Ferromagnetism and re-entrant spin-glass transition in quasicrystal approximants Au–SM–Gd (SM = Si, Ge)

Abstract

Magnetic susceptibility and specific heat measurements on quasicrystalline approximants Au–Si–Gd and Au–Ge–Gd reveal that a ferromagnetic (FM) transition occurs at Tc = 22.5(5) K for Au–Si–Gd and at Tc = 13(1) K for Au–Ge–Gd, which are the first examples of ferromagnetism in crystalline approximants. In addition, a re-entrant spin-glass (RSG) transition is observed at TRSG = 3.3 K for Au–Ge–Gd in contrast to Au–Si–Gd. The different behaviors are understood based on the recent structural models reported by Gebresenbut et al (2013 J. Phys.: Condens. Matter 25 135402). The RSG transition in Au–Ge–Gd is attributed to a random occupation of the center of the Gd12 icosahedron by Gd atoms; a central Gd spin hinders the long-range FM order.