High-field magnetization of S = 1 antiferromagnetic bond-alternating chain compounds

High-field magnetization and susceptibility measurements have been performed on S = 1 antiferromagnetic bond-alternating chain compounds: [Ni ₂(dpt)₂(μ-ox)(μ-N₃)](PF₆) [dpt=bis(3-aminopropyl)amine, ox= C₂O₄] (abbreviated as NDOAP) and [Ni(333-tet)(μ-tet)(μ-NO₂)] ClO₄ [333-tet=N,N′-bis(3-aminopropyl)-1,3-propanediamine] (abbreviated as NTENP). The magnetization of NDOAP shows two steep increases at about 200 and 500 kOe. A magnetization plateau is observed between about 300 and 500 kOe, corresponding to half the value of the saturation moment. Comparison between numerical calculations and the experimental results, including the magnetic susceptibility, shows that NDOAP has a singlet ground state due to dimerization with a bond-alternating ratio α=0.1. The half-saturation plateau is also observed around 700 kOe in the magnetization of NTENP. The magnetization process of NTENP is well reproduced by the numerical result calculated for the parameter of α=0.45 in the singlet-dimer phase. The a dependence of the magnetization processes is discussed.