Demagnetization by rapid spin transport

Jan 27, 2013

The fact that an ultrashort laser pulse is capable of demagnetizing a ferromagnetic layer in a jiffy has been well-known since approximately 1996. What we don't yet understand, however, is how exactly this demagnetization works. Now, physicist Dr. Andrea Eschenlohr and her colleagues at the Helmholtz Centre Berlin and Uppsala University in Sweden have shown that it turns out not to be the light pulse itself that prompts demagnetization.

For purposes of their research, the scientists irradiated two separate layered systems with ultrashort on the order of just one hundred femtoseconds (10-15s). One sample consisted essentially of a single thin layer of ferromagnetic nickel. By contrast, a second sample of this same nickel material was coated with a non-magnetic layer of gold. Only a mere 30 (10-9m) thick, the gold layer swallowed up the lion's share of the so that barely any light ended up reaching the nickel layer. In spite of this, the nickel layer's magnetization rapidly dissipated shortly after the laser pulse entered each sample. However, in the case of the gold-coated sample, the researchers recorded a split-second delay. The observations were based on measurements obtained using circularly polarized femtosecond x-ray pulses at BESSY II, Berlin's own electron storage ring, with the help of the femtoslicing beamline.

"This allowed us to demonstrate experimentally that during this process, it isn't the light itself that is responsible for the ultrafast demagnetization but rather hot electrons, which are generated by the laser pulse," explains Andrea Eschenlohr. Excited electrons are able to rapidly move across short distances - like the ultra-thin gold layer. In the process, they also deliver their (their "spin") to the ferromagnetic nickel layer, prompting the breakdown of the latter's magnetic order. "Actually, what we had hoped to see is how we might be able to influence the spin using the laser pulse," explains Dr. Christian Stamm, who heads the experiment. "The fact that we ended up being able to directly observe how these spins migrate was a complete surprise to everyone."

Laser pulses are thus one possibility to generate "spin currents" where the spin is transferred in place of an electric charge. This observation is relevant for spintronics research where scientists design new devices from magnetic layered systems, which perform calculations based on spins rather than electrons, enabling them to very quickly process and store information while at the same time saving energy.

Dr. Eschenlohr concluded her doctoral work at HZB, in the context of which she generated the results described above, in late 2012. As of January of this year, Dr. Eschenlohr is a scientific associate at University of Duisburg-Essen.

Explore further: Pseudoparticles travel through photoactive material

More information: "Ultrafast spin transport as key to femtosecond demagnetization" January 27, 2013, Nature Materials, doi: 10.1038/nmat3546

Related Stories

Graphene switches: Team makes it to first base

Nov 27, 2012

Ever since graphene was first isolated a few years ago, this quasi-two-dimensional network made up of a single layer of carbon atoms has been considered the magic material. Not only is graphene mechanically ...

A step forward for ultrafast spintronics

Sep 06, 2012

(Phys.org)—In spin based electronics the spin of the electron is used as a carrier of information. To meet the need for faster electronics, the speed must be increased as far as possible. Today, Uppsala physicists show ...

X-ray laser FLASH reveals fast demagnetisation process

Oct 03, 2012

(Phys.org)—Scientists from TU Berlin, DESY and the University of Paris discovered a surprising effect in the demagnetisation of ferromagnetic materials at DESY's free-electron laser FLASH. The team of researchers ...

Spin pumping effect proven for the first time

Sep 12, 2011

German physicists led by Prof. Dr. Hartmut Zabel have demonstrated the spin pumping effect in magnetic layers for the first time experimentally. The behaviour of the spin pumping had previously only been predicted theoretically. ...

Recommended for you

Pseudoparticles travel through photoactive material

Apr 23, 2015

Researchers of Karlsruhe Institute of Technology (KIT) have unveiled an important step in the conversion of light into storable energy: Together with scientists of the Fritz Haber Institute in Berlin and ...

From metal to insulator and back again

Apr 22, 2015

New work from Carnegie's Russell Hemley and Ivan Naumov hones in on the physics underlying the recently discovered fact that some metals stop being metallic under pressure. Their work is published in Physical Re ...

Electron spin brings order to high entropy alloys

Apr 22, 2015

Researchers from North Carolina State University have discovered that electron spin brings a previously unknown degree of order to the high entropy alloy nickel iron chromium cobalt (NiFeCrCo) - and may play ...

Expanding the reach of metallic glass

Apr 22, 2015

Metallic glass, a class of materials that offers both pliability and strength, is poised for a friendly takeover of the chemical landscape.

Electrons move like light in three-dimensional solid

Apr 22, 2015

Electrons were observed to travel in a solid at an unusually high velocity, which remained the same independent of the electron energy. This anomalous light-like behavior is found in special two-dimensional ...

Quantum model helps solve mysteries of water

Apr 20, 2015

Water is one of the most common and extensively studied substances on earth. It is vital for all known forms of life but its unique behaviour has yet to be explained in terms of the properties of individual ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

katesisco
1 / 5 (1) Jan 28, 2013
just thinking here: photons mazed inside a bh (LT starbody) reach a speed that grabs magnetism and eviscerates a bh leading to bleed out?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.