||We report high magnetic field magnetostructural studies on Gd2/3Ca1/3MnO3
single crystals. A giant linear magnetostrictive effect is observed in a wide temperature range
(T < 120 K). Above 25 K a large hysteresis is seen reflecting the Mn magnetic moments
ordering. At lower temperature (T < 15 K), a rather complicated field dependence arising from
the competition between the Mn and Gd magnetic sublattices is observed. The relevance of the
Gd ions in the low temperature behavior is further corroborated by specific heat experiments.