Active Magnetoelectric Control of Terahertz Spin Current (original) (raw)
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Terahertz spin current pulses controlled by magnetic heterostructures
Nature Nanotechnology, 2013
In spin-based electronics, information is encoded by the spin state of electron bunches . Processing this information requires the controlled transport of spin angular momentum through a solid 5,6 , preferably at frequencies reaching the so far unexplored terahertz regime . Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins 10-12 from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter 13 based on the inverse spin Hall effect , which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states 16 . Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters 7-9 .
Spin-Orbit-Torque Switching of Ferrimagnets by Terahertz Electrical Pulses
Physical Review Applied
In conventional spintronic devices, ferromagnetic materials are used, which have a magnetization dynamics timescale of around nanoseconds, setting a limit for the switching speed. Increasing the magnetization switching speed has been one of the major challenges for spintronic research. In this work we take advantage of the ultrafast magnetic dynamics in ferrimagnetic materials instead of ferromagnets, and we use femtosecond laser pulses and a plasmonic photoconductive switch to create THz electrical pulses for ferrimagnetic switching by spin-orbit torque. By anomalous Hall and magneto-optic Kerr effect (MOKE) measurement, we demonstrate the robust THz-electrical-pulse-driven magnetization switching of ferrimagnetic Gd-Fe-Co. The time-resolved MOKE shows more than 50-GHz magnetic resonance frequency of Gd-Fe-Co, indicating faster than 20-ps magnetic dynamics. X-ray magnetic circular dichroism demonstrates the antiferromagnetically coupled Fe and Gd sublattices. Our work provides a promising route to realize ultrafast operation speed for nonvolatile magnetic memory and logic applications.
Nature Communications, 2023
Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modeling, two excitation processes of spin dynamics in NiO: an off-resonant instantaneous optical spin torque in (111) oriented films and a strain-waveinduced THz torque induced by ultrafast Pt excitation in (001) oriented films. Both phenomena lead to the emission of a THz signal through the inverse spin Hall effect in the adjacent heavy metal layer. We unravel the characteristic timescales of the two excitation processes found to be < 50 fs and > 300 fs, respectively, and thus open new routes towards the development of fast optospintronic devices based on antiferromagnetic materials. Antiferromagnetic spintronics has recently become an important research field from both a fundamental viewpoint and its strong applicative potential 1,2. Antiferromagnets (AFM) have key advantages linked to their magnetic ordering: they are insensitive to perturbative external magnetic fields, stray fields are absent, and magnon modal frequencies reach the terahertz (THz) regime 1-3. This renders AFMs prime candidates for ultrafast spintronic devices 4 compared to their ferromagnetic counterparts. A recent work demonstrated the writing of AFM memory states with picosecond excitations 5. In parallel, narrowband sub-THz detection has been achieved using spin-pumping in AFMs 6,7. Another spintronic application is spintronic-based broadband THz emission that currently relies on ferromagnet/heavy metal
Large-Amplitude Spin Dynamics Driven by a THz Pulse in Resonance with an Electromagnon
Science, 2014
Multiferroics have attracted strong interest for potential applications where electric fields control magnetic order. The ultimate speed of control via magnetoelectric coupling, however, remains largely unexplored. Here we report on an experiment in which we drive spin dynamics in multiferroic TbMnO 3 with an intense few-cycle terahertz (THz) light pulse tuned to resonance with an electromagnon, an electric-dipole active spin excitation. We observe the resulting spin motion using time-resolved resonant soft x-ray diffraction. Our results show that it is possible to directly manipulate atomic-scale magnetic structures using the electric field of light on a sub-picosecond timescale. Main Text: Data storage devices based on ferromagnetic or ferroelectric materials depend strongly on domain reorientation, a process that typically occurs over time scales of several
Composite Multiferroic Terahertz Emitter: Polarization Control via an Electric Field
Physical review applied, 2022
Electrical control of conjugate degrees of freedom in multiferroics provides the advantage of reducing energy consumption to femto-and even attojoules per switch in spintronics and memory devices. This is achieved through the development of technologies that make it possible to fabricate artificial materials with constantly improving properties. Here, we present the design, physics, and characteristics of a composite multiferroic spintronic emitter, which provides electrical control of the emitted terahertz (THz) wave polarization. The effect is due to electrical control of the magnetization in a high-quality magnetostrictive superlattice, TbCo2/FeCo, deposited on an anisotropic piezoelectric substrate. In our approach, several mechanisms are realized in the system simultaneously: the strain-mediated coupling of the magnetic and piezoelectric subsystems, which operate in the range of the spin-reorientation transition of the magnetic superlattice, and THz-wave generation in the superlattice by an optical femtosecond pulse. This provides flexibility and control of the set of parameters. We determine the magnetoelectric parameter, which is responsible for THz polarization control. Our results offer a significant fundamental insight into the physics of composite multiferroic systems that can be used for applications of multiferroicity, primarily for THz spintronic emitters. We believe that our findings represent a decisive step towards technologies for other types of spintronic and memory devices.
Spintronic terahertz emitter with integrated electromagnetic control
Chinese Optics Letters, 2022
Spintronic thin films are considered as one of the promising terahertz (THz) source candidates, owing to their high performance and low cost. Much effort has been made to achieve spintronic THz sources with broadband and high conversion efficiency. However, the development of spintronic THz emitters with good compatibility, low cost, and miniaturized technology still faces many challenges. Therefore, it is urgent to extend commercial and portable spintronic THz emitters to satisfy many practical applications. Herein, we design a new generation of spintronic THz emitters composed of an alternating electromagnet and a miniaturized electronic controller. Not only can this new type of spintronic THz emitter largely simplify the ancillary equipment for spintronic sources, it also has a twice larger THz signal compared to the traditional THz time-domain spectroscopy systems with a mechanical chopper. Experimental results and theoretical calculations for electromagnetic coils show that our design can stably generate THz signals that are independent of the frequency and magnetic field of alternating signals. As the spin thin film is optimized, a magnetic field as low as 75 G satisfies the requirement for high performance THz emission. Hence, not only is the efficiency of the pump power enhanced, but also the driving current in the electromagnet is decreased. We believe that it has a wide range of applications and profound implications in THz technology based on spintronic emitters in the future.
Applied Physics Letters, 2019
Terahertz (THz) radiation covers the electromagnetic spectrum range between radiofrequency millimeter waves and optical farinfrared radiation, approximately 0.3 to 30 THz, and has been applied in astronomy, medical imaging, security, communication, and manufacturing 1,2 as well as a scientific tool in materials testing 3 and bio imaging, 4 or in the study of electron wakefield acceleration. 5 Among different THz sources, current extensive research focuses on emitters of ultrafast electromagnetic transients with a broad THz-range spectrum in order to control and capture spin, 6 charge, 7 or phase-transition-related processes on subpicosecond time scales. Recent observation of THz emissions from optically excited ferromagnet/metal (F/M) nanolayers 8-11 establishes a very elegant link between laser optics, spintronics, and THz radiation, merging these three very active scientific fields and having a tremendous potential for future applications. The uncomplicated fabrication of spintronic THz emitters can lead to widespread applications.
Journal of Physics D: Applied Physics, 2018
We study THz-driven spin dynamics in thin CoPt films with perpendicular magnetic anisotropy. Femtosecond magneto-optical Kerr effect measurements show that demagnetization amplitude of about 1% can be achieved with a peak THz electric field of 300 kV cm −1 , and a corresponding peak magnetic field of 0.1 T. The effect is more than an order of magnitude larger than observed in samples with easy-plane anisotropy irradiated with the same field strength. We also utilize finite-element simulations to design a meta-material structure that can enhance the THz magnetic field by more than an order of magnitude, over an area of several tens of square micrometers. Magnetic fields exceeding 1 Tesla, generated in such meta-materials with the available laser-based THz sources, are expected to produce full magnetization reversal via ultrafast ballistic precession driven by the THz radiation. Our results demonstrate the possibility of table-top ultrafast magnetization reversal induced by THz radiation.