Magnetic pair breaking inHoNi2B2C

Neutron-diffraction techniques have been used to study the interplay between superconductivity and magnetism in ${\mathrm{HoNi}}_2$ ${\mathrm{B}}_2$C (${\mathit{T}}_{\mathit{c}}$=8 K). The experimental results, obtained on single crystals, show that below approximately 4.7 K, this compound is in a simple antiferromagnetic state that coexists with superconductivity. Between approximately 4.7 and 6 K, an incommensurate modulated magnetic structure has been found. This observation strongly suggests that pair breaking associated with this incommensurate magnetic structure is responsible for the deep minimum in ${\mathit{H}}_{\mathit{c}2}$ and the near-reentrant behavior observed in this compound at approximately 5 K.