Spintronics Meets Density Matrix Renormalization Group: Quantum Spin-Torque-Driven Nonclassical Magnetization Reversal and Dynamical Buildup of Long-Range Entanglement
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75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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Results for “Magnetization switching”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Control of SiC Based Integrated DC-DC Powertrain Charger for Electric Vehicles
In this paper, an automated controller for an integrated, reconfigurable dc-dc converter for plugin electric vehicles (EVs) is presented. The integrated converter combines both an interleaved boost converter and dual active bridge (DAB) converter, sharing magnetics and switching devices. The converter switches between operating modes using the existing battery management system (BMS) contactors. The integrated converter operates in isolated DAB mode during battery charging operation. During traction operation, the integrated converter is operated in interleaved boost mode for heavy load and DAB mode during light load, high voltage operation. An online transition algorithm is used to transition from interleaved boost mode to DAB mode with minimal bus distortion. The automated controller selects the operating mode and inverter bus voltage at different torque-speed conditions to get maximum overall traction drive efficiency. An experimental prototype of the integrated converter demonstrates the automated controller functionality.
Anwar, Saeed↗
Electronics for Deep Space Cryogenic Applications
Deep space probes and planetary exploration missions require electrical power management and control systems that are capable of efficient and reliable operation in very cold temperature environments. Typically, in deep space probes, heating elements are used to keep the spacecraft electronics near room temperature. The utilization of power electronics designed for and operated at low temperature will contribute to increasing efficiency and improving reliability of space power systems. At NASA Glenn Research Center, commercial-off-the-shelf devices as well as developed components are being investigated for potential use at low temperatures. These devices include semiconductor switching devices, magnetics, and capacitors. Integrated circuits such as digital-to-analog and analog-to-digital converters, DC/DC converters, operational amplifiers, and oscillators are also being evaluated. In this paper, results will be presented for selected analog-to-digital converters, oscillators, DC/DC converters, and pulse width modulation (PWM) controllers.
Patterson, R. L.↗
Design of a High Power Density, High Efficiency, Low THD 250kW Converter for Electric Aircraft
A high efficiency, high power density, low distortion 250kW motor controller is being developed at NASA Glenn Research Center. Future electric aircraft require motor controllers which achieve the needed key performance parameters required to show benefit in increasing overall aircraft efficiency. Through a combination of carefully considered electrical topological choices and through the use of recent advancements in power switches and magnetic materials, a converter is designed which meets these requirements. A multilevel and interleaved converter architecture is chosen to meet the voltage, current, and THD requirements. The enclosure and thermal designs meet their weight targets and enable high altitude operation.
Matthew Granger↗
Electrical switching of a p-wave magnet
Magnetic states with zero magnetization but non-relativistic spin splitting are outstanding candidates for the next generation of spintronic devices. Their electronvolt (eV)-scale spin splitting, ultrafast spin dynamics and nearly vanishing stray fields make them particularly promising for several applications. A variety of such magnetic states with non-trivial spin textures have been identified recently, including even-parity d-wave, g-wave or i-wave altermagnets and odd-parity p-wave magnets. Achieving voltage-based control of the non-uniform spin polarization of these magnetic states is of great interest for realizing energy-efficient and compact devices for information storage and processing. Spin-spiral type II multiferroics are optimal candidates for such voltage-based control, as they exhibit an inversion-symmetry-breaking magnetic order that directly induces ferroelectric polarization, allowing for symmetry-protected cross-control between spin chirality and polar order. Here we combine photocurrent measurements, first-principles calculations and group-theory analysis to provide direct evidence that the spin polarization of the spin-spiral type II multiferroic NiI 2 exhibits odd-parity character connected to the spiral chirality. The symmetry-protected coupling between chirality and polar order enables electrical control of a primarily non-relativistic spin polarization. Our findings represent an observation of p-wave magnetism in a spin-spiral type II multiferroic, which may lead to the development of voltage-based switching of non-relativistic spin polarization in compensated magnets.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Progress toward picosecond on-chip magnetic memory
Here, we offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ~3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ~6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed to accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.
42 ENGINEERING↗
NMR studies of domain switching in ferroelectric rochelle salt
Nuclear magnetic resonance of domain switching in ferroelectric rochelle salt
Casabella, P. A.↗
Observation of current-induced switching in non-collinear antiferromagnetic IrMn 3 by differential voltage measurements
There is accelerating interest in developing memory devices using antiferromagnetic (AFM) materials, motivated by the possibility for electrically controlling AFM order via spin-orbit torques, and its read-out via magnetoresistive effects. Recent studies have shown, however, that high current densities create non-magnetic contributions to resistive switching signals in AFM/heavy metal (AFM/HM) bilayers, complicating their interpretation. Here we introduce an experimental protocol to unambiguously distinguish current-induced magnetic and nonmagnetic switching signals in AFM/HM structures, and demonstrate it in IrMn 3 /Pt devices. A six-terminal double-cross device is constructed, with an IrMn 3 pillar placed on one cross. The differential voltage is measured between the two crosses with and without IrMn 3 after each switching attempt. For a wide range of current densities, reversible switching is observed only when write currents pass through the cross with the IrMn 3 pillar, eliminating any possibility of non-magnetic switching artifacts. Micromagnetic simulations support our findings, indicating a complex domain-mediated switching process.
36 MATERIALS SCIENCE↗
Anomalous Thermal Hall Effect in an Insulating van der Waals Magnet
Two-dimensional (2D) van der Waals (vdW) magnets have been a fertile playground for the discovery and exploration of physical phenomena and new physics. In this Letter, we report the observation of an anomalous thermal Hall effect (THE) with κ xy ~ 1 × 10 -2 WK -1 m -1 in an insulating van der Waals ferromagnet VI 3 . The thermal Hall signal persists in the absence of an external magnetic field and flips sign upon the switching of the magnetization. In combination with theoretical calculations, we show that VI 3 exhibits a dual nature of the THE, i.e., dominated by topological magnons hosted by the ferromagnetic honeycomb lattice at higher temperatures and by phonons induced by the magnon-phonon coupling at lower temperatures. Our results not only position VI 3 as the first ferromagnetic system to investigate both anomalous magnon and phonon THEs, but also render it as a potential platform for spintronics-magnonics applications.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Collective spin dynamics under dissipative spin Hall torque
Current-induced spin torques in layered magnetic heterostructures have many commonalities across broad classes of magnetic materials. These include not only collinear ferromagnets, ferrimagnets, and antiferromagnets but also more complex noncollinear spin systems. We develop a general Lagrangian–Rayleigh approach for studying the role of dissipative torques, which can pump energy into long-wavelength magnetic dynamics, causing dynamic instabilities. While the Rayleigh structure of such torques is similar for different magnetic materials, their consequences depend sensitively on the nature of the order and, in particular, on whether there is a net magnetic moment. The latter endows the system with a unipolar switching capability, while magnetically compensated materials tend to evolve toward limit cycles, at large torques, with chirality dependent on the torque sign. Apart from the ferromagnetic and antiferromagnetic cases, we discuss ferrimagnets, which display an intricate competition between switching and limit cycles. As a simple case for compensated noncollinear order, we consider isotropic spin glasses and a scenario of their coexistence with a collinear magnetic order.
Tserkovnyak, Yaroslav (ORCID:0000000232773695)↗
Charge Density Wave and Ferromagnetism in Intercalated CrSBr
In materials with 1D electronic bands, electron–electron interactions can produce intriguing quantum phenomena, including spin-charge separation and charge density waves (CDW). Most of these systems, however, are non-magnetic, motivating a search for anisotropic materials where the coupling of charge and spin may affect emergent quantum states. Here, in this study, chemical intercalation of the van der Waals magnetic semiconductor CrSBr yields Li 0.17(2) (tetrahydrofuran) 0.26(3) CrSBr, which possesses an electronically driven quasi-1D CDW with an onset temperature above room temperature. Concurrently, electron doping increases the magnetic ordering temperature from 132 to 200 K and switches its interlayer magnetic coupling from antiferromagnetic to ferromagnetic. The spin-polarized nature of the anisotropic bands that give rise to this CDW enforces an intrinsic coupling of charge and spin. The coexistence and interplay of ferromagnetism and charge modulation in this exfoliatable material provide a promising platform for studying tunable quantum phenomena across a range of temperatures and thicknesses.
2D magnets↗
Magnetic self-mating fiber optic connector and fiber optic switch sensor
A system or method for a magnetic self-aligning coupling device for a fiber optic cable. The device includes a first end coupling comprising a first magnet and a second magnet. Both magnets include a mating surface and an annular ring defining an axial aperture. The aperture receives a distal end of a segment of fiber optic cable in a tight fit. The fiber optic cable has an exterior sleeve and a fiber core. The fiber core of the first segment and the second segment of the fiber optic cable are axially aligned by magnetic force in the first and second apertures to create a continuous fiber optic path. A method for detecting a security breach of a door using the self-aligning couplings is also described.
Neidigk, Stephen↗
Magnetic self-mating fiber optic connector and fiber optic switch sensor
A system or method for a magnetic self-aligning coupling device for a fiber optic cable. The device includes a first end coupling comprising a first magnet and a second magnet. Both magnets include a mating surface and an annular ring defining an axial aperture. The aperture receives a distal end of a segment of fiber optic cable in a tight fit. The fiber optic cable has an exterior sleeve and a fiber core. The fiber core of the first segment and the second segment of the fiber optic cable are axially aligned by magnetic force in the first and second apertures to create a continuous fiber optic path. A method for detecting a security breach of a door using the self-aligning couplings is also described.
Neidigk, Stephen↗
Programmable chiral states in flocks of active magnetic rollers
Inspired by nature, active matter exemplified by self-organization of motile units into macroscopic structures holds great promise for advanced tunable materials capable of flocking, shape-shifting, and self-healing. Active particles driven by external fields have repeatedly demonstrated potential for complex self-organization and collective behavior, yet how to guide the direction of their collective motion largely remains unexplored. Here, we report a system of microscopic ferromagnetic rollers driven by an alternating magnetic field that demonstrates programmable control of the direction of a self-organized coherent vortical motion (i.e., chirality). Facilitated by a droplet confinement, the rollers get synchronized and display either right- or left-handed spontaneous vortical motion, such that their moving direction determines the vortex chirality. Here, we reveal that one can remotely command a flock of magnetic rollers to switch or maintain its chiral state by modulating a phase shift of the sinusoidal magnetic field powering the active rollers. Building on our findings, we realize a self-assembled remotely controlled micro-pump architecture capable of switching the fluid transport direction on demand. Our studies may stimulate new design strategies for directed transport and flocking robotics at the microscale based on active colloids.
36 MATERIALS SCIENCE↗
Pressure-controlled magnetism in 2D molecular layers
Abstract Long-range magnetic ordering of two-dimensional crystals can be sensitive to interlayer coupling, enabling the effective control of interlayer magnetism towards voltage switching, spin filtering and transistor applications. With the discovery of two-dimensional atomically thin magnets, a good platform provides us to manipulate interlayer magnetism for the control of magnetic orders. However, a less-known family of two-dimensional magnets possesses a bottom-up assembled molecular lattice and metal-to-ligand intermolecular contacts, which lead to a combination of large magnetic anisotropy and spin-delocalization. Here, we report the pressure-controlled interlayer magnetic coupling of molecular layered compounds via chromium-pyrazine coordination. Room-temperature long-range magnetic ordering exhibits pressure tuning with a coercivity coefficient up to 4 kOe/GPa, while pressure-controlled interlayer magnetism also presents a strong dependence on alkali metal stoichiometry and composition. Two-dimensional molecular interlayers provide a pathway towards pressure-controlled peculiar magnetism through charge redistribution and structural transformation.
74 ATOMIC AND MOLECULAR PHYSICS↗
Proximity Spin–Orbit Torque on a Two-Dimensional Magnet within van der Waals Heterostructure: Current-Driven Antiferromagnet-to-Ferromagnet Reversible Nonequilibrium Phase Transition in Bilayer CrI 3
The recently discovered two-dimensional magnetic insulator CrI 3 is an intriguing case for basic research and spintronic applications since it is a ferromagnet in the bulk but an antiferromagnet in bilayer form, with its magnetic ordering amenable to external manipulations. Using the first-principles quantum transport approach, we predict that injecting unpolarized charge current parallel to the interface of the bilayer-CrI 3 /monolayer-TaSe 2 van der Waals (vdW) heterostructure will induce spin–orbit torque and thereby drive the dynamics of magnetization on the first monolayer of CrI 3 in direct contact with TaSe 2 . By combining the calculated complex angular dependence of spin–orbit torque with the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization, we demonstrate that current pulses can switch the direction of magnetization on the first monolayer to become parallel to that of the second monolayer, thereby converting CrI 3 from antiferromagnet to ferromagnet while not requiring any external magnetic field. We explain the mechanism of this reversible current-driven nonequilibrium phase transition by showing that first monolayer of CrI 3 carries current due to evanescent wave functions injected by metallic transition metal dichalcogenide TaSe 2 , while concurrently acquiring strong spin–orbit coupling via such a proximity effect, whereas the second monolayer of CrI 3 remains insulating. Furthermore, the transition can be detected by passing vertical read current through the vdW heterostructure, encapsulated by a bilayer of hexagonal boron nitride and sandwiched between graphite electrodes, where we find a tunneling magnetoresistance of ≃240%.
2D magnetic materials↗
Development Status of a Power Processing Unit for Low Power Ion Thrusters
An advanced breadboard Power Processing Unit (PPU) for a low power ion propulsion system incorporating mass reduction techniques was designed and fabricated. As a result of similar output current requirements, the discharge supply was also used to provide the neutralizer heater and discharge heater functions by using three relays to switch the output connections. This multi-function supply reduces to four the number of power converters needed to produce the required six electrical outputs. Switching frequencies of 20 and 50 kHz were chosen as a compromise between the size of the magnetic components and switching losses. The advanced breadboard PPU is capable of a maximum total output power of 0.47 kW. Its component mass is 0.65 kg and its total mass 1.9 kg. The total efficiency at full power is 0.89.
Pinero, Luis R.↗
Temperature-induced valence-state transition in double perovskite Ba 2 - x Sr x TbIrO 6
In this paper, a temperature-induced valence-state transition is studied in a narrow composition range 0.2 ≤ x ≤ 0.375 of Ba 2 - x Sr x TbIrO 6 by means of x-ray and neutron powder diffraction, resonant inelastic x-ray scattering, magnetic susceptibility, electrical resistivity, and specific heat measurements. The valence-state transition involves an electron transfer between Tb and Ir leading to the valence-state change between Tb 3 + / Ir 5 + and Tb 4 + / Ir 4 + phases. This first-order transition has a dramatic effect on the lattice, transport properties, and the long-range magnetic order at low temperatures for both Tb and Ir ions. Ir 5 + ion has an electronic configuration of 5 d 4 ( J eff = 0 ), which is expected to be nonmagnetic. In contrast, Ir 4 + ion with a configuration of 5 d 5 ( J eff = 1/2) favors a long-range magnetic order. For x = 0.1 with Tb 3 + / Ir 5 + configuration to the lowest temperature (2 K) investigated in this paper, a spin-glass behavior is observed around 5 K indicating Ir 5 + ( J eff = 0 ) ions act as a spacer reducing the magnetic interactions between Tb 3 + ions. For x = 0.5 with Tb 4 + / Ir 4 + configuration below the highest temperature 400 K of this paper, a long-range antiferromagnetic order at T N = 40 K is observed highlighting the importance of Ir 4 + ( J eff = 1/2) ions in promoting the long-range magnetic order of both Tb and Ir ions. For 0.2 ≤ x ≤ 0.375, a temperature-induced valence-state transition from high-temperature Tb 3 + / Ir 5 + phase to low-temperature Tb 4 + / Ir 4 + phase occurs in the temperature range 180 K ≤ T ≤ 325 K and the transition temperature increases with x . The compositional dependence demonstrates the ability to tune the the valence state for a critical region of x that leads to a concurrent change in magnetism and structure. Furthermore, this tuning ability could be employed with suitable strain in thin films to act as a switch as the magnetism is manipulated.
36 MATERIALS SCIENCE↗