Field-dependent specific heat in Fe2VAl and the question of possible 3d heavy fermion behavior

Specific heat measurements on Fe2VAl show the previously reported upturn in electronic specific heat coefficient (gamma) to be sample dependent, and related to magnetic defects. These measurements, in temperatures as low as 0.6 K and magnetic fields up to 8 T, indicate the presence of Schottky anomalies arising from magnetic clusters having a moment 37 mu(B). This result is in good agreement with theoretical estimates for Fe antisite defects in the material. The inherent gamma=1.5+/-0.3 mJ/mol K-2 deduced from this work is considerably less than previously reported, and the behavior does not appear consistent with heavy fermion behavior. However, the mass enhancement is significant when compared to nuclear magnetic resonance and band calculations, and we propose a spin-fluctuation mechanism. [S0163-1829(99)51444-6].