Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Chain instead of zigzag: RUB physicists let magnetic dipoles interact on the nanoscale

16.05.2013
Of great technical interest for future hard disk drives

Physicists at the Ruhr-Universität Bochum (RUB) have found out how tiny islands of magnetic material align themselves when sorted on a regular lattice - by measurements at BESSY II. Contrary to expectations, the north and south poles of the magnetic islands did not arrange themselves in a zigzag pattern, but in chains.

“The understanding of the driving interactions is of great technological interest for future hard disk drives, which are composed of small magnetic islands”, says Prof. Dr. Hartmut Zabel of the Chair of Experimental Physics / Solid State Physics at the RUB. Together with colleagues from the Helmholtz-Zentrum in Berlin, Bochum’s researchers report in the journal “Physical Review Letters”.

Complete chaos in the normal state

Many atoms behave like compass needles, that is, like little magnetic dipoles with a north and a south pole. If you put them close together in a crystal, all the dipoles should align themselves to each other, making the material magnetic. However, this is not the case. A magnetic material is only created when specific quantum mechanical forces are at work. Normally, the forces between the atomic dipoles are by far too weak to cause magnetic order. Moreover, even at low temperatures, the thermal energy causes so much movement of the dipoles that complete chaos is the result. “However, the fundamental question remains of how magnetic dipoles would align themselves if the force between them was big enough”, Prof. Zabel explains the research project.

Square lattice of magnetic islands

To investigate this, the researchers used lithographic methods to cut circular islands of a mere 150 nanometers in diameter from a thin magnetic layer. They arranged these in a regular square lattice. Each island contained about a million atomic dipoles. The forces between two islands were thus stronger by a factor of a million than that between two single atoms. If you leave these dipoles to their own resources, at low temperatures you can observe the arrangement that results exclusively from the interaction between the dipoles. They assume the most favourable pattern in terms of energy, the so-called ground state. The islands serve as a model for the behaviour of atomic dipoles.

Magnetic microscopy

The electron synchrotron BESSY II at the Helmholtz-Zentrum in Berlin is home to a special microscope, the photon emission electron microscope, with which the RUB physicists made the arrangement of the magnetic dipole islands visible. Using circularly polarised synchrotron light (X-ray photons), the photons stimulate specific electrons. These provide information on the orientation of the dipoles in the islands. The experiments were carried out at low temperatures so that the thermal movement could not interfere with the orientation of the dipoles.

Dipoles arrange themselves in chains

The magnetic dipoles formed chains, i.e. the north pole of one island pointed to the south pole of the next island. “This result was surprising”, says Zabel. In the lattice, each dipole island has four neighbours to which it could align itself. You cannot tell in advance in which direction the north pole will ultimately point. “In fact, you would expect a zigzag arrangement”, says the Bochum physicist. Based on the chain pattern observed in the experiment, the researchers showed that higher order interactions determine how the magnetisation was oriented. Not only dipolar, but also quadrupolar and octopolar interactions play a role. This means that a magnetic island exerts forces on four or eight neighbours at the same time.

Magnetic islands in the hard drives of the future

In future, hard disks will be made up of tiny magnetic islands (bit pattern). Each magnetic island will form a storage unit which can represent the bit states “0” and “1” - encoded through the orientation of the dipole. For a functioning computer, you need a configuration in which the dipole islands interact as little as possible and can thus assume the states “0” and “1”independently of each other. For the technical application, a precise understanding of the driving interactions between magnetic islands is therefore crucial.

Funding

The German Research Foundation (DFG) supported the work in Bochum within the Collaborative Research Centre (SFB) 491 „Magnetic hetero-structures: spin structures and spin transport“; BESSY II at the Helmholtz-Zentrum Berlin is supported by the Federal Ministry of Education and Research (BMBF).

Bibliographic record

M. Ewerlin, D. Demirbas, F. Brüssing, O. Petracic, A.A. Ünal, S. Valencia, F. Kronast, H. Zabel (2013): Magnetic Dipole and Higher Pole Interaction on a Square Lattice, Physical Review Letters, DOI: 10.1103/PhysRevLett.110.177209

Figures online

Two images related to this press release can be found online at:
http://aktuell.ruhr-uni-bochum.de/pm2013/pm00144.html.en

Further information

Prof. Dr. Hartmut Zabel, Chair of Experimental Physics / Solid State Physics at the Ruhr-Universität, 44780 Bochum, Germany, Tel. +49/234/32-23649, E-mail: hartmut.zabel@rub.de

Editor: Dr. Julia Weiler

Dr. Josef König | idw
Further information:
http://www.ruhr-uni-bochum.de

More articles from Physics and Astronomy:

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

nachricht What do Netflix, Google and planetary systems have in common?
02.12.2016 | University of Toronto

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>