Couplings of the gadolinium spin system. (a) The interaction of the different heat baths in an extended three-temperature model. After infrared laser excitation of the valence electrons, the whole system equilibrates by exchanging energy and momentum, indicated by the double arrows. The 5d and 4f spin systems couple via inter- and intra-atomic exchange, where the intra-atomic exchange Jint=130 meV is much larger than the largest (nearest neighbour) inter-atomic exchange Jij=5.9 meV. In thermal equilibrium, the combination of inter- and intra-atomic exchange interactions mediates spin order in the 4f system via the delocalized 5d valence bands. Upon femtosecond laser excitation, the dynamics of the 5d spin system is dominated by the coupling αe to the hot valence electrons described by temperature Te, while the localized 4f spins couple only to the phonon bath at temperature Tp via αp. (b) The binding energy versus parallel momentum map EB(k||) of Gd recorded with higher-order harmonic radiation (photon energy 36.8 eV) in time- and angle-resolved photoemission gives simultaneously access to the transient exchange splitting of the 5d minority and majority spin bands (↓ and ↑, respectively) and the magnetic linear dichroism of the localized 4f state. Data are plotted on the displayed normalized false colour scale.
Future computers will require a magnetic material which can be manipulated ultra-rapidly by breaking the strong magnetic coupling. Scientists have now demonstrated that even the strongest magnetic coupling may be broken within picoseconds (10-12s). This will open up an exciting new area of research.
Gadolinium is named after Uppsala chemist Johan Gadolin who discovered the 1st rare-earth metal yttrium in the late 1700s. Gadolinium is in the same class of elements and it has unique magnetic properties which make it especially interesting for magnetic data storage. Its most useful property is that it has the greatest spin magnetic moment of any element since there are 2 different magnetic moments on every atom. These spin moments are coupled in parallel so strongly that no existing magnetic field on earth could break the coupling.
An international collaboration between Karel Carva and Peter Oppeneer from Uppsala University, and researchers from Free University Berlin and Konstanz University in Germany has shown that it is possible to break the coupling between the spin moments.
Orbital-resolved spin dynamics in gadolinium.
METHOD: They use light pulses shorter than picoseconds to excite metallic gadolinium and then monitored the spin dynamics of both spin moments with ultra-short, high-energy x-ray flashes. The spin dynamics they revealed showed that the strong coupling was broken within picoseconds (10-12 s) and it remained uncoupled for almost 100 picoseconds. The theoretical calculations of the Uppsala researchers provided a detailed explanation of how this fundamental magnetic interaction can be overcome.
“Not too long ago it became clear that the weaker coupling between spin moments on different atoms of a material can be broken. We’ve now shown that even the stronger spin magnetic coupling within an individual atom can be overpowered. This provides new opportunities to manipulate magnetic materials and opens new paths to the data storage of the future,” says professor Peter Oppeneer. http://www.uu.se/en/media/press-releases/press-release/?id=2818&area=3,8&typ=pm&lang=en
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