Solid state magneto-ionic (MI) effects, which can be achieved through controlled ionic migration at atomic scale interfaces in magnetic nanostructures, have shown promise for energy-efficient nanoelectronics. Our recent efforts reach outside of the often-explored oxygen-based MI systems, and have focused on alternative ionic species, including nitrogen. Two nitrogen-based systems, Ta/CoFe/MnN/Ta and the all-nitride Mn4N/MnNx, show MI manipulation of magnetic properties including saturation magnetization and exchange bias. Such MI systems are valuable platforms to gain quantitative understanding at buried interfaces and they demonstrate contrasts with oxygen-based MI effects in terms of operating principles, switching speed, and reversibility.
Manipulation of interfacial magnetism utilizing voltage pulses can lead to energy-efficient scalable nanomagnetic devices. Through voltage-controlled magnetic anisotropy (VCMA), we had previously shown the potential to achieve non-volatile magnetoresistive random-access memory (MRAM) technology that is 100 times more energy-efficient than commercially available spin-transfer torque MRAM [1]. Building on prior work on VCMA-based skyrmion-mediated reversal of ferromagnetic states and its scaling to 20 nm [2], we will present new experimental demonstrations of manipulation of skyrmions in magnetoionic heterostructures with an electric field. This talk will also focus on energy-efficient magnetoionic control of skyrmions in (Co/Ni)N-based heterostructures for memory application. Furthermore, our talk also demonstrates implementing physical reservoir computing, a neuromorphic process typically used for classifying and predicting temporal data, with the energy-efficient magnetoionic process.
References:
[1] Bhattacharya et al. ACS applied materials & interfaces, 10(20), 17455-17462 (2018).
[2] Rajib et al. Scientific reports, 11(1), 20914 (2021).
A critical challenge towards integrating 3-dimensional (3D) magnetic nanostructures into neuromorphic circuitry is stabilizing different magnetic states that are controllable via external stimuli. Here, we demonstrate quasi-ordered and random interconnected magnetic nanowire networks as potential candidates. In these networks, step-by-step magnetization reversal mediated by domain wall (DW) pinning / depinning at the network intersections is observed. The pinning/depinning of the DWs can be further controlled by the driving current density. These properties are amenable to implement neuromorphic computing elements such as artificial synapses.
Magneto-ionics has shown promise for energy-efficient nanoelectronics, where ionic migration can be used to achieve atomic scale control of interfaces in magnetic nanostructures, and in turn modulate a wide variety of functionalities. Recently, we have discovered that chemisorbed oxygen and hydrogen on the surface of ferromagnetic films can induce significant Dzyaloshinskii–Moriya interaction (DMI) [1], a handle to introduce topology into nanoscale magnets. This has enabled direct tailoring of skyrmions winding number as well as wall type at room temperature via oxygen chemisorption. We have also demonstrated a sensitive and reversible chirality switching of magnetic domain walls [2] and writing/deleting of skyrmions [3] via hydrogen chemisorption/desorption [3] or changing the thickness of a sub-monolayer Pd capping layer [4]. These effects offer an ideal platform to gain quantitative understanding of magneto-ionics at buried interfaces, where the ionic motion can be further controlled by an electric field, leading to modulation of such functionality as exchange bias [5,6].
Hongxin Yang, Gong Chen, Alexandre A. Cotta, Alpha N’Diaye, Sergey Nikolaev, Edmar Soares, Waldemar A. Macedo, Kai Liu, Andreas Schmid, Albert Fert, Mairbek Chshiev
KEYWORDS: Silicon, Manganese, Chemical species, Magnetism, Spintronics, Magnetic semiconductors, Semiconductors, Data storage, Transition metals, Group III-V semiconductors
A recent experiment determined the magnetic moment /Mn, M, in the dilute MnxSi1-x with x = 0.1% to be 5.0 µB/Mn.
The existing calculated M values range from 2.37 to 3.1µB/Mn except the case with a fixed charge state, Mn2+, which
gives 5.0µB/Mn. We address the issue: Can a single Mn at its neutral charge state in dilute MnxSi1-x alloys have M = 5.0
µB/Mn? After carrying out extensive calculations, the only model giving this M value involves a supercell having a total
of 513 atoms with a Mn at a substitutional site and a Si at a tetrahedral interstitial site serving as a second neighbor to the
Mn. Physically, the Mn contributes 4.0 µB due to the weakening of the d-p hybridization between the transition metal
element and its nearest neighbor Si caused by the presence of the second neighbor Si. The additional 1.0 µB is the
consequence of the exchange interaction through the remaining weak overlap of the wave functions between the d-state
of the Mn and the sp3 state of the nearest neighbor Si atom. Evidences for the weakening of the d-p hybridization are
presented.
Multilayered magnetic nanowires provide ideal platforms for nanomagnetism and spin-transport studies. They exhibit complex magnetization reversal behaviors as dimensions of the magnetic components are varied, which are difficult to probe since the magnetic entities are buried inside the nanowires. We have captured magnetic and magnetoresistance "fingerprints" of Co nanodiscs in Co/Cu multilayered nanowires as they undergo a single domain to vortex state transition, using a first-order reversal curve (FORC) method. The Co/Cu multilayered nanowires have been synthesized by pulsed electrodeposition into nanoporous polycarbonate membranes. In 50 nm diameter nanowires of [Co(5nm)/Cu(8nm)]400, a 10% magnetoresistance effect is observed at 300 K. In 200 nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisc aspect ratio. The thinnest nanodiscs exhibit single domain behavior. The thicker ones exhibit vortex states, where the nucleation and annihilation of the vortices are manifested as butterfly-like features in the FORC distributions. The magnetoresistance effect shows different characteristics, which correspond to the different magnetic configurations of the Co nanodiscs.
Many types of fluorescent nanoparticles have been investigated as alternatives to conventional organic dyes in biochemistry. In addition, magnetic beads are another type of particle that have a long history of biological applications. In this work we apply flame spray pyrolysis in order to engineer a novel type of nanoparticle that has both luminescent and magnetic properties. The particles have magnetic cores of iron oxide doped with cobalt and neodymium and luminescent shells of europium-doped gadolinium oxide (Eu:Gd2O3). Measurements on a Vibrating Sample Magnetometer showed an overall paramagnetic response of these composite particles. Fluorescence spectroscopy showed spectra typical of the Eu ion in a Gd2O3 host; a narrow emission peak centered near 615 nm. Our synthesis method offers low-cost, high-rate synthesis allowing a wide range of biological applications of magnetic/fluorescent core/shell particles. We demonstrate an immunoassay using the magnetic and fluorescent properties of the particles for separation and detection purposes.
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