Magnetic Phase Transitions at Low Temperatures

Abstract

Magnetism is associated with the degree of freedom of electronic and nuclear spins. We shall defer the subject of nuclear magnetism to the end. Electronic magnetism in crystal lattices may be due to itinerant electrons, such as in metals and alloys, or to localized magnetic moments, such as in insulators. Unpaired electron spins at fixed lattice points may interact through direct exchange, superexchange, and dipolar interactions. In metals magnetic moments may interact over relatively long distances via the conduction electrons, i.e., the RKKY interaction. Do these interactions lead to phase transitions? It is experimentally known that phase transitions occur from the microkelvin to kilokelvin range, i.e., nine decades in the temperature scale.