Weak ferromagnetism inTbNi2B2C

The magnetic order of ${\mathrm{TbNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ below ${T}_{N}=15\mathrm{K}$ has been studied via ${}^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy and muon spin relaxation (\ensuremath{\mu}SR). It is shown that only below 8 K all components of the Tb moment are locked. This is traced from an unusual increase and a turning of the transferred magnetic hyperfine field at the ${}^{57}\mathrm{Fe}$ dopants, and also from a decrease of the fluctuation rate of electronic moments detected from \ensuremath{\mu}SR. We relate this locking of the moment to the ferromagnetically ordered component which was concluded from neutron diffraction experiments.