Magnetic materials are closely related to our lives, from the most ordinary refrigerator refrigeration to high-end magnetic levitation, all of which are inseparable from them. So, let's take a look at this magical material now!

Why do magnets have magnetism?

Most substances are composed of molecules, which are composed of atoms, and atoms are composed of nuclei and electrons. Within an atom, electrons continuously rotate and revolve around the nucleus, both of which generate magnetism. But in most substances, the directions of electron motion are different and disorderly, and magnetic effects cancel each other out. Therefore, most substances do not exhibit magnetism under normal circumstances.

Ferromagnetic substances such as iron, cobalt, nickel, or ferrite are different in that their internal electron spins can spontaneously align within a small range, forming a spontaneous magnetization region called a magnetic domain. After magnetization of ferromagnetic materials, the internal magnetic domains are arranged neatly and in the same direction, strengthening the magnetism and forming a magnet. The process of attracting iron by a magnet is the magnetization process of the iron block. The magnetized iron block generates attraction between the different polarities of the magnet, and the iron block firmly adheres to the magnet.

How to define the performance of a magnet?

There are three main performance parameters to determine the performance of a magnet:

Residual magnetic Br: The Br retained by a permanent magnet after being magnetized to technical saturation and removing the external magnetic field is called the residual magnetic induction strength.

The coercive force Hc: reduces the B of the permanent magnet magnetized to technical saturation to zero, and the required reverse magnetic field strength is called magnetic induced coercive force, abbreviated as coercive force.

Magnetic energy product BH: represents the magnetic energy density established by a magnet in the air gap space (the space between the two magnetic poles of the magnet), which is the static magnetic energy per unit volume of the air gap.

How to classify metal magnetic materials?

Metal magnetic materials are divided into two categories: permanent magnetic materials and soft magnetic materials. Materials with an intrinsic coercivity greater than 0.8kA/m are usually referred to as permanent magnetic materials, while materials with an intrinsic coercivity less than 0.8kA/m are referred to as soft magnetic materials.

4. Comparison of magnetic force sizes of several commonly used magnets

The magnetic forces are arranged in descending order: neodymium iron boron magnets, samarium cobalt magnets, aluminum nickel cobalt magnets, and ferrite magnets.

5. Analogy of the cost-effectiveness of different magnetic materials?

Ferrite: Low to medium performance, lowest price, good temperature characteristics, corrosion resistance, good cost-effectiveness

Neodymium iron boron: highest performance, moderate price, good strength, not resistant to high temperature and corrosion

Samarium cobalt: high performance, highest price, brittleness, excellent temperature characteristics, corrosion resistance

Aluminum nickel cobalt: low and medium performance, moderate price, excellent temperature characteristics, corrosion resistance, poor interference resistance

Samarium cobalt, ferrite, and neodymium iron boron can be manufactured using sintering and bonding methods. Sintering has high magnetic properties, poor molding, and good formability of bonded magnets, resulting in a significant decrease in performance. AlNiCo can be manufactured using casting and sintering methods. Cast magnets have high performance but poor formability, while sintered magnets have low formability and good formability.

6. Characteristics of neodymium iron boron magnets

Neodymium iron boron permanent magnet material is a permanent magnet material based on the intermetallic compound Nd2Fe14B. Neodymium iron boron has extremely high magnetic energy product and coercivity, and the advantages of high energy density have made neodymium iron boron permanent magnet materials widely used in modern industry and electronic technology, making it possible to miniaturize, lighten, and thin equipment such as instruments, electroacoustic motors, and magnetic separation magnetization.

Material characteristics: The advantages of neodymium iron boron are high cost-effectiveness and good mechanical properties; The shortcomings lie in the low Curie temperature point, poor temperature characteristics, and easy pulverization and corrosion. It must be improved by adjusting its chemical composition and adopting surface treatment methods to meet the requirements of practical applications.

Manufacturing process: The production of neodymium iron boron adopts powder metallurgy technology.

Process flow: batching → melting ingot → powder making → pressing → sintering and tempering → magnetic testing → grinding processing → cutting processing → electroplating → finished product.

7. What is a single-sided magnet?

Magnets all have two poles, but in some working positions, a magnet with a single pole is required. Therefore, one side of the magnet needs to be wrapped with an iron sheet to shield the magnetic field on the side covered by the iron sheet. Through the refraction of the iron sheet to the other side of the magnet, the magnetic force of the other side of the magnet is enhanced. Such magnets are collectively referred to as single sided magnets or single sided magnets. There is no true single-sided magnet.

The materials used for single-sided magnets are generally arc-shaped iron sheets and neodymium iron boron strong magnets. The shape of neodymium iron boron strong magnets used for single-sided magnets is generally in the shape of circular plates.

8. What is the purpose of a single-sided magnet?

(1) Single sided magnets are widely used in the printing industry, including gift packaging boxes, mobile phone packaging boxes, tobacco and alcohol packaging boxes, mobile phone packaging boxes, MP3 packaging boxes, mooncake packaging boxes, and other products.

(2) Single sided magnets are widely used in the leather goods industry, including luggage, briefcases, travel bags, phone cases, wallets, and other leather goods.

(3) Widely used in the stationery industry, single sided magnets exist in notebooks, whiteboard buckles, folders, magnetic nameplates, and more.

What are the precautions during the transportation of magnets?

Pay attention to indoor humidity and maintain it at a dry level. Do not exceed room temperature; When storing products in a black block or rough state, oil can be applied appropriately (regular engine oil is sufficient); Electroplated products should be vacuum sealed or stored in isolated air to ensure the corrosion resistance of the coating; Magnetized products should be sucked together and stored in boxes to avoid picking up other metal bodies; Magnetized products should be stored away from objects sensitive to magnetic fields such as disks, magnetic cards, magnetic tapes, computer displays, watches, etc. Magnets should be shielded during transportation when in a magnetized state, especially during air transportation, they must be completely shielded.

How to achieve magnetic isolation?

Only materials that can adsorb onto the magnet can have the effect of separating the magnetic field, and the thicker the material, the better the magnetic separation effect.

11. Which type of ferrite material can conduct electricity?

Soft magnetic material ferrite belongs to the category of magnetic conductive materials, with high magnetic permeability and high electrical resistivity. It is generally used at high frequencies and is mainly used in electronic communication. Computers and televisions that we come into contact with every day have applications inside.

Soft magnetic ferrite mainly includes manganese zinc and nickel zinc, and the permeability of manganese zinc ferrite is higher than that of nickel zinc ferrite.