Nano Magnets Research Articles

Physical Reservoir Computing with Nano Magnets

Physical Reservoir Computing with Nano Magnets

Tailoring magnon modes by extending square, kagome, and trigonal spin ice lattices vertically via interlayer coupling of trilayer nanomagnets

In this work high-frequency magnetization dynamics and statics of artificial spin-ice lattices with different geometric nanostructure array configurations are studied where the individual nanostructures are composed of ferromagnetic/non-magnetic/ferromagnetic trilayers with different non-magnetic thicknesses. These thickness variations enable additional control over the magnetic interactions within the spin-ice lattice that directly impacts the resulting magnetization dynamics and the associated magnonic modes. Specifically the geometric arrangements studied are square, kagome and trigonal spin ice configurations, where the individual lithographically patterned nanomagnets (NMs) are trilayers, made up of two magnetic layers of Ni81Fe19 of 30 nm and 70 nm thickness respectively, separated by a non-magnetic copper layer of either 2 nm or 40 nm. We show that coupling via the magnetostatic interactions between the ferromagnetic layers of the NMs within square, kagome and trigonal spin-ice lattices offers fine-control over magnetization states and magnetic resonant modes. In particular, the kagome and trigonal lattices allow tuning of an additional mode and the spacing between multiple resonance modes, increasing functionality beyond square lattices. These results demonstrate the ability to move beyond quasi-2D single magnetic layer nanomagnetics via control of the vertical interlayer interactions in spin ice arrays. This additional control enables multi-mode magnonic programmability of the resonance spectra, which has potential for magnetic metamaterials for microwave or information processing applications.

Emerging nanotechnology based advanced techniques for wastewater treatment

The increasing trend of industrialization leads to tremendous release of industrial effluents. Waste water treatment is one of the important sectors to focus in order to overcome the most threatening issue of waste disposal and to ensure sustainability. Sustainable and energy efficient treatment methods are the attractive technologies for their current implementation of waste management. Even though the existing technologies are effective, unsustainability makes them unfit for their extended applications. Conventional and advanced technologies have been extensively implemented for the treatment of wide spectrum of effluents. Hybrid technologies including chemical and biological methods also emerging as promising technologies but secondary sludge generation is still unaddressed. Even though effectiveness of biochar varies over type of contaminants, cost-effectiveness and eco-friendly nature extended their applications in waste management. Nanotechnology and membrane technology are the promising and emerging areas of interest due to their widespread applications in waste water treatment. Carbon nano structures, nano filters, graphene, nano magnets modified with activated carbon are the potential candidates for the treatment. The present review demonstrates the emerging treatment technologies with special focus to nano based waste water treatment methods.

Design and implementation of a nano magnetic logic barrel shifter using beyond-CMOS technology

Abstract Bit manipulation plays a significant role in high-speed digital signal processing (DSP) and data computing systems, and shift and rotation operations are crucial functions in it. In general, barrel shifters are used to perform these operations effectively. Nano magnetic logic circuits are among the promising beyond-CMOS alternative technologies for the design of high-speed circuits. Most of the existing circuits that have been developed using nano magnets are combinational circuits. In this work, a barrel shifter is implemented and realised using in-plane nano magnetic logic. The proposed design is the first of its kind nano magnetic logic circuit. The nano magnetic logic circuit implementation, layout generation, simulation, and validation were performed using the ToPoliNano and ModelSim tools. The logical equivalent design was synthesised and evaluated using the Synopsys Design Compiler tool. The proposed barrel shifter was realised using majority logic has 1769037 nano magnets with a boxing area of 481 × 13104 µm2 and 3276 clock zones after optimisation with the Barycenter algorithm. The proposed barrel shifter realised using Boolean logic has 315276 nano magnets with a boxing area of 265 × 5028 µm2 and 1257 clock zones after optimisation with the Barycenter algorithm. The proposed design results demonstrate that complex systems can be developed using nano magnetic logic by combining combinational and sequential circuits.

A Study on Reconfigurable Nanomagnetic Array and Effect of Gilbert Damping on Reconfigurability

A 2-D grid of circular nanomagnets (NMs) has been effectively used to solve binary quadratic optimization problems via magnetic interaction in the X-Y plane. Reconfiguring this architecture is challenging due to the geometry and spacing constraints imposed by the computational algorithm, but can be achieved by destabilizing the uniform and unidirectional magnetic influence from the non-computing cell. In this paper, we studied how the straightforward spin transfer torque (STT) can induce a rotational coupling field between the non-computing and computing cells to impair static interaction. This mechanism is also better than spin orbital torque (SOT)-based reconfiguration in terms of power, speed and system integration. Our study shows that STT-based solution requires 14× less current desnsity and is 25% faster than the SOT-based counterpart. We extended the study to achieve low-power reconfiguration by altering the Gilbert damping. A lower damping can further reduce 60% of the required current than the high damping case.

Heterometallic 3d-4f single molecule magnets containing diamagnetic metal ions.

Molecular nano magnets such as single-molecule magnets (SMMs) are a class of coordination complexes with numerous potential applications such as information storage devices, Q-bits in quantum computing and spintronics materials. One of the greatest challenges in taking these molecules to end-user applications lies in devising strategies to control and predict their magnetic properties. In this regard, lanthanide-based compounds are very attractive as they possess appealing magnetic properties such as very high barriers for magnetization reversal, very large blocking temperatures etc. Controlling the microscopic energy levels of lanthanide-based single-ion magnets (SIMs) is a challenging task and to obtain molecules having very large blocking temperatures, it is desirable to enhance the ground state-excited state gap between the mJ levels and also to quench the quantum tunnelling of magnetization that often circumvents the barrier height. One of the strategies that has been developed by us and others in this area is to employ a diamagnetic transition metal ion to achieve this goal. Over the years several diamagnetic ions such as ZnII, NiII (square planar), AlIII and CoIII have been successfully employed to obtain lanthanide-based SMMs with interesting properties. In this perspective, we discuss how incorporation of diamagnetic ion(s) in the cluster aggregation enhances the barrier height for magnetization reversal and hence improves the magnetic properties. We also discuss theoretical studies on such systems based on ab initio calculations performed using CASSCF level of theory. Such studies are helpful in affording an understanding of the role and limitation of the diamagnetic ions in enhancing the barrier height for magnetization reversal of molecular nanomagnets.

Stability Analysis of Microwave-Assisted Magnetization Reversal in Exchange Coupled Nano Magnets

The stability analysis was applied to the study of magnetization dynamics under action of microwave magnetic field in exchange coupled nano magnets. It was found that the stability criteria represe...

Theoretical study of microwave-assisted magnetization switching in exchange coupled nano magnets

Microwave-assisted magnetization switching (MAS) in an exchange-coupled-composite (ECC) nano-magnet was analyzed based on the macrospin-model. The ECC nano-magnet consists of the perpendicularly magnetized soft and hard magnetic layers which are ferromagnetically coupled with each other through the interlayer exchange coupling, χ. With increasing χ a reentrant transition from the MAS-non-effective state to the MAS-effective state appears. There exists a region of χ where the switching field is reduced by application of the microwave field. The width of this MAS-effective region of χ decreases with an increase of the frequency of the microwave field and vanishes at a certain frequency.

Reducing error rates in straintronic multiferroic nanomagnetic logic by pulse shaping

Dipole-coupled nanomagnetic logic (NML), where nanomagnets (NMs) with bistable magnetization states act as binary switches and information is transferred between them via dipole-coupling and Bennett clocking, is a potential replacement for conventional transistor logic since magnets dissipate less energy than transistors when they switch in a logic circuit. Magnets are also ‘non-volatile’ and hence can store the results of a computation after the computation is over, thereby doubling as both logic and memory—a feat that transistors cannot achieve. However, dipole-coupled NML is much more error-prone than transistor logic at room temperature because thermal noise can easily disrupt magnetization dynamics. Here, we study a particularly energy-efficient version of dipole-coupled NML known as straintronic multiferroic logic (SML) where magnets are clocked/switched with electrically generated mechanical strain. By appropriately ‘shaping’ the voltage pulse that generates strain, we show that the error rate in SML can be reduced to tolerable limits. We describe the error probabilities associated with various stress pulse shapes and discuss the trade-off between error rate and switching speed in SML.The lowest error probability is obtained when a ‘shaped’ high voltage pulse is applied to strain the output NM followed by a low voltage pulse. The high voltage pulse quickly rotates the output magnet’s magnetization by 90° and aligns it roughly along the minor (or hard) axis of the NM. Next, the low voltage pulse produces the critical strain to overcome the shape anisotropy energy barrier in the NM and produce a monostable potential energy profile in the presence of dipole coupling from the neighboring NM. The magnetization of the output NM then migrates to the global energy minimum in this monostable profile and completes a 180° rotation (magnetization flip) with high likelihood.

単一ナノ分子・磁気抵抗素子

Giant magnetoresistance (GMR) through a single phthalocyanine molecule (H2Pc) was studied by means of a spin-polarized scanning tunneling microscopy (STM) technique. Single molecular magnetic junction was fabricated by contacting a ferromagnetic STM tip to a single molecule on nano magnets. We obtained GMR of +60% and −50% through [Co/H2Pc/Co(111)] and [Fe/H2Pc/Mn(001)] junctions, respectively, in ultra-high vacuum at 4.6 K. Single organic molecules can be a new material for spintronics.

Mesoporous NiO nanomagnets as catalysts and separators of chemical agents

The development of a sustainable catalyst could potentially provide a long-term solution to industrial processes, especial those in the chemical industry, that require the production of a large quantity of raw materials manufactured from renewable resources. Therefore, establishing a proper design for a highly efficient and long-term reusable catalyst is one of the crucial environmental issues facing humanity. In this study, we developed a simple control for hierarchal mesoporous nickel oxide (NiO) nanomagnets (NMs) with flower- and sphere-like morphology and large mesocage cavities. In the fabrication of super-nanostructure NiO, features that were affected by the shape, surface, and size of particles exhibit high catalytic activities of chemical agents, such as o-aminophenol. Our findings shows that the NiO NM with flower-like morphology NFs has higher catalytic activity toward the oxidation of organic contaminates than that of nanospheres NSs or even other magnetic nanoparticles (NPs) such as Fe3O4 NPs. Furthermore, the NiO NMs are capable of the high-gradient magnetic separation of organic contaminants from aquatic life with excellent reusability even after several cycles, which may help in wastewater management and supply. To understand the effectiveness of NiO NM functionalities in terms of hierarchical mesocage parameters, as well as in terms of shape- and size-morphologies in such chemical reactions, surface interaction and magnetic separation with chemical agents and theoretical calculations were performed.

Electric Field Control of Fe Nano Magnets

Electric Field Control of Fe Nano Magnets

Electric Field Control of Fe Nano Magnets: Magnetoelectric Coupling at Metal Surfaces

Magnetoelectric coupling at metal surfaces opens up a new possibility for metallic non-volatile magnetic data-storage devices, in which the magnetic bits are controlled by an electric field. We studied the atomic and magnetic order in bilayer Fe nano-islands grown on a Cu(111) substrate with a scanning tunneling microscopy setup in ultra-high vacuum at 4.5 K. Electric field pulses (108-109 V/m) were found to be able to cause a displacement of the Fe atoms, switching simultaneously the crystalline and the magnetic order, which is the prove of magnetoelectric coupling at the metallic Fe surface. We also succeeded in controlling the direction of the switching by the polarity of the electric field.

Is a Cs Corrector Necessary for Lorentz Vector Field Tomography?

Abstract Magnetic recording media based on patterned shapes are promising for applications in high density data storage. Optimizing the design of the patterned arrays requires characterization of the particle shapes and their relative locations, and the magnetostatic interactions between particles. To achieve this, one must determine the three dimensional (3D) magnetic induction in and around the nano magnets. We propose a method based on Vector Field Electron Tomography coupled with phase reconstructed Lorentz Microscopy to determine the 3D magnetic induction. This method can be broken down into two steps 1) Determination of the magnetic phase shift of the electron wave using phase reconstructed Lorentz microscopy and 2) Reconstruction (in 3D) of the magnetic induction in and around the magnetic particle using Vector Field Electron Tomography (VFET). First, we will discuss the theoretical development of VFET and then the importance of spherical aberration (Cs) correctors for Lorentz microscopy.

Large hysteretic magnetoresistance in high-mobility semiconductor quantum wires bridged by single-domain nanomagnets

The authors discuss hysteresis in the magnetoresistance of hybrid semiconductor/ferromagnetic devices composed of high-mobility semiconductor quantum wires (QWs) bridged by single-domain Co nanomagnets (NMs). This hysteresis is shown to be consistent with the ballistic transport of electrons in the QW through the nonuniform magnetic field generated by the NM. It is also found to be strongly dependent on tilt angle, suggestive of a transition between easy- and hard-axis magnetizations.

Quantum phenomena in magnetic nano clusters

One of the fascinating fields of study in magnetism in recent years has been the study of quantum phenomena in nanosystems. While semiconductor structures have provided paradigms of nanosystems from the stand point of electronic phenomena, the synthesis of high nuclearity transition metal complexes have provided examples of nano magnets. The range and diversity of the properties exhibited by these systems rivals its electronic counterparts. Qualitative understanding of these phenomena requires only a knowledge of basic physics, but quantitative study throws up many challenges that are similar to those encountered in the study of correlated electronic systems. In this article, a brief overview of the current trends in this area are highlighted and some of the efforts of our group in developing a quantitative understanding of this field are outlined.