Observation of magnetization saturation in the S=1 one-dimensional Heisenberg antiferromagnets Ni(C₂H₈N₂)₂NO₂(ClO₄) and CsNiCl₃

The magnetization in S=1 one-dimensional Heisenberg antiferromagnets Ni(C₂H₈N₂)₂NO₂(CiO₄) (NENP) and CsNiCl₃ was measured by means of the Faraday rotation in ultrahigh magnetic fields up to 150 T. A distinct saturation of the magnetization was observed in both samples. From the saturation field, the exchange coupling constants are evaluated as J=45.5 K and 25.8 K for NENP and CsNiCl₃, respectively. The experimental magnetization curve is in good agreement with a theoretical curve for an S=1 one-dimensional Heisenberg antiferromagnet at finite temperatures.