A re-examination of concepts in magnetic metals: The 'nearly antiferromagnetic Fermi liquid'

Attempts to draw parallels between the ferromagnetic spin fluctuations of nearly ferromagnetic Fermi liquids, and the new concept of antiferromagnetic spin fluctuations in 'nearly antiferromagnetic' Fermi liquids are examined. It is argued that exchange interactions in Fermi liquids are normally purely ferromagnetic and that antiferromagnetic exchange and antiferromagnetic fluctuations arise from the breakdown of the Fermi-liquid theory as in the Mott insulator. Spin-density waves distinct phenomenon caused by umklapp effects, unrelated to local antiferromagnetic exchange interactions, and lead only to minor fluctuation effects. Experimental evidence is cited in favour of this dichotomy between two different causes for antiferromagnetism.