Magnetic neutron scattering study of single-crystal cupric oxide

Among ${\mathrm{Cu}}^{2+}$ compounds, cupric oxide (CuO) has unusual magnetic properties, some of which are shared by the superconducting copper oxides. In order to study these properties further, neutron scattering experiments on a CuO single crystal have been performed. Two magnetic phase transitions at $T_{N1}$=231 K and $T_{N2}$=212.5 K have been observed, with the magnetic structure below $T_{N2}$ antiferromagnetic and the structure between $T_{N1}$ and $T_{N2}$ helical in nature. The dynamics of the magnetism was also studied. As in ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$, the dispersion of the low-temperature spin-wave excitations is unusually steep (dE/dk=250±75 meV A${̊}^{\mathrm{-}1}$), indicating strong magnetic interactions. Inelastic magnetic scattering has also been measured above $T_{N1}$. At temperatures slightly above the 231-K phase transition, dynamic critical slowing has been observed.