Magnetic Nanodisks Research Articles

Vortex Nanodiscs Functionalization to Overcome Macrophage Recognition for Efficient Theragnosis Applications

Biological barriers prevent nanotherapeutics successful accumulation at target cells, limiting diagnosis and treatment responses. Magnetic nanodiscs with a spin‐vortex ground state have shown great promise for magnetomechanical cancer cells annihilation and for neuronal stimulation, requiring very low concentrations for an effective result. However, the biological barriers that these particles encounter upon intravenous administration remain a challenge. Herein, the synthesis of biocompatible multilayered Au/Fe/Au nanodiscs with a spin‐vortex ground state and their inert surface modification is reported. Two different surface modifications with two distinct polyethylene glycol (PEG) molecules are performed, which successfully reduce macrophage uptake, while maintaining the nanodiscs’ biocompatibility. By effectively preventing nanodisc uptake, innovative design features can be rationally incorporated to create a new generation of specific nanotherapeutics by modifying the PEG surface with specific targeting molecules.

Ultrafast manipulations of nanoscale skyrmioniums

The advancement of next-generation magnetic devices depends on fast manipulating magnetic microstructures at the nanoscale. A universal method is presented for rapid and reliable generating, controlling, and driving nano-scale skyrmioniums, through high-throughput micromagnetic simulations. Ultrafast switches are realized between skyrmionium and skyrmion states and rapidly change their polarities in monolayer magnetic nanodisks by perpendicular magnetic fields. The transition mechanism by alternating magnetic fields differs from that under steady magnetic fields. New skyrmionic textures, such as flower-like and windmill-like skyrmions, are discovered. Moreover, this nanoscale skyrmionium can move rapidly and stably in nanoribbons using weaker spin-polarized currents. Explicit discussions are held regarding the physical mechanisms involved in ultrafast manipulations of skyrmioniums. This work provides further physical insights into the manipulation and application of topological skyrmionic structures for developing low-power consumption and nanostorage devices.

Magnetoelectric fractals, Magnetoelectric parametric resonance and Hopf bifurcation

In the present work, we study the dynamics of the magnetic nanodisc coupled through a magnetoelectric coupling to a ferroelectric crystal. The model of our interest is nonlinear, and we explore the problem under different limits of weak and strong non-linearity. By applying two electric fields with different frequencies, we control the form of the confinement potential of a ferroelectric subsystem and realize different types of dynamics. We proved that the system is more sensitive to magnetoelectric coupling in the case of double-well potential. In particular, in the case of strong non-linearity, arbitrary small values of magnetoelectric coupling lead to chaotic dynamics. In essence, magnetoelectric coupling plays a role akin to the small perturbations destroying invariant tori according to the KAM theorem. We showed that bifurcations in the system are of Hopf’s type. We observed the formation of magnetoelectric fractals in the system. In the limit of weak non-linearity, we studied a problem of parametric nonlinear resonance and enhancement of magnetic oscillations through magnetoelectric coupling.

Magnetic Nanodiscs That Destroy Glioblastoma Cells in a Targeted Way in an Alternating Nonheating Magnetic Field

Magnetic Nanodiscs That Destroy Glioblastoma Cells in a Targeted Way in an Alternating Nonheating Magnetic Field

Multifunctional ultralight magnetic CNFs/MXene/Fe3O4 nanodiscs aerogel with superior electromagnetic wave absorption performance

The design of innovative microstructures and the implementation of an appropriate multi-component strategy remain challenging in the development of advanced electromagnetic wave (EMW) absorbing materials. Achieving strong absorption and a wide effective absorption bandwidth while maintaining a thin sample thickness and low filling level is particularly demanding. Herein, a three-dimensional (3D) dielectric cellulose nanofiber (CNF)/Ti3C2Tx MXene carbon aerogel, incorporating magnetic Fe3O4 nanodiscs (NDs), was fabricated using a directional-freezing technique followed by reduction. Surprisingly, the reduction process activates the multifunctional application of aerogel with better elasticity and greatly improved electromagnetic properties, killing two birds with one stone. The structured cellular arrangement and the presence of diverse dielectric/magnetic interfaces contribute to the exceptional absorption capabilities by facilitating optimal impedance matching, enabling multiple polarization modes, and fostering electric/magnetic coupling phenomena. The aerogel exhibits excellent microwave absorption properties, characterized by its ultra-lightweight (3 % of filling ratio and 4.65 mg cm−3 of density), ultra-thin (2.18 mm), ultra-wide frequency band (6.68 GHz) and strong absorption (-56.8 dB). Additionally, the aerogel provides attractive functions such as thermal insulation and great mechanical properties (100 % recovery after 1000 cycles under 50 % strain). This study lays the groundwork for the advancement of microwave-absorbing materials, showcasing their vast potential for multifaceted applications.

Elucidating Mechanotransduction Processes During Magnetomechanical Neuromodulation Mediated by Magnetic Nanodiscs.

Noninvasive cell-type-specific manipulation of neural signaling is critical in basic neuroscience research and in developing therapies for neurological disorders. Magnetic nanotechnologies have emerged as non-invasive neuromodulation approaches with high spatiotemporal control. We recently developed a wireless force-induced neurostimulation platform utilizing micro-sized magnetic discs (MDs) and low-intensity alternating magnetic fields (AMFs). When targeted to the cell membrane, MDs AMFs-triggered mechanoactuation enhances specific cell membrane receptors resulting in cell depolarization. Although promising, it is critical to understand the role of mechanical forces in magnetomechanical neuromodulation and their transduction to molecular signals for its optimization and future translation. MDs are fabricated using top-down lithography techniques, functionalized with polymers and antibodies, and characterized for their physical properties. Primary cortical neurons co-cultured with MDs and transmembrane protein chemical inhibitors are subjected to 20s pulses of weak AMFs (18 mT, 6Hz). Calcium cell activity is recorded during AMFs stimulation. Neuronal activity in primary rat cortical neurons is evoked by the AMFs-triggered actuation of targeted MDs. Ion channel chemical inhibition suggests that magnetomechanical neuromodulation results from MDs actuation on Piezo1 and TRPC1 mechanosensitive ion channels. The actuation mechanisms depend on MDs size, with cell membrane stretch and stress caused by the MDs torque being the most dominant. Magnetomechanical neuromodulation represents a tremendous potential since it fulfills the requirements of negligible heating (ΔT < 0.1°C) and weak AMFs (< 100Hz), which are limiting factors in the development of therapies and the design of clinical equipment. The online version contains supplementary material available at 10.1007/s12195-023-00786-8.

Static and dynamic magnetic characteristics in concentric permalloy nanorings

Magnetic nanodisks and nanorings have been focus of attention for quite some time due to their applicability in magnetic memory devices. In this paper, static and dynamic magnetic properties of Permalloy concentric thin ring nanostructures are reported as a function of the number of rings by using micromagnetic simulations. The maximum outer radius (R) and thickness (t) of the concentric rings are fixed at 100 nm and 20 nm respectively. The distance between any two neighbouring rings is always maintained equal to the width of each ring while the number of nanorings is increased starting from one to five. In-plane magnetic hysteresis loops show that in all cases, the remanence and coercivity values are found to be almost zero while vortex state is exhibited with opposite helicity in adjacent nanorings. When the number of nanorings reach five, the narrowest hysteresis loop is observed with almost no hysteresis at all. Dynamic susceptibility spectra was computed by relaxing the system from a out of plane saturated state followed by an in-plane excitation using a small field pulse. In most of the cases, the in plane magnetic field pulse excites azimuthal spin wave modes. The resonance frequency corresponding to these excitation modes depends on the remanent configuration and the number of peaks increase with increment in the number of rings. The ferromagnetic resonance mode that is common for all the samples considered, moves towards lower frequency with increase in number of concentric rings.

Frequency Tunability of Spin‐Torque Vortex Oscillator in Permalloy Nanodisks with Modified Material Properties

The manipulation of the vortex state in magnetic nanostructures has received a lot of interest in recent decades, with potential applications in nonvolatile magnetic random‐access memory and logic networks. For wireless communication advancements, nano‐sized, and low‐phase‐noise, adjustable transmitter‐receiver networks are critical. Herein, it is shown that by using micromagnetic simulations when the saturation magnetization is reduced in a particular region of a magnetic nanodisk, the frequency tunability in such disks can be achieved. The gyrotropic mode of the vortex core is excited with spin‐polarized current and an in‐plane static magnetic field and found that an isolated magnetic vortex shows different resonance frequencies at different saturation magnetization regions. The dynamics of the mutual synchronization between two such dipolarly coupled magnetic vortices are numerically investigated, and the essential distances at which synchronization occurs are also identified. These incredibly small vortex‐based oscillator devices have linewidths of the order of 40–60 MHz, making them prospective candidates for signal‐processing applications and a strong new tool for basic research on vortex dynamics in magnetic nanostructures.

Magnetic Nanoscalpel for the Effective Treatment of Ascites Tumors

One of the promising novel methods for radical tumor resection at a single-cell level is magneto-mechanical microsurgery (MMM) with magnetic nano- or microdisks modified with cancer-recognizing molecules. A low-frequency alternating magnetic field (AMF) remotely drives and controls the procedure. Here, we present characterization and application of magnetic nanodisks (MNDs) as a surgical instrument ("smart nanoscalpel") at a single-cell level. MNDs with a quasi-dipole three-layer structure (Au/Ni/Au) and DNA aptamer AS42 (AS42-MNDs) on the surface converted magnetic moment into mechanical and destroyed tumor cells. The effectiveness of MMM was analyzed on Ehrlich ascites carcinoma (EAC) cells in vitro and in vivo using sine and square-shaped AMF with frequencies from 1 to 50 Hz with 0.1 to 1 duty-cycle parameters. MMM with the "Nanoscalpel" in a sine-shaped 20 Hz AMF, a rectangular-shaped 10 Hz AMF, and a 0.5 duty cycle was the most effective. A sine-shaped field caused apoptosis, whereas a rectangular-shaped field caused necrosis. Four sessions of MMM with AS42-MNDs significantly reduced the number of cells in the tumor. In contrast, ascites tumors continued to grow in groups of mice and mice treated with MNDs with nonspecific oligonucleotide NO-MND. Thus, applying a "smart nanoscalpel" is practical for the microsurgery of malignant neoplasms.

Acoustic frequency multiplication and pure second-harmonic generation of phonons by magnetic transducers

We predict frequency multiplication of surface acoustic waves in dielectric substrates via the ferromagnetic resonance of adjacent magnetic transducers when driven by microwaves. We find pure second-harmonic generation (SHG) without any linear and third-harmonic components by a magnetic nanowire. The SHG and linear phonon pumping are switched by varying the saturated magnetization direction of the wire, or resolved directionally when pumped by a magnetic nanodisk. We address the high efficiency of SHG with comparable magnitude to that of the linear response, as well as a unique nonreciprocal phonon transport that is remarkably distinct in different phonon harmonics. Such an acoustic frequency comb driven by microwaves should bring exceptional tunability for miniaturized phononic and spintronic devices.

Rich topological spin textures in single-phase and core-shell magnetic nanodisks

Magnetic skyrmions have potential applications in future high-density information storage devices due to their small size, topologically protected structure, and ultralow energy consumption. Here, we use a variational method to study rich topological spin textures in magnetic nanodisks, including skyrmions and skyrmionlike objects. The existence of skyrmions and $k\ensuremath{\pi}$-skyrmions in a single-phase nanodisk and a disk with a core-shell structure is investigated theoretically, where the phase diagrams of possible spin states are obtained for various Dzyaloshinskii-Moriya interaction (DMI) constants and disk dimeters. Our calculations suggest that skyrmions can be generated spontaneously in a core-shell nanodisk. We also study the transitions of spin textures in the nanodisk induced by spin currents. This paper may provide guidelines for experimental realization of different topological spin textures in nanodisks with certain DMIs. The simple two-dimensional analytical method used in this paper can be used to study the magnetic phase diagrams of thin films with interface-induced DMIs.

Qubits based on merons in magnetic nanodisks

A meron is a classical topological soliton having a half topological charge. It could be materialized in a magnetic disk. However, it will become a quantum mechanical object when its size is of the order of nanometers. Here, we propose to use a nanoscale meron in a magnetic nanodisk as a qubit, where the up and down directions of the core spin are assigned to be the qubit states leftvert 0rightrangle and leftvert 1rightrangle. We first numerically show that a meron with the radius containing as small as 7 spins can be stabilized in a ferromagnetic nanodisk classically. Then, we show theoretically that universal quantum computation is possible based on merons by explicitly constructing the arbitrary phase-shift gate, Hadamard gate, and CNOT gate. They are executed by applying a magnetic field or spin-polarized current. Our results may be useful for the implementation of quantum computation based on topological spin textures in nanomagnets.

Wireless neuromodulation in vitro and in vivo by intrinsic TRPC-mediated magnetomechanical stimulation

Various magnetic deep brain stimulation (DBS) methods have been developing rapidly in the last decade for minimizing the invasiveness of DBS. However, current magnetic DBS methods, such as magnetothermal and magnetomechanical stimulation, require overexpressing exogeneous ion channels in the central nervous system (CNS). It is unclear whether magnetomechanical stimulation can modulate non-transgenic CNS neurons or not. Here, we reveal that the torque of magnetic nanodiscs with weak and slow alternative magnetic field (50 mT at 10 Hz) could activate neurons through the intrinsic transient receptor potential canonical channels (TRPC), which are mechanosensitive ion channels widely expressed in the brain. The immunostaining with c-fos shows the increasement of neuronal activity by wireless DBS with magnetomechanical approach in vivo. Overall, this research demonstrates a magnetic nanodiscs-based magnetomechanical approach that can be used for wireless neuronal stimulation in vitro and untethered DBS in vivo without implants or genetic manipulation.

Reliable control of magnetic vortex chirality in asymmetrically optimized magnetic nanodisk

Magnetic vortex has attracted attention in the field of information storage because their topological spin structures with chiral bistable states. If the vortex core polarity and vortex circulation sense can be controlled simultaneously in a nanodisk, which will be more beneficial to realize the multi-bit ultrahigh density storage. In this paper, a reliable control scheme for magnetic vortex chirality is proposed by optimizing the structure of Pac-Man-like nanodisk. The results show that the polarity and circulation of the vortex can be controlled simultaneously by changing the direction of the global magnetic field, and even the chiral states of the vortex can be determined by detecting the stray field distribution on the surface of the nanodisk. The optimized Pac-Man-like nanodisk provide an experimental method for the control and detection of magnetic vortex chirality, which will be beneficial to the realization of multi-bit magnetic storage or magnetic logic technology in the future.

Theoretical routes for current-free magnetization switching induced by joint effects of strain and Dzyaloshinskii–Moriya interaction

Voltage-induced strain is regarded as an energy-efficient choice of tuning spin-dynamics. However, studies on the strain-mediated switching of magnetization in a perpendicular-magnetic-anisotropy layer are few because of the uncertainties that arise from the magnetization oscillation at high strain. In this work, we demonstrate theoretically how to deterministically switch the perpendicular magnetization in an ultrathin magnetic nanodisk by combining biaxial in-plane strain with the Dzyaloshinskii–Moriya interaction (DMI). The magnetization-switching process is carefully investigated under different strains and DMI strengths. The underlying switching mechanism is attributed to the remnant magnetization component, which deviates away from the film plane during the strain-pulse-impulsion period and which is also highly dependent on the DMI. Based on simulation results, a theoretical route for obtaining deterministic switching regarding strain and DMI is established. In this route, the minimum duration of the strain pulse can be shortened to a critical time of 2.5 ns as the strain increases to 7000 ppm at a DMI value of 0.6 mJ/m2. Moreover, nonvolatile and reversible switching between the spin-up and spin-down states of perpendicular magnetization is realized using pulses of biaxial in-plane isotropic strain. This switching occurs via an intermediate skyrmion and shows potential in overcoming the edge-roughness-related pinning that occurs in spin–orbit-torque current-induced switching. This study provides a robust insight into strain-induced current-free magnetization switching, providing a guide for experimental research into the strain-mediated voltage control of memory applications.

Manipulating the shape of flexible magnetic nanodisks with meronlike magnetic states

The control of the magnetic properties of shapeable devices and the manipulation of flexible structures by external magnetic fields is a keystone of future magnetoelectronics-based devices. This work studies the elastic properties of a magnetoelastic nanodisc that hosts a meron as the magnetic state and can be deformed from structures with positive to negative Gaussian curvature. We show that the winding number of the hosted meron is crucial to determine the curvature sign of the stable obtained shape. Additionally, we show that the optimum curvature reached by the nanodisc depends on geometrical and mechanical parameters. It is shown that an increase in the external radius, thickness, and Young's modulus lead to a decrease in the optimum curvature absolute value. Finally, it is shown that the nanodisc's shape also depends on the connection between the polarity and chirality of the vortex-like meron.

Commensurate vortex-core switching in magnetic nanodisks at gigahertz frequencies

The development of future spintronic applications requires a thorough and fundamental understanding of the magnetisation dynamics. Of particular interest are magnetic nanodisks, in which the vortex state emerges as a stable spin configuration. Here, we focus on how the vortex core polarisation can be reversed periodically by an oscillating magnetic field, applied perpendicularly to the disk's surface. By means of micromagnetic simulations, we demonstrate the presence of several subharmonic switching modes, i.e., the commensurate ratio between the switching frequency of the core and the driving frequency. The underlying mechanism of this periodic behaviour depends on the disk thickness. For thin disks, the core switches periodically due to resonant excitation of radial spin wave modes, while it is due to the breathing mode in the case of thick disks. However, overlap of both modes impedes periodic vortex core switching. For thin disks, the threshold field amplitude required for periodic switching can be lowered to about 30~mT by increasing the disk diameter. For thick disks, in contrast, the minimal field is largely unaffected by the disk diameter, as only the energy density of a central region around the vortex core is relevant to excite the breathing mode. Our results contribute to the understanding of the switching mechanisms in magnetic nanodisks, which are of technological interest due to their potential in non-volatile memory devices.

Joint Effect of a Magnetic Field and a Spin-Polarized Current on Polarity Switching of Magnetic Vortices in a Spin-Transfer Nanooscillator

The combined influence of a spin polarized current and an external magnetic field for switching the polarity of vortices in spin-transfer nanooscillators 400 nm in diameter is studied. A diagram is constructed of the dependence of the magnitude of the spin-polarized current on the magnitude of the magnetic field, which separately switches the polarity of the vortex in the magnetic layers of the spin-transfer nanooscillator. Keywords: magnetic vortice, spin-transfer nanooscillator, magnetic nanodisk.

"Smart" nanoscalpel for microsurgery of glial tumors of the human brain

We studied the effectiveness of magnetomechanical therapy in the treatment of brain glial tumors using magnetic nanodiscs functionalized with DNA aptamers to human brain tumor glial cells. • Materials and methods. The formation of a model of human glioblastoma was carried out by intracranial injection of tumor cells of glioblastoma obtained from a patient with glioblastoma. Antitumor therapy was carried out using nanodiscs modified with the Gli233 aptamer. The growth of the glial tumor was monitored using NMR tomography. • Results and discussion. Therapy of a glial tumor during 4 sessions of magnetomechanical therapy using a "smart" nanoscalpel in MF (10Hz, 100Oe) led to a significant reduction in its size, while glial tumors in mice that were treated with nanodiscs modified with nonspecific aptamers continued to increase in size. • Conclusion. Microsurgery using three-layer magnetic nanodisks with a quasi-dipole structure (Au/Ni/Au) modified with the specific for glial cells Gli233 aptamer (“smart” nanoscalpel) is effective for the treatment of human glial tumors in the brain.

Micromagnetic simulation of vortex core polarity in bi-component magnetic nanodisks

The nucleation and management of the vortex state in magnetic nanostructures has received a lot of interest in recent decades, with potential applications in logic networks and non-volatile magnetic random-access memory. Because of their potential use in magnetic memory, magnetic vortex structures are of considerable technical importance. Investigation of bi-component magnetic nanodisks as prospective storage systems, in both single and coupled configurations, has been performed, where the information unit is represented by vortex core polarity. The work mainly engages in magnetic nanodisks of permalloy and iron having a diameter of 200 nm and a thickness of 40 nm. The potential of adjusting the polarity of the vortex core by the application of a magnetic field using micromagnetic simulations has been illustrated. Micromagnetic simulation studies show that bi-material structures are important not just for fundamental research but also for data storage.