In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

We review recent advances in biosensors based on one-dimensional (1-D) nanostructure field-effect transistors (FET). Specifically, we address the fabrication, functionalization, assembly/alignment and sensing applications of FET based on carbon nanotubes, silicon nanowires and conducting polymer nanowires. The advantages and disadvantages of various fabrication, functionalization, and assembling procedures of these nanosensors are reviewed and discussed. We evaluate how they have been used for detection of various biological molecules and how such devices have enabled the achievement of high sensitivity and selectivity with low detection limits. Finally, we conclude by highlighting some of the challenges researchers face in the 1-D nanostructures research arena and also predict the direction toward which future research in this area might be directed.

Nanowire‐Based Electrochemical Biosensors

TOPICAL REVIEW: Organic spintronics

The authors perform nonlocal four-probe spin-valve experiments on graphene contacted by ferromagnetic Permalloy electrodes. They observe sharp switching and often sign reversal of the nonlocal resistance at the coercive field of the electrodes, indicating the presence of a spin current between injector and detector. The nonlocal spin-valve signal changes magnitude and sign with back-gate voltage, and is observed up to T=300K. The gate voltage variation of the spin-valve signal may result from quantum-coherent transport, as evidenced by Fabry-Perot-like oscillations of the current.

/pdf/gate-tunable-graphene-spin-valve-5g4tkwnv89.pdf

Gate-tunable graphene spin valve

Spintronics aims to develop electronic devices whose resistance is controlled by the spin of the charge carriers that flow through them1,2,3. This approach is illustrated by the operation of the most basic spintronic device, the spin valve4,5,6, which can be formed if two ferromagnetic electrodes are separated by a thin tunnelling barrier. In most cases, its resistance is greater when the two electrodes are magnetized in opposite directions than when they are magnetized in the same direction7,8. The relative difference in resistance, the so-called magnetoresistance, is then positive. However, if the transport of carriers inside the device is spin- or energy-dependent3, the opposite can occur and the magnetoresistance is negative9. The next step is to construct an analogous device to a field-effect transistor by using this effect to control spin transport and magnetoresistance with a voltage applied to a gate10,11. In practice though, implementing such a device has proved difficult. Here, we report on a pronounced gate-field-controlled magnetoresistance response in carbon nanotubes connected by ferromagnetic leads. Both the magnitude and the sign of the magnetoresistance in the resulting devices can be tuned in a predictable manner. This opens an important route to the realization of multifunctional spintronic devices.

Electric field control of spin transport

Moth and butterfly ommatidial nanostructures have been extensively studied for their anti-reflective properties. Especially, from the point of view of sub-wavelength anti-reflection phenomena, the moth eye structures are the archetype example. Here, a comparative analysis of corneal nipples in moth eye (both Male and Female) and butterfly eye (both Male and Female) is given. The surface of moth(Male and Female) and butterfly(Male and Female) eye is defined with regularly arranged hexagonal facets filled with corneal nipples. A detailed analysis using high-resolution scanning electron microscopy images show the intricate hexagonal arrangement of corneal nipples within the individual hexagonal facet. Individual nipples in moth are circular with an average diameter of about 140/165 nm (Male/Female) and average internipple separation of 165 nm. The moth eye show the ordered arrangement of the corneal nipples and the butterfly eye (Male/Female) show an even more complex arrangement of the nipples. Structurally, the corneal nipples in both male and female butterflies are not circular but are polygons with 5, 6, and 7 sides. The average center-to-center separation in the butterfly(Male/Female) is about 260 nm/204 nm, respectively. We find that these corneal nipples are organized into much more dense hexagonal packing with the internipple (edge-to-edge) separation ranging from 20 to 25 nm. Each hexagonal facet is divided into multiple grains separated by boundaries spanning one or two crystallographic defects. These defects are seen in both moth and butterfly. These are typical 5-coordinated and 7-coordinated defect sites typical for a solid-state material with the hexagonal atomic arrangement. Even though the isolated defects are a rarity, interwoven (7-5) defects form a grain boundary between perfectly ordered grains. These defects introduce a low-angle dislocation, and a detailed analysis of the defects is done. The butterfly eye (Male/Female) is defined with extremely high-density corneal nipple with no apparent grains. Each corneal nipple is a polygon with "n" sides (n = 5, 6, and 7). While the 5- and 7-coordinated defects exist, they do not initiate a grain rotation as seen in the moth eyes. To find out the similarity and the difference in the reflectivity of these nanostructured surfaces, we used the effective medium theory and calculated the reflectivity in moth and butterfly eyes. From this simple analysis, we find that females have better anti-reflective properties compared to the males in both moth and butterfly.

https://pubs.acs.org/doi/pdf/10.1021/acsomega.0c02314

A Comparative Study of Crystallography and Defect Structure of Corneal Nipple Array in Daphnis nerii Moth and Papilio polytes Butterfly Eye.

Conventional computers are limited in their performance due to the physical separation of the memory and processing units. To overcome this, parallel computation using artificial synapses has been thought of as a possible replacement in computing architecture. The development of nanoelectronic devices that can show synaptic functionalities is very important. Here, we report the robust synaptic functionalities of carbon quantum dots embedded in two terminal indigo-based organic synapses. The carbon quantum dots (CQDs) are prepared using an easy-to-do process from commercial jaggery. The CQDs have a size range between 3.5 and 4.5 nm with excellent light emission in the green region. CQD+indigo-based devices show extremely stable memory characteristics, with ON and OFF states differing by more than 10 Mohm. Devices show excellent long-term potentiation and long-term depression characteristics, with both synaptic weight updates following a double exponential behavior. The extent of nonlinearity is explained using the nonlinearity factor. The linear increase in memory is established with repeated learning and forgetting (or potentiation and depression) curves. This study gives a robust way to make an artificial synapse work efficiently at room temperature with excellent memory and synaptic behavior.

Artificial synapse based on carbon quantum dots dispersed in indigo molecular layer for neuromorphic applications

8.5 ML for Ni‐Cu(100), we obtained a value of 20 ML for Fe Ni . These results can be explained on the basis of elastic and magnetoelastic properties of bulk Fe Ni alloys. Beyond this Fe concentration, we could not observe any reorientation, the magnetization stayed in the plane. At 35 Fe we could observe an “usual” transition at 1.9 ML for a sample temperature of 110 K. This value increased to 3M L for Fe Ni , beyond this concentration, we could observe “magnetic live surface layers.”

http://ieeexplore.ieee.org/iel5/20/22340/01042299.pdf

Spin Reorientation Transition in Fe Ni Alloy Films

We have investigated the evolution of magnetic properties as we grow Fe x Mn 1 - x alloys on 25 ML thick Ni/Cu(100) films. We have choosen these Ni films since they exhibit a perpendicular magnetization. Along this direction we were able to detect magnetic signals of fcc Fe x Mn 1 - x /Cu(100) as previously reported. We find that the polar Kerr intensity initially increases during Fe x Mn 1 - x alloy growth on 25 ML Ni. It peaks at ∼2 ML where we observe 1.4 times the Kerr signal of 25 ML Ni. This enhancement is equivalent to the signal of 1 ML Fe it also compares nicely with the signal levels on Fe x Mn 1 - x /Cu(100) films. Upon further deposition the signal decreases and finally returns to the value of the bare Ni film at ∼3.5 ML.Reversing the deposition order allows us to study the effect on the Spin Reorientation Transition (SRT) of Ni films. We find that the reorientation thickness d c increases by ∼3 ML if the substrate is changed from Cu(100) to Fe 5 0 Mn 5 0 .

R. Thamankar

Papers

A Comparative Study of Crystallography and Defect Structure of Corneal Nipple Array in Daphnis nerii Moth and Papilio polytes Butterfly Eye.

Artificial synapse based on carbon quantum dots dispersed in indigo molecular layer for neuromorphic applications

Spin Reorientation Transition in Fe Ni Alloy Films

Evolution of magnetic properties at the interface FexMn1-x/Ni

Structural and magnetic properties of Fe-rich FexMn1-x ultrathin alloy films on Cu(1117)