Phenomenological criteria for ferromagnetism and spin-density waves in Ce compounds and other narrow-band metals (abstract)

Recent data suggest that ferromagnetic Ce compounds are only found for a restricted range of Ce-Ce distance¹: 3.65 Å≤d≤3.83 Å. This hypothesis will be compared to the "R-γ*" correlation,² which states that magnetic order can only occur when the electronic heat capacity coefficient γ*≥γ^@B|_m ≊3.5×10⁴ erg cm^-3 K². Additional analysis suggests that, as a function of increasing γ*, weak ferromagnetism first occurs as γ* initially surpasses γ^*_m, yielding to antiferromagnetism at higher γ*. Materials such as URu₂Si₂ constitute evidence that a third region of spin-density-wave order preceeds that of ferromagnetism for γ*≊γ^@B|_m. Spin-density-wave order also competes with antiferromagnetism and coexists with heavy fermion superconductivity in the case of CeCu₂Si₂ and UPt ₃ (and possibly UBe₁₃) in a narrow region about γ*≊1×10⁵ erg cm^-3 K ². The temporary stability of ferromagnetism may be explained by the wave-vector dependence of the electronic self-energy that is responsible for heavy fermion behavior.