Extremely small magnetic nanostructures with invisibility cloak imaged

October 18, 2018

In novel concepts of magnetic data storage, it is intended to send small magnetic bits back and forth in a chip structure, store them densely packed and read them out later. The magnetic stray field generates problems when trying to generate particularly tiny bits. Now, researchers at the Max Born Institute (MBI), the Massachusetts Institute of Technology (MIT) and DESY were able to put an "invisibility cloak" over the magnetic structures. In this fashion, the magnetic stray field can be reduced in a fashion allowing for small yet mobile bits. The results were published in Nature Nanotechnology.

For physicists, magnetism is intimately coupled to rotating motion of electrons in atoms. Orbiting around the atomic nucleus as well as around their own axis, electrons generate the magnetic moment of the atom. The magnetic stray field associated with that magnetic moment is the property we know from e.g. a bar magnet we use to fix notes on pinboard. It is also the magnetic stray field that is used to read the information from a magnetic hard disk drive. In today's hard disks, a single magnetic bit has a size of about 15 x 45 nanometer, about of those would fit on a stamp.

One vision for a novel concept to store data magnetically is to send the magnetic bits back and forth in a memory chip via current pulses, in order to store them at a suitable place in the chip and retrieve them later. Here, the magnetic stray field is a bit of a curse, as it prevents that the bits can be made smaller for even denser packing of the information. On the other hand, the magnetic moment underlying the stray field is required to be able to move the structures around.

The researchers were now able to put an "invisibility cloak" on the magnetic nanostructures and to observe, how small and how fast such structures can get. To this end, different atomic elements with opposite rotation of the electrons were combined in one material. In this way, the magnetic stray field can be reduced or even completely cancelled - the individual atoms, however, still carry a magnetic moment but together appear cloaked.

In spite of this cloaking, the scientists were able to image the tiny structures. Via x-ray holography, they were able to selectively make only the magnetic moments of one of the constituent elements visible - in this way an image can be recorded in spite of the invisibility cloak.

It became apparent, that fine tuning of the strength of the invisibility cloak allows to simultaneously meet two goals which are of importance for potential applications in data storage. "In our images, we see very small, disk-like magnetic structures", says Dr. Bastian Pfau from MBI. "The smallest structures we observed had a diameter of only 10 nanometer." The information density of today's hard disk drives could be significantly increased, if such structures could be used to encode the data. Furthermore, in additional measurements the researchers realized that suitably cloaked bits can be moved particularly fast by short current pulses - an important property for actual use in a memory device. A velocity higher than 1 kilometer per second was reached in the MIT laboratory.

"This is possible as a consequence of quantum physics", explains Prof. Stefan Eisebitt from MBI. "The contribution of the electron's orbit around the nucleus to the magnetic moment is only half as large as the contribution of the electron's spin around its own axis." When combining different atom types with different direction and strength of this rotation in one material, one can cancel the total rotation - physicists talk about the total angular momentum - of the system, while still retaining a small magnetic moment. As the angular momentum leads to a drag when moving the structures via current pulses, this approach allows for high speed motion. Hence, if the strength of the invisibility cloak is adjusted just right, both small size and high speed of the magnetic bit structures can be achieved - an interesting prospect for novel magnetic data storage concepts.

Forschungsverbund Berlin

Related Electrons Articles from Brightsurf:

One-way street for electrons
An international team of physicists, led by researchers of the Universities of Oldenburg and Bremen, Germany, has recorded an ultrafast film of the directed energy transport between neighbouring molecules in a nanomaterial.

Mystery solved: a 'New Kind of Electrons'
Why do certain materials emit electrons with a very specific energy?

Sticky electrons: When repulsion turns into attraction
Scientists in Vienna explain what happens at a strange 'border line' in materials science: Under certain conditions, materials change from well-known behaviour to different, partly unexplained phenomena.

Self-imaging of a molecule by its own electrons
Researchers at the Max Born Institute (MBI) have shown that high-resolution movies of molecular dynamics can be recorded using electrons ejected from the molecule by an intense laser field.

Electrons in the fast lane
Microscopic structures could further improve perovskite solar cells

Laser takes pictures of electrons in crystals
Microscopes of visible light allow to see tiny objects as living cells and their interior.

Plasma electrons can be used to produce metallic films
Computers, mobile phones and all other electronic devices contain thousands of transistors, linked together by thin films of metal.

Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.

Researchers develop one-way street for electrons
The work has shown that these electron ratchets create geometric diodes that operate at room temperature and may unlock unprecedented abilities in the illusive terahertz regime.

Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.

Read More: Electrons News and Electrons Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.