Paramagnetism and ferromagnetism

We use magnets every day. Their magnetism actually has a quantum origin. It arises from the arrangement of the spins of atoms which form an ordered state.

Some atoms have a quantum degree of freedom, the spin, which acts like a small magnet. At high temperatures, the spins are disordered and the materials do not appear magnetic. When the temperature is lowered, a sudden change of state takes place corresponding to an ordering of the spins. If all the spins line up in the same direction, matter spontaneously becomes magnetized and we speak of a ferromagnetic state. The spins are not, however, completely frozen in one direction; Magnetic waves pass through the material, called spin waves, which lower the magnetization of a magnet when it is heated.

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High Magnetic Field setup at LNCMI (Grenoble)