Spin-glass behaviour of icosahedral Mg-Gd-Zn and Mg-Tb-Zn quasi-crystals

Abstract

The magnetic properties of icosahedral Mg₄₂RE₈Zn₅₀ (RE identical to Gd, Tb, Dy, Ho or Er) quasi-crystals have been investigated. These quasi-crystalline phases have a face-centred icosahedral lattice with a highly ordered Frank-Rasper-type structure as identified by electron diffraction and X-ray diffraction. The temperature dependence of DC magnetic susceptibility obeys a Curie-Weiss law in wide temperature ranges. The effective magnetic moments mu _eff are close to those of free RE³⁺ ions and their paramagnetic Curie temperature Theta _p is negative, indicating that the RE-RE exchange interactions are predominantly antiferromagnetic. The value of Theta _p which is the sum of all exchange interactions is almost in proportion to the de Gennes factor. At low temperatures, spin-glass behaviour has been observed in the icosahedral Mg₄₂Gd₈Zn₅₀ and Mg₄₂Tb₈Zn₅₀ quasi-crystals and their spin freezing temperatures T_f are 5.5 K and 7.6 K, respectively.