Systematic studies of the intrinsic antiferromagnetic diode effect. a, Nonlinear conductivity σ2ω and longitudinal resistance Rxx as a function of vertical electric field Ez. b, Nonlinear conductivity as a function of vertical magnetic field μ0Hz in the AFM condition. The red dotted line is the mean line of σ2ω. c, Experimentally measured longitudinal resistance (upper panel) and nonlinear conductivity (lower panel) as a function of charge density ne. The positive and negative σ2ω regions are shaded in pink and light blue, respectively. d, Scaling between the nonlinear conductivity and the square of the regular linear conductivity. The dark dotted line is the linear fit to the scaling curve. Credit: Natural electronics (2024). DOI: 10.1038/s41928-024-01219-8.
Antiferromagnets are materials in which the magnetic moments of neighboring atoms are aligned in an alternating manner, resulting in the absence of net macroscopic magnetism. These materials have interesting properties that could be favorable for the development of spintronic and electronic devices.
Researchers at Harvard University recently observed an antiferromagnetic diode effect in uniformly layered MnBi2You4an antiferromagnetic material characterized by a centrosymmetric crystal that does not exhibit directional charge separation. The observed effect could be exploited to develop various technologies, including in-plane field-effect transistors and microwave energy harvesting devices.
The research is published in the journal Natural electronics.
The diode effect, observed in many materials, results in the flow of electric current in only one direction within a device. Materials exhibiting this effect have been used to develop a variety of devices, including radio receivers, digital circuits, temperature sensors, and microwave circuits.
Recently, researchers observed a superconducting diode effect in conducting materials whose crystal structure lacks a center of symmetry, also known as noncentrosymmetric polar conductors. Building on their observations, the Harvard University team set out to probe whether a similar effect exists in the antiferromagnetic topological insulator MnBi2You4.
“Noncentrosymmetric polar conductors are intrinsic diodes that could be useful in developing nonlinear applications,” Anyuan Gao, Shao-Wen Chen, and colleagues wrote in their paper. “Such systems have recently been extended to noncentrosymmetric superconductors, and the superconducting diode effect has been observed. We report an antiferromagnetic diode effect in a centrosymmetric crystal without directional charge separation.”
The researchers fabricated devices using uniformly layered MnBi2You4 with two different electrode configurations. Some of these devices had Hall bar electrodes (i.e., longitudinal electrodes that pass current and transverse electrodes used to measure the Hall effect), while the others had radially distributed electrodes (i.e., arranged in a circular pattern around a central point).
The researchers observed an antiferromagnetic diode effect characterized by nonlinear transport in both types of devices. They subsequently collected various measurements to confirm that what they had observed was indeed an antiferromagnetic diode effect.
To study the properties of MnBi in uniform layers2You4 To uncover the antiferromagnetic diode effect, the team used a variety of techniques, including a spatially resolved optical method and electrical sum frequency generation (SFG) measurement collection techniques.
“We observed significant second harmonic transport in a nonlinear electronic device enabled by the compensated antiferromagnetic state of uniformly layered MnBi2You4” wrote Gao, Chen and their colleagues.
“We show that this antiferromagnetic diode effect can be used to create in-plane field-effect transistors and microwave energy-harvesting devices. We also show that the generation of electrical sum-frequencies can be used as a tool to detect nonlinear responses in quantum materials.”
In their paper, the authors highlight the potential of the antiferromagnetic diode effect they observed for the development of antiferromagnetic logic circuits, microwave harvesters, and spintronic devices. Their work may soon pave the way for additional studies exploring this effect and how it could be used to fabricate new, high-performance devices.
More information:
Anyuan Gao et al, An antiferromagnetic diode effect in uniform-layer MnBi2You4, Natural electronics (2024). DOI: 10.1038/s41928-024-01219-8.
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