Coexistence of ferromagnetism and cluster-glass behavior in YFe5.5Al6.5 and YFe5.8Al6.2

YFexAl12−x (x = 5.5 and 5.8) polycrystalline samples were prepared by induction melting and found to crystallize in the tetragonal ThMn12-type structure. Mössbauer spectroscopy, magnetization, and AC-susceptibility measurements show a reentrant ferromagnetic behavior. Above room temperature, there is evidence of uncorrelated iron-rich nanoclusters with short-range ferro- or ferrimagnetic order. At Tc approx. 230 K for YFe5.5Al6.5 and 270 K for YFe5.8Al6.2 a paramagnetic ferromagnetic-like transition takes place. At lower temperatures fall-offs of the DC-magnetization curves are observed. Analysis of the frequency and field dependence of the linear AC-susceptibility as well as of the higher harmonics reveal a cluster-glass behavior below 70 and 50 K for YFe5.5Al6.5 and YFe5.8Al6.2, respectively. Comparing with previous results Tc as well as the ferromagnetic character of YFexAl12−x are found to increase with increasing Fe concentration.