Structural and magnetic properties of (CH3)4NNi(NO2)3: A Haldane-gap system.

Abstract

We report investigations on the structure and the magnetic properties of (${\mathrm{CH}}_{3}$${)}_{4}$NNi(${\mathrm{NO}}_{2}$${)}_{3}$. From extended x-ray-absorption fine structure and x-ray-diffraction experiments, we show that (${\mathrm{CH}}_{3}$${)}_{4}$NNi(${\mathrm{NO}}_{2}$${)}_{3}$ has a chainlike structure of Ni(II) ions coupled via three ${\mathrm{NO}}_{2}$ anions. High-temperature susceptibility is consistent with one-dimensional antiferromagnetism with J/k=-12 K and g=2.25. Below 10 K, a strong decrease of susceptibility and proton relaxation rate is observed, in agreement with the Haldane prediction of a singlet ground state for the S=1, one-dimensional Heisenberg antiferromagnet. From the magnetization-versus-field data at low temperature, the Haldane gap is estimated to 4.5 K, close to the expected value 0.41 \ensuremath{\Vert}J\ensuremath{\Vert} for the S=1, one-dimensional Heisenberg antiferromagnet.