How are magnets magnetized during production?

How are magnets magnetized during production?
Recently, I learned that magnets are usually magnetized through the following three methods:
Electromagnetic magnetization method: This is one of the most common magnetization methods. In electromagnetic magnetization, a magnet is placed in a solenoid coil, which is a hollow cylinder in which magnets of different sizes and shapes can be placed. The coil is energized to generate a strong magnetic field, which magnetizes the magnetic material to maintain its magnetism.

Figure.1 Comparison of internal magnetic domains of ferromagnetic materials before and after magnetization

Figure.2 Schematic diagram of coil magnetic field
To avoid handling and assembling magnets under magnetization conditions, it is sometimes possible to assemble magnetic materials before magnetization.
The two most common magnetization devices in electromagnetic magnetization are DC magnetizers and capacitor discharge magnetizers.

Figure.3 DC Magnetizer

The DC magnetizer uses a large coil and applies current in a short period by closing the switch. The current flowing through the coil generates a magnetic field, usually guided by an iron core and electrode plates, and the magnet is placed in the gap between the electrode plates. DC magnetization machines are only suitable for aluminum nickel cobalt materials or small cross-section ferrite materials with low magnetic requirements.
The capacitor discharge magnetizer uses a capacitor bank to charge and then discharges through a coil. If the resistance R of the coil is greater than 2/√(L/C), where L is the inductance and C is the capacitance, then the current flowing through the coil will be unidirectional. The use of special coils and power supplies can achieve extremely high magnetization fields (within the range of 100 KOe).

Contact magnetization method: In the contact magnetization method, a strong magnet (usually a permanent magnet) that has already been magnetized is directly in contact with the magnet to be magnetized. Through contact, magnetic materials are rearranged in a strong magnetic field and gain magnetism.

Vibration magnetization method: In the vibration magnetization method, a magnet is placed in a specific device that vibrates at a specific frequency and amplitude. This vibration causes the magnetic materials of the magnet to align in the vibration, thereby achieving magnetization.
Regardless of the method used, the magnetization process of a magnet requires strict control of the strength, direction, and time of the magnetic field to ensure consistency and quality of the magnetization effect. The magnetized magnet should be tested and inspected to ensure that it meets the specified magnetic performance requirements.
So, which magnetization method can achieve maximum magnetism?

Among different magnetization methods, electromagnetic magnetization can usually provide maximum magnetism.
Some rare earth magnets require a very high magnetization field in the range of 20 to 50 KOe. These magnetic fields are difficult to generate and require high-power power supplies and carefully designed magnetization devices. Isotropic bonded neodymium materials require a high magnetic field range of 60 KOe to fully saturate. However, fields within the range of 30 KOe can reach a saturation of 98%. Ceramic magnets require a magnetic field of the order of 10 KOe, while aluminum nickel cobalt alloys require a magnetic field within the range of 3 KOe to saturate. Due to the susceptibility of aluminum nickel cobalt to unintentional demagnetization, it is best to magnetize this material before or even after the final assembly of the magnet into the equipment.

The electromagnetic magnetization method utilizes a powerful electromagnetic coil to generate a high-strength magnetic field. By adjusting the current and coil design, higher magnetic field strength and greater magnetization effect can be achieved. This method is widely used in industrial production and can generate powerful magnets.
In contrast, the contact magnetization method and vibration magnetization method often cannot provide the same magnetism as the electromagnetic magnetization method. Existing strong magnets limit the contact magnetization method, and its magnetic field strength and magnetization effect usually need to be higher.
The magnetic field strength of the vibration magnetization method is also relatively low, and its magnetization effect usually depends on the frequency and amplitude of the vibration, which requires careful optimization to achieve high magnetism.
However, it should be noted that maximum magnetism only sometimes means it is the most suitable choice.
Different applications require different magnetic properties, and in actual production, other factors such as cost, process control, and working environment also need to be considered.
Therefore, when selecting magnetization methods, multiple factors need to be comprehensively considered to meet specific needs.