R&D: Transforming Mass Storage of Digital Data Magnetic, Switching Without Magnetic Field

A team the School of Physics and SFI funded AMBER (Advanced Materials and BioEngineering Research) Centre have made a new device which could lead to a breakthrough in mass storage of digital data.

Two PhD students, Yong Chang Lau from Malaysia and Davide Betto from Italy, working with senior researcher Dr. Karsten Rode and Professors Michael Coey and Plamen Stamenov published their results in the journal Nature Nanotechnology earlier this Summer.

Professor Michael Coey, a principal investigator in the school said: “The flood of digital data is growing every year and new storage concepts are urgently needed to sustain the information revolution. Forecasts envisage 20.8 billion wirelessly-connected ‘things’ throughout the world by 2020. At present, it is estimated that 5.5 million new ones are connected every day. This is a huge challenge for mass storage, which currently relies on HDDs. Everything we download daily onto our computers or mobile phones is stored magnetically on millions of these spinning discs located in data centres scattered across the planet.”

The thin film device structure, with pinned and free ferromagnetic layers


Schematic illustration of the stack used for the SOT switching of a PMA layer (numbers in parentheses indicate layer thickness).

One main contender for the future of mass storage is MRAM (Magnetoresistive random-access memory), under development since the 1990s. MRAM is faster and offers higher density compared to other non-volatile RAMs. A large amount of research has been carried out in developing it, but MRAM has not been widely adopted in the market yet, largely due to the costs and complexity of large scale fab manufacturing.

The team in AMBER, at Trinity College Dublin, may now have solved the problem, offering a simpler solution for manufacturing a type of MRAM.

The team, who are made up of experts in magnetism and magnetic switching, which is at the heart of storage, have managed to circumvent the need to use a magnetic field. Their new device consists of a stack of five metal layers, each of them a few nanometer thick. At the bottom is a layer of platinum, and just above it is the iron-based magnetic storage layer just six atoms thick. Platinum is a favorite of researchers in spin electronics, the technology that makes use of the fact that each electron is a tiny magnet. Passing a current through the platinum separates the electrons into two groups with their magnetism pointing in opposite directions at the top and bottom surfaces thanks to an effect known as ‘spin-orbit torque’ that follows from Einstein’s theory of relativity. Electrons at the top are pumped into the storage layer and try to switch its magnetic direction, but like a pencil balanced on its point, the magnetism of the storage layer can’t decide 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 plans to demonstrate a full memory cell, and an ultra-fast oscillator based on spin-orbit torque using layers of a novel magnetic alloy they discovered recently.

The device stacks will be grown in a sophisticated 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.

Full paper