Detailed explanation of the working principle and application of permanent magnets

Permanent magnets are an indispensable material in modern industry and life. They can continuously generate a stable magnetic field without an external power supply and are widely used in many fields such as motors, sensors, and magnetic separation equipment.

What is a permanent magnet?
A permanent magnet is a material that can maintain its own magnetism for a long time. The magnetic domain structure inside it is arranged stably, so that the magnetic field persists. Compared with the electromagnet that needs continuous power supply to generate a magnetic field, the permanent magnet can maintain magnetic force without external energy input, so it is widely used in various mechanical and electronic equipment.
Common permanent magnet materials include:

NdFeB: The permanent magnet material with the strongest magnetic properties at present, with extremely high magnetic energy product, is widely used in high-performance motors and electronic equipment.

Samarium cobalt (SmCo): Excellent high temperature and corrosion resistance, suitable for high temperature environments, such as aerospace and military equipment.

Ferrite: Low cost, corrosion resistance, medium magnetic properties, widely used in home appliances, speakers, etc.

Aluminum nickel cobalt (AlNiCo): It has good temperature stability, strong magnetism, but is fragile, and is commonly used in sensors and instruments.

Permanent magnets of different materials are suitable for various application scenarios with different needs due to their different magnetic properties, costs and environmental adaptability.

Working principle of permanent magnets
The magnetism of permanent magnets comes from the magnetic moment generated by the spin and orbital motion of electrons inside the material. When a large number of atomic magnetic moments are neatly arranged at a microscopic scale, a macroscopic magnetic field is formed. The specific mechanisms include:

Magnetic domain structure
The interior of a permanent magnet is composed of thousands of tiny magnetic domains. The electron spin direction in each magnetic domain is consistent, forming a local magnetic field. The boundary between magnetic domains is called a domain wall. When an external force acts, the domain wall can move, causing the overall magnetization direction of the magnet to change. But in permanent magnets, these domains are fixed and the magnetization state is stably maintained.

Magnetic anisotropy
Magnetic anisotropy refers to the fact that magnetization in certain crystal directions in a material is easier to maintain. This property makes the magnetic domains more stably arranged in a specific direction, preventing the magnetization direction from being easily changed. The coercive force (ability to resist magnetization reversal) of a permanent magnet comes from the strong magnetic anisotropy.

Hysteresis loop
The magnetic properties of permanent magnets are usually described by hysteresis loops. This curve shows the change of the magnetic induction intensity (B) of the material with the strength of the external magnetic field (H). Permanent magnets have a wide hysteresis loop and a high residual magnetic induction intensity (Br), which means that they can maintain a strong magnetic field even if the external magnetic field disappears.

Main applications of permanent magnets
1. Motors and generators
Permanent magnets are the core components of brushless DC motors (BLDC), stepper motors and synchronous generators. Compared with traditional motors, permanent magnet motors do not require external excitation coils, have a simpler structure, smaller size and higher efficiency.

Brushless DC motor: The magnetic field generated by the permanent magnet interacts with the magnetic field generated by the current coil to achieve rotor rotation.

Stepper motor: The motor is precisely positioned by precisely controlling the direction of the current.

Synchronous generator: The permanent magnet is fixed on the rotor and generates a stable voltage output when it rotates.
Applications cover electric vehicles, robots, household appliances and other fields, helping green energy saving and intelligent manufacturing.

2. Magnetic sensor
The stable magnetic field generated by the permanent magnet is combined with the Hall sensor to detect physical quantities such as position, speed and angle. Typical applications include automotive wheel speed sensors, position detection in industrial automation, smart home devices, etc.
The stability and strength of the permanent magnet magnetic field directly affect the accuracy and response speed of the sensor, and is a key component of modern intelligent control systems.

3. Magnetic separation and magnetic levitation
Magnetic separation
In industrial production, the strong magnetic field of permanent magnets is used to effectively separate metals from ores and waste materials to improve resource recovery efficiency.

Magnetic levitation technology
Permanent magnets are used in magnetic levitation trains and magnetic levitation bearings to achieve contactless suspension, reduce friction loss, and increase operating speed and life.

4. Consumer electronics and medical devices
Consumer electronics
Permanent magnets in speakers, headphones, and hard drives are responsible for generating magnetic fields, driving the diaphragm to produce sound or controlling the head to read data.

Medical equipment
In magnetic resonance imaging (MRI) equipment, powerful superconducting permanent magnets provide a stable magnetic field to help achieve high-resolution medical imaging.

Future development trends of permanent magnets
With the continuous advancement of materials science and manufacturing technology, permanent magnets are developing towards higher performance, higher stability and environmental protection.

High-performance magnetic materials
The magnetic energy product of NdFeB permanent magnets continues to increase, achieving smaller volume and greater magnetic output. Samarium cobalt materials are continuously optimized in high-temperature performance to meet the needs of extreme environments.

Green manufacturing and recycling
Focus on the environmental protection of permanent magnet materials, promote the recycling and recovery technology of rare earth resources, and improve resource utilization efficiency.

Intelligent manufacturing and emerging applications
With the rapid development of new energy vehicles, robots, smart devices, etc., the demand for permanent magnets in high-efficiency and energy-saving motors, precision sensors and other fields is growing, and the future application prospects are broad.