Laser-induced spin dynamics of in-plane magnetized CoFeB films has been studied by using time-resolved magneto-optical Kerr effect measurements. While the effective demagnetization field shows little dependence on the pump laser fluence, the intrinsic damping constant has been found to be increased from 0.008 to 0.076 with the increase in the pump fluence from 2 mJ/cm2 to 20 mJ/cm2. This sharp enhancement has been shown to be transient and ascribed to the heating effect induced by the pump laser excitation, as the damping constant is almost unchanged when the pump-probe measurements are performed at a fixed pump fluence of 5 mJ/cm2 after irradiation by high power pump pulses.
While conventional microelectronic integrated circuits based on electron charges approach the theoretical limitations in foreseeable future, next-generation nonvolatile logic units based on electron spins have the potential to build logic networks of low power consumption. Central to this spin-based architecture is the development of a paradigm for in-memory computing with magnetic logic units. Here, we demonstrate the basic function of a transistor logic unit with patterned Y-shaped NiFe nanowires by gate-controlled domain-wall pinning and depinning. This spin-based architecture possesses the critical functionalities of transistors and can achieve a programmable logic gate by using only one Y-shaped nanostructure, which represents a universal design currently lacking for in-memory computing.
We have investigated the magnetic damping of precessional spin dynamics in defect-controlled epitaxial grown Fe 3 O 4 (111)/Yttria-stabilized Zirconia (YSZ) nanoscale films by all-optical pump-probe measurements. The intrinsic damping constant of the defect-free Fe 3 O 4 film is found to be strikingly larger than that of the asgrown Fe 3 O 4 film with structural defects. We demonstrate that the population of the first-order perpendicular standing spin wave (PSSW) mode, which is exclusively observed in the defect-free film under sufficiently high external magnetic fields, leads to the enhancement of the magnetic damping of the uniform precession (Kittel) mode. We propose a physical picture in which the PSSW mode acts as an additional channel for the extra energy dissipation of the Kittel mode. The energy transfer from Kittel mode to PSSW mode increases as in-plane magnetization precession becomes more uniform, resulting in the unique intrinsic magnetic damping enhancement in the defect-free Fe 3 O 4 film.The photo-induced precessional spin dynamics in various magnetic materials has attracted significant attention since the observation of the uniform magnetic precession (Kittel mode) and the corresponding first-order perpendicular standing spin wave (PSSW mode) in Ni films by the all-optical pump-probe technique. 1,2 After excitation by a femtosecond laser pulse, besides the uniform Kittel mode, different spin wave modes can be stimulated including first-order PSSW and Damon-Eshbach dipolar surface spin waves (DE modes). 3 At the same time, all-optical pump-probe measurements allow determination of the magnetic Gilbert damping α, 4,5 which is a key parameter for magnetic data recording and the nextgeneration spintronic memory devices such as Magnetoresistive Random Access Memory (MRAM) 6,7 . Therefore, understanding and controlling the magnetic damping is of crucial importance. Among many factors affecting the magnetic damping, structural defects are crucial because they are generally inevitable when preparing films or devices. It was proposed theoretically that defects scatter the Kittel mode into short wavelength spin waves via two magnon scattering, producing an extrinsic contribution to magnetic damping. 8 This extrinsic mechanism was verified by the fact that in thin NiFe films the FMR linewidth increases with decreasing thickness. 9
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