Research / Technical

Researchers from Monash University, part of the FLEET Centre, and China's Weifang University, have reported a generic approach towards intrinsic magnetic second-order topological insulators - materials that can be beneficial for spintronics.

Two-dimensional ferromagnetic semiconductors, such as CrI₃, Cr₂Ge₂Te₆, and VI₃, have been extensively studied in recent years and are fundamental to spintronics. Topological insulators are materials with unique properties where the interior is insulating, but the boundary can conduct electrons. In three-dimensional topological insulators like Bi₂Se₃, the surface hosts two-dimensional Dirac fermions. Second-order topological insulators, a new concept extending the idea of topological insulators, exhibit (m-2)-dimensional boundary states in m-dimensional materials, such as one-dimensional hinge states in three-dimensional materials and zero-dimensional corner states in two-dimensional materials.

Researchers at King Abdullah University of Science and Technology (KAUST) and Khalifa University of Science and Technology have investigated the transmission, tunneling magnetoresistance ratio and spin injection efficiency of bilayer LaI₂ using a combination of first-principles calculations and the non-equilibrium Green’s function method. 

Multilayer graphene electrodes were used by the team, to build a magnetic tunnel junction with bilayer LaI₂ as ferromagnetic barrier. The magnetic tunnel junction reportedly proved to be a perfect spin filter device with an impressive tunneling magnetoresistance ratio of 653% under a bias of 0.1 V and a still excellent performance in a wide bias range. The team said that in combination with the obtained high spin injection efficiency, this could hold great potential from an application point of view.

Researchers from ETH Zurich recently developed a method to control the quantum states of single electron spins using spin-polarized currents, which could enhance quantum computing technologies. The new technique offers more precise, localized control compared to traditional methods using electromagnetic fields, potentially improving the manipulation of quantum states in devices like qubits. 

Control over quantum systems is typically achieved by time-dependent electric or magnetic fields. Alternatively, electronic spins can be controlled by spin-polarized currents. In their recent work, the team demonstrated coherent driving of a single spin by a radiofrequency spin-polarized current injected from the tip of a scanning tunneling microscope into an organic molecule. With the excitation of electron paramagnetic resonance, the scientists established dynamic control of single spins by spin torque using a local electric current. In addition, their work highlights the dissipative action of the spin-transfer torque, in contrast to the nondissipative action of the magnetic field, which allows for the manipulation of individual spins based on controlled decoherence.

Researchers at India's Institute of Nano Science and Technology (INST), an autonomous research institution of Department of Science and Technology (DST), recently produced a transparent conducting interface between two insulating materials with room temperature spin polarized electron gas, which allows for see-through devices with efficient spin currents. 

Prof. Suvankar Chakraverty and his group at INST have produced a 2D Electron Gas (2DEG) with room temperature spin polarization at the interface composed of chemicals LaFeO₃ and SrTiO₃. They grew super lattices and hetero structures of oxide materials to realize new and exotic two-dimensional electron gas at the interface of two insulating oxides that could be useful for next generation quantum devices.

Researchers at the University of Tübingen, Helmholtz-Zentrum Berlin, University of Nebraska and Trinity College have used a very thin layer of radicals, 10000 times thinner than a human hair, to coat a ferromagnetic material, polycrystalline cobalt, to change the magnetic properties of cobalt at the junction with the radicals.

Purely organic radicals are a family of molecules composed only of light elements, such as carbon, nitrogen, and oxygen. They are transparent, light, and flexible materials. They promise lower costs of production and sustainable, and recyclable chemistry. These radicals are organic molecules that carry an unpaired electron, i.e., they are materials with permanent magnetic properties. They must be used as a film in a device, i.e., the radical molecules cover a substrate such as a metal surface, forming a coating. 

Researchers have developed "somersaulting" spin qubits for universal quantum logic. This achievement may enable efficient control of large semiconductor qubit arrays. This is based on two studies published by the research group: a demonstration of "hopping" spins in Nature Communications and their work on "somersaulting" spins in Science. 

In 1998, Loss and DiVincenzo published the seminal work ‘quantum computation with quantum dots’. In their original work, hopping of spins was proposed as a basis for qubit logic, but an experimental implementation remained lacking. After more than 20 years, experiments have caught up with theory. Researchers at QuTech—a collaboration between the TU Delft and TNO—have demonstrated that the original ‘hopping gates’ are indeed possible, with state-of-the-art performance.

Researchers from the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Sorbonne Université CNRS, INRS-EMT, FERMI, Uppsala University, University of York and University of Hull have developed a non-thermal method to alter magnetization using XUV radiation, utilizing the inverse Faraday effect in an iron-gadolinium alloy. This approach enables significant magnetization changes without the usual thermal effects, promising enhancements in ultrafast magnetism technologies. 

Intense laser pulses can be used to manipulate or even switch the magnetization orientation of a material on extremely short time scales. Typically, such effects are thermally induced, as the absorbed laser energy heats up the material very rapidly, causing an ultrafast perturbation of the magnetic order. The research team has now demonstrated an effective non-thermal approach of generating large magnetization changes. By exposing a ferrimagnetic iron-gadolinium alloy to circularly polarized pulses of extreme ultraviolet (XUV) radiation, they could reveal a particularly strong magnetic response depending on the handedness of the incoming XUV light burst (left- or right-circular polarization).

Researchers at MIT, DEVCOM Army Research Laboratory, The Ohio State University, and University of Ottawa have reported unique electron mobility in a new crystal film that could be the basis for wearable thermoelectric and spintronic devices.

A material with a high electron mobility is like a highway without traffic, and the electrons that flow into the material experience movement without any obstacles to slow or scatter them off their path. The higher a material’s electron mobility, the more efficient its electrical conductivity, and the less energy is lost or wasted as electrons move through. Advanced materials that exhibit high electron mobility will be essential for more efficient and sustainable electronic devices that can do more work with less power.

Spintronics relies on the transport of spin currents for computing and communication applications. New device designs would be possible if this spin transport could be carried out by both electrons and magnetic waves called magnons. But spin transport via magnons typically requires electrically insulating magnets—materials that cannot be easily integrated with silicon electronics. Recently, a novel way to bypass that requirement has been developed by researchers at ETH Zürich, Bavarian Academy of Sciences, Technical University of Munich, University of Konstanz, Munich Center for Quantum Science and Technology (MCQST) and Autonomous University of Madrid.

The researchers say that this finding could have important implications for both spintronic applications and fundamental research on spin transport. To demonstrate their concept, the scientists placed two magnetic, metallic strips—each hosting coupled electrons and magnons—on a nonmagnetic, insulating substrate. In the first strip, the researchers converted electron charge currents to electron spin currents. These spin currents were transferred first to the magnons in the same strip, then across the substrate to the magnons in the second strip, and finally to the electrons in the second strip. The researchers detected this spin transport by converting the electron spin currents in the second strip to charge currents.

Researchers at Osaka Metropolitan University, University of Nottingham, Czech Academy of Sciences, Diamond Light Source, ohannes Kepler University Linz, Johannes Gutenberg Universität Mainz, TU Wien and Masaryk University have used symmetry, ab initio theory, and experiments to explore x-ray magnetic circular dichroism (XMCD) in the altermagnetic class. The international research group recently pioneered a new method to identify altermagnets, using manganese telluride (α-MnTe) as a testbed. 

Magnetic materials have traditionally been classified as either ferromagnetic or antiferromagnetic. However, there appears to be a third class of magnetic materials exhibiting what is known as 'altermagnetism'. In ferromagnetic materials, all the electron spins point in the same direction, while in antiferromagnetic materials, the electron spins are aligned in opposite directions, half pointing one way and half the other, canceling out the net magnetism. Altermagnetic materials are proposed in theory to possess properties combining those of both antiferromagnetic and ferromagnetic materials. One potential application of altermagnetic materials is in spintronics technology, which aims to utilize the spin of electrons effectively in electronic devices such as next-generation magnetic memories. However, identifying altermagnets has been a challenge.