Gd ESR of GdCu/sub 4/Al/sub 8/ and GdMn/sub 4/Al/sub 8/ and magnetic susceptibility of GdCu/sub 4/Al/sub 8/, GdMn/sub 4/Al/sub 8/, and YMn/sub 4/Al/sub 8/ were measured in the temperature range of 290 K-460 K and 90 K-1050 K, respectively. The occurrence of the Mn moment in YMn/sub 4/Al/sub 8/, and GdMn/sub 4/Al/sub 8/ is strongly correlated with the critical value of d/spl ap/2.6 /spl Aring/ of the Mn-Mn distance below which the Mn moment is not stable. The experimental data for GdMn/sub 4/Al/sub 8/, compared with the data for the isostructural compounds GdCu/sub 4/Al/sub 8/, and YMn/sub 4/Al/sub 8/ 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 YMn/sub 4/Al/sub 8/ and GdM/sub 4/Al/sub 8/ changes from an itinerant electron type to a local-moment type with increasing temperature.< >

Magnetic susceptibility of YMn/sub x/Al/sub 12-x/ (x=4,5,6) with ThMn/sub 12/ structure was measured at temperatures 90 K to 900 K. These compounds show varied magnetic behaviors depending upon the relative abundance of Mn atoms in the 8f, 8j and 8i crystallographic sites. In the high temperature range, the temperature dependence of the susceptibility is of the Curie-Weiss type. The occurrence of a Mn moment in YMn/sub 4/Al/sub 8/ and YMn/sub 6/Al/sub 6/, is strongly correlated with the critical value d/spl ap/2.6 /spl Aring/ of Mn-Mn distance below which the Mn moment collapses, In YMn/sub 6/Al/sub 6/, both the magnetic and the nonmagnetic Mn atoms were observed to coexist. It has been revealed that the magnetic character of Mn moment in the 8f sites of these two compounds changes from an itinerant electron type to a local moment type with increasing temperature. A transition to a spin glass state at ion temperatures for YMn/sub 5/Al/sub 7/ was suggested,.< >

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