Antiferromagnetism - Page 5

Researchers at the Czech Academy of Sciences, Charles University in Prague, ETH Zurich and other universities in Europe recently introduced a method to achieve the quenching of antiferromagnets into high resistivity states by applying either electrical or ultrashort optical pulses. This strategy could open interesting new avenues for the development of spintronic devices based on antiferromagnets.

Antiferromagnetism is a type of magnetism in which parallel but opposing spins occur spontaneously within a material. Antiferromagnets, materials that exhibit antiferromagnetism, have advantageous characteristics that make them particularly promising for fabricating spintronic devices. Due to their ultrafast nature, their insensitivity to external magnetic fields and their lack of magnetic stray fields, antiferromagnets could be particularly desirable for the development of spintronic devices. However, despite their advantages, most simple antiferromagnets have weak readout magnetoresistivity signals. Moreover, so far scientists have been unable to change the magnetic order of antiferromagnets using optical techniques, which could ultimately allow device engineers to exploit these materials' ultrafast nature.

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 Exeter University, in collaboration with the Universities of Oxford, California Berkeley, and the Advanced and Diamond Light Source have experimentally demonstrated that high frequency alternating spin currents can be transmitted by, and sometimes amplified within, thin layers of antiferromagnetic NiO.

The researchers say that these results demonstrate that the spin current in thin NiO layers is mediated by evanescent spin waves, a mechanism akin to quantum mechanical tunnelling. This could lead to more efficient future wireless communication technology based on such antiferromagnetic spintronics devices.

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 University of Tokyo developed a method to partially switch between specific magnetic states at Thz frequencies. The researchers used short high-frequency pulses of terahertz radiation to flip the electron spins in ferromagnetic manganese arsenide (MnAs).

Such techniques have been attempted before, but the magnitude change in the magnetization of the MnAs was too small - but in this current research a 20% change was achieved. Such a technique could be used in the future to create Thz spintronics devices - one that operate at a much faster rate compared to today's Ghz electronics devices.

Researchers from the Johannes Gutenberg University Mainz, in cooperation with Utrecht University and the Center for Quantum Spintronics (QuSpin) at the Norwegian University of Science and Technology (NTNU), demonstrated that the antiferromagnetic material iron oxide is a promising magnon spintronics material.

Iron oxide is a cheap material (it is the main material in rusted iron) that was shown to be able to carry magnon over long distances, with low access heat. For their demonstration, the researchers used used platinum wires on top of the insulating iron oxide. An electric current was introduced which led to the creation of magnons in the iron oxide.

Researchers from Australia's RMIT found that a 'stacked' 2D material Fe₃GeTe₂ (or FGT) features hard magnetic properties coupled with a near square-shared hysteresis loop and perpendicular magnetic anisotropy.

These promising properties mean that this material could be a promising candidate for extremely thin (200 nm) vdW-heterostructure spintronics devices.

Researchers from the Moscow Institute of Physics and Technology (MIPT) designed a new spin diode, using two kinds of antiferromagnetic materials. The researchers say that this new design features triple the frequencies range under which the device can rectify alternating currents, while keeping the same sensitivity as semiconductor-based diodes.

The spin diode, in this new design, is placed between the two materials, and by adjusting the orientation of their antiferromagnetic axes, it is possible to change the resistance and the resonant frequency of the diode.

Researchers from the NIST in the US and the University of Tokyo have discovered a metallic antiferromagnet (Mn₃Sn) that exhibits a large magneto-optic Kerr (MOKE) effect, despite a vanishingly small net magnetization at room temperature.

Compared to ferromagnetic materials, metallic antiferromagnets allow for faster dynamics and more densely packed spintronic devices due to the weak interactions between antiferromagnetic cells. The researchers believe that such materials hold promise for future antiferromagnetic spintronic devices, where the magnetic state could transduced optically and switched either optically or by applying current.

Xavier Marti, the CTO at IGSresearch discusses real world applications of antiferromagnetic spintronic devices in this interesting IEEE talk: