Rust as an alternative to silicon in computer technology

Scientists working at Diamond Light Source, the UK’s national synchrotron, have developed a method of using iron oxide as an alternative to silicon in computer technology.

Information and communications technology (ICT) is projected to use over 20% of global electricity production by 2030. Therefore, finding ways to decarbonise technology is an obvious target for researchers. Working with Diamond Light Source, Professor Paolo Radaelli from Oxford’s Department of Physics has been leading research into an alternative to silicon, which is very energy inefficient.

As published in Nature, Radaelli’s group discuss how some of the antiferromagnetic textures they have found could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature.

Researchers have been working for a long time on alternative technologies to silicon. Oxides of common metals such as iron and copper are natural targets because they are already a technology staple, present in silicon-based computers. Although oxides are great to store information, they are not good at transporting it. One property of oxides that has emerged is that many are magnetic which means it might be possible to move magnetic ‘bits’ around, both in oxides and in other magnets, with very little energy required.

Radaelli explains: “The kinds of bits we are talking must be really tiny – ten nanometres (ten billionths of a metre) is the typical target figure – and must be robust even when ‘shaken and stirred’. This is very challenging, because the risk of them being simply dissipated away is very high when the bit is so small. One possible solution came from the most unlikely of directions: a curious parallel between solid-state physics and cosmology. In fact, the inspiration for this project was set in the form of a challenge: Can we replicate cosmic strings in a magnet?”

Antiferromagnet rust

Iron oxide (Fe₂O₃) is a main constituent of rust. Each iron atom acts as a tiny compass, but this particular form of Fe₂O₃ is not magnetic in the ordinary sense of attracting and being attracted by other magnets: it is an antiferromagnet, so that half of the Fe compasses point ‘north’ and the other half ‘south’.

Two years ago, working at Diamond on samples produced at University of Wisconsin, Madison, Prof. Radaelli’s Oxford group discovered the magnetic equivalent of cosmic strings in Fe₂O₃, and imaged them using a powerful X-ray microscope. These tiny objects known as ‘merons’ are magnetic whirls, where the compass needle rotates (NESW or NWSE) as one moves from one atom to the next in a nanometre-scale loop.

Radaelli said: “With hindsight, finding magnetic merons was a huge stroke of luck, since we know that they are very difficult to stabilise in the conditions used for that first experiment. For the paper published today, we extended our collaboration to the National University of Singapore and managed to find the key to create and destroy magnetic merons at will, exploiting the mathematical equivalent of the ‘Big Bang cooling’.”

Rust as an alternative to silicon

The team believe that their rust-based technology could help create super-efficient computers. This is because although very simple in architecture, the Fe₂O₃-based device contains all the ingredients to manipulate merons and bimerons quickly and efficiently – by flowing a tiny electrical current in an extremely thin metallic ‘overcoat’.

While iron oxide is extremely abundant and cheap, the fabrication techniques employed by researchers at Singapore and Madison are complex and require atomic-scale control. However, the researchers are optimistic as they recently demonstrated that it is possible to ‘peel off’ a thin layer of oxide from its growth medium and stick it almost anywhere, with its properties being largely unaffected.