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Néel, Louis (Eugène Félix)

magnetic ferrite antiferromagnetism antiferromagnetic

[nayel] (1904–2000) French physicist: discovered antiferromagnetism.

Néel graduated from the École Normale Supérieure and worked under P Weiss (1865–1940) at the University of Strasbourg. In 1940 he moved to Grenoble and became the driving force in making it one of the most important scientific centres in France, becoming director of the Centre for Nuclear Studies there in 1956.

Néel’s research was concerned with magnetism in solids. He predicted in 1936 that a special type of magnetic ordering called ‘antiferromagnetism’ should exist. Whereas unpaired electron spins align in a ferromagnet (eg Fe), they are arranged up-down-up-down from site to site in an antiferromagnetic lattice (eg in FeO). Above a critical temperature, the Néel temperature, the antiferromagnetic substance then becomes paramagnetic. This was experimentally confirmed in 1938, with full neutron diffraction confirmation in 1949. Néel also first suggested (1947) that antiferromagnetism Page 268  could occur with unequal up-and-down moments (ferrimagnetism) as in some ferrites. (These ceramics are important in magnetic devices such as the record–erase heads in audiotape and videotape recorders, and computer hard disk drives. The paint used on stealth aircraft contains ferrite crystals, which absorb radar signals, conferring invisibility to radar detection. An ancient ferrite is lodestone, used in primitive compasses.) The magnetic domains foreseen by Néel were imaged in 2000 in a ferrite, lanthanum iron oxide, and found to be a few hundred nanometres in size. Néel was awarded the Nobel Prize for physics in 1970. He also studied the past history of the Earth’s magnetic field.

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