Picosecond Spin Orbit Torque Switching

Reducing energy dissipation while increasing speed in computation and memory is a long-standing challenge for spintronics research. In the last 20 years, femtosecond lasers have emerged as a tool to control the magnetization in specific magnetic materials at the picosecond timescale. However, the use of ultrafast optics in integrated circuits and memories would require a major paradigm shift. An ultrafast electrical control of the magnetization is far preferable for integrated systems. Here we demonstrate reliable and deterministic control of the out-of-plane magnetization of a 1 nm-thick Co layer with single 6 ps-wide electrical pulses that induce spin-orbit torques on the magnetization. We can monitor the ultrafast magnetization dynamics due to the spin-orbit torques on sub-picosecond timescales, thus far accessible only by numerical simulations. Due to the short duration of our pulses, we enter a counter-intuitive regime of switching where heat dissipation assists the reversal. Moreover, we estimate a low energy cost to switch the magnetization, projecting to below 1fJ for a (20 nm)^3 cell. These experiments prove that spintronic phenomena can be exploited on picosecond time-scales for full magnetic control and should launch a new regime of ultrafast spin torque studies and applications.Comment: Includes article + supplementary information. Latest version uses full name of the first author. Nature Electronics (2020

Engineering the spin conversion in graphene monolayer epitaxial structures

Spin Hall and Rashba-Edelstein effects, which are spin-to-charge conversion phenomena due to spin-orbit coupling (SOC), are attracting increasing interest as pathways to manage rapidly and at low consumption cost the storage and processing of a large amount of data in spintronic devices as well as more efficient energy harvesting by spin-caloritronics devices. Materials with large SOC, such as heavy metals (HMs), are traditionally employed to get large spin-to-charge conversion. More recently, the use of graphene (gr) in proximity with large SOC layers has been proposed as an efficient and tunable spin transport channel. Here, we explore the role of a graphene monolayer between Co and a HM and its interfacial spin transport properties by means of thermo-spin measurements. The gr/HM (Pt and Ta) stacks have been prepared on epitaxial Ir(111)/Co(111) structures grown on sapphire crystals, in which the spin detector (i.e., top HM) and the spin injector (i.e., Co) are all grown in situ under controlled conditions and present clean and sharp interfaces. We find that a gr monolayer retains the spin current injected into the HM from the bottom Co layer. This has been observed by detecting a net reduction in the sum of the spin Seebeck and interfacial contributions due to the presence of gr and independent from the spin Hall angle sign of the HM used

Artifacts in magnetic force microscopy under in-plane applied magnetic field: Magnetic bubble as a case study

WOS:000512907600007The study of magnetic bubble configuration in Co/Ni multilayers circular dots under in-plane magnetic field enlightens two magnetic force microscopy (MFM) measurement artifacts. We demonstrate that any tilt of the magnetic field producing out-of-plane field component due to the inhomogeneity of the MFM set up strongly affects the shape and size of the magnetic bubble independently of the in-plane field component intensity. Furthermore, MFM signal variations for in-plane magnetic field larger than 0.1 Tesla can only be understood considering MFM tip magnetization rotation. These two artifacts can have strong impact on MFM images and need to be carefully checked for reliable results in imaging skyrmionic structures with MFM under-field

Commensurability and chaos in magnetic vortex oscillations

Magnetic vortex dynamics in thin films is characterized by gyrotropic motion, the sense of gyration depending on the vortex core polarity, which reverses when a critical velocity is reached. Although self-sustained vortex oscillations in nanoscale systems are known to be possible, the precise role of core reversal in such dynamics remains unknown. Here we report on an experimental observation of periodic core reversal during self-sustained vortex gyration in a magnetic nanocontact system. By tuning the ratio between the gyration frequency and the rate of core reversal, we show that commensurate phase-locked and incommensurate chaotic states are possible, resulting in Devil's staircases with driving currents. These systems could have the potential to serve as tunable nanoscale radiofrequency electrical oscillators for secure communications, allowing schemes such as encryption by chaos on demand