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Magnets have fascinated humans for several thousand years and enabled the age of digital data storage. They occur in various flavors. Ferrimagnets form the largest class of magnets and consist of two types of atoms. Similar to a compass needle, each atom exhibits a little magnetic moment, also called spin, which arises from the rotation of the atom's electrons about their own axes. In a ferrimagnet, the magnetic moments point in opposite directions for the two types of atoms (see panel A). Thus, the total magnetization is the sum of all magnetic moments of type 1 (M1) (blue arrows) and type 2 (M2) (green arrows). Due to the opposite direction, the magnitude of the total magnetization is M1-M2.
When an insulating ferrimagnet is heated, the heat is first deposited in the atomic lattice, which causes the atoms to move randomly around their cold positions. Finally, part of the heat also causes random rotation (precession) of the spins around their cold direction. Thus, magnetic order is lost; the total magnetization (M1-M2) decreases and eventually vanishes if the temperature of the ferrimagnet exceeds the so-called Curie temperature. Although this process is of fundamental importance, its dynamics are not well understood. Even for the ferrimagnet yttrium iron garnet (YIG), one of the most intensely researched ferrimagnets, it is unknown how long it takes until the heated atomic lattice and the cold magnetic spins reach equilibrium with each other. Previous estimates of this time scale differ from each other by a factor of up to 1 million.
Team - Scientists - Berlin - Collaborative - Research
A team of scientists from Berlin (Collaborative Research Center / Transregio 227 Ultrafast Spin Dynamics, Fritz Haber Institute and Max Born Institute), Dresden (Helmholtz Center), Uppsala (Sweden), St. Petersburg (Russia), and Sendai (Japan) have now revealed the elementary steps of this process.
"To instantaneously and exclusively heat up the atomic...
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