  The magnetic behavior of the compound, Gd3Ru4Al12, which has been reported to
crystallize in a hexagonal structure about two decades ago, had not been
investigated in the past literature despite interesting structural features
(that is, magnetic layers and triangles as well as Kagome-lattice features
favouring frustrated magnetism) characterizing this compound. We report here
the results of magnetization, heat-capacity, and magnetoresistance studies in
the temperature (T) range 1.8-300 K. The results establish that there is a
long-range magnetic order of an antiferromagnetic type below (TN= ) 18.5 K,
despite a much large value (about 80 K) of paramagnetic Curie temperature with
a positive sign characteristic of ferromagnetic interaction. We attribute this
to geometric frustration. The most interesting finding is that there is an
additional magnetic anomaly below about 55 K before the onset of long range
order in the magnetic susceptibility data. Concurrent with this observation,
the sign of isothermal entropy change remains positive above TN with a broad
peak above TN. This observation indicates the presence of ferromagnetic
clusters before the onset of long range magnetic order. Thus, this compound may
serve as an example for a situation in which magnetic frustration due to
geometrical reasons is faced by competition with such precursor effects. There
is also a reversal of the sign of entropy-change in the curves for lower final
fields (for H less than 30 kOe) on entering into magnetically ordered state
consistent with the entrance into antiferromagnetic state. The
magnetoresistance behavior is consistent with above conclusions.
