Louis Neel (1904-2000): Last pioneer of classical magnetism

LOUIS NEEL was born on November 22, 1904 in Lyon, France. He graduated in 1927 from the prestigious school ENS (Ecole Normale Superieure), Paris. He then joined the University of Strashourg. He chose the not so modern topic of classical magnetism for investigation, in Pierre Weiss' laboratory. He was appointed professor at the University, a position he held until 1945.

With the out break of World War II, he was enlisted in 1939 to improve the French Naval Defence. His innovation for protecting ships against magnetic mines saved the lives of thousands of soldiers.

Building a chain of Laboratories

At the end of the War (1945), he moved to the University of Grenoble. He was asked to establish the first national laboratory outside Paris, known as the CNRS Laboratory. The institution which he directed, expanded rapidly; and in 1970 it grew into separate laboratories for the study of electro-statics, very low temperatures (cryogenics) their films, crystallography and magnetism. On his retirement in 1976, the Magnetism Laboratory was renamed ``Louis Neel Laboratory'', in recognition of his pioneering work.

Neel created numerous other laboratories such as Nuclear Research Centre, Lane-Langevin Institute, European Radiation Synchrotrons Facility. Thus he succeeded in building new institutions to reverse the brain drain to Paris, the capital, which he saw at the beginning of his career.

Three years after moving to Grenoble, he started research work in new directions, building on his earlier work done in Strasbourg. This embraced topics such as the magnetism of thin films and the random aspects of magnetic hysteresis. It has long been known that ferrites, a class of materials exhibit anomalous magnetic behaviour in relation to ferro- magnetic substances with which they were then classified Neel concluded that ferrites would form a separate class.

He proposed initially a theory of antiferromagnetism and presented a model for crystals built up from two inter-laced lattices with equally strong magnetic fields in opposite directions. Thus he showed that Zero net magnetisation would occur below a certain temperature, now know as the Neel point (in analogy with the Curie point).

Theory of Ferromagnetism

Neel expanded his earlier theory of antiferromagnetism and proposed another form of magnetisation, which he named ``ferrimagnetism''. This allowed the properties of ferrites and garnets to be understood.

Ferrites, which are not electrical conductors, have since proved extremely useful in the coating of magnetic tape, in computer memory cores and in communication technology. The production of synthetic ferrites for such purposes resulted largely from Neel's research.The research directions that he initiated are now intensely pursued by his collaborators at Grenoble: magnetic creep, namely changes that occur in ferromagnetism over time; the properties of fine-grained ferromagnetic substances (nanomagmetism); methods for improving the magnetic properties of materials, the magnetic memory of rocks during changes in the earth's magnetic field. (paleomagnetism).Neel received several honours and honorary degrees for his fundamental contributions. Physics and magnetism played a dominant role in his life. The day before his death (November 17, 2000) he was preparing a TV programme for the French Academy of Sciences.

His recreations were diverse; taking long walks through the countryside, reading French literature of the 18th century and carpentry. In a tribute to his passion for research the journal Science (Vol. 291, 9 February 2001) says: ``He inspired his former students, and their students, with an eagerness that is not ready to fade. At the height of his career, Neel greatly impressed young researchers, so great was his prestige and so elegant his manner.

During one of his weekly seminars for young physicists that he organised at the Laboratory of Magnetism, he blurted out ``If I were you, I could not go to sleep before managing to explain this phenomenon.''

R. Parthasarathy

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