  We study the multiplicity and concentration of complex valued solutions for a
fractional magnetic Schr\"odinger equation involving a scalar continuous
electric potential satisfying a local condition and a continuous nonlinearity
with subcritical growth. The main results are obtained by applying a
penalization technique, generalized Nehari manifold method and
Ljusternik-Schnirelman theory. We also prove a Kato's inequality for the
fractional magnetic Laplacian which we believe to be useful in the study of
other fractional magnetic problems.
