Optimal diamagnetic dilution concentration for suppressing dipole-dipole interaction in single-ion magnets
The effect of screening CoII moment of the monomeric [CoIIL2(H2O)] (L = 8-Hydroxyquinaldine), having a trigonal bipyramid coordination, by diamagnetic Zn in CoxZn1-x solid solutions on the magnetic relaxation has been explored using ac-susceptibility, high-field electron-spin-resonance measurements and CASPT2 calculations. The retention of the crystal structure for all solid solutions was demonstrated using single crystal diffraction. The dc-magnetization and theoretical fittings of the susceptibility for Co1 and Co0.1Zn0.9 gave a large zero-field-splitting (ZFS) D of +50±6 cm-1, and very weak dipole interaction between nearest neighbors, while EPR and calculations confirm the positive sign of the axial component (D). Consistent parameters were obtained from experiments and theory. Importantly, only field-induced relaxation can be observed for samples with less than 50% Co and gradual change of barrier energy to moment reversal and relaxation times were observed between 11 and 20% Co while both are enhanced for higher dilution. The results establish a clear barrier for extending the longevity of the magnetism for such single-ion species by lowering intramolecular interactions. The results suggest that magnetic interaction persists up to the second sphere, that is for dilution of 1 in 9 (11% Co). Importantly, this method is applicable to all single-ion magnet systems, that is, the optimum dilution concentration to overcome the dipole field can be given only by the single crystal structure.