Memory

Some of the latest advances in spintronics are based on nanometric thin film structures with perpendicular magnetic anisotropy in which the spin currents are used to produce changes in the magnetization of a magnetic layer. This effect is known as spin-orbit torque (SOT) and can be enhanced by suitably engineering multilayer stacks composed by alternated magnetic/non-magnetic metals. The typical structures employed to manipulate the magnetization via SOT are multilayers whose basic constituent is a ferromagnetic layer adjacent to heavy metal(s), which confer large spin-orbit coupling and promote the perpendicular magnetic anisotropy. These systems are the basic elements for spin-orbit torque magnetization switching, used in the next generation of magnetoresistive random access memory (MRAM) devices.

The SpinOrbitronics research team, guided by Dr. Paolo Perna at IMDEA Nanociencia, have observed the emergence of an interfacially enabled increase of the spin-orbit torque when an ultrathin Cu interlayer is inserted between Co and Pt in symmetric Pt/Co/Pt trilayer, in which the effective spin-orbit torque is expected to vanish. The enhancement of SOT is accompanied by a reduction of the spin-Hall magnetoresistance, indicating that the spin memory loss effect in the Co/Cu and Cu/Pt interfaces is responsible of both enhanced SOT and reduction in the spin-Hall magnetoresistance.

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.

Researchers from the University of Arizona discovered that in common Magnetic Tunnel Junctions (MTJ), there's a thin (2D) layer of Iron Oxide. This layer was found to act as a contaminant which lowers the performance achieved by MTJs.

This Iron Oxide layer, however, can also be seen as a blessing - the researchers discovered that the layer behaves as a so-called antiferromagnet at extremely cold temperatures (below -245 degrees Celsius). Antiferromagnets are promising as these can be manipulated at Terahertz frequencies, about 1,000 times faster than existing, silicon-based technology. This is the first research that shows how Antiferromagnets can be controlled as part of MTJs.

Researchers from the Tokyo Institute of Technology (Tokyo Tech) developed a new MRAM cell structure that relies on unidirectional spin Hall magnetoresistance (USMR). The new cell structure is reportedly very simple with only two layers which could lead to lower-cost MRAM devices.

The spin Hall effect leads to the accumulation of electrons with a certain spin on the lateral sides of a material. By combining a topological insulator with a ferromagnetic semiconductor, the researchers managed to create a device with giant USMR.