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Review of Nanopharmaceuticals
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
In bulk material, like in a piece of metal, all atoms are arranged in a lattice structure and each of the atoms occupying a lattice position possesses a magnetic moment, i.e., represents a magnetic dipole. However, of uttermost importance is the direction of each individual dipole. Putting only a limited number of atoms together, the likelihood that all magnetic dipole moments are aligned with each other, i.e., point into the same direction is very high; we call this group of atoms a magnetic domain. By definition, a magnetic domain is a region in solid material and in particular in magnetic material in which all individual magnetic moments are aligned with each other, therefore pointing into the same direction. Depending on the material, particles with a size below about 50 nm are usually single-domain particles. Larger particles, i.e. bulk material, possess multiple domains, the magnetic dipoles of which point into random directions, consequently canceling each other out.
Electric Machines
Published in Patrick Hossay, Automotive Innovation, 2019
Of course, to understand magnetic fields we need to understand magnets. Three elements, iron, nickel, and cobalt, demonstrate the property of ferromagnetism, or the ability to be permanently magnetized when placed in a magnetic field. This magnetization happens at the atomic level. The atoms that compose these materials are themselves like tiny magnets with opposing poles, or magnetic moments, that produce a magnetic field, interact with other magnetic moments and change their orientation in response to magnetic fields. When these atoms are similarly oriented throughout the material, their fields combine together and define a uniform magnetic domain. So, by exposing a ferromagnetic material to a powerful magnetic field, the orientation of these crystals can be aligned so that all the magnetic axes point in the same direction, thus creating a magnet. Importantly, with these three materials, when the magnetic field is removed the polarization remains, defining a permanent magnet (PM). When certain rare earth elements, in particular neodymium and samarium–cobalt, are combined with these elements, they can form magnets that are several orders of magnitude more powerful than the simple ferrite magnets on your refrigerator. In addition, as we will see later, some metals, such as copper and aluminum, do not become PMs themselves, but can exhibit magnetic qualities when an electric current is passed through them. This allows us to define controllable magnets that can be switched on and off, called electromagnets.
Spin-Orbit Torques
Published in Evgeny Y. Tsymbal, Žutić Igor, Spintronics Handbook: Spin Transport and Magnetism, Second Edition, 2019
Aurélien Manchon, Hyunsoo Yang
The electrical control of magnetic domain walls (DW) is among the most active topics in spintronics [130]. While earlier experiments mainly focused on NiFe nanowires, it has been recently observed that DWs in asymmetric magnetic multilayers display gigantic velocities [13,131,132]. Such large velocities, exceeding the one attainable by conventional STT, arise from the cooperation between two effects unique to non-centrosymmetric magnets: [14,49,133,134] a large damping-like SOT, usually coming from spin Hall effect, and Dzyaloshinskii-Moriya interaction (DMI), an antisymmetric exchange interaction that emerges in magnets lacking inversion symmetry [135,136]. The latter interaction distorts the DW texture in such a way that the damping-like SOT becomes very efficient, leading to ultrafast domain wall motion [133]. The dynamics of chiral magnetic textures in non-centrosymmetric systems is currently attracting significant attention, with the recent observation of room-temperature skyrmions [137–141] and chiral magnetic damping [142, 143].
Inverse estimation of parameters for the magnetic domain via dynamics matching using visual-perceptive similarity
Published in Science and Technology of Advanced Materials: Methods, 2022
Ryo Murakami, Masaichiro Mizumaki, Ichiro Akai, Hayaru Shouno
Magnetic materials are used in industrial equipment such as sensors, indicators, and transformers, as well as in large equipment such as automobiles, trains, and aircraft. The performance of magnetic devices is governed by the magnetic domain parameters (e.g. magnetic anisotropy, exchange interaction, dipole interaction) of magnetic materials; however, it is difficult to observe the magnetic domain parameters directly. Therefore, the time evolution of magnetic domain patterns formed by magnetic spins was observed in the research and development of magnetic materials [1]. The magnetic domain is a region wherein almost all spins point in the same direction. Magnetic domain patterns (i.e. texture structure) are formed by exchange and dipole interactions between magnetic spins; various patterns appear depending on the magnetic domain parameters [2,3]. Advances in measurement technology have enabled us to measure magnetic domain patterns and obtain information on the magnetic domain parameters of materials from spin dynamics. Coherent X-ray diffraction imaging and scanning microscopy based on X-ray magnetic circular dichroism are powerful methods in terms of element selectivity and high spatial resolution [4,5].
Structural and magnetic properties of CoTi thin films deposited by magnetron sputtering method
Published in Phase Transitions, 2021
Maheswari Mohanta, S. K. Parida, Ananya Sahoo, Mukul Gupta, V.R.R. Medicherla
Figure 8 shows the domain images of hcp Co0.7Ti0.3 thin film. The value of applied magnetic fields is 3.03, 0.81, 0.51, 1.02, 2.34, and 3.24 mT along 0° (EA), 20°, 40°, 60°, 80° and 90° to the easy axis respectively. Magnetic domains are generated to reduce the overall free energy, mainly the magnetostatic energy in a magnetic system. The image of domains does not show any significant changes. The magnetization reversal process can be characterized by nucleation and motion of magnetization vortices. The image of the domain wall does not show the signature of nucleation. The evidence of the formation of magnetization vortices is due to comparatively high magnetostatic energy loss. When a thin film becomes sufficiently thin, then the magnetization vortices become longer in shape. The domain image analysis suggests that only contrast of the images change during magnetization reversal processes. Therefore, we may conclude that magnetization reversal occurs via the coherent rotation of spins along the hard axis.
A comparative study of the influence of the deposition technique (electrodeposition versus sputtering) on the properties of nanostructured Fe70Pd30 films
Published in Science and Technology of Advanced Materials, 2020
Matteo Cialone, Monica Fernandez-Barcia, Federica Celegato, Marco Coisson, Gabriele Barrera, Margitta Uhlemann, Annett Gebert, Jordi Sort, Eva Pellicer, Paola Rizzi, Paola Tiberto
Morphology and stoichiometry of the films were studied using atomic force microscope (AFM), scanning electron microscope (SEM, FEI Inspect F) and transmission electron microscope (TEM, Jeol JEM-3010). The latter was equipped with an energy dispersive X-ray spectrometer (EDS). The crystallographic structure of the films was investigated by grazing incidence X-ray diffraction (GIXRD) on a Panalytical X’Pert PRO MPD using the Cu Kα radiation, at a grazing angle of 0.4º. The magnetic properties were investigated using avibrating sample magnetometer (VSM) from Lakeshore, at room temperature, up to a maximum field of 20 kOe. Magnetic force microscopy (MFM) was used to image the magnetic domain patterns. A Bruker Multimode V Nanoscope 8 microscope equipped with a fully non-magnetic head and scanner, and a commercial Bruker MESP-HR10 cantilever coated with Co/Cr hard magnetic alloy were utilized. The mechanical properties of the films were measured by nanoindentation using a pyramidal-shaped Berkovich-type diamond tip [24]. Indentation experiments were performed in raster across the sample surface and the values for the reduced Young’s modulus, Er, and the Berkovich hardness, HB, were determined as the average from ≈ 300 indentations for each film using the method of Oliver and Pharr [25]. A complete list of the samples synthesized both via electrodeposition and via sputtering and analyzed in this work is reported in Table 1.