Magnetic Nanowires Research Articles

Predictions of optimal heating by magnetic reversal behavior of magnetic nanowires (MNWs) with different materials

Objective Magnetic nanowires (MNWs) are potential candidates for heating in biomedical applications that require rapid and uniform heating rates, such as warming cryopreserved organs and hyperthermia treatment of cancer cells. Therefore, it is essential to determine which materials and geometries will provide the optimal heating using available alternating magnetic fields (AMF). Method Micromagnetic simulations are used to investigate the heating ability of MNWs by predicting their hysteretic behavior. MNWs composed of iron (Fe), nickel (Ni), cobalt (Co) or permalloy (FeNi alloy, Py) with different diameters (10-200 nm) are simulated using object oriented micromagnetic framework (OOMMF). Results Hysteresis loops are obtained for each simulated MNW, and the 2D/3D magnetic moment map is simulated to show the reversal mechanism. The heating ability, in terms of specific loss power (SLP), is calculated from the area of the hysteresis loop times frequency for each MNW for comparison with others. Conclusion It is estimated that a theoretical optimal heating ability of 2730 W/g can be provided by isolated Co MNWs with 50 nm diameters using a typical AMF system that can supply 72 kA/m field amplitude and 50 kHz in frequency. Generalized correlation between coercivity and size/material of MNWs is provided as a guidance for researchers to choose the most appropriate MNW as a heater for their AMF system and vice versa.

1D cobalt nanocrystals confined in vertically aligned carbon nanotubes: One-step synthesis and magnetic properties

We report on the one-step synthesis of vertically aligned multiwalled carbon nanotubes (MWCNTs) filled with Co magnetic nanowires via bias-assisted plasma enhanced chemical vapor deposition (PECVD) method. Co/Pd bilayer, both of nanometric thicknesses, deposited onto 50 nm thick TiSiN serving as a diffusion barrier was used as catalysts for nanotube growth. The process gas was a mixture of acetylene (carbon source) and ammonia. A 6 mbar growth pressure combined with 200 W plasma power permitted to achieve simultaneously the growth, alignment and filling of the carbon nanotubes. The plasma was activated by applying a negative bias between − 500 and − 600 V to the substrate. Structural investigations of 1D cobalt rich nanocrystals confined in vertically aligned carbon nanotubes were carried out by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) to elucidate the growth mechanisms. Statistical analysis was performed on the nanotubes peeled from the forest and dispersed. Spatially resolved electron energy loss spectroscopy (EELS) and energy filtered elemental mapping revealed that the nanotubes are mainly filled with cobalt X-ray photoelectron spectroscopy (XPS) confirmed the presence of Co, Pd, C, N and O, with weak degrees of oxidation of the metallic Co and carbide Co formation. Hysteresis cycles, from vibrating sample magnetometer (VSM) measurements at room temperature, exhibited a ferromagnetic behavior with coercive field HC values well above those usually reported for continuous layers. HC is also observed to be higher when the Co nanoparticles embedded in the CNTs exhibit nail shape than spherical or cylindrical one. This can be explained by a lower mean diameter. This shape aspect influences the nature of the magnetization reversal probably operating through curling process. These results open up the potential for one step growth, alignment and filling of carbon nanotubes with potential applications as spintronic devices.

Magneto-optical spatial light modulator driven by current-induced domain wall motion for holographic display applications.

We have developed a magneto-optical spatial light modulator (MO-SLM) with a 10 k × 5 k pixel layout and with a pixel pitch horizontally of 1 µm and vertically of 4 µm. An MO-SLM device pixel has a magnetic nanowire made of Gd-Fe magneto-optical material whose magnetization was reversed by current-induced magnetic domain wall motion. We successfully demonstrated the reconstruction of holographic images, showing large viewing zone angles as wide as 30 degrees and visualizing different depths of the objects. These characteristics are unique to holographic images, providing physiological depth cues which may play a vital role in three-dimensional (3D) perception.

Nucleation and Stability of Toron Chains in Non-Centrosymmetric Magnetic Nanowires.

This work analyzes the magnetic configurations of cylindrical nanowires with a bulk Dzyaloshinskii-Moriya interaction and easy-plane anisotropy. We show that this system allows the nucleation of a metastable toron chain even when no out-of-plane anisotropy exists in the nanowire's top and bottom surfaces, as usually required. The number of nucleated torons depends on the nanowire length and the strength of an external magnetic field applied to the system. The size of each toron depends on the fundamental magnetic interactions and can be controlled by external stimuli, allowing the use of these magnetic textures as information carriers or nano-oscillator elements. Our results evidence that the topology and structure of the torons yield a wide variety of behaviors, revealing the complex nature of these topological textures, which should present an exciting interaction dynamic, depending on the initial conditions.

Exploring the Magnetic Properties of Individual Barcode Nanowires using Wide-Field Diamond Microscopy.

A barcode magnetic nanowire typically comprises a multilayer magnetic structure in a single body with more than one segment type. Interestingly, due to selective functionalization and novel interactions between the layers, it has attracted significant attention, particularly in bioengineering. However, analyzing the magnetic properties at the individual nanowire level remains challenging. Herein, the characterization of a single magnetic nanowire is investigated at room temperature under ambient conditions based on magnetic images obtained via wide-field quantum microscopy with nitrogen-vacancy centers in diamond. Consequently, critical magnetic properties of a single nanowire can be extracted, such as saturation magnetization and coercivity, by comparing the experimental result with that of micromagnetic simulation. This study opens up the possibility for a versatile in situ characterization method suited to individual magnetic nanowires.

Flexible Active Peltier Coolers Based on Interconnected Magnetic Nanowire Networks.

Thermoelectric energy conversion based on flexible materials has great potential for applications in the fields of low-power heat harvesting and solid-state cooling. Here, we show that three-dimensional networks of interconnected ferromagnetic metal nanowires embedded in a polymer film are effective flexible materials as active Peltier coolers. Thermocouples based on Co-Fe nanowires exhibit much higher power factors and thermal conductivities near room temperature than other existing flexible thermoelectric systems, with a power factor for Co-Fe nanowire-based thermocouples of about 4.7 mW/K2m at room temperature. The effective thermal conductance of our device can be strongly and rapidly increased by active Peltier-induced heat flow, especially for small temperature differences. Our investigation represents a significant advance in the fabrication of lightweight flexible thermoelectric devices, and it offers great potential for the dynamic thermal management of hot spots on complex surfaces.

Nano-Patterned Magnetic Edges in CrGeTe3 for Quasi 1-D Spintronic Devices.

The synthesis of two-dimensional van der Waals magnets has paved the way for both technological applications and fundamental research on magnetism confined to ultra-small length scales. Edge magnetic moments in ferromagnets are expected to be less magnetized than in the sample interior because of the reduced amount of neighboring ferromagnetic spins at the sample edge. We recently demonstrated that CrGeTe3 (CGT) flakes thinner than 10 nm are hard ferromagnets; i.e., they exhibit an open hysteresis loop. In contrast, thicker flakes exhibit zero net remnant field in the interior, with hard ferromagnetism present only at the cleaved edges. This experimental observation suggests that a nontrivial interaction exists between the sample edge and the interior. Here, we demonstrate that artificial edges fabricated by focus ion beam etching also display hard ferromagnetism. This enables us to write magnetic nanowires in CGT directly and use this method to characterize the magnetic interaction between the interior and edge. The results indicate that the interior saturation and depolarization fields depend on the lateral dimensions of the sample. Most notably, the interior region between the edges of a sample narrower than 300 nm becomes a hard ferromagnet, suggesting an enhancement of the magnetic exchange induced by the proximity of the edges. Last, we find that the CGT regions amorphized by the gallium beam are nonmagnetic, which introduces a novel method to tune the local magnetic properties of CGT films, potentially enabling integration into spintronic devices.

Modulating the magnetization dynamic properties of zigzag magnetic nanowires by the four-fold magnetic anisotropy

The magnetization dynamic properties of zigzag magnetic nanowires with varied fourfold magnetic anisotropy, which modulated novel microwave responses without any external magnetic field, were investigated. The microwave properties associated with two different remanent magnetic states were found to be highly sensitive to fourfold magnetic anisotropy. A large frequency shift between the two remanent magnetic states was observed when fourfold magnetic anisotropy was added at a particular direction. The results are valuable for the realization of bias field-free microwave applications. In addition, the microwave properties demonstrated by two different remanent magnetic states could be transformed using a nanosecond pulse magnetic field, and fast switching in the system could be achieved with the fourfold magnetic anisotropy.

Multi-segmented nanowires for vortex magnetic domain wall racetrack memory

A vortex domain wall’s (VW) magnetic racetrack memory’s high performance depends on VW structural stability, high speed, low power consumption and high storage density. In this study, these critical parameters were investigated in magnetic multi-segmented nanowires using micromagnetic simulation. Thus, an offset magnetic nanowire with a junction at the center was proposed for this purpose. This junction was implemented by shifting one portion of the magnetic nanowire horizontally in the x-direction (l) and vertically (d) in the y-direction. The VW structure became stable by manipulating magnetic properties, such as magnetic saturation (M s) and magnetic anisotropy energy (K u). In this case, increasing the values of M s ≥ 800 kA/m keeps the VW structure stable during its dynamics and pinning and depinning in offset nanowires, which contributes to maintenance of the storage memory’s lifetime for a longer period. It was also found that the VW moved with a speed of 500 m/s, which is desirable for VW racetrack memory devices. Moreover, it was revealed that the VW velocity could be controlled by adjusting the offset area dimensions (l and d), which helps to drive the VW by using low current densities and reducing the thermal-magnetic spin fluctuations. Further, the depinning current density of the VW (J d) over the offset area increases as d increases and l decreases. In addition, magnetic properties, such as the M s and K u, can affect the depinning process of the VW through the offset area. For high storage density, magnetic nanowires (multi-segmented) with four junctions were designed. In total, six states were found with high VW stability, which means three bits per cell. Herein, we observed that the depinning current density (J d) for moving the VW from one state to another was highly influenced by the offset area geometry (l and d) and the material’s magnetic properties, such as the M s and K u.

Targeting multifunctional magnetic nanowires for drug delivery in cancer cell death: an emerging paradigm.

Apoptosis, often known as programmed cell death is a mechanism used by numerous species to maintain tissue homeostasis. The process leading to cell death is complicated because it requires the stimulation of caspases. According to several studies, nanowires have important medical benefits, can kill cells by adhering to cancer cells, destroying them, and killing the entire cell using a triple attack that integrates vibration, heat, and drug delivery to trigger apoptosis. The sewage effluents and industrial, fertilizer and organic wastes decomposition can produce elevated levels of chemicals in the environment which may interrupt the cell cycle and activate apoptosis. The purpose of this review is to give a thorough summary of the evidence that is currently available on apoptosis. Current review discussed topics like the morphological and biochemical alterations that occur during apoptosis, as well as the various mechanisms that cause cell death, including the intrinsic (or mitochondrial), extrinsic (or death receptor), and intrinsic endoplasmic reticulum pathway. The apoptosis reduction in cancer development is mediated by (i) an imbalance between pro- and anti-apoptotic proteins, such as members of the B-cell lymphoma-2 (BCL2) family of proteins, tumour protein 53 and inhibitor of apoptosis proteins, (ii) a reduction in caspase activity, and (iii) impaired death receptor signalling. This review does an excellent task of outlining the function of nanowires in both apoptosis induction and targeted drug delivery for cancer cells. A comprehensive summary of the relevance of nanowires synthesised for the purpose of inducing apoptosis in cancer cells has been compiled collectively.

Preparation and Magnetic Properties of Fe-Co–Ni Magnetic Nanowire Arrays with Three-Dimensional Periodic Structures

Preparation and Magnetic Properties of Fe-Co–Ni Magnetic Nanowire Arrays with Three-Dimensional Periodic Structures

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.

High-performance, thermal management and long-term preservation Epoxy/TPEDA -Fe3O4@ carboxylic carbon nanotube electromagnetic shielding composites

In this work, a high-performance electromagnetic interference (EMI) latent curing epoxy composites with combination of modified Fe3O4 and carboxylic carbon nanotube (CNTs) were prepared by magnetic orientation. The unique heterogeneous interface among magnetic nanoparticles and conductive nanowires facilitates the loss of interface polarization, the wave absorbance and the dipole polarization, makes EMI SET of the material reach respectively 45.86 dB in X-band at the thickness of 2 mm ± 0.1 mm, significantly exceeding that of other epoxy-based shielding materials. In addition, the composites show excellent thermal capacity reaching 1.59 W/m·K. What's more, the oriented epoxy mixture can be preserved at room temperature for 40 days maintaining a low viscosity state without curing, which has a strong practical application prospect in the field of electronic packaging materials.

Thermal and Dynamic Radiation in the THz Range Under Spin Current Injection in Magnetic Junctions

An experimental approach to the problem of the energy distribution of radiation in the THz range created by an electron flow passing through a magnetic junction between thermal and dynamic is considered. The experimental results obtained during the operation of a spin-injection emitter based on an array of heterogeneous magnetic nanowires (NWs) confirmed the assumption about the “competition” of thermal and dynamic radiation processes.

Analyzing the Magnetic Influence on Magneto-optical Interactions

Here, we study the magneto-optical interactions in magnetic structures considering the dependence of the interactions with the magnetic field. We perform numerical simulations in a structure of magnetic nanowires, considering them as one chain of strongly interacting single-domain particles. Robustly, we obtained a quantitative value for the interactions, which allows us to classify them in two magneto-optical states: when the predominant magneto-optical interactions are demagnetizing (PMOID), or when the predominant magneto-optical interactions are magnetizing (PMOIM).

An energy-efficient cache replacement policy for ultra-dense racetrack memory

Racetrack memory (RTM) based caches provide improved energy and area efficiencies compared to traditional SRAM caches via multi-bit storage capability. The RTM cell arranges multiple bits in a magnetic nanowire track and is equipped with a shared port to access the data. Accessing a bit necessitates to shift the bit under the port. Since the serial access nature of the RTM cell induces energy penalty, it is crucial to reduce the number of shifts. To do so, we have devised an energy-efficient cache replacement policy that first calculates the shift cost of a group of rarely reused cache lines in a cache set. After that, it chooses a victim cache line from that group that incurs minimum shift cost. Employing 1MB RTM cache for single-programmed workloads, the proposed policy outperforms the state-of-the-art by 23.2% and 48.8% in terms of energy consumption and shift cost respectively. For multi-programmed workloads, the energy saving and shift improvement translates to 22.8% and 39.8% respectively using 4MB RTM shared cache.

Operating characteristics of domain walls in perpendicularly magnetized ferrimagnetic cylindrical nano-wires for three-dimensional magnetic memory

We observed field- and current-induced domain wall motion (DWM) in a ferrimagnetic cylindrical nano-wire using a micromagnetic simulation. Two types of domain walls, namely the Hedgehog Bloch point (HBP) and transverse domain wall (TDW), can be generated by controlling the initial state of these systems. In the case of the field-induced HBP motion, depinning and Walker breakdown were observed, whereas they did not appear in the field-induced TDW motion. According to the observation of current-induced DWM, we found that the domain wall mobility in ferrimagnetic cylindrical nano-wires is higher than that in conventional ferromagnetic cylindrical nano-wires owing to the small saturation magnetization. The current-induced HBP motion exhibits depinning, unlike the TDW motion, which corresponds to field-driven DWM. These differences are attributed to the symmetry of the magnetization in the domain walls. These results provide notable insight into the design of three-dimensional memory based on current-induced DWM.

Structural, morphological, angular dependent of magnetic properties and FORC analysis of CoFeIn novel nanowire alloys

CoFeIn Magnetic alloy nanowire arrays with controlled composition were grown into the AAO template as novel nanowires. The influence of composition, annealing temperature, and electrodeposition frequency on the structure and magnetic properties of cylindrical nanowires have been investigated. Obtained data show that the coercivity and squareness of nanowires was improved with addition of In content. The effect of electrodeposition frequency on the magnetic properties of nanowire arrays were investigated. The results show a rapid increasing of the coercivity and squareness with increasing of the frequency up to 600 Hz but the slope of increasing was clearly reduced at higher frequencies. The angular-dependent magnetic properties of nanowires were studied using First-order reversal curve (FORC) analysis and main hysteresis of arrays, by changing the angle of the applied magnetic field from θ = 0° (parallel) to 90◦ (perpendicular to the wire).

Writing domains in nanowires using a spin torque oscillator

Magnetic nanowires can be used to store information. There are various ways to write magnetic domains in nanowires, usually involving the use of an Oersted field. In this work the use of a spin torque oscillator to write domains in magnetic nanowires is investigated using micromagnetic modelling. It is shown that domains can be written using a lower magnetic field than if an Oersted field were used. Writing of multiple domains in a nanowire is also demonstrated.

GMR biosensing with magnetic nanowires as labels for the detection of osteosarcoma cells

GMR biosensing with magnetic nanowires as labels for the detection of osteosarcoma cells