Low-Temperature Susceptibilities of Rh and Ir with Fe Impurities

The magnetic susceptibilities of dilute (<1%) solid solutions of Fe in Ir and Rh have been measured from 293° to 0.37°K in magnetic fields up to 11 000 G. Neither system shows the properties of a normal local moment in that they do not obey a Curie law when μβH/kT≪1 and the moment does not saturate at μβH/kT≫1; the magnetic moment is practically linear with field at all temperatures and fields measured. The temperature and field dependence cannot be explained on the basis of Fe–Fe ordering because (a) neither system has a field-dependent susceptibility below 1°K, (b) both systems show a heat capacity increase over that of the pure material that is too small to be explained on the basis of Fe–Fe order,1,2 (c) the increase of the susceptibility over that of pure Rh or Ir is linear in concentration of Fe and (d) a Curie-Weiss law can be made to fit the data only over a small temperature range. It is concluded, therefore, that these systems cannot be explained on the simple model of localized magnetic impurities in a weakly paramagnetic host.