Magnetic response function of the itinerant ferromagnet CeFe2

Neutron inelastic scattering experiments on single crystals of the itinerant ferromagnet CeFe2 show that there is a strong competition between the ferromagnetic ground state and an antiferromagnetic (AF) ground state with the wave vector q=[1/2 1/2 1/2]. The ferromagnetic spin wave has a small temperature-independent gap of 0.25 meV and a reduced (compared to other rare-earth Fez Laves phases) stiffness constant of D = 155(5) meV Angstrom(2). The strong fluctuations around the AF wave vector give rise to an AF spin-wave dispersion relationship that can be followed across the reduced AF Brillouin zone. The gap in the AF excitation spectrum is similar to 1 meV at 15 K and rises to similar to 5 meV above 100 K. At low temperature with a window of +/-20 GHz, we observe an apparent static AF component of similar to 0.05 mu(B) superimposed on the ferromagnetic component of 1.2 mu(B), per Fe atom. The spatial correlations of these AF fluctuations extend over many unit cells at low temperature. Our measurements have not detected any response directly from the Ce moments; so we assume that their response is spread over a wide energy range. Mossbauer spectra show an anomalous behavior of the Lamb-Mossbauer factor as a function of temperature and also show that the magnetic system is not saturated even at large (5 T) fields, suggesting that short-range AF order may persist to higher temperatures than the medium-range order observed in the neutron experiments. [S0163-1829(98)09241-8].