Magnon excitations and the specific heat of EuxSr1- xS spin glasses in strong magnetic fields

The density of states of magnon-like excitations of Eu x Sr 1−x S spin glasses with x=0.25, 0.44 and 0.54 is calculated for very strong magnetic fields B, i.e. B>3 T. It is found that for these high fields the magnon-like excitations can be treated as non-interacting bosons up to temperatures far beyond the spin glass freezing temperature at B=0. From the density of states the magnetic part C H of the specific heat is calculated, without any fit-parameter. The results agree quantitatively with recent experiments, for T between 0.3 K and 5 K (10 K) in magnetic fields of 3.6 T (6.6 T) Etude des excitations de quasi-magnons dans ces composes pour x=0,25, 0,44 et 0,54 en champ magnetique intense (B>3 T). Traitement de ces quasi-magnons comme des bosons non interagissants bien au-dessous de la temperature de transition de verre de spin a B=0. Calcul, sans parametre ajustable, de la densite d'etats des magnons et de la chaleur massique magnetique