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 Tf are 5.5 K and 7.6 K, respectively.
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