A small region inside a ferromagnet or ferrimagnet in which the magnetization points in one direction. The material splits into many domains to lower the magnetostatic energy of its surface poles.
Japanese name: 磁区
Magnetic domain appears in 5 practice questions across 2 topics, including Magnetic materials, Electronic, magnetic and optical materials.
Field: Magnetic materials
Inside a ferromagnet, the exchange interaction tends to align the magnetic moments of neighboring atoms parallel. If the whole crystal is magnetized in one direction, however, large magnetic poles appear on its surface, creating fields in the surrounding space and inside, with a large magnetostatic energy. Splitting into domains with different directions lets the poles cancel and lowers this energy greatly. Triangular closure domains can also form near the surface so that the flux closes on itself. This is why iron, though ferromagnetic, does not act as a magnet when no external field has been applied.
The boundary between domains is called a domain wall, and within it the magnetic moments turn gradually over a width of tens to hundreds of atoms. Turning abruptly raises the exchange energy, while turning slowly increases the number of moments tilted away from the easy axis and raises the anisotropy energy, so the wall thickness is set by the balance between the two and is proportional to √(A/K), where A is the exchange stiffness and K the anisotropy constant. A wall has an energy per unit area, so dividing into too many domains does not pay. The actual domain size is set by the balance between the decrease in magnetostatic energy and the increase in wall energy.
When a field is applied to a demagnetized ferromagnet, the domains oriented closest to the field first grow by domain-wall motion. As the field is increased further, the magnetization inside the domains rotates from the easy axis toward the field, approaching the saturation magnetization. Domain walls get caught at grain boundaries, precipitates and sites of internal stress, so how easily the walls move governs the coercivity and permeability. In soft magnetic materials, impurities and strain are reduced so the walls move easily; in permanent magnets, microstructures are created in which reversed domains are hard to nucleate or grow.
Domains can be observed by the Bitter method, in which a liquid of fine magnetic particles is applied to the surface and the particles gathering at the walls are viewed; by magneto-optical Kerr effect microscopy, which uses the rotation of polarized light; and by magnetic force microscopy (MFM), which detects the stray field from the surface with a magnetic tip. In electron microscopes, Lorentz microscopy and electron holography reveal the distribution of magnetization inside a specimen. In grain-oriented electrical steel, a technique is used in which fine grooves or strain are introduced on the surface by laser to refine the domains and lower the loss due to eddy currents.
Answer: B. To lower the magnetostatic (demagnetizing-field) energy of the poles that appear on the surface when the whole body is uniformly magnetized
If the whole crystal is magnetized in one direction, large magnetic poles appear on its surface, creating fields outside and inside (the demagnetizing field inside), with a large magnetostatic energy. Splitting into domains with different directions lets the poles cancel and lowers this energy greatly. On the other hand, inside a domain wall at the boundary between domains the moments turn gradually, so the energy rises by the exchange and anisotropy energies. The actual domain size is set by the balance between the two. The exchange interaction acts to align all the moments, so splitting into domains actually increases the exchange energy. Moments randomized by thermal vibration describe the paramagnetic state above the Curie temperature.
No. A grain is a region in which the atoms are arranged with the same orientation, and a domain is a region in which the magnetization points in the same direction. One grain can contain many domains, and a small particle can be a single domain as a whole (single-domain). Domain walls, the boundaries between domains, move under an applied field independently of grain boundaries.
As the temperature rises the spontaneous magnetization decreases, and above the Curie temperature the spontaneous magnetization itself disappears and the material becomes paramagnetic, so the domains vanish as well. Cooling below the Curie temperature forms domains again, but without an external field they split into many domains with unaligned directions, so the magnet's magnetization does not return.
In particles smaller than a certain size (the critical size), the energy needed to create a domain wall exceeds the reduction in magnetostatic energy, so the whole particle becomes a single domain. This is a single-domain particle. Reversing its magnetization requires rotating the whole magnetization, so the coercivity is large. Making it smaller still, however, leads to superparamagnetism, in which the magnetization reverses thermally.
Splitting into domains with different directions lets the poles cancel and lowers this energy greatly.
What is the main reason a ferromagnet splits into many magn…A demagnetized ferromagnet is divided internally into many domains with different directions of magnetization, which cancel overall.
When an external magnetic field is applied to a demagnetize…Macroscopically a ferrimagnet shows domains and hysteresis just as a ferromagnet does, but its saturation magnetization is smaller than that of ferromagnetic metals such as iron.
Which statement correctly describes the ferrimagnetism show…Large particles contain many domains, and their magnetization reverses by the motion of domain walls, which move even in weak fields, so the coercivity is small.
As particles of a ferromagnet are made smaller, from a few …The actual coercivity is much smaller than HA because reversed domains nucleate at places such as grain surfaces, and it is raised by controlling the microstructure, such as the grain-boundary phase.
What is the main material reason that neodymium magnets, wi…Domain wall Saturation magnetization Coercivity Curie temperature Ferrimagnetism Superparamagnetism Magnetocrystalline anisotropy Eddy-current loss Maximum energy product