Zhi-xiong Li

Spin-wave propagation in domain wall magnonic crystal

We present a new type of magnonic crystal consisting of a series of periodically distributed magnetic domain walls in a uniform strip. When spin waves propagate in such a structure, allowed and forbidden bands are formed due to translation symmetry and scattering of the spin waves at the domain wall boundaries caused by the dynamic stray field in the domain wall region. The control of the bandgap position in frequency and its width by the period of magnonic crystal and the domain wall width is investigated. It is found that the bandgap position decreases monotonously with the increase of the period or domain wall width, while the bandgap width displays an oscillated behavior. The origin of the oscillation of the bandgap width is discussed. This work may provide a new way of designing reconfigurable magnonic devices.

Internal friction peak associated with the interface motion in the martensitic transformation of CuAlNiMnTi shape memory alloy

Two internal friction peaks were observed in a CuAlNiMnTi polycrystalline shape memory alloy during the martensitic transformation through an incomplete phase transformation method, of which the high-temperature peak PH is discussed in the present study. It has been found that the PH peak is discernible only at relatively low frequencies and its maximum corresponds to the inflection point of the relative dynamic modulus rather than its minimum, i.e., this peak is related to a process without soft mode effect. An internal friction model is proposed to describe the PH peak based on the theory of phase nucleation and growth in the thermoelastic martensitic transformation and is verified by the experimental results.

Conversion of electronic to magnonic spin current at a heavy-metal magnetic-insulator interface

Electronic spin current is convertible to magnonic spin current via the creation or annihilation of thermal magnons at the interface of a magnetic insulator and a metal with a strong spin-orbital coupling. So far this phenomenon was evidenced in the linear regime. Based on analytical and fulledged numerical results for the non-linear regime we demonstrate that the generated thermal magnons or magnonic spin current in the insulator is asymmetric with respect to the charge current direction in the metal and exhibits a nonlinear dependence on the charge current density, which is explained by the tuning effect of the spin Hall torque and the magnetization damping. The results are also discussed in light of and are in line with recent experiments pointing to a new way of non-linear manipulation of spin with electrical means.

Spin waves in the soft layer of exchange-coupled soft/hard bilayers

The magnetic dynamical properties of the soft layer in exchange-coupled soft/hard bilayers have been investigated numerically using a one-dimensional atomic chain model. The frequencies and spatial profiles of spin wave eigenmodes are calculated during the magnetization reversal process of the soft layer. The spin wave modes exhibit a spatially modulated amplitude, which is especially evident for high-order modes. A dynamic pinning effect of surface magnetic moment is observed. The spin wave eigenfrequency decreases linearly with the increase of the magnetic field in the uniformly magnetized state and increases nonlinearly with field when spiral magnetization configuration is formed in the soft layer.

Effects of spin-polarized current on pulse field-induced precessional magnetization reversal

We investigate effects of a small DC spin-polarized current on the pulse field-induced precessional magnetization reversal in a thin elliptic magnetic element by micromagnetic simulations. We find that the spin-polarized current not only broadens the time window of the pulse duration, in which a successful precessional reversal is achievable, but also significantly suppresses the magnetization ringing after the reversal. The pulse time window as well as the decay rate of the ringing increase with increasing the current density. When a spin-polarized current with 5 MA/cm2 is applied, the time window increases from 80 ps to 112 ps, and the relaxation time of the ringing decreases from 1.1 ns to 0.32 ns. Our results provide useful information to achieve magnetic nanodevices based on precessional switching.