China
Africa
Explore chapters and articles related to this topic
Magnonic Crystals: From Simple Models toward Applications
Published in Jean-Claude Levy, Magnetic Structures of 2D and 3D Nanoparticles, 2018
Jarosław W. Kłos, Maciej Krawczyk
The magnetocrystalline anisotropy is a static magnetic field related to spin-orbit coupling in atomic lattice (Getzlaff, 2008; Stohr and Siegmann, 2006). At the distances much larger than interatomic distances the averaging of discrete atomic system to continuous medium allows us to relate the magnetocrystalline anisotropy field to the principal directions of the atomic lattice and assume its spatial independence in homogeneous sample. In heterostructures (or finite structures), where the interfaces (surfaces) between different materials appear, additionally the interface (surface) magnetic anisotropy can occur as a result of distortion of atomic orbitals in the vicinity of the interface. The field related to the interface (surface) anisotropy decays with the distance from the interface (surface), but this contribution is also often replaced with homogeneous bulk contribution (Vaz et al., 2008). Both bulk and surface magnetocrystalline anisotropy fields are local and depend only on the atomic structure of the system.
Nanomaterials
Published in Mohammad E. Khosroshahi, Applications of Biophotonics and Nanobiomaterials in Biomedical Engineering, 2017
When a grain size becomes so small that it is comparable to a magnetic domain, i.e., a single domain, its hysteresis loop will exhibit no area and the material will have zero remanence and coercivity. This commonly is referred to as superparamagnetism which approximately applies for particles with dimensions smaller than 15 nm. At this scale ferromagnetism is no longer observed and no permanent magnetization remains after the particles have been subject to external magnetic field. But, the particles will have a considerable degree of paramagnetism with a very large χ, as the name suggests. The underlying physics behind this is found in the material crystal anisotropy. Magnetocrystalline anisotropy is an intrinsic property of any magnetic material, independent of grain size. The energy required to magnetize a ferro or ferromagnetic crystal depends on the direction of the magnetic field relative to the orientation of the crystal. In superparamagnetic material, the magnetization vector fluctuates between different easy magnetic directions, hence overcoming hard directions. The magnetic moment of the particle as a whole is free to fluctuate in response to thermal energy, while the individual atomic moments maintain their ordered state relative to each other. The direct proportionality between the energy barrier to moment reversal ΔE, and particle volume V (i.e., ΔE = KV) where K is the anisotropy energy density.
Growth, Magnetic and Transport Studies of Ferromagnetic GaMnSb Semiconductors
Published in J Kono, J Léotin, Narrow Gap Semiconductors, 2006
H. Luo, G. B. Kim, S. Wang, M. Eginligil, M. Cheon, B.D. McCombe, H. Zeng
The coercive field also showed strong temperature dependence, even at temperatures well below Tc, as shown in Fig. 4(a); this is similar to behavior seen for GaMnAs. [10] For Sample 1, the coercive field is close to 1000 Oe at 2.0 K, which is substantially greater than that for MnSb films or MnSb precipitates (typically less than 600 Oe). [6, 11, 12] The temperature dependence can come from two major factors: the temperature dependence of the magnetocrystalline anisotropy and thermally activated magnetization reversal. For Sample 1 with JSb/JGa = 4.6 shown in Fig. 4a, 80% reduction in He is observed as the temperature increases from 2 K. to 7 K (~1/3 of Tc), a range within which the temperature dependence of the magnetocrystalline anisotropy is expected to be small. This indicates that the magnetization reversal is likely to be thermally activated. In the case of GaMnAs, this behavior was attributed to interactions between defects and the magnetic ions, which is consistent with the thermally activated mechanism for magnetization reversal. [13]
A review of processing techniques for Fe-Ni soft magnetic materials
Published in Materials and Manufacturing Processes, 2019
SCS is an advanced technique to produce nanocrystalline powders.[217,218] The nanocrystalline Fe-Ni alloy powders fabricated via mechanical alloying but this method is not energy efficient and required a very long time.[36,37] SCS technique has advantages of self-sustaining instantaneous reaction, low external energy consumption, high yield of fine powder and low processing time as compared to other techniques.[41,219] Furthermore, the aqueous combustion reaction enables the molecular level mixture of materials. Therefore, iron and nickel particles are homogeneously dispersed in the powder mixture. The crystallite size variation has a major effect on permeability and coercivity of nanocrystalline Fe-Ni alloys. The magnetocrystalline anisotropy reduced significantly when crystallite size became smaller than single-domain particle which results in low coercivity and high permeability.[220–222] Ye Liu et al.[223] synthesized nanocrystalline Fe-50Ni powder by solution combustion synthesis and studied the reduction temperature effect on crystallite size. The crystallite size below 100 nm of porous γ-Fe–Ni powder was reported after hydrogen reduction. The magnetization of 156.33 emu/g and coercive force of 37.2 Oe were achieved by increasing reduction temperature of nanocrystalline Fe-50Ni powder. The solution combustion synthesis route is very cost-effective for the bulk production of nanocrystalline materials due low-cost raw materials and low syntheses temperature.
Electroless deposited ternary alloys: third element chemical state, localisation and influence on the properties. A short review
Published in Transactions of the IMF, 2018
S. Armyanov, E. Valova, D. Tatchev, J. Georgieva
When HCP crystallographic modification dominates in electrodeposited Co-based alloys, the magnetic properties depend strongly on their structure. The reason is the high value of the energy of magnetocrystalline anisotropy.43 This is the explanation for the similarity in the shape of the hysteresis loop of electroless Co–W–P (Figure 8(a)) and electrodeposited Co,43 both having texture <0001>. The value of the ratio of remanence to saturation magnetisation (Ir/Is) is 0.37 and 0.33, respectively. The lower <0001> texture perfection of Co–W–P causes this small difference. For the influence of the texture perfection on Ir/Is see Armyanov.43 The coercivity of LP Co–W–P is higher (195 Oe) than in the mentioned case of electrodeposited Co (145 Oe), due to the segregation of W and P along the grain boundaries, and, to a smaller extent, due to the lower <0001> texture perfection.
A micromechanical constitutive model for porous ferromagnetic shape memory alloys considering magneto-thermo-mechanical coupling
Published in Advanced Composite Materials, 2023
The magnetocrystalline anisotropy energy represents the energy required to move the magnetization vector away from the magnetically easy axis. When the magnetization vector is aligned along the easy axis, this energy is minimum (or zero), and when rotating 90° away from the easy axis, this energy is the maximum. Thus, this energy can be described as