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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

CeNi 1−x Cu x is a substitutional magnetic system where the interplay of the different magnetic interactions leads to the disappearance of the long-range magnetic order on the CeNi side. The existence of inhomogeneities ͑spin clusters or phase coexistence͒ has been previously detected by magnetization and muon spin relaxation ͑SR͒ spectroscopy measurements. These inhomogeneities are always observed regardless of the different preparation methods and must, then, be considered as intrinsic. We present a detailed specific heat study in a large temperature range of 0.2 to 300 K. The analysis of these data, considering also previous neutron scattering, magnetic characterization, and SR results, allows us to present a convenient description of the system as inhomogeneous on the nanometric scale. Two regimes are detected in the compositional range depending on the dominant Ruderman-Kittel-Kasuya-Yosida or Kondo interactions. We propose that the longrange magnetic order at low temperatures is achieved by a percolative process of magnetic clusters that become static below the freezing temperature T f . In this scenario the existence of a quantum critical point at the magnetic-nonmagnetic crossover must be discarded. This situation should be considered as an example for other substitutional compounds with anomalous magnetic or superconducting properties.