Iridium, a member of the platinum family of metals, is used in all spin electronic devices, from the read/write heads that transfer data to and from the hard disk in your computer, to emerging magnetic random access memory, MRAM, a higher performance, energy efficient alternative to conventional RAM and DRAM. Fused with manganese into an antiferromagnetic alloy, it is stable, durable and heat resistant. But it is also extremely scarce.

“Iridium is one of the scarcest elements on Earth, twice as rare as other critical raw materials such as platinum, gold and ruthenium. Accordingly the price has risen ten-fold over the last decade, and is forecast to increase by a factor of 100 as more applications emerge in the future,” explains Atsufumi Hirohata, a physicist at the University of York in the UK.

Hirohata is leading a team of European and Japanese researchers in the search for a viable alternative to iridium-manganese alloys in spin electronics. The project, known as HARFIR and funded by the European Commission and the Japanese Science and Technology Agency, has identified five potential candidates so far – a landmark achievement that could lead to commercial implementations within the next 10 years.

Low-cost substitute for a critical element

“To our knowledge, we are the only project working in this area in the world, even though it is widely recognised that spin electronic technologies will displace volatile semiconductor memory technology within the next decade,” Hirohata says. “Therefore the lack of availability of one crucial element from within the periodic table is a critical issue that needs to be solved urgently.”

The team began by setting out a series of objectives for a new type of Heusler alloy that would be a viable alternative to iridium-manganese in spin electronic devices. Heusler alloys are composed of elements that in their pure form are not magnetic, but can be induced electronically to display ferromagnetic properties, causing their atoms to ‘spin-polarise’ – a feature that enables them to store data.

Among other objectives, the researchers sought an alloy that would display an exchange bias and magnetic properties similar to iridium-manganese, as well as comparable operational temperatures, a similar nano-scale thickness of application in multilayer devices and high resistance to corrosion.

With that target in mind, different teams in Europe and Japan have been growing experimental polycrystalline and epitaxial Heusler alloy films, while other partners have developed new modelling techniques to calculate their spin rates and properties. According to the HARFIR coordinator, two key challenges still need to be overcome: attaining a room temperature or near-room temperature operating range, an issue that in theory can be addressed by atomically modifying the electronic properties of the elements; and achieving corrosion resistance similar to iridium-manganese, something the team hopes to demonstrate by the end of the project in a prototype nano-pillar device.

The researchers believe that some of the five alloys they have identified could meet those requirements using combinations of lower cost metals, such as vanadium, iron, nickel and aluminium. Over the coming years, they will be further analysed, tested and refined to produce one or two alloys that have the potential to be used in commercial spin electronics technologies.

Currently, over 600 million hard disk ‘read heads’ are sold worldwide each year, while other applications, such as non-volatile memory based on a similar magnetic structure to that being developed in HARFIR, are under development by several companies.

The HARFIR partners plan to continue the consortium after the project ends and will seek additional funding to advance their research, possibly through granting patent rights to an electronics manufacturer.

“Our Heusler alloy is expected to reduce the price of spin electronics elements by a factor of three,” Hirohata says. “HARFIR will therefore have a very large economic impact on the electronics industry.”