Magnon Blocking Effect and Magnonic Skin Effect Shown in Antiferromagnetically Coupled Heterojunction

Spin waves, or magnons, as the elementary excitation of the magnetic system, can move spin angular momentum, giving vast prospects for the Non-volatile, low-energy-consumption, high-speed, and small-size microelectronic devices in the post-Moore period. Magnonics, including the generation, transportation, and handling of magnons, has ended up being the most recent advancement direction of spintronics as well as the emerging discipline of compressed matter physics.

In more recent years, Professor HAN Xiufeng’s research team at the Institute of Physics of the Chinese Academy of Sciences (CAS) has created a magnon valve with a core framework of magnetic insulator (MI)/ spacer(S)/ magnetic insulator (MI) (such as YIG/Au/YIG), a magnon joint (such as YIG/NiO/YIG) and also a magnetoelectric separator which can be utilized as magnon generator as well as magnon detector (such as Pt/YIG/Pt), aiming to make use of pure electrical techniques and the change of the magnetic structures to properly control the generation and transportation of magnons, therefore to make a 100% transmission switch on-off ratio of the magnon currents.

For that reason, a further extensive understanding of the transport properties of incoherent or coherent magnons in an entirely electrically insulated magnon junction will undoubtedly end up being the vital physical basis for the evolution of practical magnonic devices and circuits in the future.

In order to better comprehend the mechanism of magnon transmission in magnon junction from the microscale, Ph.D. student YAN Zhengren, Associate Professor WAN Caihua, as well as Prof. HAN Xiufeng researched the magnon transmission in the sandwich structure of ferromagnetic insulator (FMI)/ antiferromagnetic insulator (AFI)/ ferromagnetic insulators (FMI) by atomistic spin-model simulations.

They discovered that the magnon junction effect (MJE) or magnon valve effect (MVE) could be duplicated, showing the magnetization-dependent magnon transmission. The MJE, as well as MVE, stem from the polarization of spin-wave.

Generally, spin-up (spin-down) latticeworks only can accommodate right- (left-) handed circularly polarized magnons. While only right-handed circular is preferred in AFI with upward magnetization, both left- and right-handed circular polarizations are permitted in AFI owing to two spin-opposite lattices. This selection regulation thus makes the complete reflection of spin-wave occur when magnons attempt to diffuse into a spin-lattice, which does not support their polarization.

For example, when excited right-handed round magnons in the spin-up region are infused right into the spin-down region, the selection rule would cause low magnon transmission over the interface. This phenomenon is called the magnon blocking effect, showing that spin-wave polarization plays an essential role in magnon transmission.

Furthermore, in theory, they researched the spreading behavior of spin waves at the interface of an antiferromagnetically paired heterojunction. It is revealed that the spin waves going through the interface are evanescent waves, and also, the incident waves are all reflected back, showing a magnetization-dependent magnon blocking effect in this framework.

The result shows that with the rise of the spin-wave frequency, the decay length lowers, and the evanescent wave concentrates more at the interface, revealing a magnonic skin effect similar to the skin impact of electromagnetic waves.

Moreover, a positive magnonic Goos-Hänchen shift of the reflected waves was additionally forecasted. It can be inferred by an effective reflection of interface shift triggered by the nonzero degeneration length of the evanescent waves.

In conclusion, the outcomes show that the efficient manipulation of coherent/incoherent magnons by magnon joints originates from the absolute chirality of magnons in magnetic materials. These discoveries confirm the physical basis of magnon tools to manipulate magnon transportation efficiently and offer a brand-new development direction and technological course for the growth of pure magnon-type storage and logic devices.

Originally published on Phys.org. Read the original article.

Reference:  Z. R. Yan et al, Magnonic skin effect and magnon valve effect in an antiferromagnetically coupled heterojunction, Physical Review B (2021). DOI: 10.1103/PhysRevB.104.L020413