Louis Néel

Louis Néel (1904–2000) was a French physicist whose theories of antiferromagnetism and ferrimagnetism transformed the study of magnetic materials. He received the 1970 Nobel Prize in Physics.

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Magnetism: The physical phenomena produced by moving electric charges and magnetic moments. Néel studied how atomic magnetic moments organize within materials.
Néel temperature: The temperature above which an antiferromagnet loses its long-range magnetic order. Néel predicted the transition separating ordered antiferromagnetism from paramagnetism.
Pierre Weiss: A French physicist known for the molecular-field theory of ferromagnetism. Weiss’s ideas supplied a framework Néel adapted to explain antiferromagnetic order.
Ferrite: A ceramic material composed chiefly of iron oxide combined with other metallic elements. Ferrites exhibit magnetic orders that Néel’s framework helped classify and explain.
Magnetic moment: A vector quantity describing the strength and direction of a magnetic source. His theories describe how atomic moments align or oppose one another.
Curie–Weiss law: A relation describing magnetic susceptibility as a function of temperature in a paramagnet. Néel extended the interpretation of magnetic behavior beyond the simple ferromagnetic case.
Hendrik Casimir: A Dutch physicist whose work included theoretical physics and statistical mechanics. Casimir’s research intersected with the theoretical development of magnetic ordering.
Magnetic recording: The storage of information by changing magnetic states in a recording medium. Understanding magnetic domains and stability supported the development of recording materials.
Ferromagnetism: Magnetic order in which neighboring moments align, producing spontaneous magnetization. Néel’s theories addressed magnetic behaviors that differ from this familiar order.
Molecular field theory: An approximation that treats each magnetic moment as responding to an average field from its surroundings. Néel used molecular-field reasoning to develop theories of ordered magnetic states.