Spin pumping effect proven for the first time

September 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. The research team at the Ruhr-University Bochum 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 spinning tops", as Bochum's research group confirmed in its experiments.

Magnetic rotation in the gigahertz range

Once triggered, the rotate in a until their rotation energy is exhausted through of and 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 in the read heads of hard disks and which encode the logical bits "0" and "1" in non-volatile magnetic . 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.

Explore further: Nanoscale Dominoes: Magnetic Moments Topple Over in Rows

More information: 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, 092509 (2011), DOI: 10.1063/1.3633115

Related Stories

Nanoscale Dominoes: Magnetic Moments Topple Over in Rows

September 24, 2008

Physicists at the Institut für Festkörperforschung in Germany have discovered a type of domino effect in rows of individual manganese atoms on a nickel surface. They determined that the magnetic arrangement of these nanowires ...

Electric control of aligned spins improves computer memory

January 19, 2010

Researchers from Helmholtz-Zentrum Berlin (HZB, Germany) and the French research facility CNRS, south of Paris, are using electric fields to manipulate the property of electrons known as "spin" to store data permanently. ...

Half-a-loaf method can improve magnetic memories

August 24, 2010

Chinese scientists have shown that magnetic memory, logic and sensor cells can be made faster and more energy efficient by using an electric, not magnetic, field to flip the magnetization of the sensing layer only about halfway, ...

Creating a pure spin current in graphene

February 7, 2011

(PhysOrg.com) -- Graphene is a material that has the potential for a number of future applications. Scientists are interested in using graphene for quantum computing and also as a replacement for electronics. However, in ...

Recommended for you

Scientists float new approach to creating computer memory

October 8, 2015

What can skyrmions do for you? These ghostly quantum rings, heretofore glimpsed only under extreme laboratory conditions, just might be the basis for a new type of computer memory that never loses its grip on the data it ...

Fusion reactors 'economically viable' say experts

October 2, 2015

Fusion reactors could become an economically viable means of generating electricity within a few decades, and policy makers should start planning to build them as a replacement for conventional nuclear power stations, according ...


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.