MRAM could store data in nanoseconds

February 21, 2020 //By Julien Happich
Some years ago, while investigating so-called magnetic RAMs (MRAMs), a team of researchers from IMEC and ETH Zurich had shown that current-induced spin-transfer torques (STT) and spin–orbit torques (SOT) enable the electrical switching of magnetic tunnel junctions (MTJs) in non-volatile magnetic random access memories.

In a new Nature Technology paper titled “Single-shot dynamics of spin–orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions”, the researchers have now resolved, temporally, the exact dynamics of a single such storage event.

Storing data magnetically requires inverting the direction of magnetization of a ferromagnetic (that is, permanently magnetic) material in order to represent the information as a logic value, zero or one. In older technologies, such as magnetic tapes or hard drives, this was achieved through magnetic fields produced inside current-carrying coils.

The tunnel junctions used to measure the timing of the
magnetisation reversal are located at the centre.
(Image courtesy of IMEC). Credit: IMEC

Modern MRAM technology, by contrast, directly uses the spins of electrons, which flow directly through a magnetic layer as an electric current. In the ETH zurich experiments, electrons with opposite spin directions are spatially separated by the spin-orbit interaction. This, in turn, creates an effective magnetic field, which can be used to invert the direction of magnetization of a tiny metal dot.

"We know from earlier experiments in which we stroboscopically scanned a single magnetic metal dot with X-rays that the magnetization reversal happens very quickly, in about a nanosecond," explains Eva Grimaldi, a post-doc at the Department for Materials of the ETH in Zurich, in Pietro Gambardella's group.

"However, those were mean values averaged over many reversal events. Now, we wanted to know how exactly a single such event takes place and to show that it can work on an industry-compatible magnetic memory device."

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