Achieving unidirectional propagation of twisted magnons in a magnetic nanodisk array

Twisted magnons (TMs) have great potential applications in communication and computing owing to the orbital angular momentum (OAM) degree of freedom. Realizing the unidirectional propagation of TMs is the key to design functional magnonics devices. Here we theoretically study the propagation of TMs in one-dimensional magnetic nanodisk arrays. By performing micromagnetic simulations, we find that the one-dimensional nanodisk array exhibits a few bands due to the collective excitations of TMs. A simple model by considering the exchange interaction is proposed to explain the emerging multiband structure and theoretical results agree well with micromagnetic simulations. Interestingly, for a zigzag structure, the dispersion curves and propagation images of TMs show obvious nonreciprocity for specific azimuthal quantum number ($l$), which originates from a geometric effect depending on the phase difference of TMs and the relative angle between two adjacent nanodisks. Utilizing this feature, one can conveniently realize the unidirectional propagation of TMs with arbitrary nonzero $l$. Our work provides important theoretical references for controlling the propagation of TMs.Comment: 7 pages, 6 figure

(chiral) Quantum well Rashba splitting in Sb monolayer on Au(111)

We present atomic and electronic structure investigations of Single-layer (110) surface of rhombohedral crystal formed Sb on Au(111) substrate. Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) reveal a pure 2D Sb stripe structure with mirror symmetry broken along the x axis direction. The electronic band structure is determined by angle-resolved photoemission spectroscopy (ARPES). The significantly complex surface band structure results from a combination of a surface band originating from the three different azimuthal orientations of the (110) rhombohedral phase and Umklapp scattered branches of Au sp band. The experimental bands are compared to the calculated band structure of $3\times\sqrt{3}$ periodicity of Sb(110). Most of the experimental band dispersions are qualitatively reproduced by the theoretical band structure except Umklapp scattered surface band. Taking advantage of our DFT calculations, we found the quantum well(QW) Rashba splitting bands appear at both $\bar{\Gamma}$ point and $\bar{X}$ point. Considering the surface Brillouin zone (SBZ) relationship between Sb(110) sub-unit cell and Au(111) surface, the distinct in energy position of QW states at $\bar{\Gamma}$ point and $\bar{X}$ point is found be a combination of the relative spin-orbital coupling(SOC) and the buckling of Sb monolayer on Au surface that work together. The orbital decomposition of the Sb(110) projected band structure indicates hybridization between Sb py state and Au state can modify the spin splitting of QW states due to the intrinsic large SOC of Au state introduced into the QW states

Backward magnetostatic surface spin waves in exchange coupled Co/FeNi bilayers

Propagation of backward magnetostatic surface spin waves (SWs) in exchange coupled Co/FeNi bilayers are studied by using Brillouin light scattering (BLS) technique. Two types of SWs modes were identified in our BLS measurements. They are magnetostatic surface waves (MSSWs) mode and perpendicular standing spin waves (PSSWs) mode. The dispersion relations of MSSWs obtained from the Stokes and Anti-Stokes measurements display respectively positive and negative group velocities. The Anti-Stokes branch with positive phase velocities and negative group velocities, known as backward magnetostatic surface mode originates from the magnetostatic interaction of the bilayer. The experimental data are in good agreement with the theoretical calculations. Our results are useful for understanding the SWs propagation and miniaturizing SWs storage devices

Thermal gradient driven domain wall dynamics

The issue of whether a thermal gradient acts like a magnetic field or an electric current in the domain wall (DW) dynamics is investigated. Broadly speaking, magnetization control knobs can be classified as energy-driving or angular-momentum driving forces. DW propagation driven by a static magnetic field is the best known example of the former in which the DW speed is proportional to the energy dissipation rate, and the current-driven DW motion is an example of the latter. Here we show that DW propagation speed driven by a thermal gradient can be fully explained as the angular momentum transfer between thermally generated spin current and DW. We found DW-plane rotation speed increases as DW width decreases. Both DW propagation speed along the wire and DW-plane rotation speed around the wire decrease with the Gilbert damping. These facts are consistent with the angular momentum transfer mechanism, but are distinct from the energy dissipation mechanism. We further show that magnonic spin-transfer torque (STT) generated by a thermal gradient has both damping-like and field-like components. By analyzing DW propagation speed and DW-plane rotational speed, the coefficient ( ) of the field-like STT arising from the non-adiabatic process, is obtained. It is found that does not depend on the thermal gradient; increases with uniaxial anisotropy (thinner DW); and decreases with the damping, in agreement with the physical picture that a larger damping or a thicker DW leads to a better alignment between the spin-current polarization and the local magnetization, or a better adiabaticity

Current-Driven Dynamics of Magnetic Hopfions

opological magnetic textures have attracted considerable interest since they exhibit new properties and might be useful in information technology. Magnetic hopfions are three-dimensional (3D) spatial variations in the magnetization with a nontrivial Hopf index. We find that, in ferromagnetic materials, two types of hopfions, Bloch-type and Néel-type hopfions, can be excited as metastable states in the presence of bulk and interfacial Dzyaloshinskii-Moriya interactions, respectively. We further investigate how hopfions can be driven by currents via spin-transfer torques (STTs) and spin-Hall torques (SHTs). Distinct from 2D ferromagnetic skyrmions, hopfions have a vanishing gyrovector. Consequently, there are no undesirable Hall effects. Néel-type hopfions move along the current direction via both STT and SHT, while Bloch-type hopfions move either transverse to the current direction via SHT or parallel to the current direction via STT. Our findings open the door to utilizing hopfions as information carriers

Study on the Evolution Law of Wellbore Stability Interface during Drilling of Offshore Gas Hydrate Reservoirs

The study of wellbore stability in offshore gas hydrate reservoirs is an important basis for the large-scale exploitation of natural gas hydrate resources. The wellbore stability analysis model in this study considers the evolution of the reservoir mechanical strength, wellbore temperature, and pressure parameters along the depth and uses plastic strain as a new criterion for wellbore instability. The wellbore stability model couples the hydrate phase transition near the wellbore area under the effect of the wellbore temperature and pressure field and the ‘heat–fluid–solid’ multifield evolution characteristics, and then simulates the stability evolution law of the wellbore area during the drilling process in the shallow seabed. The research results show that, owing to the low temperature of the seawater section and shallow formation, the temperature of the drilling fluid in the shallow layer of the wellbore can be maintained below the formation temperature, which effectively inhibits the decomposition of hydrates in the wellbore area. When the wellbore temperature increases or pressure decreases, the hydrate decomposition rate near the wellbore accelerates, and the unstable area of the wellbore will further expand. The research results can provide a reference for the design of drilling parameters for hydrate reservoirs

Magnetodynamic properties of dipole-coupled 1D magnonic crystals

Magnonic crystals are magnetic metamaterials, that provide a promising way to manipulate magnetodynamic properties by controlling the geometry of the patterned structures. Here, we study the magnetodynamic properties of 1D magnonic crystals consisting of parallel NiFe strips with different strip widths and separations. The strips couple via dipole–dipole interactions. As an alternative to experiments and/or micromagnetic simulations, we investigate the accuracy of a simple macrospin model. For the case of simple strips, a model with a single free parameter to account for an overestimation of the out of plane demagnetization of the magnonic lattice is described. By adjusting this parameter, a good fit with experimental as well as micromagnetic results is obtained. Moreover, the Gilbert damping is found independent of lattice constant however the inhomogeneous linewidth broadening found to increase with decreasing stripe separation