Controlling Magnetic Ordering in Ca1–xEuxCo2As2 by Chemical Compression

To investigate the interplay between electronic structure and itinerant magnetism, Ca1–xEuxCo2As2 solid solutions (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.9, 1.0) were prepared by reactions between constituent elements in molten Bi. All of the samples crystallize in the ThCr2Si2 structure type. The crystal structure refinement revealed the formation of Co vacancies, the concentration of which decreases as the Eu content increases. The Eu site exhibits mixed valence in all samples. X-ray absorption near-edge structure spectroscopy revealed that the average Eu oxidation state decreases from +2.17 at 0 < x ≤ 0.6 to +2.14 at x ≥ 0.65. The same borderline behavior is observed in magnetic properties. The substitution of Eu for Ca causes the transition from the antiferromagnetic (AFM) ordering of Co moments in CaCo2As2 to ferromagnetic (FM) ordering of Co moments in Ca1–xEuxCo2As2 with 0.1 ≤ x ≤ 0.6. At higher Eu content, AFM ordering of Eu moments is observed, whereas the Co sublattice exhibits only parama...