Theoretical and experimental study of the magnetic properties of the singlet-ground-state system Cu(N $O_{3}$ ) ${}_{2}\cdot$ 2.5 $H_{2}$ O: An alternating linear Heisenberg antiferromagnet

The thermodynamic properties of Cu(N

O_{3}

)

{}_{2}\cdot

2.5

H_{2}

O are compared with calculated properties of the one-dimensional alternating Heisenberg antiferromagnet as described by the Hamiltonian:

H = - 2 J Σ n^{} ({\vec{S}}_{2 n} \cdot {\vec{S}}_{2 n + 1} + α {\vec{S}}_{2 n} \cdot {\vec{S}}_{2 n - 1}) - g μ_{B} Σ n^{} \vec{H} \cdot {\vec{S}}_{n}

, with

α = 0.27

and

\frac{J}{k} = - 2.6

K. The thermodynamic properties, obtained from exact calculations of the eigenvalues of

H

, for 2, 4, 6, 8, 10, and 12 spins, have been extrapolated to

n = \infty

to obtain the behavior of the infinitely long alternating chain.

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Theoretical and experimental study of the magnetic properties of the singlet-ground-state system Cu(NO3)·22.5H2O: An alternating linear Heisenberg antiferromagnet