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In this era of rapid technological development, our lives are surrounded by various intelligent devices and efficient machinery. From new energy vehicles we drive every day, to air conditioners and refrigerators running at home, to nuclear magnetic resonance instruments in hospitals, automated production lines in factories, and even satellites soaring in space, there is a crucial “invisible force” behind them – rare earth permanent magnets. You may be familiar with the term “rare earth”, but do you really understand it? Why is it called the “industrial vitamin”? How does it endow permanent magnets with magical power to support many fields of modern technology? This article will take you into the world of rare earths and permanent magnets and uncover their mysterious veil.

I. Rare Earths are not “Earth”

(1) Definition and Composition of Rare Earths

When hearing the name “rare earth”, many people may mistakenly think that it is a special kind of “soil”. However, in fact, rare earths are not “earth” but a general term for a group of metal elements. They include 17 elements, specifically, 15 lanthanide elements in Group IIIB of the periodic table (lanthanum La, cerium Ce, praseodymium Pr, neodymium Nd, promethium Pm, samarium Sm, europium Eu, gadolinium Gd, terbium Tb, dysprosium Dy, holmium Ho, erbium Er, thulium Tm, ytterbium Yb, lutetium Lu), as well as scandium (Sc) and yttrium (Y) which have similar chemical properties to lanthanide elements.

These elements are collectively called “rare earths” due to their discovery history. At the end of the 18th century, when rare earth elements were first discovered, they often existed in minerals in the form of oxides. At that time, such minerals were considered a kind of “earth”, and because their content in nature was relatively small and difficult to obtain, they were named “rare earths”. Although with the development of science and technology, people have found that the total reserves of rare earths in nature are not small, the name “rare earths” has been used until now.

(2) Characteristics of Rare Earths

The important status of rare earth elements is inseparable from their unique physical and chemical properties.

In terms of physical properties, rare earth elements have unique electronic structures. Their outer electron configurations are similar, but the number of electrons in the inner 4f electron layer is different. This special electronic structure gives rare earth elements rich optical, magnetic and electrical properties. For example, in terms of magnetism, rare earth elements have high magnetization and magnetic moment, which makes them key raw materials for manufacturing high-performance permanent magnet materials.

In terms of chemical properties, rare earth elements are highly active and easy to react with other elements to form various compounds. They can combine with elements such as oxygen, sulfur and nitrogen to form stable compounds, which makes rare earths widely used in metallurgy, chemical industry and other fields. At the same time, the ionic radius of rare earth elements is large, which enables them to form a special coordination environment in the crystal structure, thus endowing materials with unique properties.

(3) Distribution and Mining of Rare Earths

The distribution of rare earth resources worldwide is uneven, with obvious regional concentration. China is one of the countries with the richest rare earth resources in the world, occupying an important position in both reserves and output. China’s rare earth resources are widely distributed. The Bayan Obo Mine in Inner Mongolia is one of the largest rare earth deposits in the world. In addition, provinces such as Jiangxi, Guangdong and Sichuan also have rich rare earth resources.

In addition to China, countries such as the United States, Russia, Australia and India also have certain amounts of rare earth resources. Different countries have different types of rare earth resources, some are mainly light rare earths, and some are rich in heavy rare earths. Heavy rare earths are more valuable due to their important applications in high-tech fields.

The mining and extraction of rare earths is a complex process. First, rare earth deposits are found through geological exploration, and then mining is carried out. The mining methods mainly include open-pit mining and underground mining, and the specific method used depends on the burial depth and geological conditions of the deposit. The mined ore needs to go through crushing, beneficiation and other processes to obtain rare earth concentrates. Then, chemical methods are used to separate and purify the rare earth concentrates to obtain various single rare earth elements or their compounds.

II. Permanent Magnets: “Magical Stones” that Retain Magnetism

(1) Definition and Classification of Permanent Magnets

Permanent magnets, as the name implies, are objects that can maintain their own magnetism for a long time. Unlike electromagnets, permanent magnets can generate magnetic fields without external current excitation, which makes them widely used in various equipment and instruments.

According to different materials, permanent magnets can be divided into traditional permanent magnets and rare earth permanent magnets.

Traditional permanent magnets include ferrite permanent magnets, alnico permanent magnets, etc. Ferrite permanent magnets are a kind of permanent magnet material with iron oxide as the main raw material. They have the advantages of low cost and good corrosion resistance, but their magnetic properties are relatively low, and they are mainly used in occasions with low requirements for magnetic properties, such as speakers and small motors. Alnico permanent magnets have high Curie temperature and good temperature stability, but their magnetic energy product is low, and they are mainly used in instruments, metering and other fields.

Rare earth permanent magnets are a new generation of permanent magnet materials developed on the basis of traditional permanent magnets. They take rare earth elements as the main component and have extremely high magnetic properties. At present, the most widely used rare earth permanent magnets are mainly neodymium-iron-boron permanent magnets and samarium-cobalt permanent magnets. Neodymium-iron-boron permanent magnets are currently the most magnetic permanent materials, with the advantages of high magnetic energy product and high coercivity, and are widely used in new energy vehicles, wind power generation, aerospace and other fields. Samarium-cobalt permanent magnets have good high-temperature stability and corrosion resistance, and are mainly used in special environments such as high temperature and high vacuum.

(2) Performance Indicators of Permanent Magnets

The key indicators to measure the performance of permanent magnets are three: magnetic energy product, coercivity and Curie temperature.

Magnetic energy product refers to the magnetic energy stored per unit volume of a permanent magnet, which is an important indicator to measure the strength of the permanent magnet’s magnetic force. The larger the magnetic energy product, the stronger the magnetic field generated by the permanent magnet, and the greater the magnetic force that can be provided under the same volume. For example, the magnetic energy product of neodymium-iron-boron permanent magnets is much higher than that of traditional ferrite permanent magnets, which makes it widely used in some equipment with high requirements for magnetic force.

Coercivity refers to the ability of a permanent magnet to resist demagnetization, which represents the reverse magnetic field strength required to make the permanent magnet lose its magnetism. The greater the coercivity, the stronger the anti-demagnetization ability of the permanent magnet, and the less likely it is to lose its magnetism during use. This indicator is crucial for the application of permanent magnets in complex environments. For example, in high temperature, strong magnetic field interference and other environments, permanent magnets need to have high coercivity.

Curie temperature is the critical temperature at which a permanent magnet loses its magnetism. When the temperature exceeds the Curie temperature, the magnetism of the permanent magnet will drop sharply until it disappears. Therefore, the level of Curie temperature determines the operating temperature range of the permanent magnet. Different permanent magnets have different Curie temperatures. For example, the Curie temperature of neodymium-iron-boron permanent magnets is relatively low, while that of samarium-cobalt permanent magnets is higher, which is suitable for high-temperature environments.

III. Rare Earths: The “Core Engine” of Permanent Magnets

(1) Rare Earths Endow Permanent Magnets with Super Strong Magnetic Force

The magnetic strength of permanent magnets mainly depends on their magnetic energy product, and the addition of rare earth elements can significantly improve the magnetic energy product of permanent magnets, which contains profound scientific principles.

The atomic structure of rare earth elements is the key to their ability to improve the magnetic energy product of permanent magnets. The 4f electron layer of rare earth atoms is not filled, and this electronic structure makes rare earth elements have high magnetic moment. When rare earth elements combine with transition metals (such as iron and cobalt), they form a special crystal structure – intermetallic compounds. In this crystal structure, there is a strong exchange interaction between rare earth atoms and transition metal atoms, which can make the magnetic moments of atoms arrange orderly, thus producing a strong spontaneous magnetization phenomenon.

Taking neodymium-iron-boron permanent magnets as an example, the Nd₂Fe₁₄B compound formed by neodymium (a rare earth element) combined with iron and boron has a unique tetragonal crystal structure. In this structure, the magnetic moments of neodymium atoms and iron atoms can be arranged in the same direction, forming a strong magnetic field. This structure makes the magnetic energy product of neodymium-iron-boron permanent magnets more than 10 times that of traditional ferrite permanent magnets, which can generate a strong magnetic field in a small space, meeting the needs of high-power equipment such as new energy vehicle motors and wind turbines for strong magnetic fields.

(2) Rare Earths Improve the Stability of Permanent Magnets

The stability of permanent magnets is directly related to the service life and reliability of equipment, and rare earth elements can significantly improve the anti-demagnetization ability and temperature stability of permanent magnets.

In terms of anti-demagnetization ability, adding heavy rare earth elements (such as dysprosium and terbium) is an effective method to improve the coercivity of permanent magnets. The atomic radius of heavy rare earth elements is large. When they enter the crystal structure of permanent magnets, they will form “pinning centers”, which can hinder the movement of domain walls, thereby improving the coercivity of permanent magnets.

In terms of temperature stability, rare earth elements also play an important role. The Curie temperature of permanent magnets is closely related to their crystal structure and the interaction between atoms. By adding appropriate rare earth elements, the crystal structure of permanent magnets can be adjusted, and the exchange interaction between atoms can be enhanced, thereby increasing their Curie temperature.

In addition, some rare earth elements (such as lanthanum and cerium) can form a dense oxide film on the surface of permanent magnets. This oxide film can prevent the erosion of permanent magnets by oxygen, moisture, etc. in the air, thereby improving the corrosion resistance of permanent magnets and prolonging their service life.

(3) The Unique Roles of Different Rare Earth Elements in Permanent Magnets

Different rare earth elements play different roles in permanent magnets, and their respective characteristics enable permanent magnets to adapt to different application scenarios.

Neodymium is one of the main components of neodymium-iron-boron permanent magnets, and its addition is the key to the high magnetic energy product of neodymium-iron-boron permanent magnets. Neodymium has a high atomic magnetic moment and can form a strong exchange interaction with iron atoms, thus ensuring that permanent magnets have strong magnetism.

Dysprosium and terbium, as heavy rare earth elements, are mainly used to improve the coercivity and temperature stability of permanent magnets. As mentioned earlier, they can form “pinning centers” in the crystal structure, hinder the movement of domain walls, and at the same time improve the Curie temperature of permanent magnets, making them suitable for high-temperature environments. However, due to the relatively small reserves and high price of heavy rare earth elements, it is necessary to reasonably control their dosage in practical applications.

Samarium is the core component of samarium-cobalt permanent magnets. The SmCo₅ and Sm₂Co₁₇ compounds formed by samarium and cobalt have high magnetic energy product and good temperature stability. Samarium-cobalt permanent magnets have a high Curie temperature and can work stably in high-temperature environments of 250-350℃, so they are widely used in aerospace, military equipment and other fields.

Light rare earth elements such as lanthanum and cerium can replace neodymium to a certain extent for manufacturing low-cost neodymium-iron-boron permanent magnets. Although their magnetic properties are slightly lower than that of neodymium, due to their relatively abundant reserves and low price, they can reduce the production cost of permanent magnets and are suitable for occasions with not too high requirements for magnetic properties.

IV. Technical Evolution of Rare Earth Permanent Magnets: From Laboratory to Industrial Application

(1) Limitations of Early Permanent Magnet Materials

Before the emergence of rare earth permanent magnets, traditional permanent magnet materials had many limitations. For example, although ferrite permanent magnets have low cost and good corrosion resistance, their magnetic energy product is low, which cannot meet the needs of high-power equipment for strong magnetic fields; alnico permanent magnets have good temperature stability, but their magnetic energy product is also low and their processing performance is poor.

The limitations of these traditional permanent magnet materials have seriously restricted the technological development in many fields. For example, in the field of motors, the low magnetic energy product of traditional permanent magnets makes the motor large in size and low in efficiency; in the aerospace field, the temperature stability of traditional permanent magnets is insufficient to adapt to extreme environmental conditions.

(2) Birth and Development of Rare Earth Permanent Magnets

In the 1960s, the advent of samarium-cobalt permanent magnets marked the arrival of the era of rare earth permanent magnet materials. Samarium-cobalt permanent magnets have much higher magnetic energy product than traditional permanent magnets, and have good temperature stability and corrosion resistance. Their emergence has opened up a path for the application of permanent magnet materials in high-end fields.

In the 1980s, the successful development of neodymium-iron-boron permanent magnets triggered a revolution in the field of permanent magnet materials. Neodymium-iron-boron permanent magnets have higher magnetic energy product than samarium-cobalt permanent magnets, and the cost of raw materials is relatively low, which makes them quickly replace part of the market share of samarium-cobalt permanent magnets and become the most widely used rare earth permanent magnets.

With the continuous progress of technology, the performance of rare earth permanent magnets is still improving. By optimizing component design and improving preparation processes (such as sintering process, bonding process, etc.), the performance indicators of rare earth permanent magnets such as magnetic energy product, coercivity and temperature stability are constantly，further expanding their application fields.

(3) Promotion of Rare Earth Permanent Magnets to Modern Science and Technology

The emergence and development of rare earth permanent magnets have had a profound impact on modern science and technology, promoting technological innovation in many fields.

In the field of new energy vehicles, rare earth permanent magnets are the core components of drive motors. Due to the characteristics of high magnetic energy product and high efficiency of rare earth permanent magnets, new energy vehicles using rare earth permanent magnet motors have the advantages of strong power and long cruising range. Compared with traditional induction motors, the efficiency of rare earth permanent magnet motors can be increased by 5%-10%, which is of great significance for reducing the energy consumption of new energy vehicles and improving their competitiveness.

In the field of wind power generation, rare earth permanent magnets are widely used in permanent magnet synchronous generators of wind turbines. Permanent magnet synchronous generators have the advantages of high efficiency, small size and light weight, which can achieve stable power generation at low wind speeds and improve the economy and reliability of wind power generation.

In the aerospace field, rare earth permanent magnets, with their excellent performance, are used in key components such as attitude control systems and navigation systems of spacecraft. In the extreme space environment, rare earth permanent magnets can maintain stable magnetism to ensure the normal operation of spacecraft.

In addition, rare earth permanent magnets also play an important role in medical equipment (such as nuclear magnetic resonance instruments), consumer electronics (such as vibration motors of smart phones, speakers of headphones) and other fields, bringing many conveniences to people’s lives.

V. Wide Applications of Rare Earth Permanent Magnets

(1) New Energy Vehicles

New energy vehicles are one of the important application fields of rare earth permanent magnets. In the drive system of new energy vehicles, the permanent magnet synchronous motor is the core component, and the rare earth permanent magnet is the “heart” of the permanent magnet synchronous motor.

Rare earth permanent magnet synchronous motors have the advantages of high efficiency, high power density and fast response speed. Because rare earth permanent magnets can generate strong magnetic fields, the motor does not need excitation current during operation, thereby reducing energy loss and improving the efficiency of the motor. At the same time, the high power density makes the motor smaller in size and lighter in weight, which is conducive to saving car space and improving the cruising range of the car.

Taking Tesla Model 3 as an example, its permanent magnet synchronous motor uses a large number of neodymium-iron-boron permanent magnets. These permanent magnets can generate a strong magnetic field inside the motor, enabling the motor to output strong power to meet the acceleration and driving needs of the car. According to statistics, the drive motor of a new energy vehicle requires about 5-10 kilograms of neodymium-iron-boron permanent magnets. With the rapid development of the new energy vehicle market, the demand for rare earth permanent magnets is also growing.

(2) Wind Power Generation

Wind power generation, as a clean and renewable energy source, has developed rapidly in recent years. In wind turbines, permanent magnet synchronous generators are widely used due to their excellent performance, and rare earth permanent magnets are the core materials of permanent magnet synchronous generators.

Compared with traditional doubly-fed asynchronous generators, permanent magnet synchronous generators using rare earth permanent magnets have higher power generation efficiency. Under low wind speed conditions, permanent magnet synchronous generators can capture wind energy more effectively and increase power generation. At the same time, because there is no need for an excitation system, the structure of the permanent magnet synchronous generator is simpler, the maintenance cost is lower, and the reliability is higher.

Large wind turbine permanent magnet synchronous generators usually need to use a large number of rare earth permanent magnets. For example, a 1.5 MW wind turbine needs to use about 1 ton of neodymium-iron-boron permanent magnets. With the increasing global demand for clean energy, the rapid development of the wind power industry will drive the continuous growth of demand for rare earth permanent magnets.

(3) Medical Equipment

In the medical field, rare earth permanent magnets are also widely used, and the most representative one is magnetic resonance imaging (MRI) equipment.

Magnetic resonance imaging equipment uses strong magnetic fields and radio frequency pulses to image the human body, which can clearly show the internal tissue structure of the human body and provide an important basis for disease diagnosis. The main magnet in the equipment needs to generate a strong and uniform magnetic field, and rare earth permanent magnets have become the ideal material for manufacturing the main magnet due to their high magnetic energy product.

Compared with traditional superconducting magnets, permanent magnet type magnetic resonance imaging equipment has the advantages of simple structure and low operating cost. Superconducting magnets need to work at extremely low temperatures (liquid nitrogen temperature) and require complex refrigeration systems, while permanent magnet type magnets do not, which greatly reduces the operation and maintenance costs of the equipment. Therefore, permanent magnet type magnetic resonance imaging equipment has been widely used in small and medium-sized hospitals.

(4) Consumer Electronics

Rare earth permanent magnets are also widely used in the consumer electronics field, from smart phones and tablet computers to headphones and smart watches.

In smart phones, rare earth permanent magnets are used in components such as vibration motors and automatic focusing systems of cameras. The vibration motor generates vibration through the interaction between the permanent magnet and the coil to provide tactile feedback for users; the automatic focusing system of the camera uses the magnetic force of the permanent magnet to drive the lens to move, achieving fast and accurate focusing.

In headphones, rare earth permanent magnets are the core components of speakers. The speaker drives the diaphragm to vibrate through the interaction between the magnetic field generated by the permanent magnet and the current in the coil, making sounds. Due to the high magnetic energy product of rare earth permanent magnets, they can generate a strong magnetic field in a small space, making the sound quality of the headphones clearer and fuller.

VI. Future Prospects of Rare Earth Permanent Magnets

(1) Sustainable Utilization of Rare Earth Resources

With the continuous expansion of the application fields of rare earth permanent magnets, the demand for rare earth resources is also increasing. However, rare earth resources are non-renewable resources, and their mining and extraction processes will have a certain impact on the environment. Therefore, realizing the sustainable utilization of rare earth resources has become an urgent problem to be solved.

On the one hand, it is necessary to strengthen the exploration and development of rare earth resources and improve the utilization rate of resources. By developing advanced mining and extraction technologies, resource waste can be reduced and environmental damage during mining can be reduced. On the other hand, it is necessary to vigorously develop rare earth recycling technologies. Rare earth permanent magnets still contain a large number of rare earth elements in scrapped equipment (such as new energy vehicles, wind turbines, consumer electronics, etc.). By recycling rare earths from these scrapped equipment, not only the dependence on primary rare earth resources can be reduced, but also environmental pollution can be reduced.

(2) Research and Development of New Rare Earth Permanent Magnet Materials

In order to further improve the performance and reduce the cost of rare earth permanent magnets, the research and development of new rare earth permanent magnet materials has always been the focus of researchers.

One is the application of high-abundance rare earths. Light rare earth elements (such as lanthanum and cerium) have relatively abundant reserves in nature and low prices. At present, researchers are studying how to use light rare earth elements to partially replace heavy rare earth elements (such as dysprosium and terbium) to reduce the cost of permanent magnets while ensuring their performance. For example, by optimizing the composition design and preparation process, adding an appropriate amount of lanthanum or cerium to neodymium-iron-boron permanent magnets can improve their coercivity and temperature stability to a certain extent.

The second is nano-composite rare earth permanent magnet materials. Nano-composite rare earth permanent magnet materials are composite materials composed of soft magnetic phases and hard magnetic phases, which have the characteristics of potential high magnetic energy product and low coercivity. By controlling the size and distribution of nano-particles, effective exchange coupling between soft magnetic phases and hard magnetic phases can be achieved, thereby improving the magnetic properties of the materials. At present, the research and development of nano-composite rare earth permanent magnet materials has made certain progress and is expected to become a new type of high-performance permanent magnet materials in the future.