Generation and utilization of pure spin current have revolutionized energy-efficient spintronic devices. Spin pumping effect generates pure spin current, and for its increased efficiency, spin-mixing conductance and interfacial spin transparency are imperative. The plethora of reports available on generation of spin current with giant magnitude overlook the interfacial spin transparency. Here, we investigate spin pumping in β-Ta/CoFeB thin films by an all-optical time-resolved magneto-optical Kerr effect technique. From variation of Gilbert damping with Ta and CoFeB thicknesses, we extract the spin diffusion length of β-Ta and spin-mixing conductances. Consequently, interfacial spin transparency is derived as 0.50 ± 0.03 from the spin Hall magnetoresistance model for the β-Ta/CoFeB interface. Furthermore, invariance of Gilbert damping with Cu spacer layer thickness inserted between β-Ta and CoFeB layers confirms the absence of other interface effects including spin memory loss. This demonstrates a reliable and noninvasive way to determine interfacial spin transparency and signifies its role in generation of pure spin current by spin pumping effect.

Nanomagnets form the building blocks for a gamut of miniaturized energyefficient devices including data storage, memory, wave-based computing, sensors and biomedical devices. They also offer a span of exotic phenomena and stern challenges. The rapid advancements of nanofabrication, characterization and numerical simulations during last two decades have made it possible to explore a plethora of science and technology related to nanomagnet dynamics. The progress in the magnetization dynamics of single nanomagnets and one-and two-dimensional arrays of nanostructures in the form of dots, antidots, nanoparticles, binary and bicomponent structures and patterned multilayers have been presented in details.Progress in unconventional and new structures like artificial spin ice and three-dimensional nanomagnets and spin textures like domain walls, vortex and skyrmions have been presented. Furthermore, a huge variety of new topics in the magnetization dynamics of magnetic nanostructures are rapidly emerging. An overview of the steadily evolving topics like spatiotemporal imaging of fast dynamics of nanostructures, dynamics of spin textures, artificial spin ice have been discussed. In addition, dynamics of contemporary and newly transpired magnetic architectures such as nanomagnet arrays with complex basis and symmetry, magnonic quasicrystals, fractals, defect structures, novel three-dimensional structures have been introduced. Effects of various spin-orbit coupling and ensuing spin textures as well as quantum hybrid systems comprising of magnon-photon, magnon-phonon and magnon-magnon coupling, antiferromagnetic nanostructures are rapidly growing and are expected to dominate this research field in the coming years. Finally, associated topics like nutation dynamics and nanomagnet antenna are briefly discussed. Despite showing a great progress, only a small fraction of nanomagnetism and its ancillary topics have been explored so far and huge efforts are envisaged in this evergrowing research area in the generations to come.

Three-dimensional magnetic nanostructures are now attracting intense interest due to their potential as ultrahigh density future magnetic storage devices. Here, we report on the study of ultrafast magnetization dynamics of a complex three-dimensional magnetic nanostructure. Arrays of magnetic tetrapod structures were fabricated using a combination of two-photon lithography (TPL) and electrodeposition. All-optical time-resolved magneto-optical Kerr microscopy was exploited to probe the spin-wave modes from the junction of a single tetrapod structure. Micromagnetic simulations reveal that the nature of these modes originates from the intricate three-dimensional tetrapod structure. Our findings enhance the basic knowledge about the dynamic control of spin waves in complex three-dimensional magnetic elements which are imperative for the construction of modern spintronic devices.

The development of advanced spintronics devices hinges on the efficient generation and utilization of pure spin current. In materials with large spin-orbit coupling, the spin Hall effect may convert charge current to pure spin current and a large conversion efficiency, which is quantified by spin Hall angle (SHA), is desirable for the realization of miniaturized and energy efficient spintronic devices. Here, we report a giant SHA in beta-tungsten (β-W) thin films in Sub/W(t)/Co 20 Fe 60 B 20 (3 nm)/SiO 2 (2 nm) heterostructures with variable W thickness.We employed an all-optical time-resolved magneto-optical Kerr effect microscope for an unambiguous determination of SHA using the principle of modulation of Gilbert damping of the adjacent ferromagnetic layer by the spin-orbit torque from the W layer. A non-monotonic variation of SHA with W layer thickness (t) is observed with a maximum of about 0.4 at about t = 3 nm, followed by a sudden reduction to a very low value at t = 6 nm. This variation of SHA with W-thickness correlates well with the thickness dependent structural phase transition and resistivity variation of W above the spin diffusion length of W, while below this length the interfacial electronic effect at W/CoFeB influences the estimation of SHA.2

Magneto-elastic (or "straintronic") switching has emerged as an extremely energy-efficient mechanism for switching the magnetization of magnetostrictive nanomagnets in magnetic memory, logic and non-Boolean circuits. Here, we investigate the ultrafast magneto-dynamics associated with straintronic switching in a single quasi-elliptical magnetostrictive Co nanomagnet deposited on a piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) substrate using time-resolved magneto-optical Kerr effect (TR-MOKE) measurements. The pulsed laser pump beam in the TR-MOKE plays a dual role: it causes precession of the nanomagnet's magnetization about an applied bias magnetic field and it also generates surface acoustic waves (SAWs) in the piezoelectric substrate that produce periodic strains in the magnetostrictive nanomagnet and modulate the precessional dynamics. This modulation gives rise to intriguing hybrid magneto-dynamical modes in the nanomagnet, with rich spin wave texture. The characteristic frequencies of these modes are 5-15 GHz, indicating that strain can affect magnetization in a magnetostrictive nanomagnet in time scales much smaller than 1 ns (~100 ps). This can enable ~10 GHz-range magneto-elastic nanooscillators that are actuated by strain instead of a spin-polarized current, as well as ultrafast magneto-electric generation of spin waves for magnonic logic circuits, holograms, etc.

We study the spin-wave dynamics in nanoscale antidot lattices based on Co/Pd multilayers with perpendicular magnetic anisotropy. Using time-resolved magneto-optical Kerr effect measurements we demonstrate that the variation of the antidot shape introduces significant change in the spin-wave spectra, especially in the lower frequency range. By employing micromagnetic simulations we show that additional peaks observed in the measured spectra are related to narrow shell regions around the antidots, where the magnetic anisotropy is reduced due to the Ga + ion irradiation during the focused ion beam milling process of the antidot fabrication. The results point at new possibilities for exploitation of localized spin waves in outof-plane magnetized thin films, which are easily tunable and suitable for magnonics applications.I.

Development of all-magnetic transistor with favorable properties is an important step towards a new paradigm of all-magnetic computation. Recently, we showed such possibility in a Magnetic Vortex Transistor (MVT). Here, we demonstrate enhanced amplification in MVT achieved by introducing geometrical asymmetry in a three vortex sequence. The resulting asymmetry in core to core distance in the three vortex sequence led to enhanced amplification of the MVT output. A cascade of antivortices travelling in different trajectories including a nearly elliptical trajectory through the dynamic stray field is found to be responsible for this amplification. This asymmetric vortex transistor is further used for a successful fan-out operation, which gives large and nearly equal gains in two output branches. This large amplification in magnetic vortex gyration in magnetic vortex transistor is proposed to be maintained for a network of vortex transistor. The above observations promote the magnetic vortex transistors to be used in complex circuits and logic operations.

Laser induced modulation of the magnetization dynamics occurring over various time-scales have been unified here for a Ni80Fe20 thin film excited by amplified femtosecond laser pulses. The weak correlation between demagnetization time and pump fluence with substantial enhancement in remagnetization time is demonstrated using three-temperature model considering the temperatures of electron, spin and lattice. The picosecond magnetization dynamics is modeled using the Landau-Lifshitz-Gilbert equation. With increasing pump fluence the Gilbert damping parameter shows significant enhancement from its intrinsic value due to increment in the ratio of electronic temperature to Curie temperature within very short time scale. The precessional frequency experiences noticeable red shift with increasing pump fluence. The changes in the local magnetic properties due to accumulation and dissipation of thermal energy within the probed volume are described by the evolution of temporal chirp parameter in a comprehensive manner. A unification of ultrafast magnetic processes and its control over broad timescale would enable the integration of various magnetic processes in a single device and use one effect to control another. 2