Neel, << nay EHL, >> Louis-Eugene-Felix (1904-2000), a French physicist, made important discoveries in the field of magnetism. His work gave rise to such applications as the coating of magnetic recording tape and magnetic computer storage. Neel developed the concepts of antiferromagnetism and ferrimagnetism, which explain the magnetic properties of certain materials based on the arrangement of their atoms. For this work, Neel was awarded half of the 1970 Nobel Prize in physics. The other half went to Swedish physicist Hannes Alfven for unrelated work.
The magnetism of materials arises from the combined magnetism of the atoms making it up. Each atom, or group of atoms, is a tiny magnet. A phenomenon known as ferromagnetism is the type of magnetism shown by iron. The atomic magnets pull on each other, with the result that groups of atoms become lined up with each other, forming an arrangement called a domain. The magnetic fields of the different domains are normally jumbled and cancel each other out. However, they can be lined up by the pull of an outside magnetic field. As more and more domains point in roughly the same direction, they produce a stronger and stronger total magnetism. If the material is heated, causing the atoms to vibrate faster, the atoms no longer line up, and the overall magnetism is lost.
Neel discovered that some materials, such as manganese fluoride, show antiferromagnetism. At low temperatures, the atoms line up in opposite directions, so that their magnetism cancels out. However, when the substance is heated above a temperature known as the Neel temperature, the grip of the atoms on each other is loosened, and they can line up under the influence of an external magnetic field.
Neel also discovered ferrimagnetism, a special form of antiferromagnetism in which the atomic magnets pointing in opposite directions are not of equal strengths. An antiferromagnetic material is magnetized even at lower temperatures, while at higher temperatures its magnetization depends on the magnetic field in which it is placed in.
Neel was born in Lyon and studied at the Ecole Normale Superieure in Paris, where he also taught for some years. He received his Ph.D. in physics at the University of Strasbourg in France in 1932. He served as a professor there beginning in 1937. At Strasbourg, Neel studied magnetism and did the work that was to bring him the Nobel Prize. Neel put his expertise to use when World War II broke out in 1939, inventing a defense for ships against magnetic mines. In 1945, he went to Grenoble, France, and established a laboratory concerned with the physics of metals. From 1956 to 1971, he served as director of the Center for Nuclear Studies at Grenoble.
