We foresee future works exploiting dipolar interactions, integrating different magnetic materials and more complex geometries, incorporating optical and electrical readout methods, and further integration into biological environments. In particular, 3D nano- and micro-scale mechanical actuators are a key part of the tool-kit of mechano-biology 94 , 95 , an emerging field which tries to understand the role of cell and tissue mechanics in diseases. Single 3D magnetic nanostructures subjected to laboratory-scale magnetic fields can generate tens of nanonewton of force locally and controllably to cells.
This is sufficient to probe the phenotype of cells 96 , mechanically induce differentiation of bone stem cells 97 , burst payload-carrying neural stem cells 98 and destroy cancer cells Additionally, mammals use motile cilia flagella-like microtubules beating together to sweep objects through organs such as removing dirt from the lungs or transporting eggs through female Fallopian tubes.
Magnetic NWs could perhaps form artificial cilia , transporting reagents through on-chip microfluidic channels. The realization of 3D magnetic memories could be implemented using perhaps the original racetrack architecture Alternatively, existing magnetic random access memory technology could be enhanced by increasing the number of data storing magnetic layers in the stack, such that each cell can store a data word instead of a data bit In both of these cases, digital shift-register action is an essential ingredient 68 , allowing data bits in magnetic form to be sequentially pumped into the nanomagnet during writing and then pumped back out during reading.
Also, a recent trend in microelectronics is to create 2. Magnetic NWs could use these ideas to enable 2. Magnetic interconnect is a particularly interesting idea because it can host both magnetic DWs and magnetic spin waves The former would carry digital information in a very compact form but at low speed, while the latter would offer long-range transmission.
Intriguingly, the magnetic hysteresis and non-linearity present in many magnetic NWs mean that the interconnect is potentially also both a memory element and a logic gate , opening up new computing architectures in which the traditional boundaries between memory, logic and interconnect are eliminated. Such chips could even go beyond conventional Boolean logic and implement neuromorphic computing architectures in which 3D networks of magnetic NWs mimic the neurons and synapses in living brains.
However, significant challenges still remain before such applications become reality. In particular, modern microelectronics makes great use of precision interfaces between materials; many of the growth techniques used for 3D structures do not currently offer sufficient purity and control to engineer interfaces with single atomic layer precision.
Also, while planar microchips successfully integrate and connect 10 8 transistors on a single chip, complex interconnectivity in 3D is still to be developed. A human brain may connect up to 10 4 synapses to each neuron ; there are currently no known 3D fabrication techniques able to achieve this. The integrated circuits of the future will increasingly incorporate a wider range of technologies onto a single die to form full systems Fig. The inclusion of physical sensors and energy harvesters into the menu of devices available to designers is particularly important for the Internet-of-Things.
Recent advances in spin caloritronics and multiferroic materials will provide the necessary interconversion between the electronic, magnetic and thermal worlds. The chip is comprised of a microfluidic channel with two types of magnetic nanoparticles flowing from a common reservoir. The motion of fluid is achieved by magnetic NWs acting as artificial cilia.
After particle separation by chemical means, individual particles entering each channel are detected via a nanomembrane magnetic flexible sensor. Neuromorphic computing processes are carried out by a dense array of interconnected NWs. The move from 2D to 3D is not only a current trend within nanomagnetism, but is part of a wider theme within nanotechnology in general. Nanoelectronics, nanophotonics, energy storage and harvesting, and nanomedicine, all stand to benefit from a new era of greener, more capable, multi-functional technologies brought about by moving into the third dimension.
Despite the great challenges ahead, recent advances in bottom-up lithography, microscopy and computational techniques make its future realization feasible. The experimental realization of spintronic devices requires high-quality materials, for example, DW motion may be severely affected by the presence of defects.lastsurestart.co.uk/libraries/cam/4021-mobile-snooping.php
Spin Dynamics in Confined Magnetic Structures II
Achieving such a quality with unconventional synthesis methods is still work in progress. Also, next-generation 3D nanomagnets will require advanced magnetic materials such as Heusler alloys, multi-layered and epitaxial thin films, and highly functional interfaces. These barriers could be overcome using fabrication strategies which combine multiple synthesis techniques, including innovative ways to exploit differential strain The low throughput currently achievable in 3D nano-printing could be significantly enhanced by moving from the gas phase to the liquid phase This may enable the development of complex architectures, mass fabrication and the creation of multi-functional designs.
Future years will also see rapid progress in the synthesis of novel magnetic materials such as 3D nanocomposites , where strong electric fields at interfaces or magnetostrictive effects could be used for energy harvesting.
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Magnetic tools able to probe 3D nanomagnets are essential as well. Vectorial magnetometry and magnetic microscopy of nanostructures require a phenomenal combined effort comprising instrumentation, electronics and data analysis. Recent progress in magnetic microscopy methods , , , , pushing further spatial and temporal resolution, is expected to bring new opportunities in this area.
An essential cornerstone still missing due to its technical complexity is the development of methodologies to electrically contact individual 3D nano-geometries. Advances in these areas are essential to study 3D spin textures further. Recent experimental work has confirmed theoretical and computational predictions about their magnetic structure and static behaviour.
The next step is now to focus on the experimental realization of specific dynamic features driven by different mechanisms. Interest is also growing in composite spin textures such as coupled bilayers , where flux closure and moment compensation can enhance magnetic DW motion within the plane, as well as leading to motion between horizontal planes.
The search for and realization of ever more complex geometries will continue, for example, by connecting planar and vertical structures, creating core-shell 3D objects, or exploiting topological effects via the interplay between 3D shapes and spin configurations The possibility of creating complex 3D networks of nanomagnets could lead to new computational paradigms , and is also expected to elucidate open questions regarding effects involving numerous interacting magnetic particles, for example, artificial spin-ice lattices Three-dimensional nanomagnetism, with its vast amount of unexplored science and huge potential to impact society, is a fascinating new research area, which will flourish in the years to come.
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Emerging physics of 3D nanomagnetism
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