Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNon-stationary magnetization dynamics driven by spin transfer torque
151
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
This paper shows that the presence of two dynamical regimes, characterized by different precessional-axis, is the origin of the non-monotonic behavior of the output integrated power for large-amplitude magnetization precession driven by spin-polarized current in nanoscale exchange biased spin-valves. In particular, at the transition current between those two regimes exists an abruptly loss in the integrated output power. After the introduction of a time-frequency analysis of magnetization dynamics based on the wavelet transform, we performed a numerical experiment by means of micromagnetic simulations. Our results predicted that, together with a modulation of the frequency of the main excited mode of the magnetization precession, at high non-linear dynamical regime the instantaneous output power of the spin-torque oscillator can disappear and then reappear at nanosecond scale.
rate research
Read More
We present a time-resolved study of the magnetization dynamics in a microstructured Cr$|$Heusler$|$Pt waveguide driven by the Spin-Hall-Effect and the Spin-Transfer-Torque effect via short current pulses. In particular, we focus on the determination of the threshold current at which the spin-wave damping is compensated. We have developed a novel method based on the temporal evolution of the magnon density at the beginning of an applied current pulse at which the magnon density deviates from the thermal level. Since this method does not depend on the signal-to-noise ratio, it allows for a robust and reliable determination of the threshold current which is important for the characterization of any future application based on the Spin-Transfer-Torque effect.
Magnetic hopfion is three-dimensional (3D) topological soliton with novel spin structure that would enable exotic dynamics. Here we study the current driven 3D dynamics of a magnetic hopfion with unit Hopf index in a frustrated magnet. Attributed to spin Berry phase and symmetry of the hopfion, the phase space entangles multiple collective coordinates, thus the hopfion exhibits rich dynamics including longitudinal motion along the current direction, transverse motion perpendicular to the current direction, rotational motion and dilation. Furthermore, the characteristics of hopfion dynamics is determined by the ratio between the non-adiabatic spin transfer torque parameter and the damping parameter. Such peculiar 3D dynamics of magnetic hopfion could shed light on understanding the universal physics of hopfions in different systems and boost the prosperous development of 3D spintronics.
The concept of perpendicular shape anisotropy spin-transfer torque magnetic random-access memory (PSA-STT-MRAM) consists in increasing the storage layer thickness to values comparable to the cell diameter, to induce a perpendicular shape anisotropy in the magnetic storage layer. Making use of that contribution, the downsize scalability of the STT-MRAM may be extended towards sub-20 nm technological nodes, thanks to a reinforcement of the thermal stability factor $Delta$. Although the larger storage layer thickness improves $Delta$, it is expected to negatively impact the writing current and switching time. Hence, optimization of the cell dimensions (diameter, thickness) is of utmost importance for attaining a sufficiently high $Delta$ while keeping a moderate writing current. Micromagnetic simulations were carried out for different pillar thicknesses of fixed lateral size 20 nm. The switching time and the reversal mechanism were analysed as a function of the applied voltage and aspect-ratio (AR) of the storage layer. For AR $<$ 1, the magnetization reversal resembles a macrospin-like mechanism, while for AR $>$ 1 a non-coherent reversal is observed, characterized by the nucleation of a transverse domain wall at the ferromagnet/insulator interface which then propagates along the vertical axis of the pillar. It was further observed that the inverse of the switching time is linearly dependent on the applied voltage. This study was extended to sub-20 nm width with a value of $Delta$ around 80. It was observed that the voltage necessary to reverse the magnetic layer increases as the lateral size is reduced, accompanied with a transition from macrospin-reversal to a buckling-like reversal at high aspect-ratios.
The classical impact of electrical currents on magnetic nanostructures is analyzed with numerical calculations of current-density distributions and Oersted fields in typical contact geometries. For the Oersted field calculation, a hybrid finite element / boundary element method (FEM/BEM) technique is presented which can be applied to samples of arbitrary shape. Based on the FEM/BEM analysis, it is argued that reliable micromagnetic simulations on spin-tranfer-torque driven magnetization processes should include precise calculations of the Oersted field, particularly in the case of pillar contact geometries. Similarly, finite-element simulations demonstrate that numerical calculations of current-density distributions are required, e.g., in the case of magnetic strips with an indentation. Such strips are frequently used for the design of devices based on current-driven domain-wall motion. A dramatic increase of the current density is found at the apex of the notch, which is expected to strongly affect the magnetization processes in such strips.
The spin-transfer-torque-driven (STT-driven) dynamics of a domain wall in an easy-axis rare-earth transition-metal ferrimagnet is investigated theoretically and numerically in the vicinity of the angular momentum compensation point $T_A$, where the net spin density vanishes. The particular focus is given on the unusual interaction of the antiferromagnetic dynamics of a ferrimagnetic domain wall and the adiabatic component of STT, which is absent in antiferromagnets but exists in the ferrimagnets due to the dominant coupling of conduction electrons to transition-metal spins. Specifically, we first show that the STT-induced domain-wall velocity changes its sign across $T_A$ due to the sign change of the net spin density, giving rise to a phenomenon unique to ferrimagnets that can be used to characterize $T_A$ electrically. It is also shown that the frequency of the STT-induced domain-wall precession exhibits its maximum at $T_A$ and it can approach the spin-wave gap at sufficiently high currents. Lastly, we report a numerical observation that, as the current density increases, the domain-wall velocity starts to deviate from the linear-response result, calling for a more comprehensive theory for the domain-wall dynamics in ferrimagnets driven by a strong current.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
