A beam of ions has been used to successfully engrave magnetic regions into an alloy with a resolution of 10 atoms. This new method of producing nanoscale magnets could be widely used in the electronics industry.
Lines of magnetic flux of the nanomagnets, generated by ion beam. Source: TU Dresden/Falk Röder.
The team found that an ultra-fine beam, only 10 neon ions wide, was capable of making hundreds of iron-aluminum alloy atoms become disordered, and this enabled the direct embedding a nanomagnet into a layer of the material.
Researchers used a special holographic technique with a transmission-electron microscope (TEM), which allowed the researchers to see the magnetic field lines and allowed the researchers to measure the exact dimensions of the nanomagnets.
Physicist Dr. Rantej Bali wanted to find out new ways to miniaturizing magnets. An iron-aluminum alloy was chosen as the candidate as they demonstrate paramagnetism when in its ordered state. This means that when atoms occupy localized positions the spin (a quantum mechanical property that is linked to magnetism) of electrons in the material is randomly oriented, meaning they are decoupled and no magnetism is observed.
Whereas, ferromagnetic materials are made up of coupled spins, meaning they display magnetism.
Nanosized ferromagnets are widely used in magnetoresistive random access memory (MRAM) devices and in computer hard drives. The nanomagnets enable the reading and storage of binary information.
Using ion beams to write magnets onto alloy layers directly is a new method. The team at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) successfully fabricated nanomagnets, without using a lithography mask, in an iron-aluminum layer material layer that was as thin as a wafer.
With our highly focused ion beam, which we use like a magnetic stylus, we can very quickly generate prototypes of complex magnetic geometries
Dr. Rantej Bali - HZDR
All of the electron spins in iron point in the same direction meaning the material is ferromagnetic. However, in iron-aluminum alloys aluminum atoms are adjacent to many iron atoms which decouples the spins of iron and meaning the material is paramagnetic.
Bombardment of the alloy with ions creates chaos in its atomic arrangement and leads to disorder. This causes iron atoms to be in closer proximity to each other and interact more. This specific area becomes ferromagnetic as the spins of the electrons align in the same direction. This means it is possible to create localized regions of magnetism on the alloy at a high resolution.
According to theory, a single ion should have the capability to generate a nanomagnet in Fe60Al40 iron-aluminum alloy.
It is the same as in a game of billiards where one single ball can set a cascade in motion. We have calculated that one ion can displace up to 300 atoms. The team used a special ion microscope for these experiments. Just six neon atoms are implanted in an area measuring one square nanometer. "For our magnets we scan the sample with a beam of just two nanometers in diameter. Thus we generate a sequence of ferromagnetic stripes with narrow paramagnetic spacings.
Dr. Gregor Hlawacek - HZDR
The researchers intend to further their study on single ion effects and explore magnetism in disordered materials.
The research titled, "Direct Depth- and Lateral-Imaging of Nanoscale Magnets Generated by Ion Impact," has been published in the journal Scientific Reports.