Local spin density in the Cr7Ni antiferromagnetic molecular ring and 53Cr-NMR

We present 53Cr-NMR spectra collected at low temperature in a single crystal of the heterometallic antiferromagnetic (AF) ring Cr7Ni in the S D 1=2 ground state with the aim of establishing the distribution of the local electronic moment in the ring. Due to the poor S=N we observed only one signal which is ascribed to three almost equivalent 53Cr nuclei in the ring. The calculated spin density in Cr7Ni in the ground state, with the applied magnetic field both parallel and perpendicular to the plane of the ring, turns out to be AF staggered with the greatest component of the local spin hsi for the Cr3C ions next to the Ni2C ion. The 53Cr-NMR frequency was found to be in good agreement with the local spin density calculated theoretically by assuming a core polarization field of Hcp = -11 T=B for both orientations, close to the value found previously in Cr7Cd. The observed orientation dependence of the local spin moments is well reproduced by the theoretical calculation and evidences the importance of single-ion and dipolar anisotropies.