Permanent magnets are a vital part of modern life. They are found in or used to produce almost every modern convenience today, from air conditioners and washing machines to speakers in mobile phones and electric motors in hybrid cars. Permanent magnets are used increasingly in technological applications, including traveling wave tubes, Hall effect sensors, high-temperature-resistant permanent magnets, thin-film coating equipment and flywheel storage systems.

In all of these applications, it is important for the designed permanent magnet to be high strength, resistant to corrosion, and resistant to demagnetization due to excessive heat. Manufacturers have gained experience in designing and producing permanent magnets to meet these needs for industries with permanent magnet and magnetic assembly applications.

Magnet Types

Permanent or hard magnetic materials retain a large amount of residual magnetism after exposure to a strong magnetic field. These materials typically have coercive force (HC) values of several hundred to several thousand oersteds (Oe).

A number of major families of permanent magnets are available for designers, ranging from ferrite, known for its low cost and low energy, to rare earth (RE) materials, which are more expensive and offer higher performance. Designers need to analyze magnetizing field strength and magnetic output of magnetic materials prior to deciding on the appropriate one.

Four major families of permanent magnet materials available commercially include ferrite, alnico, samarium cobalt (SmCo) and neodymium-iron-boron (NdFeB). Other factors also affect the choice of magnetic materials, such as operating temperature, size and weight constraints, environmental concerns, and required magnetic energy. Each family of materials has several grades with a range of magnetic properties.

Ceramic magnets, often called “ferrites” or “hard ferrites,” are predominantly complex oxides. These magnets are made of a sintered composite of powdered iron oxide and barium/strontium carbonate ceramic. Introduced in the 1950s, ceramic magnets have become the most widely used permanent magnet materials. Due to their low cost and excellent resistance to demagnetization and corrosion, ceramic magnets are the most popular permanent magnets today. Ferrite magnets are brittle and must be treated like other ceramics.

The ceramic hard ferrites have the advantage of being made of less expensive raw materials than their metal counterparts, such as alnico and rare earth-cobalt. They also have coercive fields, unlike the mass-produced metal magnet types. This allows them to be made into shapes involving high demagnetizing fields.

Alnico magnets are made by casting or sintering a combination of aluminum, nickel and cobalt with iron and small amounts of other elements added to enhance the properties of the magnet. Sintering offers superior mechanical characteristics, whereas casting delivers higher magnetic fields and allows for the design of intricate shapes. Alnico magnets resist corrosion and have physical properties more forgiving than ferrite, but not quite as desirable as a metal. Trade names for alloys in this family include Alni, Alcomax, Hycomax, Columax and Ticonal.

Injection-molded magnets are a composite of various types of resin and magnetic powders, allowing parts of complex shapes to be manufactured by injection molding. The physical and magnetic properties of the product depend on the raw materials, but are generally lower in magnetic strength and resemble plastics in their physical properties.

Flexible magnets are similar to injection-molded magnets, using a flexible resin or binder such as vinyl. Produced in flat strips, shapes or sheets, these magnets are lower in magnetic strength but can be very flexible depending on the binder used. Flexible magnets can be used in industrial printers.

Rare earth magnets are strong permanent magnets made from alloys of RE elements. Developed in the 1970s and 1980s, RE magnets are the strongest type of permanent magnets, producing significantly stronger magnetic fields than other types. The typical magnetic field of these magnets can be in excess of 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5-1.0 tesla. There are two types: neodymium magnets and samarium-cobalt magnets. Rare earth magnets are extremely brittle and vulnerable to corrosion, so they are usually plated or coated to protect them from breaking and chipping.

Improved Properties

Permanent magnets today are 60 times as strong as they were about 90 years ago. Strong permanent magnets that can be used in industrial applications were developed in the 20th century, and Japanese and Western European researchers and technologies have played major roles in the development of permanent magnets.

Permanent magnet materials are identified by several principal magnetic properties. The maximum energy product, BHmax, is measured in mega-gauss-oersteds (MGOes). The residual induction, Br, is measured in gauss or kilogauss. Coercive force (HC) and intrinsic coercive force (HCi) are measured in oersteds.

The important characteristics of permanent magnet materials are high induction, high resistance to demagnetization, and maximum energy content. Magnetic induction is limited by composition; the highest saturation induction is found in binary iron-cobalt alloys. Resistance to demagnetization is conditioned less by composition than by shape or crystal anisotropies and the mechanisms that subdivide materials into microscopic regions. Precipitation, strains and other material imperfections, and fine particle technology are all used to obtain a characteristic resistance to demagnetization.

Permanent magnet materials properties are shown in Table 1. Coercive force is a measure of the magnetizing force required to reduce the magnetic induction to zero after the material has been magnetized. It is measured in oersteds (Oe).

Maximum energy content is the most important property, because permanent magnets are used primarily to produce a magnetic flux field (which is a form of potential energy). Maximum energy content, and certain other characteristics of materials used for magnets, is best described by the hysteresis loop. Hysteresis is measured by successively applying magnetizing and demagnetizing fields to a sample and observing the related magnetic induction.

With the heavy reliance on Neo magnets in manufacturing, the RE materials neodymium and dysprosium are playing an important role because of the scarcity of these materials and the dominance of a single country (China) in providing them. However, new supplier countries of these materials are now easing the shortage.

A Range of Applications

Hard ferrites have three major applications: acoustics (rings), motors (segments) and holding instruments (including magnet separators). The largest share goes to acoustics, followed by motors and holding instruments. Within these categories, applications of hard ferrites vary in different countries. Holding instruments refer to applications that make use of the tractive and/or repelling force of the magnet—i.e., the attraction between a magnet and a soft magnetic material, such as a piece of iron or steel, or the attraction or repulsion between two magnets—to do mechanical work. The applications in this category include magnetic separators, magnetic holding devices (such as magnetic latches), magnetic torque drives and magnetic bearing device, among others. The sidebar shows 15 major application areas for NdFeB permanent magnets.

Samarium is combined with cobalt to create a permanent magnet with the highest resistance to demagnetization of any known material. Because of its ability to take continuous temperatures above 250°C, it is essential in both aerospace and military applications. Precision-guided munitions use SmCo permanent magnet motors to direct the flight control surfaces (fins). SmCo can be used as part of stealth technology in helicopters to create white noise to cancel or hide the sound of the rotor blades. These permanent magnets are also used as part of aircraft electrical systems, and to move flight control surfaces of aircraft, including flaps, rudder and ailerons. Samarium is used in both missile and radar systems’ traveling wave tubes (TWTs). SmCo magnets are used in defense radar systems, as well as in several types of electronic counter-measure equipment, such as the tail warning function.

Although there is serious competition from other types of magnets, such as ferrite and RE magnets, alnico is still widely used for meters (e.g., watt-hour meter, voltmeter, ampere meter, mileage meter), acoustic devices, motors, and sensors in automobiles and motorcycles, due to its excellent thermal stability. The biggest application for produced alnico is the watt-hour meter. Its absolute output tonnage has increased slightly, although its output percentage has significantly decreased. Alnico magnets are also used in communications, aerospace and defense, industrial and consumer products, meters, and instrumentation.

The historical intention for developing bonded neo was to compete with hard ferrites (non-bonded), which are the most-used magnet material in the world (by weight). Today, because of the flexibility offered in making different shapes and sizes, bonded magnets find a wide range of applications.

With the increase in the cost of producing bonded ferrite magnets, the industry has shifted from developed countries to developing countries, including China, just as has happened for other types of magnets. The use of bonded magnets in each country is different; therefore, the direction in which the industry develops in each country is also different.

Highlighting Industry Developments

A recent study has been prepared to highlight the many new developments in the permanent magnet industry, as well as the industry structure and markets. Major findings of the report include:

•  The global market for permanent magnets reached $11.3 billion in 2013 and is expected to grow to $15 billion by 2018, with a compound average growth rate of 5.7%.

•  When combined, metallic magnets (NdFeB, alnico and SmCo) dominated the market in 2013, followed by ceramic magnets (ferrites). Bonded magnets ranked a distant third.

•  In terms of regional demand, the market is large in the Asia-Pacific region. It is growing at a fast pace due to rising demand from end-user industries, especially in countries such as China and Japan. The five-year period of 2013-2018 will see more of the industry centered in China.

•  The market is growing slowly in Europe, but will continue to grow at a significant rate in North America.

•  The market is still in its infancy in Africa and Latin America, but these regions are experiencing high growth due to increased infrastructure spending and a low base effect. This market will experience an escalation in the demand of permanent magnets in the years to come.

•  The U.S. is a net importer of permanent magnets, for as much as 60% of its consumption. However, the U.S. still dominates in high-performance magnets used in military and other strategic applications.

Many of the market segments are mature, while others are growing at fast rates. Developing economies such as China and India are also emerging as growth engines for many industries that use permanent magnets. The markets in these new economies are expected to experience maximum revenue growth during the next five years.

The permanent magnet industry has grown in the last decade and is likely to continue this growth into the next decade due to increased usage of magnetic circuit components in a variety of industrial equipment and devices. Electromechanical devices constitute the largest market for permanent magnet materials, and this market is growing rapidly. Large motors use ceramic magnets, and, for certain military applications, SmCo is still the preferred magnet.

Among all categories of magnets, ceramic ferrites constitute the largest market and have been estimated to have reached a usage volume of 900,000 tons (valued at $4.5 billion) in 2013; the ceramic ferrite market is projected to grow to 1.1 million tons (valued at $6.6 billion) in 2018.

Applications related to permanent magnet direct current motors—brushless direct current (BLDC) and brush-type (PMDC)—and power generation will be the largest usage segment of NdFeB permanent magnets, followed by voice coil motors (VCMs) in disk drives, because of the need for reduced size and higher performance. The third major usage segment is hybrid and electric automotive drives.

Several RE elements are essential ingredients in the highest performance magnets available in the world today; these magnets have enabled miniaturization and a significant increase in power density in hundreds of applications.

The market experienced a boom in 2011 due to increased demand for RE permanent magnets. But as demand increased, supply chain interruptions resulted in a scarcity of RE permanent magnets. This affected the market adversely, and it plunged in 2012. As the supply of REs became stable, the market became stable; it is expected to further stabilize in the future.

The permanent magnet market includes a large number of small manufacturers, coupled with a few medium-sized manufacturers. The market is dominated by Chinese manufacturers. There is a scarcity of manufacturers for rare earth magnets, and they are geographically scattered. 

Major Application Areas for NdFeB Permanent Magnets

• Automotive industry

• HDD/CD/DVD

• Electric bicycles

• Transducers, loudspeakers

• Magnetic separation

• MRI

• Torque-coupled drives

• Sensors

• Hysteresis clutches

• Generators

• Energy storage systems

• Wind power generators

• Air conditioning compressors and fans

• Hybrid/electric drives

 • Miscellaneous: gauges, brakes, relays and switches, pipe inspection, levitated transportation, reprographics, refrigeration