Gd3+-ESR and magnetic susceptibility of GdCu4Al8 and GdMn4Al8

Gd ESR of GdCu₄Al₈ and GdMn₄Al ₈ and magnetic susceptibility of GdCu₄Al₈ , GdMn₄Al₈, and YMn₄Al₈ were measured in the temperature range of 290 K-460 K and 90 K-1050 K, respectively. The occurrence of the Mn moment in YMn₄Al₈, and GdMn₄Al₈ is strongly correlated with the critical value of d≈2.6 Å of the Mn-Mn distance below which the Mn moment is not stable. The experimental data for GdMn₄Al₈, compared with the data for the isostructural compounds GdCu₄Al₈, and YMn₄Al₈ show that near the critical value of d, the existence of Mn moment depends not only on the value of d, but also on the local magnetic surroundings. It has been revealed that the magnetic character of Mn moment in YMn₄Al₈ and GdM ₄Al₈ changes from an itinerant electron type to a local-moment type with increasing temperature