Laser-Induced Magnetization Dynamics in Interlayer-Coupled [Ni/Co]₄/Ru/[Co/Ni]₃ Perpendicular Magnetic Films for Information Storage

Abstract

Rapid manipulation of magnetization orientation by a femtosecond pulse laser is an efficient way for advanced information storage technology. We report a comprehensive study of the interlayer coupling effect on the magnetization dynamics in [Ni/Co]4/Ru­(t Ru)/[Co/Ni]3 perpendicular magnetic films by the time-resolved magneto-optical Kerr effect approach. By controlling the antiferromagnetic (AF) interlayer coupling field H ex and external magnetic field H, we demonstrate distinctly different dynamic behaviors upon laser excitation. First, three kinds of demagnetization process, including nonchange, ultrafast increase, or decrease in Kerr signal, can occur within the short time delay of 2 ps. Second, in the relaxation process, in addition to the normal coherent precession, an additional out-of-phase mode is detected for the AF-coupled samples, whose amplitude and frequency depend also strongly on H ex and H. The H-dependent frequency curves of both modes are well interpreted with the deduced analytical expression by taking the bilinear and biquadratic coupling into account. Additionally, the magnetic damping of optical mode not only is coupling-dependent but also shows a strong peak at a critical field H crit, which is found to scale with H ex. These results provide new insights into the magnetic dynamics in perpendicularly exchange-coupled systems for spintronic applications with ultrafast control of information operation.

Ultrafast optical manipulation of magnetic order in ferromagnetic materials

“…Therefore, the magnetization dynamics is governed by a transient tilt of magnetization from the effective magnetic field and successive spin precession around the effective magnetic field. For example, in the case of the magnetic anisotropy change-induced torque, laser energy would thermalize metallic ferromagnets and reduce the magnetization amplitude [78,79], or change the exchange coupling strength in composite thin films [86,87]. Both effects will change the effective magnetic field direction and produce torque.…”

Materials Engineering Enabled by Time-Resolved Magneto-Optical Kerr Effect for Spintronic Applications

“…For SAF, both the damping and the interlayer coupling strength are important properties that affect the dynamics of the system. Such properties have been successfully characterized by FMR in the literature; however, most of the SAF structures studied by FMR possess an in-plane magnetic anisotropy (IMA-SAF). ,− Very recently, TR-MOKE has extended the dynamic studies of SAF structures to cover both IMA-SAF and PMA-SAF materials, − owing to its capabilities of reaching high precessional frequencies and large external fields. ,, …”

“…The dependence of f vs H ext can be well described by a theoretical model which considers the coupling strength between two layers. , The exchange field ( H ex ) can be extracted from the model fitting of frequency data in the high-field region . To date, the damping studies using TR-MOKE for PMA-SAF structures are still limited in scope, and only the effective damping constant has been reported in the literature. , A comprehensive model for separating the intrinsic α from the inhomogeneous broadening contribution is still missing and needs further development.…”

Temperature-Dependent Magnetization Dynamics in Nanoscale Cu(tCu)/[Co/Ni]N Perpendicular Multilayers: Implications for Spintronic Applications

“…In order to clearly address the variation behaviors of K u and α with T varying as well as their underlying mechanisms in perpendicular magnetic systems, in this work, we perform a detailed magnetization dynamics study on nanoscale Ta/Cu­( t Cu )/[Co/Ni] N /Ta multilayers at various temperatures, which is known to own high spin polarization and controllable PMA strength. , Compared with the traditional ferromagnetic resonance technique in the frequency domain, the polar time-resolved magnetic optical effect (TR-MOKE) technique used in this work has a much higher signal-to-noise ratio for the PMA films. − It is found that for the [Co/Ni] N multilayer films of N = 2 and 5, both the effective perpendicular anisotropy field H keff and intrinsic damping α 0 exhibit a nonmonotonic varying behavior with T decreasing from room temperature (296 K) down to 80 K, as a result of the competition between the increased K u and decreased TMS. In contrast, H keff and α 0 for the sample of N = 8 keep increasing within the same T range.…”