  We report the ground state magnetic structure and in-field magnetostrictive
effects of NiTiO$_3$ studied by means of zero field and in-field single-crystal
neutron diffraction, magnetization, and high-resolution dilatometry
experiments. Zero-field neutron diffraction on NiTiO$_3$ single crystals
reveals an easy-plane antiferromagnet with a multidomain ground state. Upon
application of external magnetic fields, neutron diffraction shows the
evolution of domains with spins perpendicular to the applied field. The
rotation of spins in the multidomain state exhibits pronounced lattice changes
in the magnetostriction measurements. We see magnetization and magnetostriction
measurements sale with each other in the multidomain state revealing the strong
coupling of spins to the lattice.
