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We report investigations on the magnetic structure through the martensitic structural transformation in the GdCu system obtained by means of neutron-diffraction experiments. At room temperature, the as-cast bulk samples adopt a CsCl-type crystallographic structure, but when the temperature is lowered a martensitic structural transformation CsCl→FeB takes place at around 250 K propagating down to 120 K. After a thermal cycle through the forward and the reverse transformation, at room temperature the percentage of both phases is found to be ϳ25% for the CsCl-type structure and ϳ75% for the FeB-type one. In contrast, in powdered samples the CsCl-type phase is stable at any temperature. A comparative neutron thermodiffractometric study in both types of samples allows us to separate and investigate the magnetic behavior of these phases. The magnetic structure of the CsCl-type phase below T N CsCl ϭ150 K is most consistent with a simple antiferromagnetic one with a propagation vector Q CsCl ϭ(

We present evidence for the existence of magnetic clusters of approximately 20 A in the strongly correlated alloy system CeNi 1-x Cux (0.7