Nonreciprocal Transmission of Incoherent Magnons with Asymmetric Diffusion Length

Giant Spin-Orbit Induced Magnon Nonreciprocity in Ultrathin Ferromagnets

The propagation characteristics of fermionic and bosonic quasiparticles determine the fundamental transport properties of solids and are of great technological relevance for designing logic devices. In particular, nonreciprocity, which describes that a quasiparticle flows preferably along a certain direction of a symmetry path, is an essential requirement to realize logic architectures, e.g., switches, diodes, transistors, etc. Here we introduce a mechanism, which leads to giant nonreciprocity of ultrafast terahertz magnons in ferromagnetic films with a large spin-orbit coupling. The mechanism is based on the competition between the exchange and spin-orbit scattering. We anticipate that the effect can be used to excite nonreciprocal or even unidirectional magnons in a large class of ultrathin films and nanostructures grown on substrates with a large spin-orbit coupling.

Efficient Gating of Magnons by Proximity Superconductors

Electrostatic gating confines and controls the transport of electrons in integrated circuits. Magnons, the quanta of spin waves of the magnetic order, are promising alternative information carriers, but difficult to gate. Here we report that superconducting strips on top of thin magnetic films can totally reflect magnons by their diamagnetic response to the magnon stray fields. The induced large frequency shifts unidirectionally block the magnons propagating normal to the magnetization. Two superconducting gates parallel to the magnetization create a magnonic cavity. The option to gate coherent magnons adds functionalities to magnonic devices, such as reprogrammable logical devices and increased couplings to other degrees of freedom.

Piezoelectric Strain-Controlled Magnon Spin Current Transport in an Antiferromagnet

As the core of spintronics, the transport of spin aims at a low-dissipation data process. The pure spin current transmission carried by magnons in antiferromagnetic insulators is natively endowed with superiority such as long-distance propagation and ultrafast speed. However, the traditional control of magnon transport in an antiferromagnet via a magnetic field or temperature variation adds critical inconvenience to practical applications. Controlling magnon transport by electric methods is a promising way to overcome such embarrassment and to promote the development of energy-efficient antiferromagnetic logic. Here, the experimental realization of an electric field-induced piezoelectric strain-controlled magnon spin current transmission through the antiferromagnetic insulator in the Y₃Fe₅O₁₂/Cr₂O₃/Pt trilayer is reported. An efficient and nonvolatile manipulation of magnon propagation/blocking is achieved by changing the relative direction between the Néel vector and spin polarization, which is tuned by ferroelastic strain from the piezoelectric substrate. The piezoelectric strain-controlled antiferromagnetic magnon transport opens an avenue for the exploitation of antiferromagnet-based spin/magnon transistors with ultrahigh energy efficiency.

Tunable Magnonic Chern Bands and Chiral Spin Currents in Magnetic Multilayers

Realization of novel topological phases in magnonic band structures represents a new opportunity for the development of spintronics and magnonics with low power consumption. In this work, we show that in antiparallelly aligned magnetic multilayers, the long-range, chiral dipolar interaction between propagating magnons generates bulk bands with nonzero Chern integers and magnonic surface states carrying chiral spin currents. The surface states are highly localized and can be easily toggled between nontrivial and trivial phases through an external magnetic field. The realization of chiral surface spin currents in this dipolarly coupled heterostructure represents a magnonic implementation of the coupled wire model that has been extensively explored in electronic systems. Our work presents an easy-to-implement system for realizing topological magnonic surface states and low-dissipation spin current transport in a tunable manner.