Types of Magnets

Magnets are objects that generate a magnetic field, a force-field that either pulls or repels certain materials, such as nickel and iron. Of course, not all magnets are composed of the same elements, and thus can be broken down into categories based on their composition and source of magnetism. Permanent magnets are magnets retain their magnetism once magnetized. Temporary magnets arematerials magnets that perform like permanent magnets when in the presence of a magnetic field, but lose magnetism when not in a magnetic field. Electromagnets are wound coils of wire that function as magnets when an electrical current is passed through. By adjusting the strength and direction of the current, the strength of the magnet is also altered.

Permanent Magnets

There are typically four categories of permanent magnets: neodymium iron boron (NdFeB), samarium cobalt (SmCo), alnico, and ceramic or ferrite magnets.

• Neodymium Iron Boron (NdFeB)

This type of magnet is composed of rare earth magnetic material, and has a high coercive force. They have an extremely high energy product range, up to 50 MGOe. Because of this high product energy level, they can usually be manufactured to be small and compact in size. However, NdFeB magnets have low mechanical strength, tend to be brittle, and low corrosion-resistance if left uncoated. If treated with gold, iron, or nickel plating, they can be used in many applications. They are very strong magnets and are difficult to demagnetize.

• Samarium Cobalt (SmCo)

Like NdFeB magnets, SmCo magnets are also very strong and difficult to demagnetize. They are also highly oxidation-resistant and temperature resistant, withstanding temperatures up to 300 degrees Celsius. Two different groups of SmCo magnets exist, divided based on their product energy range. The first series (Sm1Co5) has an energy product range of 15-22 MGOe. The second series (Sm2Co17) has a range that falls between 22 and 30 MGOe. However, they can be expensive and have low-mechanical strength.

• Alnico

Alnico magnets get their name from the first two letters of each of three main ingredients: aluminum, nickel, and cobalt. Although they feature good temperature resistance, they can easily be demagnetized and are sometimes replaced by ceramic and rare earth magnets in certain applications. They can be produced by either sintering or casting, with each process yielding different magnet characteristics. Sintering produces enhanced mechanical traits. Casting results in higher energy products and enables the magnets to achieve more complicated design features.

• Ceramic or Ferrite

Comprised of sintered iron oxide and barium or strontium carbonate, ceramic (or ferrite) magnets are typically inexpensive and easily produced, either through sintering or pressing. However, because these magnets tend to be brittle, they require grinding using a diamond wheel. They are one of the most commonly used types of magnet, and are strong and is not easy to demagnetize.

Temporary Magnets

Temporary magnets can vary in composition, as they are essentially any material that behaves like a permanent magnet when in the presence of a magnetic field. Soft iron devices, such as paper clips, are often temporary magnets.

Electromagnets

Electromagnets are made by winding a wire into multiple loops around a core material—this formation is known as a solenoid. To magnetize electromagnets, an electrical current is passed through the solenoid to create a magnetic field. The field is strongest on the inside of the coil, and the strength of the field is proportionate to the number of loops and the strength of the current.

The material at the center of the coil, the core of the solenoid, can also affect the strength of an electromagnet. If a wire is wrapped around a nonmagnetic material, such as a piece of wood, the overall magnetic field will not be very strong. However, if the core is composed of ferromagnetic material, such as iron, the strength of the magnet will dramatically increase.

Applications

Within the industrial sector, magnets are often used as magnetic sweepers, sorters, and to separate impure metals during metal manufacturing or recycling. In electronic applications, magnets are used in speakers, televisions, telephones, radios, and videotapes. Typically, electromagnets are used within televisions, computers, and telephones because of their extreme strength. For this same reason, they are also used in on-off applications, such as cranes sued for heavy lifting.

Permanent magnets are perhaps the most common type—they are used to manufacture refrigerator magnets, as well as in jewelry making. Temporary magnets can be useful in applications that generate a temporary magnetic field and require a magnetic response for the duration of the field.