Magnetic properties of the Ag-In-rare-earth 1/1 approximants

We have performed magnetic susceptibility and neutron scattering measurements on polycrystalline Ag-In-RE (RE, rare-earth) 1/1 approximants. In the magnetic susceptibility measurements, for most of the RE elements, inverse susceptibility shows linear behaviour in a wide temperature range, confirming well localized isotropic moments for the RE³⁺ ions. Exceptionally for the light RE elements, such as Ce and Pr, nonlinear behaviour was observed, possibly due to significant crystalline field splitting or valence fluctuation. For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the field-cooled and zero-field-cooled susceptibility at T_f = 3.7 K, suggesting a spin-glass-like freezing. On the other hand, neutron scattering measurements detect significant development of short-range antiferromagnetic spin correlations in the elastic channel, which is accompanied by a broad peak at hω = 4 meV in the inelastic scattering spectrum. These features have striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the short-range spin freezing behaviour is due to local high-symmetry clusters commonly seen in both systems.