HYPERFINE INTERACTIONS OF ISOLATED AND OF EXCHANGE-COUPLED IRIDIUM IONS IN (NH4)2PTCL6

The hyperfine interactions of single and of exchange-coupled pairs of Ir4+ ions in (NH4)2PtCl6 have been investigated by ENDOR methods at 4°K. Recent investigations of electron transfer between magnetic ions have suggested that a measurable difference may occur. Experimentally, however, the difference is found to be less than 0·15%. The hyperfine constants are determined to be negative, leading to a value K = 0·85±0·4 for the core polarization constant for 5d electrons. The nuclear dipole moments of 193Ir and 191Ir are determined to be 193μ = +0·162± 0·006 nuclear magnetons and 191μ = +0·146± 0·008 nuclear magnetons, in agreement with recent measurements by nuclear magnetic resonance in the pure metal. A hyperfine anomaly of 191193Δ = (0·20±0·30)% is found. The ratio of the nuclear quadrupole moments is determined to be 193Q:191Q = 0·92±0·09.