Pressure effects of an S=1 Heisenberg antiferromagnetic bond alternating chain

By the measurement of magnetic susceptibility under pressures (P) up to 8 k bar, we investigated pressure effects of the S = 1 Heisenberg antiferromagn etic bond alternating chain compound [{Ni(333-tet)(mu -N-3)}(n)] (ClO4), (3 33-tet denotes N,N ' -bis(3-aminopropyl)-1,3-propanediamine), whose alterna ting interaction ratio (a) at ambient pressure is very close to the theoret ical value for the gapless point (alpha (c) similar or equal to 0.59). Ther e are two kinds of intrachain interactions duc to bond alternation (J(1) an d J(2)), both of which are increased linearly against the pressure. At P = 8 kbar those magnitudes exceed 1.4 times of those at ambient pressure. The magnitude of alpha equivalent to J(2)/J(1), however, does not change largel y. The normalized magnetic susceptibility chi /J(1)/k(B) around k(B)T//J(1) / = 0.1 has the maximum value at P = 2 kbar, and this suggests the possibil ity of the slight changes of alpha and D.