Coercivity, also known as coercivity or magnetic force retention, is one of the characteristics of magnetic materials. It refers to the magnetic field strength required for reducing the magnetization of magnetic materials to zero after they have been magnetized to saturation. Coercivity represents the resistance of A magnetic material to demagnetization and is denoted by A symbol of HC in either A/m(international standard) or Oe(gaussian system of units). Coercivity can be measured with a magnetometer or a b-h analyzer.
If the coercivity of ferromagnetic materials (including ferromagnetic materials) is large, it is called hard magnetism, can be used as a ****** * magnet materials. ****** ** magnets can be used in motors, magnetic storage media (such as hard disks, disk disks or magnetic tapes), and magnetic separators for ore processing.
Ferromagnetic materials called soft magnetic coercive force are small, can be used in the iron core transformer and inductor, the read/write head of magnetic storage media (English: recording head), microwave devices and Electromagnetic shielding (English: Electromagnetic shielding) devices.
The coercivity of magnetic materials is generally obtained by measuring hysteresis curve (also known as magnetization curve). Collect data instruments tend to use the vibrating sample magnetometer or alternating gradient magnetometer. When the measured magnetic flux density data is zero, the corresponding magnetic field intensity is the coercive force.If the product contains ferromagnetic materials, the measured coercivity will be different when the magnetic field increases and decreases. This is due to the effect of the exchange bias field (English: exchange bias).
The coercivity measured by the material is also related to the time spent in measuring the magnetization curve process. The magnetization of a magnet material measured in a reverse magnetic field will be less than the coercive force, and if it is measured under the same conditions for a long time, its value will relax to zero. Relaxation phenomenon is due to the effect of heat generated by the magnetic domain under the reverse magnetic field, and is also affected by the magnetic viscosity . The coercivity of some materials would increase with frequency, which would be a major obstacle for high bandwidth magnetic storage devices to improve data speed, since increasing the storage density would mean a higher coercivity of the storage devices.
The coercivity of soft ferromagnetic materials and hard ferromagnetic materials
The "hardness" of ferromagnetic materials increases as the crystals grow larger
With the increase in smoothness and the quality of the glass decreased
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Fe:4Ni, permeable alloy
0.01-1 (0.8 80)
Fe: Si, silicon steel
0.4 0.9 (32-72)
Wrought iron (1896).
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Ferrite used in multicavity magnetron
2 fe: Co , the magnet pole
>. 99 cobalt
Al: 18 fe: 8 co, Cu, and ni -
3 ti: 8 al: 20 fe: 20 co, cu 2:8 ni, aluminum nickel and cobalt
Alnico 5-9, refrigerator magnets or stronger magnets
640-2000 (51000-1.6 * 105)
Cr: Co: Pt,
The storage medium for a hard disk
1700 (1.4 * 105)
2Nd:14Fe:B, ndfeb magnet
10000-12000 (105), (8-9.5) *
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12300 (9.8 * 105)
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25600-26300 / (2 * 106)
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"The 500-35000 (40000-2.8 * 106)
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40000 (3.2 * 106)
If a ferromagnetic material is placed in a coercive external magnetic field, the component of the magnetization along the direction of the external magnetic field is zero. There are two ways of magnetic reversal: single domain rotation and domain wall movement. When the magnetization of the material is reversed due to single-domain rotation, the component of the magnetization along the direction of the external magnetic field is zero, and the magnetization will be perpendicular to the external magnetic field. When the magnetization of the material is reversed due to the movement of the domain wall, the total magnetization of all small domains is close to zero, and the total magnetization is very small. Being used in some basic research, better magnetic materials, the magnetization intensity is mainly influenced by single domain rotation and magnetocrystalline anisotropy . In the magnetic materials used in practical engineering, Impurity and grain boundary are the nucleation sources of reverse magnetization magnetic field, and the reverse magnetization intensity is mainly controlled by the movement of magnetic domain wall. However, the influence of domain wall motion on coercivity is rather complex, so crystal defects may be the source of nucleation, but they may also fix domain walls. The role of domain walls in ferromagnetic materials is similar to that of grain boundaries in plastic deformation because both domain walls and grain boundaries are surface defects in crystal defects.
If the material has hysteresis and has been magnetized, the area in the magnetization curve is the work required to apply the reverse external magnetic field to the material, so that the material has the reverse magnetization strength, and the energy will finally be dissipated in the form of heat energy. The common dissipation processes in magnetic materials include magnetostriction and the movement of domain walls. Coercivity can be used to measure the degree of magnetic hysteresis or as an indicator of the loss of soft ferromagnetic materials in general applications.
Squareness of magnetic materials is the quotient of remanence divided by coercivity. Squareness and coercivity of hard ferromagnetic materials are two important performance indexes of hard ferromagnetic materials, but the product of the two is more commonly mentioned.