Role of Spin–Orbit Coupling on Ultrafast Spin Dynamics in Nonmagnet/Ferromagnet Heterostructures

Abstract

Spin-orbit coupling (SOC), the interaction between spin and orbital angular momentum of electrons, is imperative to control magnetic properties of nonmagnet (NM)/ferromagnet (FM) heterostructures and design energy-efficient and faster spin-based devices. Here, femtosecond pulsed laser-induced time-resolved magneto-optical Kerr effect magnetometry is employed to investigate magnetization dynamics in different NM/Co 20 Fe 60 B 20 heterostructures, where the NM layer varies as Cu, Ta, W, Pt, Ta/Ru/Ta, and Si/SiO 2 (no underlayer) that differ in SOC strength. It is observed that there is a systematic variation in ultrafast demagnetization time (𝝉 m ), fast remagnetization time (𝝉 r ), and Gilbert damping parameter (𝜶) with the SOC strength of the underlayer and an inverse relationship between 𝜶 and 𝝉 m , 𝝉 r is established due to the dominant contribution of spin current transport in ultrafast demagnetization and fast remagnetization processes. The spin pumping formalism estimates the effective spin-mixing conductance (G eff ) for different interfaces, which signifies that the high SOC strength of underlayers results in high G eff indicating more efficient transport of spin current through it. This study suggests that the SOC strength of the NM underlayer plays a significant role in controlling the ultrafast demagnetization process through interfacial spin current transport in a NM/FM heterostructure which can be beneficial for the development of ultrafast spintronics devices.

Mid-infrared optical properties of non-magnetic-metal/CoFeB/MgO heterostructures

“…We emphasize that considering the 2DEG layer at the NM/-CoFeB interface, as shown in figure 1, was a matter of choice from the point of view of ellipsometric modeling as no difference in calculated results was detected when placing it at the CoFeB/MgO interface. However, the final decision on the location is physically sustained by fast demagnetization/remagnetization measurements carried on NM/CoFeB heterostructures, similar to the present ones, where interfacial SOC exists in the absence of the MgO layer [43]. The 2DEG DF and its effects are presented in section 4.3.…”

“…A direct comparison is shown in figure S7 in the Supplemental Information. Similarly, the strength of the interfacial SOC-related peak shows a progression, in terms of the seeding NM, as Pt ≳ W ≫ Cu, which relates to the SOC strength of the underlying NM itself [43]. On the other hand, the energy positions of the peaks do not reveal any ordering: 280 for Pt-, 300 for W-, and a shoulder at around 200 meV for the Cu-seeded samples as shown in the inset of figure 6(a).…”

Heavy metal deposition temperature tuned spin pumping efficiency control in permalloy/tantalum bilayers

“…Spin pumping strongly depends on the choice of materials used for FM and HM layers [13][14][15][16][17]. Among these material classes permalloy (Py)/tantalum (Ta) bilayer has emerged as one of the promising heterostructure having significant spin pumping efficiency [17][18][19][20][21][22][23].…”

“…Permalloy is an extremely important spintronic material [24,25] having useful properties like high spin density, high magnetic permeability and low magnetic damping [26,27]. On the other hand Ta is being widely explored in FM/HM bilayers due to its high spin-orbit coupling that allows efficient charge current to spin current conversion and vice-versa [14][15][16][17][18][19]. Spin mixing conductance is a key parameter that is used to characterize the spin pumping efficiency.…”

Femtosecond Laser-Induced Transient Magnetization Enhancement and Ultrafast Demagnetization Mediated by Domain Wall Origami

“…Over the two decades since the advent of ultrafast demagnetization, different mechanisms have been proposed to explain the associated ultrafast dissipation of energy and angular momentum. ,, Spin-flip processes were originally considered to be the primary channel for angular momentum transfer at ultrafast time scales but often cannot be straightforwardly applied to explain the varied physics that may arise in magnetically heterogeneous systems such as magnetic alloys, compounds, and multilayers. A theory of superdiffusive spin transport (SST) was later developed to understand ultrafast demagnetization in layered ferromagnet (FM)/metal, FM/semiconductor (SC), and FM/metal/FM heterostructures.…”