December 2020

A team of researchers has discovered a mechanism in antiferromagnets that could be useful for spintronic devices. They theoretically and experimentally demonstrated that one of the magnetization torques arising from optically driven excitations has a much stronger influence on spin orientation than previously given credit for. The result of their study could provide a new and efficient mechanism for manipulating spin. which has so far proven to be a challenging task.

Antiferromagnetic materials (AFMs) are good candidates for spintronics because they are resistant to external magnetic fields and allow for switching spin values in timescales of picoseconds. One promising strategy to manipulate spin orientation in AFMs is using an optical laser to create extremely short-lived magnetic field pulses, a phenomenon known as the inverse Faraday effect (IFE). Although the IFE in AFMs generates two very distinct types of torque (rotational force) on their magnetization, it now seems the most important of the two has been somewhat neglected in research.

Researchers from Seoul National University, Pohang University of Science and Technology, Korea Atomic Energy Research Institute and the Center for Quantum Materials in Korea have designed a prototype of a non-volatile magnetic memory device entirely based on a nanometer-thin layered material, which can be tuned with a tiny current. This finding opens up a new window of opportunities for future energy-efficient magnetic memories based on spintronics.

The choice of magnetic material and device architecture depends on the fact that non-volatile memory technologies have to guarantee safe storage, but also reliable reading and writing access. Hard magnets are perfect for long-term memory storage, because they magnetize very strongly and are difficult to demagnetize. On the contrary, soft magnets are desirable for adding new information to the memory device, because their magnetization can be easily reversed during the writing process. Put simply, ideal magnetic materials can be kept at a hard magnetic state to ensure the stability of the stored information, but be soft on demand.

University of Groningen researchers have measured the presence of electron-spin-dependent nonlinearity in a van der Waals heterostructure spintronic device. The team went on to demonstrate its application for basic analog operations such as essential elements of amplitude modulation and frequency sum (heterodyne detection) on pure spin signals, by exploiting the second-harmonic generation of the spin signal due to nonlinear spin injection.

Graphene (light green) with boron nitride (blue) on top. Measuring points indicated in orange.

The researchers also showed that the presence of nonlinearity in the spin signal has an amplifying effect on the energy-dependent conductivity-induced nonlinear spin-to-charge conversion effect. The interaction of the two spin-dependent nonlinear effects in the spin-transport channel leads to a highly efficient modulation of the spin-to-charge conversion effect, which in principle can also be measured without using a ferromagnetic detector. These effects are measured both at room and low temperatures, and are suitable for their applications as nonlinear circuit elements in the fields of advanced spintronics and spin-based neuromorphic computing.

Researchers from the University of New South Wales (UNSW) demonstrated spin detection using a spin filter to separate spin orientation according to their energies.

In this new study, UNSW researchers have exploited the non-linear interactions between spin accumulation and charge currents in gallium-arsenide holes, demonstrating all-electrical spin-to-charge conversion without the need for a magnetic field. This is an important achievement for spintronics devices, as detection of spin-to-charge conversion has always required a large range of magnetic fields, thus limiting the speed and practicality.