Posted on 14 April 2011
Scientists from Radboud University Nijmegen, Netherlands and the University of York demonstrated ultrafast magnetic reversal by a new and unconventional route, using thin films of an alloy of gadolinium-iron-cobalt (GdFeCo) and ultrafast heating with a laser.
The results, reported in the journal Nature, are among the fastest ever recorded for magnetic reversal.
The quicker a magnet can be reversed, the faster data can be recorded and processed. Using the current technology, data processing by a hard drive occurs in a nanosecond. The technique used by the international team has the potential to make this process between a hundred and a thousand times faster.
The behaviour of magnetic materials is governed by a quantum-mechanical effect - the exchange interaction - which causes neighbouring atomic magnetic moments, or ‘spins’, to align in parallel or opposite (antiparallel) directions. Atoms, in effect, act like spinning tops, some of them carrying a magnetic moment and the exchange interaction keeps the atoms pointing in the same direction. This spontaneous ordering of spins, and the ability to manipulate them using an external magnetic field, forms the basis for magnetic recording technologies.
This study is very important in terms of establishing the fundamental limits on the speed of magnetic recording and information processing
Professor Roy Chantrell
Professor Roy Chantrell, from the University of York’s Department of Physics, said: “Our study demonstrated that by using heat and gadolinium-iron-cobalt, there is the potential to make magnetic reversal occur much faster. This study is therefore very important in terms of establishing the fundamental limits on the speed of magnetic recording and information processing.”
The samples tested were made by Nihon University in Japan, while researchers from Radboud University Nijmegen carried out the ultrafast heating with a laser in collaboration with colleagues at the BESSY research facility in Berlin. Funding for the project came from the European Community’s Seventh Framework Programme.
Dr Alexey Kimel, from the Institute for Molecules and Materials at Radboud University Nijmegen, said: “Aiming to observe the ultimately fast magnetisation reversal we pushed the magnet into a regime that had not been described by any of the existing theories in magnetism. It became obvious that we had entered an unexplored territory - terra incognita of modern science.”
The most surprising discovery was of a completely unexpected transient state in which spins that are normally aligned in opposite (antiparallel) directions lined up parallel to one another for about 300 to 400 femtoseconds when heat was applied.
Professor Chantrell said: “The results of initial research carried out by our colleagues at Nijmegen were so unusual that they asked the York Theoretical Physics Team to simulate the research ‘blind’ with no prior knowledge of the outcome. Our calculations were in complete agreement. We have since given a theoretical explanation which has provided deep understanding of the underlying physics of the ultrafast magnetic phenomena.”