Magnetic Nanodevices Research Articles

Spintronic Artificial Neurons Showing Integrate-and-Fire Behavior with Reliable Cycling Operation.

The rich dynamics of magnetic materials makes them promising candidates for neural networks that, like the brain, take advantage of dynamical behaviors to efficiently compute. Here, we experimentally show that integrate-and-fire neurons can be achieved using a magnetic nanodevice consisting of a domain wall racetrack and magnetic tunnel junctions in a way that has reliable, continuous operation over many cycles. We demonstrate the domain propagation in the domain wall racetrack (integration), reading using a magnetic tunnel junction (fire), and reset as the domain is ejected from the racetrack with over 100 continuous cycles. Both the pulse amplitude and pulse number encoding are shown. By simulating a spiking neural network task, we benchmark the performance of the devices against an ideal leaky, integrate-and-fire neuron, showing that the spintronic neuron can match the performance of the ideal. These results achieve demonstration of reliable integrated-fire reset in domain wall-magnetic tunnel junction-based neuron devices for neuromorphic computing.

Ultralow-energy multiferroic majority gates via magnetostrictive heterogeneity

Multiferroic nanomagnetic technology represents a cutting-edge domain with considerable potential for advancing the frontier of ultra-low energy, high precision, and swift responsive nanomagnetic nonvolatile logic gates. This manuscript introduces an innovative majority logic gate that capitalizes on the disparate magnetostrictive responses of materials with positive and negative coefficients under uniform strain conditions, through the implementation of a heterogeneous multiferroic structure integrated with a strain clocking mechanism. Distinct from traditional nanomagnetic majority logic gates, which rely on a single material within a stairs-type global strain clocking paradigm, our proposed design realizes an order-of-magnitude reduction in energy dissipation per operational cycle. Furthermore, simulate each scenario in a thermal noise field, with different logic value inputs getting the correct output, the majority gate supports pipelining capabilities, and offers significant insights for the engineering of energy-efficient multiferroic nanomagnetic logic devices.

Enhancing the Thermal Stability of Skyrmion in Magnetic Nanowires for Nanoscale Data Storage.

Magnetic skyrmion random switching and structural stability are critical limitations for storage data applications. Enhancing skyrmions' magnetic properties could improve their thermal structural stability. Hence, micromagnetic calculation was carried out to explore the thermal nucleation and stability of skyrmions in magnetic nanodevices. Different magnetic properties such as uniaxial magnetic anisotropy energy (Ku), saturation magnetization (Ms) and Dzyaloshinskii-Moriya interaction (DMI) were used to assess the thermal stability of skyrmions in magnetic nanowires. For some values of Ms and Ku, the results verified that the skyrmion structure is stable at temperatures above 800 K, which is higher than room temperature. Additionally, manipulating the nanowire geometry was found to have a substantial effect on the thermal structural stability of the skyrmion in storage nanodevices. Increasing the nanowire dimensions, such as length or width, enhanced skyrmions' structural stability against temperature fluctuations in nanodevices. Furthermore, the random nucleation of the skyrmions due to the device temperature was examined. It was shown that random skyrmion nucleation occurs at temperature values greater than 700 K. These findings make skyrmion devices suitable for storage applications.

Imaging nanomagnetism and magnetic phase transitions in atomically thin CrSBr

Since their first observation in 2017, atomically thin van der Waals (vdW) magnets have attracted significant fundamental, and application-driven attention. However, their low ordering temperatures, Tc, sensitivity to atmospheric conditions and difficulties in preparing clean large-area samples still present major limitations to further progress, especially amongst van der Waals magnetic semiconductors. The remarkably stable, high-Tc vdW magnet CrSBr has the potential to overcome these key shortcomings, but its nanoscale properties and rich magnetic phase diagram remain poorly understood. Here we use single spin magnetometry to quantitatively characterise saturation magnetization, magnetic anisotropy constants, and magnetic phase transitions in few-layer CrSBr by direct magnetic imaging. We show pristine magnetic phases, devoid of defects on micron length-scales, and demonstrate remarkable air-stability down the monolayer limit. We furthermore address the spin-flip transition in bilayer CrSBr by imaging the phase-coexistence of regions of antiferromagnetically (AFM) ordered and fully aligned spins. Our work will enable the engineering of exotic electronic and magnetic phases in CrSBr and the realization of novel nanomagnetic devices based on this highly promising vdW magnet.

On the Origin of the Above-Room-Temperature Magnetism in the 2D van der Waals Ferromagnet Fe3GaTe2.

2D magnetic materials have attracted growing interest driven by their unique properties and potential applications. However, the scarcity of systems exhibiting magnetism at room temperature has limited their practical implementation into functional devices. Here we focus on the van der Waals ferromagnet Fe3GaTe2, which exhibits above-room-temperature magnetism (Tc = 350-380 K) and strong perpendicular anisotropy. Through first-principles calculations, we examine the magnetic properties of Fe3GaTe2 and compare them with those of Fe3GeTe2. Our calculations unveil the microscopic mechanisms governing their magnetic behavior, emphasizing the pivotal role of ferromagnetic in-plane couplings in the stabilization of the elevated Tc in Fe3GaTe2. Additionally, we predict the stability, substantial perpendicular anisotropy, and high Tc of the single-layer Fe3GaTe2. We also demonstrate the potential of strain engineering and electrostatic doping to modulate its magnetic properties. Our results incentivize the isolation of the monolayer and pave the way for the future optimization of Fe3GaTe2 in magnetic and spintronic nanodevices.

Channeling skyrmions: Suppressing the skyrmion Hall effect in ferrimagnetic nanostripes

Channeling skyrmions: Suppressing the skyrmion Hall effect in ferrimagnetic nanostripes

Elastic, electronic, magnetic and magnetocaloric properties of janus MnXO (X=S, Se and Te) monolayers: First-principles and Monte Carlo investigations

In this work, we present the first theoretical analysis of the elastic, electronic, magnetic and magnetocaloric properties of 1T-phase Janus MnXO (X = S, Se and Te) monolayers using first-principle calculations based on density functional theory combined with Monte Carlo simulation. The stability of the studied monolayers has been analyzed by using the elastic constants Cij and formation energy, which indicate that all monolayers are stable. Moreover, the electronic properties reveal the metal characteristics of all monolayers, with a total magnetic moment of 3.25 μB, 3.81 μB and 4.09 μB for MnSO, MnSeO, and MnTeO, respectively. Further, the extracted critical temperature values (Tc) from Monte Carlo simulation are Tc = 115 K, Tc = 130 K and Tc = 82 K, for MnSO, MnSeO and MnTeO, respectively. Interestingly, the predicted maximum magnetic entropy change −ΔSmax and maximum relative cooling power RCP (and adiabatic temperature change) are 10,38 J/kg.K and 763,43 J/kg (7,11 K) for MnSO, 6,79 J/kg.K and 515,57 J/kg (3,25K) for MnSeO, and 6,39 J/kg.K and 407,16 J/kg (3,46 K) for MnTeO at a magnetic field of 5T. These results suggest that the Janus MnXO (X = S, Se and Te) monolayers are a potential materials for use in magnetic nanodevices and low-dimensional magnetic refrigeration.

Thickness dependence of structural and magnetic properties of electrodeposited Co2FeSn films

Co2FeSn films have been electrochemically deposited on polycrystalline Cu substrates in potentiostatic mode. Processed films with thicknesses of 320 nm, 780 nm, and 1400 nm exhibited highly ordered L21 type crystal structure with saturation magnetizations of 1023.38 kA/m (5.08 ± 0.04 μB/f.u.), 1035.31 kA/m (5.14 ± 0.04 μB/f.u.) and 1044.34 kA/m (5.18 ± 0.04 μB/f.u.) at 5 K and 965.00 kA/m (4.79 ± 0.04 μB/f.u.), 967.75 kA/m (4.81 ± 0.04 μB/f.u.), and 1003.52 kA/m (4.97 ± 0.04 μB/f.u.) at 300 K, respectively. The soft ferromagnetic films possess coercivity of ∼ 15.92 kA/m (200 Oe) with a high effective anisotropy constant of ∼ 105 J/m3. Thermo-magnetization measurements yielded high Curie temperatures of 995 K, 1005 K, and 1123 K for films of thicknesses 320 nm, 780 nm, and 1400 nm, respectively. Tailoring the thickness from 320 to 1400 nm could be achieved by merely varying the electrodeposition time without appreciable departure from chemical stoichiometry or compromise in crystalline order or magnetic properties. This establishes a methodology to prepare high quality L21 ordered Co2FeSn films with a few hundred nanometers thickness by electrodeposition. Electrodeposited Co2FeSn films with high magnetic moment, high Keff value, and high Curie temperature are potential candidates for fabricating nanomagnetic devices.

A Detachable Magnetic Nanodevice for the Efficient Capture and Subtype Identification of Circulating Tumor Cells

AbstractThe effective capture and accurate identification of heterogeneous circulating tumor cells (CTCs) aid in guiding clinical diagnosis and personalized treatment of tumors. Herein, a core‐satellite‐sized magnetic separable nanodevice (denoted as MS‐RI) is developed for the capture and subtype identification of heterogeneous CTCs by identifying the protein targets of CTCs in vitro and imaging intracellular nucleic acid targets of CTCs in situ. Upon the separation of CTCs by MS‐RI using aptamers as capture elements, the programmatically dissociated satellite particles aim to internalize into the cells for simultaneous profiling of microRNA‐21 and microRNA‐141. By virtue of the validated magnetic separation of the core structure, the high affinity of the aptamer, and the high sensitivity of the recognition imaging (RI) module, MS‐RI allows the isolation and subtyping of CTCs in clinical samples from breast cancer patients. This strategy of combining extracellular recognition and intracellular imaging pioneers a new paradigm for the capture and precision subtyping of heterogeneous CTCs.

Quantifying the orbital-to-spin moment ratio under dynamic excitation

The orbital component of magnetization dynamics, e.g., excited by ferromagnetic resonance (FMR), may generate “orbitronic” effects in nanomagnetic devices. Yet, distinguishing orbital dynamics from spin dynamics remains a challenge. Here, we employ x-ray magnetic circular dichroism (XMCD) to quantify the ratio between the orbital and spin components of FMR-induced dynamics in a Ni80Fe20 film. By applying the XMCD sum rules at the Ni L3,2 edges, we obtain an orbital-to-spin ratio of 0.108 ± 0.005 for the dynamic magnetization. This value is consistent with 0.102 ± 0.008 for the static magnetization, probed with the same x-ray beam configuration as the dynamic XMCD experiment. The demonstrated method presents a possible path to disentangle orbitronic effects from their spintronic counterparts in magnetic media.

Thermal nanoconversion of ferromagnetic nanoislands

In this work, we investigate the use of post-fabrication thermal nanoconversion (TNC), using a heated scanning probe tip, to modify the magnetic properties of Ni80Fe20 elliptical nanoislands with varying aspect ratio. Despite Ni80Fe20 being unoptimized for TNC, by comparing quasistatic and dynamic magneto-optical Kerr effect microscopy measurements, we demonstrate that TNC at a contact temperature of 250 °C increases the saturation magnetization of the treated nanoislands, reaching a value close to 800 kA/m. Micromagnetic simulations of the nanoislands indicate that the TNC technique can be used to alter the remanent state, from a single domain to a vortex. These results demonstrate the opportunities afforded by TNC to modify the properties of selected areas in a thin film or a patterned sample, particularly when designing magnonic crystals and other nanomagnetic devices.

Single-domain Fe2CoGa0.5Al0.5 Heusler alloy nanoparticles with enhanced properties.

Fine quaternary single-domain Heusler alloy nanoparticles with a composition of Fe2CoGa0.5Al0.5 have been synthesized using a simple template-less chemical route for the first time. Ab initio calculations and standard models have been used to analyze and interpret the experimental findings. The synthesized nanoparticles with an average crystallite size of 42 nm exhibited high saturation magnetization (>5 μB f.u.-1), high effective anisotropy constant (≈8 × 106 erg cc-1), high Curie temperature (>1200 K), low magnetic remanence (<0.2 μB f.u.-1) and low coercive field (<90 Oe), declaring their suitability for fabricating various nanomagnetic devices.

Dominant higher-order vortex gyromodes in circular magnetic nanodots.

The transition to the third dimension enables the creation of spintronic nanodevices with significantly enhanced functionality compared to traditional 2D magnetic applications. In this study, we extend common two-dimensional magnetic vortex configurations, which are known for their efficient dynamical response to external stimuli without a bias magnetic field, into the third dimension. This extension results in a substantial increase in vortex frequency, reaching up to 5 GHz, compared to the typical sub-GHz range observed in planar vortex oscillators. A systematic study reveals a complex pattern of vortex excitation modes, explaining the decrease in the lowest gyrotropic mode frequency, the inversion of vortex mode intensities, and the nontrivial spatial distribution of vortex dynamical magnetization noted in previous research. These phenomena enable the optimization of both oscillation frequency and frequency reproducibility, minimizing the impact of uncontrolled size variations in those magnetic nanodevices.

Two-dimensional inverse double sandwich CoB7: strain-induced non-magnetic to ferromagnetic transition.

A full-scale structural search was performed using density functional theory calculations and a universal structural prediction evolutionary algorithm. This produced a lowest energy two-dimensional (2D) CoB7 structure. The CoB7-1 global minimum structure has unusual inverse double sandwich features. The structure consists of two outer borophene layers which are held together with a layer of Co atoms. This is a B-Co-B sandwich structure. Density functional theory calculations predict that CoB7-1 has good thermodynamic stability, kinetic stability, and mechanical stability. The overall bonding framework is able to survive molecular dynamics annealing up to 1000 K for 10 ps. The DFT results predict that this structure is very stable and should be amenable to experimental synthesis. Surprisingly, we found that this material can change from a non-magnetic ground state to a ferromagnetic state under the influence of biaxial strain. This unusual property of having a magnetic transition while at the same temperature leads us to conclude that this new 2D CoB7 crystal may have potential applications in future nano-magnetic devices at or near room temperature.

Enhanced magnetic anisotropy of iridium dimers on antisite defects of two-dimensional transition-metal dichalcogenides.

The combination of transition-metal (TM) elements with two-dimensional (2D) transition-metal dichalcogenides (TMDs) provides an effective route to realizing a 2D controllable magnetic order, leading to significant applications in multifunctional nanospintronics. However, in most TM atoms@TMDs nanostructures, it is challenging for the magnetic anisotropy energy (MAE) to exceed 30 meV when affected by the crystal field. Hence, the stronger magnetic anisotropy of TMDs has yet to be developed. Here, utilizing first-principle calculations based on density functional theory (DFT), a feasible method to enhance the MAEs of TMDs via configurating iridium dimers (Ir2) on 2D traditional and Janus TMDs with antisite defects is reported. Calculations revealed that 28 of the 54 configurations considered possessed structure-dependent MAEs of >60 meV per Ir2 in the out-of-plane direction, suggesting the potential for applications at room temperature. We also showed the ability to tune the MAE further massively by applying a biaxial strain as well as the surface asymmetric polarization reversal of Janus-type substrates. This approach led to changes to >80 meV per Ir2. This work provides a novel strategy to achieve tunable large magnetic anisotropy in 2D TMDs. It also extends the functionality of antisite-defective TMDs, thereby providing theoretical support for the development of magnetic nanodevices.

Metabolic Glycoengineering-Programmed Nondestructive Capture of Circulating Tumor Cells.

Circulating tumor cells (CTCs) are the "seeds" for malignant tumor metastasis, and they serve as an ideal target for minimally invasive tumor diagnosis. Abnormal glycolysis in tumor cells, characterized by glycometabolism disorder, has been reported as a universal phenomenon observed in various types of tumors. This provides a potential powerful tool for universal CTC capture. However, to the best of our knowledge, no metabolic glycoengineering-based CTC capture strategies have been reported. Here, we proposed a nondestructive CTC capture method based on metabolic glycoengineering and a nanotechnology-based proximity effect, allowing for highly specific, sensitive, and universal CTC capture. To achieve this goal, cells are first labeled with DNA tags through metabolic glycoengineering and then captured through a DNA tetrahedra-functionalized dual-tentacle magnetic nanodevice. Due to the difference in metabolic performance, only tumor cells are labeled with more densely packed DNA tags and captured through enhanced intermolecular interaction mediated by the proximity effect. In summary, we have constructed a versatile platform for nondestructive CTC capture, offering a novel perspective for the application of CTC liquid biopsy in tumor diagnosis and treatment.

Preparation and study of B and P doped SiNTs

The unique properties of silicon nanotubes (SiNTs) are expected to provide them with a very wide range of application potential in nanoelectronic devices, lithium-ion batteries, sensors, field-effect transistors, magnetic nanodevices, hydrogen reservoirs, optoelectronic devices, field emission display devices, and quantum computers, and they are a new one-dimensional nanomaterial with a wide range of applications in the future. Although researchers have already prepared SiNTs in the laboratory, there are not many research reports on SiNTs, especially the preparation of B and P doped SiNTs and analysis based on spectroscopic techniques. Our research group used silicon sources (SiO2 and Si) that had not been previously reported or catalyzed by the rare earth element lanthanum (La). The optimal experimental conditions for the preparation of SiNTs, as well as the doping preparation and study of B and P, were explored by thermal evaporation. Finally, SEM, Raman spectroscopy, selected area electron diffraction, HRTEM, XRD, PL spectroscopy, and other characterization methods were performed on the experimental samples. The experimental results show that 1280 °C was the best experimental temperature for the preparation of SiNTs. Under experimental conditions of 1280 °C, doping of B favored the synthesis of silicon nanowires and SiNTs, and the number of products generated was from least to most: no added B2O3 &amp;lt; 0.1 g B2O3 &amp;lt; 0.2 g B2O3 &amp;lt; 0.3 g B2O3 &amp;lt; 0.4 g B2O3. Under the experimental conditions of 1280 °C, when the amount of doped B2O3 is large (2.2 g), a “needle” structure product is generated. Under experimental conditions of 1400 °C, when the ratio of doped P to the original material is 1:9, a new material that has not been previously reported is generated. Through relevant research and the findings of this paper, it is hoped that it can be helpful for the future research and application of SiNTs.

Slonczewski-spin-current driven dynamics of 180∘ domain walls in spin valves with interfacial Dzyaloshinskii–Moriya interaction

Steady-flow dynamics of ferromagnetic 180∘ domain walls (180DWs) in long and narrow spin valves (LNSVs) with interfacial Dzyaloshinskii–Moriya interaction (IDMI) under spin currents with Slonczewski factor are examined. Depending on the magnetization orientation of polarizers (pinned layers of LNSVs), dynamics of 180DWs in free layers of LNSVs are subtly manipulated: (i) for parallel polarizers, stronger spin polarization leads to higher Walker limit thus ensures the longevity of faster steady flows. Meantime, IDMI induces both the stable-region flapping and its width enlargement. (ii) For perpendicular polarizers, a wandering of 180DWs between bi- and tri-stability persists with the criticality adjusted by the IDMI. (iii) For planar-transverse polarizers, IDMI makes the stable region of steady flows completely asymmetric and further imparts a high saturation wall velocity under large current density. Under the last two polarizers, the ultrahigh differential mobility of 180DWs survives. The combination of Slonczewski spin current and IDMI provides various possibilities of fine controlling on 180DW dynamics, hence opens avenues for magnetic nanodevices with rich functionality and high robustness.

Excellent magnetic properties in multiferroic BiFeO3 based thin films for magnetic devices application

The operation of magnetic devices with a magnetic field or spin current causes high energy consumption. Very low energy consumption can be achieved by using multiferroic thin films, where we can control the magnetization direction by applying an electric field. Good magnetic properties in multiferroic thin films are needed for these magnetic device applications. However, multiferroic thin films generally do not have such good magnetic characteristics, like high saturation magnetization (Ms), perpendicular magnetic anisotropy (PMA, the ratio of coercivity between the alignment of film plane perpendicular and parallel to the applied field (Hc⊥/Hc//)), magneto-optical Kerr rotation angle (Θk) and Curie temperature (Tc). In this research, we have looked into improving magnetic characteristics such as Ms, Hc⊥/Hc//, Θk and Tc in (Bi,L)(Fe,Co)O3(L = Lanthanides) thin films by substituting different lanthanides with cobalt. The highest Ms value of 140 emu/cm3 and large Hc⊥/Hc// ratio of 2.6 were found in (Bi,Nd)(Fe,Co)O3 thin film, and maximum Θk of 0.67° and relatively high Hc⊥/Hc// of 1.6 were found for the (Bi,La)(Fe,Co)O3 thin film. These properties are suitable for magnetic recording devices and optical devices, respectively. A very small coercivity of 0.8 kOe, along with a high Ms value of 110 emu/cm3 and Tc of 450 °C, were observed in the (Bi,Eu)(Fe,Co)O3 thin film. So, the (Bi,Eu)(Fe,Co)O3 thin film is suitable for magnetic sensor applications because of its high sensitivity to magnetic fields. Moreover, the domain size of the above-mentioned thin films was observed in the small nano range, which is suitable for magnetic nano device applications.

DYNAMICS NOISE BEHAVIORS ON MAGNETO-OPTICAL KERR EFFECT MEASUREMENT SYSTEM

Nowadays, computer and data processing industry are moving to nanomagnetic devices technology. One of the common measurement systems to observe nanomagnetic device are magneto optical Kerr effect and Faraday effects. The magneto-optical Kerr effect measurement system has been fabricated and precision noise measurement configuration was observed. A light intensity, which was reflected by thin film nanomagnetic surface, was measured accompany with its noise level. The lock-in amplifier was attached to pick up hysteresis signal and low noise level. Different frequency of lock-in amplifier was carried out to observe dynamics noise level behavior. Interestingly, we found butterfly shape noise corresponding to hysteresis loop shape. Furthermore, noise behavior with 0.94 scaling exponent, was found with respect to lock-in amplifier frequencies suggested that measuring in low frequency became more challenging.