Tomohiro Taniguchi

We have investigated the interlayer chiral coupling (ICC) phenomenon, which occurs via the interlayer Dzyaloshinskii–Moriya interaction, in a ferromagnet/non-magnet/ferromagnet tri-layer structure using sub-micron-sized magnetic tunnel junctions. The tri-layer films were fabricated into sub-micron lateral size tunnel junctions, which exhibited an order of magnitude enhancement of the ICC-induced effective field compared to larger films. Moreover, the magnitude and even the sign of the effective field was observed to vary between devices, indicating that polycrystallinity plays an important role in ICC. We also demonstrate ICC-mediated in-plane magnetization switching induced by out-of-plane magnetic fields.

Spin-based computing is emerging as a powerful approach for energy-efficient and high-performance solutions to future data processing hardware. Spintronic devices function by electrically manipulating the collective dynamics of the electron spin, which is inherently non-volatile, nonlinear and fast operating, and can couple to other degrees of freedom such as photonic and phononic systems. This Technical Review explores key advances in integrating magnetic and spintronic elements into computational architectures, ranging from fundamental components such as radiofrequency neurons or synapses and spintronic probabilistic bits to broader frameworks such as reservoir computing and magnetic Ising machines. For each of these systems, we discuss hardware-specific and task-dependent metrics to evaluate their computing performance and evaluate the physical processes that need to be optimized to increase performance. Finally, we discuss challenges and future opportunities, highlighting the potential of spin-based computing in next-generation technologies.

Artificial spin ices (ASIs) consisting of 72 stadium-shaped magnetic tunnel junction (MTJ) cells arranged in a honeycomb lattice were fabricated. The magnetization state of each cell was electrically detected using magnetoresistance. Measurements on the MTJ-based ASIs with a lattice constant a ranging from 980 nm to 2 μm confirmed the following: (1) the switching field of the cells depends on the angle of the long axis of the cell with respect to the field direction, reflecting the shape anisotropy of the free layer in the MTJ cells; (2) the switching field distribution was ∼10% of the mean value; and (3) the magnetic coupling increased monotonically with the reduction in a and reached ∼1 mT for the smallest a, which was close to the switching field distribution. Furthermore, during the magnetization of this ASI, reversed cells aligned in a string appeared, corresponding to the dipole strings previously reported for ASIs fabricated with single-layer ferromagnetic films. The appearance of a dipole string connecting emergent monopoles is a feature of the ASI dynamics. The observation of such emergent dynamics in the ASIs microfabricated using MTJ arrays highlights their potential for advancing the development of novel functional devices.

Physical reservoir computing by using artificial spin ice (ASI) has been proposed on the basis of both numerical and experimental analyses. ASI is a many-body system consisting of ferromagnets with various interactions. Recently, fabricating magnetic tunnel junctions (MTJs) as ferromagnets in an ASI was achieved in the experiment, which enables an electrical detection of magnetic state of each MTJ independently. However, performing a recognition task of time-dependent signal by such an MTJ-based ASI has not been reported yet. In this work, we examine numerical simulation of a recognition task of time-dependent input and evaluate short-term memory and parity-check capacities. These capacities change significantly when the magnitude of the input magnetic field is comparable to a value around which the magnetization alignment is greatly affected by the dipole interaction. It implies that the presence of the dipole interaction results in a loss of echo state property. This point was clarified by evaluating Lyapunov exponent and confirming that the drastic change of the memory capacities appears near the boundary between negative and zero exponents, which corresponds to the edge of echo state property.

Physical reservoir computing by using artificial spin ice (ASI) has been proposed on the basis of both numerical and experimental analyses. ASI is a many-body system consisting of ferromagnets with various interactions. Recently, fabricating magnetic tunnel junctions (MTJs) as ferromagnets in an ASI was achieved in the experiment, which enables an electrical detection of magnetic state of each MTJ independently. However, performing a recognition task of time-dependent signal by such an MTJ-based ASI has not been reported yet. In this work, we examine numerical simulation of a recognition task of time-dependent input and evaluate short-term memory and parity-check capacities. These capacities change significantly when the magnitude of the input magnetic field is comparable to a value around which the magnetization alignment is greatly affected by the dipole interaction. It implies that the presence of the dipole interaction results in a loss of echo state property. This point was clarified by evaluating Lyapunov exponent and confirming that the drastic change of the memory capacities appears near the boundary between negative and zero exponents, which corresponds to the edge of echo state property.

Antiferromagnetic magnons possess a distinctive feature absent in their ferromagnetic counterparts: the presence of two distinct handedness modes, the right-handed (RH) and left-handed (LH) precession modes. The magnon handedness determines the sign of spin polarization carried by the propagating magnon, which is indispensable for harnessing the diverse functionalities in magnonic devices, such as data encoding, magnon polarization-based logic systems, and quantum applications involving magnons. However, the control of coherently propagating magnon handedness in antiferromagnets has remained elusive. Here we demonstrate the manipulation and electrical readout of propagating magnon handedness in perpendicularly magnetized synthetic antiferromagnets (SAF). We find that the antiferromagnetic magnon handedness can be directly identified by measuring the inverse spin Hall effect (ISHE) voltage, which arises from the spin pumping effect caused by the propagating antiferromagnetic magnons in the SAF structure. The RH and LH modes of the magnon can be distinguishable when the SAF structure is sandwiched by heavy metals with the same sign of spin Hall angle. This work unveils promising avenues for harnessing the unique properties of antiferromagnetic magnons.