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Register a new userElectrical manipulation of skyrmions in a chiral magnet
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Writing, erasing and computing are three fundamental operations required by any working electronic devices. Magnetic skyrmions could be basic bits in promising in emerging topological spintronic devices. In particular, skyrmions in chiral magnets have outstanding properties like compact texture, uniform size and high mobility. However, creating, deleting and driving isolated skyrmions, as prototypes of aforementioned basic operations, have been grand challenge in chiral magnets ever since the discovery of skyrmions, and achieving all these three operations in a single device is highly desirable. Here, by engineering chiral magnet Co$_8$Zn$_{10}$Mn$_2$ into the customized micro-devices for in-situ Lorentz transmission electron microscopy observations, we implement these three operations of skyrmions using nanosecond current pulses with a low a current density about $10^{10}$ A/m$^2$ at room temperature. A notched structure can create or delete magnetic skyrmions depending on the direction and magnitude of current pulses. We further show that the magnetic skyrmions can be deterministically shifted step-by-step by current pulses, allowing the establishment of the universal current-velocity relationship. These experimental results have immediate significance towards the skyrmion-based memory or logic devices.
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We demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. In our study we use an electrical detection technique of the ferromagnetic resonance driven by an in-plane ac-current in a NiFe/IrMn bilayer. At room temperature, we observe antidamping-like spin torque acting on the NiFe ferromagnet, generated by the in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the NiFe/IrMn interface. It highlights that, in addition to strong spin-orbit coupling, the antiferromagnetic order in IrMn governs the observed phenomenon.
Recent years have witnessed significant progresses in realizing skyrmions in chiral magnets1-4 and asymmetric magnetic multilayers5-13, as well as their electrical manipulation2,7,8,10. Equally important, thermal generation, manipulation and detection of skyrmions can be exploited for prototypical new architecture with integrated computation14 and energy harvesting15. It has yet to verify if skyrmions can be purely generated by heating16,17, and if their resultant direction of motion driven by temperature gradients follows the diffusion or, oppositely, the magnonic spin torque17-21. Here, we address these important issues in microstructured devices made of multilayers: (Ta_CoFeB_MgO)15, (Pt_CoFeB_MgO_Ta)15 and (Pt_Co_Ta)15 integrated with on-chip heaters, by using a full-field soft X-ray microscopy. The thermal generation of densely packed skyrmions is attributed to the low energy barrier at the device edge, together with the thermally induced morphological transition from stripe domains to skyrmions. The unidirectional diffusion of skyrmions from the hot region towards the cold region is experimentally observed. It can be theoretically explained by the combined contribution from repulsive forces between skyrmions, and thermal spin-orbit torques in competing with magnonic spin torques17,18,20,21 and entropic forces22. These thermally generated skyrmions can be further electrically detected by measuring the accompanied anomalous Nernst voltages23. The on-chip thermoelectric generation, manipulation and detection of skyrmions could open another exciting avenue for enabling skyrmionics, and promote interdisciplinary studies among spin caloritronics15, magnonics24 and skyrmionics3,4,12.
When an electron moves in a smoothly varying non-collinear magnetic structure, its spin-orientation adapts constantly, thereby inducing forces that act on both the magnetic structure and the electron. These forces may be described by electric and magnetic fields of an emergent electrodynamics. The topologically quantized winding number of so-called skyrmions, i.e., certain magnetic whirls, discovered recently in chiral magnets are theoretically predicted to induce exactly one quantum of emergent magnetic flux per skyrmion. A moving skyrmion is therefore expected to induce an emergent electric field following Faradays law of induction, which inherits this topological quantization. Here we report Hall effect measurements, which establish quantitatively the predicted emergent electrodynamics. This allows to obtain quantitative evidence of the depinning of skyrmions from impurities at ultra-low current densities of only 10^6 A/m^2 and their subsequent motion. The combination of exceptionally small current densities and simple transport measurements offers fundamental insights into the connection between emergent and real electrodynamics of skyrmions in chiral magnets, and promises to be important for applications in the long-term.
Skyrmions, topologically protected vortex-like nanometric spin textures in magnets, have been attracting increasing attention for emergent electromagnetic responses and possible technological applications for spintronics. In particular, metallic magnets with chiral and cubic/tetragonal crystal structure may have high potential to host skyrmions that can be driven by low electrical current excitation. However, experimental observations of skyrmions have so far been limited to below room temperature for the metallic chiral magnets, specifically for the MnSi-type B20 compounds. Toward technological applications, it is crucial to transcend this limitation. Here we demonstrate the formation of skyrmions with unique spin helicity both at and above room temperature in a family of cubic chiral magnets: beta-Mn-type Co-Zn-Mn alloys with a different chiral space group from that of B20 compounds. Lorentz transmission electron microscopy (LTEM), magnetization, and small angle neutron scattering (SANS) measurements unambiguously reveal the formation of a skyrmion crystal under the application of magnetic field (H<~1 kOe) in both thin- plate (thickness<150 nm) and bulk forms.
Colour centres with long-lived spins are established platforms for quantum sensing and quantum information applications. Colour centres exist in different charge states, each of them with distinct optical and spin properties. Application to quantum technology requires the capability to access and stabilize charge states for each specific task. Here, we investigate charge state manipulation of individual silicon vacancies in silicon carbide, a system which has recently shown a unique combination of long spin coherence time and ultrastable spin-selective optical transitions. In particular, we demonstrate charge state switching through the bias applied to the colour centre in an integrated silicon carbide opto-electronic device. We show that the electronic environment defined by the doping profile and the distribution of other defects in the device plays a key role for charge state control. Our experimental results and numerical modeling evidence that control of these complex interactions can, under certain conditions, enhance the photon emission rate. These findings open the way for deterministic control over the charge state of spin-active colour centres for quantum technology and provide novel techniques for monitoring doping profiles and voltage sensing in microscopic devices.
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