Magnetism in EuAlSi and the Eu₁-ₗ Srₗ solid solution

The magnetic properties of EuAlSi, a compound comprising a honeycomb lattice of Al/Si atoms and a triangular lattice of Eu atoms, are presented. By means of single-crystal x-ray diffraction, we find that EuAlSi crystallizes in an AlB2-type structure with space group P6/ and unit cell parameters a=4.2229(10)Å and c=4.5268(12)Å. Our magnetic measurements indicate that EuAlSi is a soft ferromagnetic material with TCurie=25.8K. The susceptibility follows the Curie-Weiss law at high temperatures, which allowed us to determine the paramagnetic Curie temperature θP=36.2(1)K and an effective magnetic moment μeff=8.07(1)µB/Eu. This value is in agreement with the theoretical value of 7.9µB for Eu2+ free ion. Moreover, we have prepared the Eu1−xSrxAlSi solid solution, where the atoms in the triangular lattice were systematically exchanged, in order to study the evolution of the collective quantum properties from the ferromagnetic EuAlSi toward the superconducting SrAlSi. Across the Eu1−xSrxAlSi solid solution, the unit cell parameters change linearly, following Vegard’s law, and making the system reliable for studying composition dependence of the interplay between the crystal structure and physical properties. As the Sr content increases, i.e., x increases, we note a consistent reduction of μeff and TCurie. Long-range magnetic order in Eu1−xSrxAlSi persists up to x=0.95, whereas superconductivity is only observed for samples with x>0.97.