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Theory and Modeling of Spintronics of Nanomagnets
Published in Ram K. Gupta, Sanjay R. Mishra, Tuan Anh Nguyen, Fundamentals of Low Dimensional Magnets, 2023
Mehmet C. Onbaşli, Ahmet Avşar, Saeedeh Mokarian Zanjani, Arash Mousavi Cheghabouri, Ferhat Katmis
We reviewed many theoretical approaches to nanomagnetism. Classical micromagnetic models based on the Landau-Lifshitz-Gilbert equation predict a wide range of experimentally reproducible spin dynamics and equilibria. The modified LLG equation with spin-orbit torques and spin-torque transfer allows for accurate estimation of spin current flow and current-driven domain wall or spin-wave dynamics. As a result, these models are increasingly being utilized to build spintronic nanodevices. Hence, micromagnetic models could assist in the development of new spintronic devices in the future.
Important Parameters and Magnetic Measurements
Published in Chen Wu, Jiaying Jin, Frontiers in Magnetic Materials, 2023
The above-introduced techniques have been widely applied to investigate magnetic properties from macroscopic quantity to microscopic structure. The measurement techniques are, however, by no means exhaustive. Apart from experimental techniques, theoretical calculations and simulations have also advanced our understandings on magnetism and magnetic materials. For instance, ab initio has been used to calculate spin and distribution of magnetic moment. Micromagnetic simulation provides additional method to study local magnetic properties at the nano/microscale. Electromagnetic simulation packages based on finite element method such as COMSOL, CST and HFSS software have also been adopted to investigate the distribution of magnetic field. To understand a specific case, combined magnetic measurement techniques and theoretical calculation tools may be necessary to provide an all-around picture.
Spin Waves in Thin Films and Magnonic Crystals with Dzyaloshinskii–Moriya Interactions
Published in Gianluca Gubbiotti, Three-Dimensional Magnonics, 2019
Rodolfo A. Gallardo, David Cortés-Ortuño, Roberto E. Troncoso, Pedro Landeros
A micromagnetic simulation is based on numerically discretizing the continuum description of the magnetic system into a mesh of magnetic moments whose arrangement depends on the discretization method. The two most commonly used methods are finite differences and finite elements. For the former, the sample is divided into a regular grid of cuboids, which each represents a magnetic moment (see Fig. 5.2a), and the expressions of the magnetic interactions are approximated according to this numerical method. The spacing between cuboids is usually chosen with a magnitude smaller than the exchange length. To simulate the dynamics of the magnetization, the Landau–Lifshitz–Gilbert equation of motion is numerically integrated for every magnetic moment. Three publicly available finite difference micromagnetic simulation codes are OOMMF [139], MuMax3 [140], and Fidimag [141].
Experimental approaches for micromagnetic coercivity analysis of advanced permanent magnet materials
Published in Science and Technology of Advanced Materials, 2021
Micromagnetics is the mathematical energy-minimization method used to find the equilibrium magnetization state of a finite magnet body, which was originally developed by Brown [27]. Based on this approach, Aharoni formulated the curling- and buckling-type nucleation processes for spheroids and infinite cylinders with a size larger than a certain critical diameter dc [28–30]. For a sphere, dc is given as [31],
Synthesis of mesoscopic particles of multi-component rare earth permanent magnet compounds
Published in Science and Technology of Advanced Materials, 2021
T. Thuy Trinh, Jungryang Kim, Ryota Sato, Kenshi Matsumoto, Toshiharu Teranishi
Magnetism on the mesoscopic scale, which is known as micromagnetism, exhibits particularly rich extrinsic behavior. is an extrinsic property of crucial importance in permanent magnetism and is governed by the real structure of materials under Brown’s paradox [23,24]: is reduced to by defects, where the factor (0 ≤ < 1) describes microstructural details [25–29]. The MMPs, especially magnetic nanoparticles (MNPs), are an important class of magnet building blocks that can be used to fabricate high-performance anisotropic PMs [30–32]. Their unique feature is the size-dependent coercivity: of a single-domain grain increases beyond the superparamagnetic critical size () as , reaches the maximum at the single-domain critical size () given by where is the exchange stiffness and is the first anisotropy constant, and then decreases as , provided that the grain has a strong cubic anisotropy [33–36]. The grain-size dependent coercivities of representative R2T17 and RT12 compounds are named a few and shown in Figure 2 [37–50]. Owing to the phase-stabilization challenges, control over the microstructure of R–T multielement materials is still a non-trivial task, though the R–T permanent magnetic materials have been established since 1960s [51] and the Nd2Fe14B compound has been utilized since its discovery in 1984 [52–55].