Spin-based electronics (aka spintronics or magnetoelectronics) is an emerging field of nanoscale electronics that could lead to electronic devices that are smaller, more versatile and more robust than any currently available. The potential market is estimated to be worth hundreds of billions of dollars a year.
How does it work? Spintronics involves control of electron spin as well as electron charge. Electrons can only spin clockwise or counter-clockwise, so the spin of a single electron can represent a ‘one’ or a ‘zero’ for conveying binary data.
Ben Ruck from the MacDiarmid Institute for Advanced Materials and Nanotechnology at Victoria University Wellington in New Zealand is using soft x-ray techniques at the AS to investigate the electronic structure of a zinc oxide material with spintronics potential.
Left: L-R: PhD students Tanmay Maity and Do Le Binh with ‘spin doctor’ Ben Ruck and the vacuum system in Wellington that the group use to grow europium nitride. Image: Ben Ruck
Zinc oxide is probably best known as an ingredient in sunscreens, cosmetics and skin care products, although it also has quite a few heavier industrial applications.
When zinc oxide is doped with small quantities of a rare earth ion such as gadolinium and then annealed – heated and cooled again slowly to toughen the material – in a particular way, it can become ferromagnetic (like an ordinary, permanent magnet) above room temperature. This turns the zinc oxide into a 'dilute magnetic semiconductor' of potential interest for spintronics applications. Ben's aim is to determine where the gadolinium ions are located in the zinc oxide structure, how this is influenced by gadolinium concentration and annealing temperature, and whether the magnetic behaviour is intrinsic or results from impurities such as clusters of rare-earth metal ions.
Ben also previously used soft x-rays at the AS and other synchrotrons to investigate the electronic structure of polycrystalline europium nitride. Rare earth nitrides such as europium nitride (EuN) are of keen interest due to their intriguing properties and possible spintronics applications. Some rare earths are ferromagnetic semiconductors, while others are predicted to be half-metals. Europium can adopt a 3+ or 2+ valency state in EuN, creating challenges for those seeking to determine its electronic band structure by theoretical or experimental approaches. Ben's synchrotron results imply that EuN is a narrow band-gap semiconductor with potential for tuning both magnetic and electronic states.
"The unique capabilities of synchrotron radiation with regard to element and chemical state specificity allowed us fast, reliable and unambiguous determination of the electronic properties of europium nitride," Ben said.
“Our most recent results suggest that EuN can become ferromagnetic if it has enough 2+ europium, making it a dilute magnetic semiconductor without the need for additional magnetic impurities. We’re planning further synchrotron-based studies to make sense of this material.”