Nonvolatile voltage-controlled magnetization reversal in a spin-valve multiferroic heterostructure

Pure voltage-controlled magnetism, rather than a spin current or magnetic field, is the goal for next-generation ultralow power consumption spintronic devices. To advance toward this goal, we report a voltage-controlled nonvolatile 90° magnetization rotation and voltage-assisted 180° magnetization reversal in a spin-valve multiferroic heterostructure. Here, a spin valve with a synthetic antiferromagnetic structure was grown on a (110)-cut Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrate, in which only the magnetic moment of the free layer can be manipulated by an electric field (E-field) via the strain-mediated magnetoelectric coupling effect. As a result of selecting a specified PMN-PT substrate with defect dipoles, nonvolatile and stable magnetization switching was achieved by using voltage impulses. Accordingly, a giant, reversible and nonvolatile magnetoresistance modulation was achieved without the assistance of a magnetic field. In addition, by adopting a small voltage impulse, the critical magnetic field required for complete 180° magnetization reversal of the free layer can be tremendously reduced. A magnetoresistance ratio as large as that obtained by a magnetic field or spin current under normal conditions is achieved. These results indicate that E-field-assisted energy-efficient in-plane magnetization switching is a feasible strategy. This work is significant to the development of ultralow-power magnetoresistive memory and spintronic devices.

Ultralow-power all-optical switching via a chiral Mach-Zehnder interferometer

All-optical switching increasingly plays an important role in optical information processing. However, simultaneous achievement of ultralow power consumption, broad bandwidth and high extinction ratio remains challenging. We experimentally demonstrate an ultralow-power all-optical switching by exploiting chiral interaction between light and optically active material in a Mach-Zehnder interferometer (MZI). We achieve switching extinction ratio of 20.0(3.8) and 14.7(2.8) dB with power cost of 66.1(0.7) and 1.3(0.1) fJ/bit, respectively. The bandwidth of our all-optical switching is about 4.2 GHz. Our theoretical analysis shows that the switching bandwidth can, in principle, exceed 110 GHz. Moreover, the switching has the potential to be operated at few-photon level. Our all-optical switching exploits a chiral MZI made of linear optical components. It excludes the requisite of high-quality optical cavity or large optical nonlinearity, thus greatly simplifying realization. Our scheme paves the way towards ultralow-power and ultrafast all-optical information processing.