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A Magnetic Field Switching Circuit
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Topological insulator-based high efficiency switching of magnetic unit, method and applications
A magneto-electronic device may include: a spin-orbit torque (SOT) generator layer; a magnetic memory layer; and/or sensing electrodes configured to measure a Hall effect of the magnetic memory layer. The SOT generator layer may include topological insulator material, and the magnetic memory layer may include ferromagnetic material with perpendicular magnetic anisotropy. A magneto-electronic device may include: a spin-orbit torque (SOT) generator layer; a first magnetic memory layer on the SOT generator layer; an insulating layer on the first magnetic memory layer; and/or a second magnetic memory layer on the insulating layer. The SOT generator layer may include topological insulator material. The first magnetic memory layer and the second magnetic memory layer may include ferromagnetic material with either perpendicular magnetic anisotropy or in-plane magnetic anisotropy.
Spin-neurons: A possible path to energy-efficient neuromorphic computers
Recent years have witnessed growing interest in the field of brain-inspired computing based on neural-network architectures. In order to translate the related algorithmic models into powerful, yet energy-efficient cognitive-computing hardware, computing-devices beyond CMOS may need to be explored. The suitability of such devices to this field of computing would strongly depend upon how closely their physical characteristics match with the essential computing primitives employed in such models. In this work, we discuss the rationale of applying emerging spin-torque devices for bio-inspired computing. Recent spin-torque experiments have shown the path to low-current, low-voltage, and high-speed magnetization switching in nano-scale magnetic devices. Such magneto-metallic, current-mode spin-torque switches can mimic the analog summing and “thresholding” operation of an artificial neuron with high energy-efficiency. Comparison with CMOS-based analog circuit-model of a neuron shows that “spin-neurons” (spin based circuit model of neurons) can achieve more than two orders of magnitude lower energy and beyond three orders of magnitude reduction in energy-delay product. The application of spin-neurons can therefore be an attractive option for neuromorphic computers of future.
Spin-orbit torques in ferrimagnetic GdFeCo alloys
In this work, the spin-orbit torque switching of ferrimagnetic Gd x (Fe 90 Co 10 ) 100-x films was studied for both transition metal (TM)-rich and rare earth (RE)-rich configurations. The spin-orbit torque driven magnetization switching follows the same sense in TM-rich and RE-rich samples with respect to the total magnetization, but the sense of the switching is reversed with respect to the TM magnetization. This indicates that the sign of the spin-orbit-torque-driven magnetic switching follows the total magnetization, although transport based techniques such as anomalous Hall effect are only sensitive to the transition metal magnetization. Finally, these results provide important insight into the physics of spin angular momentum transfer in materials with antiferromagnetically coupled sublattices.
Room-Temperature, Current-Induced Magnetization Self-Switching in A Van Der Waals Ferromagnet
2D layered materials with broken inversion symmetry are being extensively pursued as spin source layers to realize high-efficiency magnetic switching. Such low-symmetry layered systems are, however, scarce. In addition, most layered magnets with perpendicular magnetic anisotropy show a low Curie temperature. Here, in this study, the experimental observation of spin–orbit torque magnetization self-switching at room temperature in a layered polar ferromagnetic metal, Fe 2.5 Co 2.5 GeTe 2 is reported. The spin–orbit torque is generated from the broken inversion symmetry along the c-axis of the crystal. These results provide a direct pathway toward applicable 2D spintronic devices.
Switching current reduction in magnetoresistive random access memories
We present an approach for minimizing the critical current for the magnetization switching in magnetic tunnel junctions by optimizing the spatial distribution of the current density. We show that such a minimization is possible because critical current is determined by the condition of making one of the magnetization eigenstates grow in time. The excitation of the eigenstates is enhanced when the spatial distributions of the eigenstates and current density overlap. Critical current can be viewed as a functional of the current density spatial distribution and it can be minimized by optimizing this distribution. Such an optimization results in a major reduction of the critical current and increase of the switching efficiency, viz. the ratio between the energy barrier and critical current. The minimized critical current increases approximately linearly with the magnetic tunnel junction size, which is much slower than critical current for the case of a uniform current density. The optimized efficiency can be approximately a constant with respect to the magnetic tunnel junction size, which is much higher than the efficiency for the uniform current density. Additional optimization can be achieved by spatially modulating the material parameters, e.g., the saturation magnetization. The presented approach and obtained scaling of the critical current and efficiency offers opportunities for the magnetic tunnel junction optimization.
Voltage-driven spin-transfer torque in a magnetic particle
We discuss a spin-transfer torque device, where the role of the soft ferromagnetic layer is played by a magnetic particle or a magnetic molecule, in weak tunnel contact with two spin polarized leads. We investigate if the magnetization of the particle can be manipulated electronically, in the regime where the critical current for magnetization switching is negligibly weak, which could be due to the reduced particle dimensions. Using master equation simulations to evaluate the effects of spin-orbit anisotropy energy fluctuations on spin-transfer, we obtain reliable reading and writing of the magnetization state of such magnetic particle, and find that the device relies on a critical voltage rather than a critical current. The critical voltage is governed by the spin-orbit energy shifts of discrete levels in the particle. This finding opens a possibility to significantly reduce the power dissipation involved in spin-transfer torque switching, by using very small magnetic particles or molecules.
Transient current interruption mechanism in a magnetically delayed vacuum switch
The capacity of a magnetically delayed vacuum switch to conduct current depends on the density of plasma injected into the switch. Exceeding the current capacity results in the switch entering a lossy mode of operation characterized by a transient interruption of the main current (opening behavior) and a rapid increase of voltage across the vacuum gap. Streak and framing photographs of the discharge indicate that a decrease of luminosity near the middle of the gap preceeds the transition to the opening phase. The zone of low luminosity propagates toward the cathode. This evidence suggests that the mechanism causing the opening phase is erosion of the background plasma in a manner similar to that in a plasma-opening switch. The resulting ion depletion forces a space-charge-limited conduction mode. The switch inductance maintains a high discharge current even during the space-charge-limited conduction phase, thus producing high internal fields. The high accelerating voltage, in turn, produces electron and ion beams that heat the electrode surfaces. As a result of the heating, jets of electrode vapor issue from the electrodes, either cathode or anode, depending on the selection of electrode materials.
Analysis of reliable sub-ns spin-torque switching under transverse bias magnetic fields
The switching process of a magnetic spin-valve nanosystem subject to spin-polarized current pulses is considered. The dependence of the switching probability on the current pulse duration is investigated. The further application of a transverse field along the intermediate anisotropy axis of the particle is used to control the quasi-random relaxation of magnetization to the reversed magnetization state. The critical current amplitudes to realize the switching are determined by studying the phase portrait of the Landau-Lifshtz-Slonczewski dynamics. Macrospin numerical simulations are in good agreement with the theoretical prediction and demonstrate reliable switching even for very short (below 100 ps) current pulses.
Constant-voltage drive current-steering switch
Two-element voltage control system regulates a magnetic switch consisting of dual ferrite-core shift registers. The system has a magnetic, two-core-per-bit, voltage-controlled shift register.
Exchange bias switching in an antiferromagnet/ferromagnet bilayer driven by spin-orbit torque
Here the electrical manipulation of magnetization and exchange bias in antiferromagnet/ferromagnet thin films could be of use in the development of the next generation of spintronic devices. Current-controlled magnetization switching can be driven by spin-orbit torques generated in an adjacent heavy metal layer, but these structures are difficult to integrate with exchange bias switching and tunnelling magnetoresistance measurements. Here, we report the current-induced switching of the exchange bias field in a perpendicularly magnetized IrMn/CoFeB bilayer structure using a spin-orbit torque generated in the antiferromagnetic IrMn layer. By manipulating the current direction and amplitude, independent and repeatable switching of the magnetization and exchange bias field below the blocking temperature can be achieved. The critical current density for the exchange bias switching is found to be larger than that for CoFeB magnetization reversal. X-ray magnetic circular dichroism, polarized neutron reflectometry measurements and micromagnetic simulations show that a small net magnetization within the IrMn interface plays a crucial role in these phenomena.
Reliable time multiplexing by replacement
Electromechanical, magnetic switching circuit for redundant time division multiplex transmission - behavior and failure analysis
Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser
Not Available
Electrical switching of the magnetic vortex circulation in artificial multiferroic structure of Co/Cu/PMN-PT(011)
For this research, Co films and micron sized disks were grown on top of piezoelectric PMN-PT(011) and Cu/PMN-PT(001) substrates and investigated by the Magneto-Optic Kerr Effect and Photoemission Electron Microscopy. By applying an electric field in the surface normal direction, we find that the strain of the ferroelectric PMN-PT(011) substrate induces an in-plane uniaxial magnetic anisotropy in the Co overlayer. Under specific conditions, the Co magnetic vortex could be switched between clockwise and counter-clockwise circulations. The variations of the Co vortex switching were attributed to the variations of the ferroelectric domains under the Co disks. Lastly, we speculate that the switching of the magnetic vortex circulation is a dynamical process which may involve pulses of appropriate magnitude and duration of the uniaxial magnetic anisotropy delivered to the magnetic vortex.
Topological Transitions Induced by Antiferromagnetism in a Thin-Film Topological Insulator
Magnetism in topological insulators (TIs) opens a topologically nontrivial exchange band gap, providing an exciting platform for manipulating the topological order through an external magnetic field. Here, we show that the surface of an antiferromagnetic thin film can magnetize the top and the bottom TI surface states through interfacial couplings. During the magnetization reversal, intermediate spin configurations are ascribed from unsynchronized magnetic switchings. This unsynchronized switching develops antisymmetric magnetoresistance spikes during magnetization reversals, which might originate from a series of topological transitions. With the high Néel ordering temperature provided by the antiferromagnetic layers, the signature of the induced topological transition persists up to ~$90 K$.
Magnetic properties of Sr 3 NiIrO 6 and Sr 3 CoIrO 6 : Magnetic hysteresis with coercive fields of up to 55 T
Here, we report extraordinarily large magnetic hysteresis loops in the iridates Sr 3 NiIrO 5 and Sr 3 CoIrO 6 . We find coercive magnetic fields of up to 55 T with switched magnetic moments ≈1μ B per formula unit in Sr 3 NiIrO 6 and coercive fields of up to 52 T with switched moments ≈3μ B per formula unit in Sr 3 CoIrO 6 . We propose that the magnetic hysteresis involves the field-induced evolution of quasi-one-dimensional chains in a frustrated triangular configuration. In conclusion, the striking magnetic behavior is likely to be linked to the unusual spin-orbit-entangled local state of the Ir 4+ ion and its potential for anisotropic exchange interactions.
Characterization of switching field distributions in Ising-like magnetic arrays
Not Available