Study of the magnetic properties of the Cex La1−x Pt alloy system: Which interaction establishes ferromagnetism in Kondo systems?

• We have found that for CexLa1−xPt the temperature of the ferromagnetic transition linearly depends on x.
• The Kondo temperature is independent of x.
• Hence, RKKY interaction is not responsible for the ferromagnetism.
• The lattice parameters show that direct exchange interaction is possible.
• We expect that the investigations of CexY1−x will confirm our conclusions.

In order to study Kondo ferromagnetism, particularly of the CePt compound, we investigate the magnetic properties of the CexLa1−xPt alloy system in the temperature range from 1.8 K to 320 K. The results of these investigations can be summarized as follows: dc-susceptibility can be described by the Curie–Weiss law at higher temperatures down to about 100 K, but also at the low temperatures above the phase transition. At higher temperatures, the extracted Curie–Weiss constant, θp, is negative in contrast to the low temperatures, where θC is positive. The extracted effective magnetic moment from the higher temperatures is the same for all the alloys and is close to the theoretical value of the isolated Ce3+ ion, μ=2.54 μB, indicating the hybridization is weak and, and consequently, Kondo interaction is weak. These observations confirm the main important conclusions inferred from an earlier transport properties investigation of this alloy system. The Curie temperature extracted by various approaches was compared to the extraction from the ac-susceptibility measurements. We show that its concentration dependence is not consistent with Doniach's diagram. Hence, RKKY interaction is not responsible for the ferromagnetism in this alloy system.