tunnel junction (MTJ) with Dzyaloshinskii-Moriya
interactions (DMI) by a spin-polarized current with the assistance of stray
fields from the pinned layer. The size, stability and number of created
skyrmions can be tuned by either the DMI strength or the stray field
distribution. The interaction between the stray field and the DMI effective
field is discussed. A device with multi-level tunneling magnetoresistance is
proposed, which could pave the ways for skyrmion-MTJ-based multi-bit storage
and artificial neural network computation. Our results may facilitate the
efficient nucleation and electrical detection of skyrmions.
