Magnetic properties of AlB${}_2$-type holmium silicides and germanides

Abstract

Discovery of the large magnetocaloric effect in HoB${}_2$ has highlighted the practical advantage of heavy rare-earth ions. Other holmium compounds are of interest, and we here report the synthesis and the magnetic properties of HoSi${}_{1.67}$ and HoGe${}_{1.67}$ which form the same AlB${}_2$-type structure but with vacancies. They are found to show the antiferromagnetic order with the Neel temperature 17.6(2)K for HoSi${}_{1.67}$ and 9.9(2)K for HoGe${}_{1.67}$, and the magnetic entropy changes at the temperature are 0.05(1)J/cm${}^3$K for HoSi${}_{1.67}$ and 0.08(1)J/cm${}^3$K for HoGe${}_{1.67}$. Magnetic orders were suppressed by replacing vacancies with nickel, resulting in an increase of magnetic entropy changes. Distance between the in-plane Ho${}^{3+}$ ions appears to be an important parameter leading to the transition between the antiferromagnetic (HoSi${}_{1.67}$) and the ferromagnetic (HoB${}_2$) order. The finding may aid the exploration of other heavy rare-earth compounds for similar applications.

18 pages, 6 figures, 2 tables