Comparative study of ferromagnetism in non-Heisenberg 1/1 and 2/1 quasicrystal approximants

We report comparative study of ferromagnetic properties in non-Heisenberg 1/1 and 2/1 approximant crystals (ACs) with close chemical compositions in the quinary Au-Cu-Al-In-Tb alloy system. The 1/1 and 2/1 ACs exhibit comparable Weiss temperatures [θw=+17.8(5)and+14.6(5)K], Curie temperatures (TC=15.8 and 14.3 K), and magnetic entropy changes (ΔSM) under 5 T magnetic field change (-3.8 and-3.7 J/K mol Tb), respectively, showing insignificant role of the AC degree in the magnetism of the non-Heisenberg ACs. Moreover, the magnetic behavior of the quinary 1/1 AC is almost identical to that of the ternary Au64Al22Tb14 1/1 AC [N. Kikugawa, J. Alloys Compd. 882, 160669 (2021)10.1016/j.jallcom.2021.160669.], which implies that chemical disorder introduced in the quinary 1/1 AC does not appreciably affect the ferromagnetic behavior, pointing toward the dominant magnetic interactions on a shorter length scale. The comparable magnetic behaviors between the 1/1 and 2/1 ACs are partly understood in terms of the similar distribution profiles of the interspin distances, up to third-nearest neighbor interactions, well beyond the common icosahedral cluster.