ESR in Gadolinium-Group V Compounds

Exchange narrowed paramagnetic resonance lines have been observed in GdP, GdAs, GdSb, and GdBi, at 9.3 GHz over the temperature range 17°–400°K. The exchange parameter derived from the linewidth by the theory of Anderson and Weiss has been expressed as a combination of nearest-neighbour superexchange and a temperature-dependent term. This latter term shows good agreement with the theory of Karpenko and Berdyshev and indicates that the predominant exchange, over the temperature range examined, is an indirect interaction via the impurity semiconductor current carriers. In all the compounds the impurity level excitation energy is found to be about 10−2 eV.