Characterization of Ferromagnetic Nanowires by Partial First Order Reversal Curves PDF Download

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ISBN:
Category :
Languages : en
Pages : 10

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Author: Battogtokh Jugdersuren
Publisher:
ISBN: 9781109491036
Category : Ferromagnetism
Languages : en
Pages : 109

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Nanotechnology offers tremendous potential for future technology. A better understanding of ferromagnetism, half-metallicity and magnetostriction on the smallest scales are expected to improve technological performance. Processing and characterization of nanostructured materials, therefore, are central in modern solid state physics. One of the techniques to grow nanostructures is electrospinning which offers simplicity, low cost and flexibility. This dissertation focuses on functionally different colossal magnetoresistance strontium and calcium doped lanthanum manganites and magnetostrictive iron-gallium nanowires. We have tailored the conventional electrospinning method to grow high quality manganites and iron-gallium nanowires below 100 nm in diameter for the first time. We have shown that these ferromagnetic nanostructures can be grown parallel to one another for understanding the basic physics as well as for fabricating advanced device structures. Single nanowire devices were fabricated by electron-beam lithography. Details of the growth, morphology, structure and magnetic characterization, device fabrication and performance of the devices will be discussed in this thesis. Manganite nanowires have been grown by anodized alumina oxide template and by the pulsed laser deposition methods by other groups, nanowires grown from these techniques are difficult to use for device fabrication. Devices based on electrospun manganite and iron-gallium nanowires have shown improved electrical and magneto-transport properties. Half-metallic lanthanum-strontium manganite nanowires with 80- 300 nm in diameters display enhanced magnetoresistance behavior at room temperature and the large magnetoresistance is exhibited at low magnetic field which will play an important role for creation of novel-next generation devices. Although inter-metallic, bulk iron-gallium is one of the highly attractive magnetostrictive materials, at nano level, it is very rarely studied due to difficulty of growing high-quality materials. Alumina templates or by melt-spinning are only methods applied so far to grow iron-gallium wires. Melt-spinning yields microscale ribbons and the growth using templates results in nanowires with varying stoichiometry over the entire length of the nanowire. This work has produced high quality, stoichiometric, parallel bundles of iron-gallium nanowires with diameters varying from 80-500 nm. These iron gallium nanowires exhibit enhanced magnetic properties. Devices with bundles of iron-gallium nanowires are explored for various applications such as submarine sonar, as highly sensitive magnetic sensors and nanoscale valves.

Author: PoChing Tsai
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Ferromagnetic nanocrystals with shape anisotropy have drawn great attention in the past decades because of their unique magnetic properties and for their potential applications in ultra-high-density magnetic recording media, exchange-coupled nanocomposite magnets and related nanodevices. In this thesis, synthesis and characterixation of ferromagnetic CoNi and CoFe nanowires are reported. CoNi nanocrystals with different size, shape and composition were successfully synthesized via a catalyst chemical solution method. It was found out that the structure and morphology can be controlled by altering the NaOH concentration, and the elongation of the nanowires can be adjusted by changing surfactants ratio and catalyst amount. Unlike the CoNi, CoFe nanocrystals were prepared by a non-catalyst chemistry solution method. The particle size and shape are controlled by varying parameters such as solvent amount, surfactant ratio, reducing agent and heating rate. Morphological, structural, and compositional characterizations of the nanoparticles were performed by using Transmission Electron Microscopy (TEM), high resolution TEM (HRTEM), and X-Ray Diffractometer (XRD). Magnetic properties of nanoparticles of different size were studied by Alternating Gradiant Magnetometer (AGM).

Author: Zackary Flansberry
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"Spin-polarized currents generated by the Spin Hall Effect (SHE) in normal metals (such as platinum) can be used to apply an efficient and localized torque to the magnetization of neighboring ferromagnetic layers. In contrast to field-induced torques, the efficiency of the Spin Hall torque increases as the size of the ferromagnetic system shrinks, attracting a lot ofattention for applications including magnonic data processing and high-speed non-volatile data storage.A long-term goal of the Childress and Sankey labs is to couple SHE-driven ferromagnetic nanocircuits to the spin degrees of freedom of Nitrogen-Vacancy (NV) centres found in bulk diamond; these optically active, atom-like crystal defects can act as local probes of magnetic dynamics through the stray fields of the ferromagnet, and, in principle, the stray fields canbe used to exert a new level of control over the quantum state of the NV centre. This thesis focuses on the modeling, design, fabrication, and preliminary characterization of nanoscale Py/Pt bilayers on the surface of single-crystal diamond substrates implanted with individually-resolvable NV centres (∼100 nm below the surface). We first develop an intuitive "macrospin" toy model to understand the SHE-driven magnetization dynamics and compare with micromagnetic simulations, then use this understanding to choose the geometries of Py/Pt nanowires in which ferromagnetic resonance can be driven with SHEinduced currents and detected by anisotropic magnetoresistance (AMR) measurements. We then develop a 3-step lithographic fabrication technique used to create nanowires of dimensions (∼ 5 μm × ∼ 0.25 μm × ∼ (10 nm Py + 10 nm Pt)) on single crystal diamond, which achieves a device yield of ∼70%. Finally, we perform a preliminary set of SHE-driven ferromagnetic resonance measurements, finding clear evidence of the resonance - appearing as a self-rectified voltage of ∼10 μV - whose frequency and linewidth can be tuned as expected (semi-quantitatively) by applied fields and currents. In particular, we are able to tune the resonant frequency (nominally ∼ 2 GHz) by > 1 GHz with modest external fields on theorder of 10 mT, and provide evidence that DC currents can be used to drive spontaneous large-angle magnetization dynamics." --

Author: Zhiyuan Wei
Publisher:
ISBN:
Category :
Languages : en
Pages : 108

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This dissertation describes experimental studies of the structures and properties, and their correlations in ferromagnetic nanowires and nanotubes fabricated using porous templates. Ferromagnetic Ni and Fe nanowires with diameters 30 ~ 250 nm were electroplated into the pores of anodic aluminum oxide membranes. The effects of nanowire diameter on structural and magnetic properties were investigated. The microstructures of these nanowires were studied using X-ray diffraction and selected-area electron diffraction measurements. The magnetic properties of the nanowires were investigated using magnetic hysteresis measurements and magnetic force microscopy. Additionally, ferromagnetic Ni-P nanotubes were fabricated using an electroless chemical deposition method. Structure and composition analyses were conducted using X-ray diffraction and energy-dispersive spectroscopy. The magnetic properties of the nanotube arrays and the electronic properties of individual nanotubes were studied. Hysteresis measurements revealed that the 250-nm diameter Ni nanowires had a poor squareness in their hysteresis loops, indicating the existence of multi-domain states. In comparison, the squareness in the hysteresis loops of 60-nm and 30-nm Ni nanowires was much improved, suggesting the existence of single domain states in these smaller diameter nanowires. Magnetic force microscopy measurements confirmed the magnetic domain structures suggested by magnetic hysteresis measurements. Similar investigations of Fe nanowires with diameters of 250 nm and 60 nm found that they all have multidomain magnetic structures. This is expected based on their material properties and polycrystalline structures. Furthermore, magnetic structures of Y-branches and multi-wire clusters were also studied using magnetic force microscopy. The as-prepared Ni-P nanotubes had an amorphous structure. Following a heat treatment, however, a structural phase transformation from the amorphous phase to a crystalline phase was observed using X-ray diffraction measurements. The tetragonal crystalline phase of Ni3P and the face-centered-cubic phase of Ni were confirmed via simulations by the GSAS software. The high Ni3P content accounts for the semiconducting behavior and a low magnetic anisotropy observed in the Ni-P nanotubes. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/149593

Author: Victorino Franco
Publisher: Springer Nature
ISBN: 3030704432
Category : Technology & Engineering
Languages : en
Pages : 814

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This book discusses the most commonly used techniques for characterizing magnetic material properties and their applications. It provides a comprehensive and easily digestible collection and review of magnetic measurement techniques. It also examines the underlying operating principles and techniques of magnetic measurements, and presents current examples where such measurements and properties are relevant. Given the pervasive nature of magnetic materials in everyday life, this book is a vital resource for both professionals and students wishing to deepen their understanding of the subject.

Author: I.D. Mayergoyz
Publisher: Springer Science & Business Media
ISBN: 1461230284
Category : Technology & Engineering
Languages : en
Pages : 225

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The purpose of this book is to describe in sufficient detail the mathematical models of hysteresis nonlinearities with "nonlocal memories. " The distinct feature of these nonlinearities is that their future states depend on past histories of input variations. It turns out that memories of hysteresis nonlinearities are quite selective. Indeed, experiments show that only some past input extrema (not the entire input variations) leave their marks upon future states of hysteresis nonlinearities. Thus, special mathematical tools are needed to describe nonlocal selective memories of hysteresis nonlinearities. The origin of such tools can be traced back to the landmark paper of Preisach. The book is primarily concerned with Preisach-type models of hysteresis. All these models have a common generic feature; they are constructed as superposi tions of simplest hysteresis nonlinearities-rectangular loops. The discussion is by and large centered around the following topics: various generalizations and extensions of the classical Preisach model (with special emphasis on vector generalizations), finding of necessary and sufficient conditions for the represen tation of actual hysteresis nonlinearities by various Preisach-type models, solution of identification problems for these models, and numerical implementa tion and experimental testing of Preisach-type models. Although the study of Preisach-type models constitutes the main subject of the book, some effort is also made to establish some interesting connections between these models and such topics as the critical state model for superconducting hysteresis, the classi cal Stoner-Wohlfarth model for vector magnetic hysteresis, thermal activation type models for viscosity, magnetostrictive hysteresis and neural networks.

Author: Hari Singh Nalwa
Publisher:
ISBN: 9781588830005
Category : Science
Languages : en
Pages : 0

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Twelve contributions comprise a reference source that is a coherent presentation of the state of the art in this fast growing area of nanotechnology research. Magnetic nanostructures are important for their phenomenal potential for storage; their great commercial value will come from applications in

Author: David Gubbins
Publisher: Springer Science & Business Media
ISBN: 1402044232
Category : Science
Languages : en
Pages : 1061

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This reference encompasses the fields of Geomagnetism and Paleomagnetism in a single volume. Both sciences have applications in navigation, in the search for minerals and hydrocarbons, in dating rock sequences, and in unraveling past geologic movements such as plate motions they have contributed to a better understanding of the Earth. The book describes in fine detail the current state of knowledge and provides an up-to-date synthesis of the most basic concepts. It is an indispensable working tool not only for geophysicists and geophysics students but also for geologists, physicists, atmospheric and environmental scientists, and engineers.

Author: Ekkes H. Brück
Publisher: Elsevier
ISBN: 0128210249
Category : Technology & Engineering
Languages : en
Pages : 216

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Handbook of Magnetic Materials, Volume 29, highlights new advances in the field, with this new volume presenting interesting chapters written by an international board of authors on topics such as spin-orbit torque. - Provides the authority and expertise of leading contributors from an international board of authors - Presents the latest release in the Handbook of Magnetic Materials series