  We study the emergence and dynamics of in-plane skyrmions in collinear
ferromagnetic heterostructures. We present a minimal energy model for this
class of magnetic textures, determine the crystal symmetries compatible with it
and propose material candidates, based on symmetries only, for the observation
of these topological solitons. We calculate exact solutions of the energy model
for in-plane skyrmions in the absence of dipolar interactions at critical
coupling, the latter defined by the relations $H = K$ and $D = \sqrt{AK}$ for
the strength of the external magnetic field and the Dzyaloshinskii coupling
constant, respectively, with $K$ and $A$ being the anisotropy constant and the
exchange stiffness of the material. Through micromagnetic simulations, we
demonstrate the possibility of in-plane skyrmion production via i) the motion
of domain walls through a geometrical constriction and ii) shedding from a
magnetic impurity driven both by spin-transfer torques. In-plane skyrmion
dynamics triggered by spin-orbit torques are also investigated analytically and
numerically. Our findings point towards the possibility of designing racetracks
for in-plane skyrmions, whose speed could be tuned by adjusting the angle
between the charge current and the uniform background magnetization; in
particular, the speed is maximum for currents parallel to the easy axis and
becomes zero for currents transverse to it.
