Theoretical prediction of rotating magnon wavepacket in ferromagnets

We theoretically show that the magnon wavepacket has a rotational motion in two ways; a self-rotation and a motion along the boundary of the sample (edge current). They are similar to cyclotron motion of electrons, but unlike electrons the magnons have no charge and the rotation is not due to Lorenz force. These rotational motions are caused by the Berry phase in momentum space from magnon band structure. Furthermore, these rotational motions of the magnon give an additional correction term to the magnon Hall effect. We also discuss the Berry curvature effect in the classical limit of long-wavelength magnetostatic spin waves having macroscopic coherence length.Comment: 4pages, 2figures, accepted for publication in Phys. Rev. Let

Indentation plastic joining of steel rod and polycarbonate plate

Matsumoto R., . Indentation plastic joining of steel rod and polycarbonate plate. Journal of Materials Processing Technology 283, 116719 (2020); https://doi.org/10.1016/j.jmatprotec.2020.116719.A plastic joining method for fixing rods and plates, called “indentation plastic joining”, was applied to join a steel rod with a polycarbonate plate. The relationship between the indentation conditions and the joining characteristics was investigsted in joining and pullout experiments. The joining strength of the indented rod–plate was approximately 40 MPa in shear bonding stress (70 N/mm in pullout energy per unit area of the interface) in pullout test of the indented rod from the plate. The clamping associated with piercing of the plate was dominant in the joining strength of the indented rod–plate. This was confirmed from pullout test of the indented rod–plate under a releasing condition of the residual strain of the plate and the finite element analysis of the strain distribution of the plate. This was strongly derived from the Young's modulus–yield strength relationship of polycarbonate. To verify the unique characteristics of polycarbonate in indentation plastic joining of the steel rod and the polycarbonate plate, the indentation in an aluminum plate and the indentation of a steel rod with a notch were demonstrated

Chiral spin-wave edge modes in dipolar magnetic thin films

Based on a linearized Landau-Lifshitz equation, we show that two-dimensional periodic allay of ferromagnetic particles coupled with magnetic dipole-dipole interactions supports chiral spin-wave edge modes, when subjected under the magnetic field applied perpendicular to the plane. The mode propagates along a one-dimensional boundary of the system in a unidirectional way and it always has a chiral dispersion within a band gap for spin-wave volume modes. Contrary to the well-known Damon-Eshbach surface mode, the sense of the rotation depends not only on the direction of the field but also on the strength of the field; its chiral direction is generally determined by the sum of the so-called Chern integers defined for spin-wave volume modes below the band gap. Using simple tight-binding descriptions, we explain how the magnetic dipolar interaction endows spin-wave volume modes with non-zero Chern integers and how their values will be changed by the field.Comment: 18 pages, 16 figures, some trivial typo in equations are fixe

Topological chiral magnonic edge mode in a magnonic crystal

Topological phases have been explored in various fields in physics such as spintronics, photonics, liquid helium, correlated electron system and cold-atomic system. This leads to the recent foundation of emerging materials such as topological band insulators, topological photonic crystals and topological superconductors/superfluid. In this paper, we propose a topological magnonic crystal which provides protected chiral edge modes for magnetostatic spin waves. Based on a linearized Landau-Lifshitz equation, we show that a magnonic crystal with the dipolar interaction acquires spin-wave volume-mode band with non-zero Chern integer. We argue that such magnonic systems are accompanied by the same integer numbers of chiral spin-wave edge modes within a band gap for the volume-mode bands. In these edge modes, the spin wave propagates in a unidirectional manner without being scattered backward, which implements novel fault-tolerant spintronic devices.Comment: 12 pages, 7 figure