What it is
Magnetic tunnel junctions built from ferromagnets are canonical spintronic devices, with wide-ranging applications in data storage, computing and sensing: their magnetic order is detected electrically through tunnelling magnetoresistance (TMR) and controlled through spin-transfer torque. Both effects were long assumed unable to be sizeable in all-antiferromagnetic tunnel junctions (AATJs), which have no net magnetization. Recent work showed that AATJs based on chiral antiferromagnets do exhibit TMR, owing to their non-relativistic momentum-dependent spin polarization and cluster magnetic octupole moment, but the reciprocal effect, an antiferromagnetic counterpart of spin-transfer torque, was assumed non-existent because the total electric current is spin-neutral. The authors report nanoscale AATJs that display it, an effect they term octupole-driven spin-transfer torque (OTT), and demonstrate current-induced OTT switching of PtMn3|MgO|PtMn3 junctions with a room-temperature TMR of 363% and switching current densities of the order of 10 MA per square centimetre. Their theoretical modelling explains the origin of OTT in terms of an imbalance between intra- and inter-sublattice spin currents across the junction or, equivalently, in terms of the non-zero net cluster octupole polarization of each PtMn3 layer. They present the work as a new materials platform for antiferromagnetic spintronics and a pathway toward deeply scaled magnetic memory and room-temperature terahertz technologies.
Why it matters
A current switched nanoscale all-antiferromagnetic tunnel junctions by a spin-transfer torque assumed not to exist, with 363% room-temperature magnetoresistance. Ferromagnet-based tunnel junctions are canonical spintronic devices in data storage, computing and sensing, read through magnetoresistance and written through spin-transfer torque. All-antiferromagnetic junctions, with no net magnetization, were long assumed to show neither effect sizeably; chiral-antiferromagnet junctions were recently shown to give the readout, but the write effect was assumed non-existent because the total current is spin-neutral. These PtMn3|MgO|PtMn3 junctions switched at current densities of the order of 10 MA per square centimetre, and the authors see a pathway toward deeply scaled magnetic memory and room-temperature terahertz technologies.
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Filed underMagnetic properties of thin films, Advanced Condensed Matter Physics, Magnetic Properties of Alloys