Magnetismus von Europium-Clustern in intermetallischen Verbindungen mit Magnesium Teil 2 Über den Einfluβ von Aluminium auf die Intra- und Intercluster-Wechselwirkungen in Eu(Mg 1− xAl x) 5,2

Abstract

The magnetic susceptibilities of the phases Eu(Mg 1− x Al x ) 5.2 with x=0.05 and 0.10 (which crystallize with a EuMg 5.2-type structure containing triangular Eu(4f 7) clusters) have been determined between 3.2 and 295 K. In the temperature range 40–295 K where the compounds obey the Curie-Weiss law with μ≈8.1 μ B , in contrast with EuMg 5.2, the paramagnetic Curie temperatures Θ p decrease from 7 K (EuMg 5.2) to 4.5 K ( x=0.05) or 0.5 K ( x=0.10). Below 40 K characteristic deviations from the Curie-Weiss straight line occur which on the basis of the Heisenberg and molecular field models allow the separation of intra- and intercluster exchange interactions. Within the triangular clusters the interaction is ferromagnetic whereas the intercluster effect is antiferromagnetic. The change in Θ p values with increasing aluminium content, tending towards an increase in antiferromagnetic contributions, results from a reduction in the ferromagnetic intracluster coupling and a strengthening of the antiferromagnetic intercluster effect.