Spin pumping effect proven for the first time: Applied Physics Letters reports

ALICE test chamber built by RUB physicists in Berlin<br>

Bochum’s 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.

The research team at the RUB has now succeeded in measuring the effect using ultrafast X-ray scattering with picosecond resolution. Through their rotation of the magnetic moments, the so-called magnetic precession, single electrons can mutually influence each other’s rotation (spin) through a non-magnetic intermediate layer.

This is a crucial insight for future generations of magnetic sensors in hard disk read heads and other data storage. The researchers reported on their findings in Applied Physics Letters.

Magnetic spinning tops are different

Once put into motion and left to itself, a spinning top will slow down after a few rotations and eventually come to a halt. Friction losses deprive it of energy, until it finally stops spinning. Also, two spinning tops put at a certain distance to avoid touching show by and large the same behaviour. “In particular, we do not expect that one spinning top can affect the rotation of the other”, said Prof. Hartmut Zabel. Whether both tops rotate in the same or in the opposite direction, should have no impact on the number of rotations before they come to a stop. “But that's precisely what happens with magnetic spinning tops”, as Bochum’s research group confirmed in its experiments.

Magnetic rotation in the gigahertz range

Once triggered, the magnetic moments rotate in a crystal lattice until their rotation energy is exhausted through excitation of lattice vibrations and spin waves. Spin waves are excitations of the magnetic moments in a crystal, which propagate in form of waves. The research team separated two ultra-thin magnetic layers with a layer of copper. The copper layer was made thick enough that the two ferromagnetic layers can have no influence on each other – at least no static influence. However, once one of the two ferromagnetic layers is stimulated to a very fast precession in the gigahertz range, the damping of the precession depends of the orientation of the second magnetic layer. If both layers have the same orientation, then the damping is lower. If both are oriented in opposite directions, then the damping is higher.

Dynamic interaction

Up to now, it had not been possible to research the effect described as “spin-pumping” experimentally. The scientists have now been able to demonstrate the effect in the ALICE test chamber built by RUB physicists in Berlin. The precession of the magnetic moments in a ferromagnetic layer is “pumped” through the non-magnetic intermediate copper layer and absorbed by the second ferromagnetic layer. In other words, ferromagnetic layers, which do not interact with each other statically because the intermediate layer is too thick, are still able to “affect” each other dynamically through pumping and diffusion of spins from one layer to another.

A typical “spin valve” in data storage

The sequence of layers selected in the experiment is that of a typical spin valve. These are nano-magnetic layer structures which are used as magnetic sensors in the read heads of hard disks and which encode the logical bits “0” and “1” in non-volatile magnetic data storage. The speed at which data can be read and written, depends crucially on the precession of the magnetic moments and their damping. “Therefore, the finding that the damping of the magnetic precession is influenced by spin pumping through non-magnetic intermediate layers is not only of fundamental but also of practical interest for industrial applications” said Professor Zabel.

Bibliographic record

R. Salikhov,R. Abrudan, F. Brüssing, St. Buschhorn, M. Ewerlin, D. Mishra, F. Radu, I. A. Garifullin, and H. Zabel, “Precessional Dynamics and Damping in Co/Cu/Py Spin Valves”, Applied Physics Letters Vol. 99, page 092509 (2011), DOI: 10.1063/1.3633115

Further information

Prof. Dr. Hartmut Zabel, Chair for Experimental Physis / Solid State Physics at the Ruhr-Universität Bochum, tel. +49 234 32 23649, e-mail: hartmut.zabel@rub.de

Editor: Jens Wylkop

Media Contact

Dr. Josef König idw

All latest news from the category: Physics and Astronomy

This area deals with the fundamental laws and building blocks of nature and how they interact, the properties and the behavior of matter, and research into space and time and their structures.

innovations-report provides in-depth reports and articles on subjects such as astrophysics, laser technologies, nuclear, quantum, particle and solid-state physics, nanotechnologies, planetary research and findings (Mars, Venus) and developments related to the Hubble Telescope.

Back to home

Comments (0)

Write a comment

Newest articles

Lighting up the future

New multidisciplinary research from the University of St Andrews could lead to more efficient televisions, computer screens and lighting. Researchers at the Organic Semiconductor Centre in the School of Physics and…

Researchers crack sugarcane’s complex genetic code

Sweet success: Scientists created a highly accurate reference genome for one of the most important modern crops and found a rare example of how genes confer disease resistance in plants….

Evolution of the most powerful ocean current on Earth

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets….

Partners & Sponsors