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.
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.
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).
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
Two images related to this press release can be found online at: http://aktuell.ruhr-uni-bochum.de/pm2013/pm00144.html.en
Further informationProf. Dr. Hartmut Zabel
Hartmut Zabel | EurekAlert!
Move over, lasers: Scientists can now create holograms from neutrons, too
21.10.2016 | National Institute of Standards and Technology (NIST)
Finding the lightest superdeformed triaxial atomic nucleus
20.10.2016 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.
Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
21.10.2016 | Health and Medicine
21.10.2016 | Information Technology
21.10.2016 | Materials Sciences