Third harmonic characterization of antiferromagnetic heterostructures

Observation of Real-Time Spin-Orbit Torque Driven Dynamics in Antiferromagnetic Thin Film

In the burgeoning field of spintronics, antiferromagnetic materials (AFMs) are attracting significant attention for their potential to enable ultra-fast, energy-efficient devices. Thin films of AFMs are particularly promising for practical applications due to their compatibility with spin-orbit torque (SOT) mechanisms. However, studying these thin films presents challenges, primarily due to the weak signals they produce and the rapid dynamics driven by SOT, that are too fast for conventional electric transport or microwave techniques to capture. The time-resolved magneto-optical Kerr effect (TR-MOKE) has been a successful tool for probing antiferromagnetic dynamics in bulk materials, thanks to its sub-picosecond (sub-ps) time resolution. Yet, its application to nanometer-scale thin films has been limited by the difficulty of detecting weak signals in such small volumes. In this study, the first successful observation of antiferromagnetic dynamics are presented in nanometer-thick orthoferrite films using the pump-probe technique to detect TR-MOKE signal. This paper report an exceptionally low damping constant of 1.5 × 10-4 and confirms the AFM magnonic nature of these dynamics through angular-dependent measurements. Furthermore, it is observed that electrical currents can potentially modulate these dynamics via SOT. The findings lay the groundwork for developing tunable, energy-efficient spintronic devices, paving the way for advancements in next-generation spintronic applications.

Spin Hall-induced bilinear magnetoelectric resistance

Magnetoresistance is a fundamental transport phenomenon that is essential for reading the magnetic states for various information storage, innovative computing and sensor devices. Recent studies have expanded the scope of magnetoresistances to the nonlinear regime, such as a bilinear magnetoelectric resistance (BMER), which is proportional to both electric field and magnetic field. Here we demonstrate that the BMER is a general phenomenon that arises even in three-dimensional systems without explicit momentum-space spin textures. Our theory suggests that the spin Hall effect enables the BMER provided that the magnitudes of spin accumulation at the top and bottom interfaces are not identical. The sign of the BMER follows the sign of the spin Hall effect of heavy metals, thereby evidencing that the BMER originates from the bulk spin Hall effect. Our observation suggests that the BMER serves as a general nonlinear transport characteristic in three-dimensional systems, especially playing a crucial role in antiferromagnetic spintronics.

Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque

Sagnac interferometry can provide a substantial improvement in signal-to-noise ratio compared to conventional magnetic imaging based on the magneto-optical Kerr effect. We show that this improvement is sufficient to allow quantitative measurements of current-induced magnetic deflections due to spin-orbit torque even in thin-film magnetic samples with perpendicular magnetic anisotropy, for which the Kerr rotation is second order in the magnetic deflection. Sagnac interferometry can also be applied beneficially for samples with in-plane anisotropy, for which the Kerr rotation is first order in the deflection angle. Optical measurements based on Sagnac interferometry can therefore provide a cross-check on electrical techniques for measuring spin-orbit torque. Different electrical techniques commonly give quantitatively inconsistent results so that Sagnac interferometry can help to identify which techniques are affected by unidentified artifacts.

Intrinsic Nonlinear Hall Detection of the Néel Vector for Two-Dimensional Antiferromagnetic Spintronics

The respective unique merit of antiferromagnets and two-dimensional (2D) materials in spintronic applications inspires us to exploit 2D antiferromagnetic spintronics. However, the detection of the Néel vector in 2D antiferromagnets remains a great challenge because the measured signals usually decrease significantly in the 2D limit. Here we propose that the Néel vector of 2D antiferromagnets can be efficiently detected by the intrinsic nonlinear Hall (INH) effect which exhibits unexpected significant signals. As a specific example, we show that the INH conductivity of the monolayer manganese chalcogenides MnX (X=S, Se, Te) can reach the order of nm·mA/V^{2}, which is orders of magnitude larger than experimental values of paradigmatic antiferromagnetic spintronic materials. The INH effect can be accurately controlled by shifting the chemical potential around the band edge, which is experimentally feasible via electric gating or charge doping. Moreover, we explicitly demonstrate its 2π-periodic dependence on the Néel vector orientation based on an effective k·p model. Our findings enable flexible design schemes and promising material platforms for spintronic memory device applications based on 2D antiferromagnets.

Unidirectional Spin Hall Magnetoresistance in Antiferromagnetic Heterostructures

Unidirectional spin Hall magnetoresistance (USMR) has been widely reported in the heavy metal/ferromagnet bilayer systems. We observe the USMR in Pt/α-Fe_{2}O_{3} bilayers where the α-Fe_{2}O_{3} is an antiferromagnetic (AFM) insulator. Systematic field and temperature dependent measurements confirm the magnonic origin of the USMR. The appearance of AFM-USMR is driven by the imbalance of creation and annihilation of AFM magnons by spin orbit torque due to the thermal random field. However, unlike its ferromagnetic counterpart, theoretical modeling reveals that the USMR in Pt/α-Fe_{2}O_{3} is determined by the antiferromagtic magnon number with a non-monotonic field dependence. Our findings extend the generality of the USMR which pave the ways for the highly sensitive detection of AFM spin state.

Antiferromagnetic spintronics: An overview and outlook

Over the past few decades, the diversified development of antiferromagnetic spintronics has made antiferromagnets (AFMs) interesting and very useful. After tough challenges, the applications of AFMs in electronic devices have transitioned from focusing on the interface coupling features to achieving the manipulation and detection of AFMs. As AFMs are internally magnetic, taking full use of AFMs for information storage has been the main target of research. In this paper, we provide a comprehensive description of AFM spintronics applications from the interface coupling, read-out operations, and writing manipulations perspective. We examine the early use of AFMs in magnetic recordings and conventional magnetoresistive random-access memory (MRAM), and review the latest mechanisms of the manipulation and detection of AFMs. Finally, based on exchange bias (EB) manipulation, a high-performance EB-MRAM is introduced as the next generation of AFM-based memories, which provides an effective method for read-out and writing of AFMs and opens a new era for AFM spintronics.