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Femtomagnetism
Published in Guo-ping Zhang, Georg Lefkidis, Mitsuko Murakami, Wolfgang Hübner, Tomas F. George, Introduction to Ultrafast Phenomena from Femtosecond Magnetism to high-harmonic Generation, 2020
Guo-ping Zhang, Georg Lefkidis, Mitsuko Murakami, Wolfgang Hübner, Tomas F. George
Between magnetic domains, there are domain walls. Figures 5.1(c) and (d)) show two common walls: Ne´el and Bloch walls. Spins inside these walls smoothly transition from one orientation of one domain to another orientation of a neighboring domain. If we arrange the wall normal direction along the y-axis, with the spin directions in two neighboring domains along the +z- or −z-axis, the Bloch wall has the spins that tilt within the xz-plane, but the Néel wall has the spins that tilt within the xy-plane. The width of the wall is determined by the total energy. The total energy in ferromagnets consists of the exchange energy, magnetocrystalline anisotropy energy (MAE), which further consists of volume anisotropy and surface anisotropy energies, and a weaker magnetic dipole-dipole interaction. MAE originates from the spin-orbit coupling. The unquenched orbital moment renders the spins to energetically align them along a few energetically preferred directions, which are called easy axes [Kittel (1996)].
Introduction to Metallic Glasses
Published in Sumit Sharma, Metallic Glass–Based Nanocomposites, 2019
Coercivity is the intensity of the applied magnetic field required to reduce the magnetization of a ferromagnetic material to zero. It is a measure of resistance of a ferromagnetic material to become demagnetized. Coercivity is usually measured in oersted or ampere/meter units and is denoted HC. It can be measured using a magnetometer. Magnetically hard materials have high coercivity whereas soft magnetic materials have low coercivity. BMGs have generally soft magnetic character because of the absence of structural inhomogeneities such as grain boundaries and crystal defects. Grain boundaries and crystal defects hinder the domain wall motion during magnetization. In magnetism, a domain wall is an interface separating magnetic domains. The thickness of the domain wall is 100–150 atoms. A domain wall of soft magnetic material is easily movable. In contrast to this, crystalline metallic alloys show hard magnetic behavior. Very few BMGs, e.g., of Nd-Fe-Al, Pr-Fe-Al and Sm-Fe-Al, show hard magnetic character. These glasses also show the magnetocaloric effect. The magnetocaloric effect is a reversible temperature-changing phenomena that occurs when a material is imposed on a changing magnetic field. This effect can be used for magnetic refrigeration—an energy-efficient and environmentally friendly approach although a few severe limitations were displayed by such BMGs.
The Basis of Nanomagnetism: An Overview of Exchange Bias and Spring Magnets
Published in S. K. Sharma, Exchange Bias, 2017
Navadeep Shrivastava, M. Singh Sarveena, S. K. Sharma
The formation of interfaces (walls) between the domains leads to an increase in energy due to MA and to the exchange interaction. The width of the domain wall is defined by the competition between the anisotropy energy and the exchange energy; the former is reduced for narrow walls, and the latter is reduced for thick walls. Domain walls can have many different forms; however, there are two main types, known as Bloch walls and Néel walls. They are distinguished from one another based on the way the atomic magnetic moments in the wall turn. In Bloch domain walls, magnetization turns outside the plane of the magnetization of the neighbor domains, and in Néel walls, the moments turn in the same plane as that of the domain moments. Bloch domain wall and Néel wall arrangements are illustrated in the case of a 180° magnetic domain wall in Figure 1.4.
Domain wall motion in multiferroic nanostructures under the influence of spin-orbit torque and nonlinear dissipative effect
Published in Mechanics of Advanced Materials and Structures, 2022
Chiranjeev K. Shahu, Shruti Dubey, Sharad Dwivedi
Magnetic domain structures in ferromagnetic materials have been extensively investigated theoretically and numerically. The application of ferromagnetic materials is widespread in various science and engineering sectors. In particular, in modern technological devices, the state-of-the-art applications include sensors, data storage, logic devices, and spintronics devices [1–5]. Domains are the uniformly magnetized regions separated by thin continuum zones called domain walls (DWs). Over the few decades, remarkable progress in the study of DWs in ferromagnetic nanostructures has been reported. The formation and evolution of DWs can be tuned via magnetic fields/spin-polarized currents.
Temperature-dependent model for ferroelectrics embedded into two-dimensional polygonal finite element framework
Published in Mechanics of Advanced Materials and Structures, 2023
Dheeraj Kailas Valecha, Jayabal K, Amirtham Rajagopal
Each orientation is referred to as a tetragonal variant, and the tetragonal crystal structures can have up to six variants. A domain is an area that contains a group of unit cells with identical polarization orientations. To bring down the total energy of the material during phase transformation, different domains are formed separated by domain walls. Domains with tetragonal crystal structure can encounter two types of domain walls, namely the 90° and 180° domain walls.