We are reporting a new type of synchronization, termed dancing synchronization, between two spin-torque nano-oscillators (STNOs) coupled through spin waves. Different from the known synchronizations in which two STNOs are locked with various fixed re
lative phases, in this new synchronized state two STNOs have the same frequency, but their relative phase varies periodically within the common period, resulting in a dynamic waving pattern. The amplitude of the oscillating relative phase depends on the coupling strength of two STNOs, as well as the driven currents. The dancing synchronization turns out to be universal, and can exist in two nonlinear Van der Pol oscillators coupled both reactively and dissipativly. Our findings open doors for new functional STNO-based devices.
Ferroelectric materials are spontaneous symmetry breaking systems characterized by ordered electric polarizations. Similar to its ferromagnetic counterpart, a ferroelectric domain wall can be regarded as a soft interface separating two different ferr
oelectric domains. Here we show that two bound state excitations of electric polarization (polar wave), or the vibration and breathing modes, can be hosted and propagate within the ferroelectric domain wall. Specially, the vibration polar wave has zero frequency gap, thus is constricted deeply inside ferroelectric domain wall, and can propagate even in the presence of local pinnings. The ferroelectric domain wall waveguide as demonstrated here, offers new paradigm in developing ferroelectric information processing units.
The spontaneous Hall effect is usually governed by three conventional mechanisms, such as the Berry curvature, skew scattering and side jump, which widely exist in ferromagnetic or antiferromagnetic materials. However, in this work, based on first pr
inciple calculations, we predict a giant crystal Hall effect (CHE) in the antiferromagnetic $gamma$-FeMn, which can not be understood by the previous three conventional mechanisms and the Hall angle therein can be as large as 18.4% at low temperature. Furthermore, with Boltzmann transport equation and a tight-binding model, we conclude that, the asymmetric group velocities on Fermi surface is the origin of this CHE in $gamma$-FeMn. And with a systematic symmetry argument, we show that, this unusual effect is not dependent on specific materials but universal in any crystals with similar symmetry even without local magnetization.
Based on the exact muffin-tin orbitals (EMTOs), we developed a first-principles method to calculate the current operators and investigated the anomalous Hall effect in bcc Fe as an example, with which we successfully separated the skew scattering con
tribution from the side jump and intrinsic contributions by fitting the scaling law with the introduction of sparse impurities. By investigating the temperature dependence of the anomalous Hall effect in bulk Fe, we predicted a fluctuated anomalous Hall angle as a function of temperature when considering only phonons, which, in the future, can be measured in experiments by suppressing magnon excitation, e.g., by applying a high external magnetic field.
The processional switching mechanism governs magnetic switching in magnetic tunnel junctions (MTJs) in the sub-nanosecond range, which limits the application of spin transfer torque magnetic random access memory (STT-MRAM) in the ultrafast region. In
this paper, we propose a new picosecond magnetic switching mechanism in a synthetic antiferromagnetic (SAF) structure using the adjustable Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction controlled by an external electric field (E-field). It is shown that along with the sign change of the RKKY interaction in the SAF structure with an external E-field, the critical switching current density can be significantly reduced by one order of magnitude compared to that of a normal MTJ design at 100 ps; thus, this novel STT-MRAM can be written with a very low switching current density to avoid the MTJ breakdown problem and reduce the writing energy. To understand the physical origin of this abnormal phenomenon, a toy model is proposed in which the external-E-field-controlled sign change of the RKKY interaction in the SAF structure provides an extra contribution to the total energy that helps thespins overcome the energy barrier and break the processional switching mechanism.
