Comparative study of the magnetic properties of TbFe4Al8 and YFe4Al8 compounds

ZF-, LF- and TF- mu SR-measurements were started with the aim to study the interplay of the R- and Fe-sublattices in establishing the magnetic order b y comparing TbFe4Al8 and YFe4Al8. Comparison of the spin-lattice relaxation rates between the two compounds shows that the fast relaxation visible in TbFe4Al8 arises from the Tb 4f moments and is best fitted with a streched e xponential (exp ( - lambda t)(beta)). The slowing down of the spin dynamics in Tb with beta decreasing from 1 to 1/3 on approaching T-N from above, is characteristic for the universal behaviour of a classical spin glass. Howe ver, the T-dependence of lambda, resembles more that of a conventional AF s ystem involving rare earth moments. As neutron diffraction has shown long-r ange magnetic order sets in immediately below T-N. The present experiment s uggests that the slowing down of the spin dynamics is governed by competing interactions leading to a wide distribution of time correlations. However, the ensuing frustration does not seem to be strong enough to prevent the o nset of long-range magnetic order below T-N involving both the Tb and the F e moments. These results confirm the complex long-range ordering process as sociated with two distinct order parameters and the simultaneous ordering o f the two sublattices found by neutron diffraction. (C) 2000 Elsevier Scien ce B.V. All rights reserved.