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Register a new userElectrical manipulation of a ferromagnet by an antiferromagnet
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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.
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We consider the details of the near-surface electronic band structure of a prototypical ferromagnet, Fe(001). Using high resolution angle-resolved photoemission spectroscopy we demonstrate openings of the spin-orbit induced electronic band gaps near the Fermi level. The band gaps and thus the Fermi surface can be manipulated by changing the remanent magnetization direction. The effect is of the order of $Delta$E = 100 meV and $Delta text {k} = 0.1,text{AA}^{-1}$. We show that the observed dispersions are dominated by the bulk band structure. First-principles calculations and one-step photoemission calculations suggest that the effect is related to changes in the electronic ground state, rather than caused by the photoemission process itself. The symmetry of the effect indicates that the observed electronic bulk states are influenced by the presence of the surface, which might be understood as related to a Rashba-type effect. By pinpointing the regions in the electronic band structure where the switchable band gaps occur, we demonstrate the significance of spin-orbit interaction even for elements as light as 3d ferromagnets.
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.
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.
While the electrical current manipulation of antiferromagnets (AFMs) has been demonstrated, the extent of the studied AFM materials has been limited with few systematic experiments and a poor understanding. We compare the electrical current switching of the exchange-bias field ($H_{ex}$) in AFM-Mn$_3A$N/ferromagnet-Co$_3$FeN bilayers. An applied pulse current can manipulate $H_{ex}$ with respect to the current density and FM layer magnetization, which shifts exponentially as a function of the current density. We found that the saturation current density and exponential decay constant $tau$ increase with the local moment of AFM Mn atoms. Our results highlight the effect of the AFM local moment to electrical current switching of $H_{ex}$, although it has a near-zero net magnetization, and may provide a facile way to explore the electrical current manipulation of AFM materials.
Spin waves (SWs), the collective precessional motion of spins in a magnetic system, have been proposed as a promising alternative system with low-power consumption for encoding information. Spin Hall nano-oscillator (SHNO), a new-type spintronic nano-device, can electrically excite and control spin waves in both nanoscale magnetic metals and insulators with low damping by the spin current due to spin Hall effect. Here, we will review recent progress about spin-wave excitation and experimental parameters dependent spectrum in SHNOs. The nanogap SHNOs based on in-plane magnetization Py/Pt exhibits a nonlinear self-localized bullet soliton localized at the center of the gap between the electrodes and a secondary high-frequency mode which coexists with the primary bullet mode at higher currents. While in the nanogap SHNOs with strong perpendicular magnetic anisotropy (PMA), besides both nonlinear bullet soliton and propagating spin-wave mode are achieved and controlled by varying the external magnetic field and current, the magnetic bubble skyrmion mode also can be excited at a low in-plane magnetic field. These SW modes show thermal-induced mode hopping behavior at high temperature due to the coupling between modes mediated by thermal-magnon-mediated scattering. Moreover, thanks to PMA-induced effective field, a single coherent mode also can be achieved without applying an external magnetic field. The strong nonlinear effect of spin-waves makes SHNOs easy to achieve synchronization with external microwave signals or mutual synchronization between multiple oscillators with improving the coherence and power of oscillation modes significantly. Spin-waves in SHNOs with an external free magnetic layer have a wide range of applications from as a nanoscale signal source of low-power consumption magnonic devices to spin-based neuromorphic computing systems in the field of artificial intelligence.
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