Spin-glass freezing above the ordering temperature for the Kondo ferromagnet CeNi0.4Cu0.6

The low-temperature magnetic and transport properties of the orthorhombic CeNi0.4Cu0.6 compound have been determined from the analysis of specific heat, ac magnetic susceptibility, electrical resistivity, elastic and inelastic neutron scattering. These measurements present intriguing experimental results that could not be explained within the usual phenomenology of Ce-based compounds. C-p and chi(ac) present anomalies around 1 K corresponding to ferromagnetic order as confirmed by neutron diffraction. The magnetic structure is collinear with very reduced moments, 0.6 mu(B)/Ce lying in the b direction. Additionally, a clear Kondo behavior is observed with a Kondo temperature T-K=1.9 K estimated from quasielastic neutron scattering. Above the ordering temperature, further anomalies are observed in C-p and chi(ac) that could not be explained as originating from crystal electric field or Kondo effects. From the frequency and field dependence of the chi(ac), above T-c, a spin-glass state with a freezing temperature T-f=2 K is proposed for this compound. This unusual magnetic behavior is discussed in terms of mixed (positive and negative) Ruderman-Kittel-Kasuya-Yosida interactions, randomness (structural disorder), large hybridization (Kondo effect), and strong magnetocrystalline anisotropy (crystal electric field effects). [S0163-1829(97)05242-9].