What is spintronics?

With devices having been miniaturised to the scale of nanometres, quantum mechanics now affects the operation of electrons.

Quantum mechanics informs a scale that is smaller than atoms. Unlike classical mechanics, where objects exist in a specific place in a specific time, objects in quantum mechanics can exist in different points based on probability. In fact, unlike conventional electronic devices, which rely on an electron’s negative charge to manipulate motion, the very mathematics of spintronics is comparable to that of a spinning top.

An electron’s spin is coupled to its magnetic moment so its manipulation is closely related to external magnetic fields. Unlike charge-based electronics, spin-based electronics are non-volatile and have the potential to achieve much higher speeds.

The Giant Magnetoresistance (GMR) effect is an example of spintronics, and prior to its realisation, electronic devices used charge-based methods to process information.

GMR draws energy from the quantised spin of atom which was previously overlooked in mainstream electronics. Spintronics not only reduces power consumption but increases memory and processing capabilities.

Spin-polarises or spin-analysers operate to control spin polarisation via magnetic layers. The waves carry the spin current through spin-orbit coupling.

MRAM in spintronics

GMR was discovered by Albert Fert and Peter Grunberg in 1988. Their studies around the magnetic multilayers resulted in magnetic sensors which could be used to boost the areal density (i.e. the number of bits per square inch of storage surface) of information on hard disk drives.

The spin-valve is a spintronic device that is widely used. Most hard disk drives use them to read the magnetic bits contained on the spinning platters.

Magnetoresistive RAM (MRAM) is a method of storing data using magnetic states over electrical charges by devices like dynamic random access memory (DRAM). DRAM uses an electrical charge to determine if a bit is 1 or 0, whereas MRAM uses a pair of ferromagnetic metal plates separated by a thin insulating material layer.

MRAM is a combination of the high density of DRAM, with the high speed of static random access memory (SRAM) to store and access larger amounts of data and improve speeds. Accordingly, MRAM can be found in commercial products across the market – a recent example being an ultra low power BiSb-based SOT MRAM device. This technology offers a large spin Hall angle and high electrical conductivity, thereby meeting the requirements for the SOT-MRAM (spin orbit torque magnetic RAM) implementation.

MRAM is integral to the use of spintronics and is used across a range of industries, not least aerospace, automotive, robotics and much more.

For more information on spintronics, see Nature Materials' article, 'New horizons in spintronics', which was published in December 2021 and looks at recent developments in spintronics.