Comprehensive Guide to Magnet Magnetization
- Ethan
- Knowledge base
Magnetization essentially refers to the process of imparting magnetism to metallic materials through methods such as magnetization, thus making them inherently magnetic. When a material that is not originally magnetic is placed in a strong magnetic field, it will become magnetized. However, not all materials can be magnetized, only a few metals and metal compounds can achieve this.
How Are Magnets Magnetized?
Pulsed magnetic field magnetization: is the most commonly used magnetization method, suitable for the final magnetization of most permanent magnets. In electromagnetic magnetization equipment, a strong magnetic field is generated by energizing the coil within the magnet, eliminating the need for continuous power supply. An ultra-high current pulse creates a field intensity far exceeding the saturation magnetization required for the material within milliseconds.
Steady-State Magnetic Field Magnetization: This uses large electromagnets to generate a stable, strong magnetic field. It is commonly used in applications requiring extremely high uniformity.
Multipole Magnetization: This employs specially designed fixtures and coils to magnetize the magnet into a pattern with multiple alternating north and south poles in a single step.
Pulsed magnetic field magnetization: is the most commonly used magnetization method, suitable for the final magnetization of most permanent magnets. In electromagnetic magnetization equipment, a strong magnetic field is generated by energizing the coil within the magnet, eliminating the need for continuous power supply. An ultra-high current pulse creates a field intensity far exceeding the saturation magnetization required for the material within milliseconds.
Steady-State Magnetic Field Magnetization: This uses large electromagnets to generate a stable, strong magnetic field. It is commonly used in applications requiring extremely high uniformity.
Multipole Magnetization: This employs specially designed fixtures and coils to magnetize the magnet into a pattern with multiple alternating north and south poles in a single step.
What is Magnetization Intensity?
Magnetic susceptibility is a physical quantity reflecting the degree of magnetization within a material. When an external magnetic field is applied to atomic magnetic moments, it causes these moments to align in a macroscopically averaged sense. Magnetic susceptibility represents the remanence of a permanent magnet.
Magnetization intensity M is the vector sum of all atomic magnetic moments per unit volume. When these microscopic magnetic moments are completely randomly oriented, M = 0; when they partially or fully align under an external magnetic field, M becomes greater than 0, and the more aligned they are, the larger the M value.
Magnetization method
Unsaturated Magnetization: When magnetizing a magnetic material, the magnetizing energy does not reach more than 95% of the saturation level. This method is reversible, and over time, under the combined effects of time and external magnetic fields, the remanence of the magnet will gradually decline. A typical example is in certain magnetic encoders or sensors where the surface magnetic field strength needs to be at a very precise, non-maximum specific value. In such cases, unsaturated magnetization is achieved by controlling the magnetizing energy, followed by aging treatment to stabilize the magnetic performance at the desired “suboptimal” point. This method is only used in special applications and is generally not employed.
Saturated Magnetization: When magnetizing a magnetic material, the magnetizing energy reaches the level required for the material’s magnetization characteristic inflection point, generally 1.5 to 2 times the intrinsic coercivity of the material. This method allows the magnet to achieve saturated magnetization, and under normal circumstances, demagnetization will not occur.
Over-Saturated Magnetization: In engineering practice, the goal of over-saturated magnetization is to ensure that all regions and all magnetic domains within the material complete 100% reorientation and alignment. Due to possible microscopic inhomogeneities inside the material, the actual magnetic field strength used is typically 1.5 to 3 times the field required for saturation magnetization.
Magnetization Directions
The main magnetization directions are simple dipole magnetization, multipole magnetization, and special array magnetization.
Simple Dipole Magnetization: This primarily makes the entire magnet behave as a simple magnetic dipole, including methods such as axial magnetization, radial magnetization, thickness-direction magnetization, axial multipole magnetization, inner circular magnetization, and radiation magnetization.
Multipole Magnetization: The surface exhibits multiple alternating magnetic poles. Custom magnetizing fixtures are used, resulting in multiple alternating N/S poles on the same magnet after magnetization.
Special array magnetization: It is a directional magnetization process for unitary magnets, aiming to create a unique Harbach magnetic field. Its core principle is to design different magnetization directions based on the magnet’s application orientation to maximize the magnetic field strength in the same direction. A Harbach array is a magnet combination structure. By combining permanent magnets with different magnetization directions, the magnetic field on one side of the array can be significantly enhanced, while the magnetic field on the other side can be almost negligible.
Some FAQs
Can all metals be magnetized into magnets?
No. Only ferromagnetic materials can be strongly magnetized and retain permanent magnetism. Most metals can only produce very weak temporary magnetization, which disappears once the external magnetic field is removed.
How does natural magnetite have magnetism?
Natural magnetite acquires its magnetism during formation through exposure to natural strong magnetic fields, such as the Earth’s magnetic field or lightning strikes. It is already naturally magnetized.
Can a magnet be demagnetized after magnetization?
Yes. High temperatures, strong opposing external magnetic fields, violent impacts, etc., can cause demagnetization. A demagnetized magnet can be remagnetized.
What are the special uses of multipole magnetized magnets?
By arranging multiple magnets at specific angles, the magnetic field on one side is significantly enhanced while the field on the other side is nearly zero. This allows for the strongest possible magnetic field in the working area using less magnetic material.
What is so magical about the Halbach array?
Multipole magnets have multiple alternating N/S poles on their surface and are commonly used in motor rotors, magnetic encoders, magnetic couplings, etc., to produce more uniform or complex magnetic field distributions, improving efficiency and precision.
Will magnets naturally demagnetize over time?
High-performance neodymium magnets are very stable at room temperature, with decay of less than 5% over decades.
Conclusion
In the early stages of ancient civilisation, humans had already discovered the existence of natural magnetite, but were curious about why it possessed magnetism. It was commonly believed to be a gift from the heavens bestowed upon humanity. With the rapid development of human civilisation, magnets can now be customised according to different performance requirements, applied in various fields, and have brought progress to human civilisation.
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