Evidence of spin singlet ground state in the frustrated antiferromagnetic ring Cr8Ni

The magnetic properties of an odd spin number antiferromagnetic ring Cr8Ni have been investigated by high-field magnetization, specific-heat, and nuclear-magnetic-resonance measurements at very low temperatures (below 1 K). It is found that the ground state of this frustrated spin ring is a singlet state with total spin value S-T=0 and zero expectation value of the local spins. The energy-level structure for low-lying excited total spin state S-T not equal 0 shows a breakdown of the Lande interval rule in agreement with theoretical results. Evidences of sizeable Dzyaloshinski-Moriya interactions have been found in the magnetic-field dependence of low-temperature specific-heat and magnetization data.