The hottest magnetic material and its magnetizatio

2022-07-28
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Magnetic materials and their magnetization

basic phenomena of magnetic materials:

I. spontaneous magnetization:

from the "magnetic source", we know that the spin magnetic moment of the extranuclear electrons of some atoms cannot be offset, resulting in the residual magnetic moment. However, if the magnetic moment of each atom is still disordered, the whole object cannot be magnetic. Only when the magnetic moments of atoms are aligned in one direction, just like many small magnets connected end to end, can objects show magnetism and become magnetic materials. This orderly arrangement of atomic magnetic moments is called spontaneous magnetization

since there is spontaneous magnetization in the magnetic material, are all the atoms in the object aligned in one direction? Of course not. Otherwise, all iron and steel will always be magnetic and become a big magnet that can always attract each other (in fact, the two soft irons will not attract each other by themselves). In fact, the vast majority of magnetic materials have magnetic domain structure, so that they do not show magnetism when they are not magnetized

the nylon screen suspended below will form a huge floating dustpan. 2. Magnetic domain:

the so-called magnetic domain refers to small areas inside the magnetic material, each area contains a large number of atoms, and the magnetic moments of these atoms are arranged like small magnets, but the directions of atomic magnetic moments are different between adjacent areas, as shown in the right figure. The interface between magnetic domains is called domain wall. Macro objects generally have a total insulation resistance of not less than 1 megohm at the ungrounded part of the experimental motor air equipment. In this way, the magnetic moment of the magnetic domain is square, but the proportion of the extruder outlet is still low, and the results are offset each other. The vector sum is zero, and the magnetic moment of the whole object is zero, so it cannot attract other magnetic materials. That is to say, magnetic materials do not show magnetism under normal circumstances. Only when the magnetic material is magnetized can it show magnetism. The figure below shows the common domain shapes in magnetic materials observed in the microscope. The left side is the common strip domain of soft magnetic materials. The black and white parts have different brightness because of different magnetic moment directions of different magnetic domains. Their interface is the domain wall; In the middle are dendritic domains and domain walls; On the right is the domain shape that can be seen in the thin film material. In practical magnetic materials, the results of magnetic domains are various, such as strip domain, labyrinth domain, wedge domain, ring domain, dendritic domain, bubble domain and so on

since the magnetic moments inside the domain are arranged orderly, how are the atomic magnetic moments arranged at the domain wall? On one side of the domain wall, the atomic magnetic moment points in a certain direction, assuming that on the other side of the domain wall, the atomic magnetic moment has the opposite direction. Then, within the domain wall, the atomic magnetic moment must be in some form of transition state. In fact, the domain walls are composed of many layers of atoms. In order to realize the turning of magnetic moment, from one side, the magnetic moment of each layer of atoms is deflected by an angle relative to the direction of magnetic moment in the magnetic domain, and the deflection angle of each layer of atoms' magnetic moment gradually increases. To the other side, the magnetic moment has completely turned to the same direction as the magnetic moment of the magnetic domain on this side. The figure above shows the typical domain wall structure

III. Curie temperature:

for all magnetic materials, they are not magnetic at any temperature. Generally, magnetic materials have a critical temperature Tc. Above this temperature, the arrangement of atomic magnetic moments is disordered due to the violent thermal motion of atoms at high temperature. Below this temperature, the atomic magnetic moments are arranged neatly, resulting in spontaneous magnetization, and the object becomes ferromagnetic

with this feature, many control components have been developed. For example, the electric cooker we use takes advantage of the Curie point of magnetic materials. A magnet and a magnetic material with a Curie point of 105 degrees are installed in the center of the bottom of the electric cooker. When the water in the pot dries, the temperature of the food will rise from 100 degrees. When the temperature reaches about 105 ℃, as the magnetism of the magnetic material absorbed by the magnet disappears, the magnet loses its attraction. At this time, the spring between the magnet and the magnetic material will separate them, and drive the power switch to be disconnected to stop heating

IV. common physical quantities related to magnetic materials:

magnetic field strength: refers to the size of a magnetic field somewhere in space, expressed in H, and its unit is ampere/meter (a/m)

magnetization: refers to the sum of magnetic moment vectors per unit volume inside the material, expressed in M, and the unit is ampere/meter (a/m)

magnetic induction intensity: the definition of magnetic induction intensity B is: b=m0 (h+m), where h and m are magnetization and magnetic field intensity respectively, and M0 is a coefficient, which is called vacuum permeability. Magnetic induction intensity is also known as magnetic flux density. According to Jinan new era assay instrument Co., Ltd., the most common fault bit is Tesla (T)

permeability: the definition of permeability is m=b/m0h, which is the ratio of B and h at any point on the magnetization curve (see static magnetization of materials). Permeability actually represents the ease with which a magnetic material is magnetized, or the sensitivity of a material to an external magnetic field

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