Magnetic switching without a magnetic field
Magnetic and electric switches underpin the information revolution. The magnetic switches are tiny patches of magnetic material that store the information; they can be magnetized in one of two opposite directions ‘up’ or ‘down’ to represent the binary digits ‘0’ and ‘1’. Everything we download daily onto our computers or mobile phones is stored magnetically on millions of spinning discs located in data centres scattered across the world.
Unfortunately, writing and erasing all this information currently needs a magnetic field to switch the magnetic bits. These fields are produced by passing current pulses through minute coils, consuming vast amounts of energy in the process. Now a team in the Magnetism and Spin Electronics Group at Trinity College Dublin have devised an elegant scheme for magnetic switching that does away with any need for a magnetic field.
Two PhD students, Yong Chang Lau from Malaysia and Davide Betto from Italy, working with senior researcher Karsten Rode and physics professors Michael Coey and Plamen Stamenov publish their results in the prestigious journal Nature Nanotechnology this week.
Their device consists of a stack of five metal layers, each of them a few nanometers thick. At the bottom of the stack is a layer made of platinum, and above it is the iron-based magnetic storage layer just six atoms thick. Platinum is a favourite of researchers in spin electronics (also known as spintronics), the technology that makes use of the property that each electron is a tiny magnet. Passing a current through the platinum separates the electrons with their magnetism pointing in opposite directions at the top and bottom surfaces. Those pumped into the storage layer try to switch its magnetic direction, thanks to an effect known a ‘spin-orbit torque’ that follows from Einstein’s theory of relativity. But like a pencil balanced on its point, the magnetism of the storage layer doesn't know which way to fall. The team designed the rest of the stack to solve that dilemma by acting like a nanoscale permanent magnet that creates the small field necessary to make the switching determinate, at zero cost in energy.
The Group now plan to demonstrate a full memory cell, and an ultra-fast oscillator based on spin-orbit torque and layers of a novel magnetic alloy they developed recently. The thin film device stacks will be grown in a new SFI-funded thin film facility in the AMBER Centre at Trinity’s CRANN Institute for nanoscience. These new spintronic devices have potential to deliver the breakthrough needed to sustain the information revolution for another 25 years.