Low-temperature magnetism in icosahedral ${\mathrm{Al}}_{70}$${\mathrm{Mn}}_9$${\mathrm{Pd}}_{21}$

We report measurements of the specific heat ${\mathit{C}}_{\mathit{p}}$(T), magnetic susceptibility χ(T), and magnetization M(H) of icosahedral ${\mathrm{Al}}_{70}$ ${\mathrm{Mn}}_9$ ${\mathrm{Pd}}_{21}$ at low temperatures. Below room temperature, the static magnetic susceptibility is well described by a Curie-Weiss-type law above 50 K with a paramagnetic Curie temperature FTHETA=-108 K, implying fairly strong antiferromagnetic coupling between individual Mn moments. The Curie constant is compatible with a mean effective moment ${\mathit{p}}_{\mathit{e}\mathit{f}\mathit{f}}$=1.7 ${\mathrm{\mu }}_{\mathit{B}}$/(Mn atom). The ac susceptibility shows a spin-glass-like maximum at 0.5 K, which, in view of the value of FTHETA, implies a high degree of frustration. The saturation magnetization and the magnetic specific-heat data below 10 K both indicate a very low concentration of magnetic moments (1.2% of all Mn atoms) as being involved in the spin-glass transition. Comparisons are made with previously reported data for highly frustrated spin glasses.