  The performance of iron-based superconductors in high magnetic fields plays
an important role for their practical application. In this work, we measured
the magnetostriction and magnetization of BaFe$_{1.908}$Ni$_{0.092}$As$_{2}$
single crystals using pulsed magnetic fields up to 60 T and static magnetic
fields up to 33 T, respectively. A huge longitudinal magnetostriction (of the
order of 10$ ^{-4} $) was observed in the direction of the twin boundaries. The
magnetization measurements evidence a high critical-current density due to
strong bulk pinning. By using magnetization data with an exponential
flux-pinning model, we can reproduce the magnetostriction curves qualitatively.
This result shows that the magnetostriction of
BaFe$_{1.908}$Ni$_{0.092}$As$_{2}$ can be well explained by a
flux-pinning-induced mechanism.
