Observation of fractional spinS=1/2 on open ends ofS=1 linear antiferromagnetic chains: Nonmagnetic doping

Approximately 0. 5% of nonmagnetic divalent ions Zn, Cd, and Hg have been alternatively substituted for Ni in the linear chain of antiferromagnetically coupled Ni^2+ (S=1) spins in Ni (C₂H₈N₂) ₂ (NO₂) CIO₄ (NENP). While at low temperature the pure NENP shows no EPR signal, the doped NENP shows identical EPR spectra corresponding to the fractional spin S=1/2 states at the ``open'' ends of the Ni chains adjacent to the nonmagnetic substitutions.