Types of Magnets

There are various types of magnets depending on their properties. Some of the most well known are listed below.

Permanent Magnets

These are the most common type of magnets that we know and interact with in our daily lives. E.g.: the magnets on our refrigerators. These magnets are permanent in the sense that once they have been magnetized they retain a certain degree of magnetism. Permanent magnets are generally made of ferromagnetic material. Such material consists of atoms and molecules that each have a magnetic field and are positioned to reinforce each other.

Classification

Permanent Magnets can further be classified into four types based on their composition:

  1. Neodymium Iron Boron (NdFeB or NIB)
  2. Samarium Cobalt (SmCo)
  3. Alnico
  4. Ceramic or Ferrite

NIB and SmCo are the strongest types of magnets and are very difficult to demagnetize. They are also known as Rare Earth or Lathanoid series of elements in the periodic table. The 1970's and 1980's saw the development of these magnets.

Alnico is a compound made of Aluminium, Nickel and Cobalt. Alnico magnets are commonly used magnets and first became popular around the 1940's. Alnico magnets are not as strong as NIB and SmCo and can be easily demagnetized. This magnet is however, least affected by temperature. This is also the reason why bar magnets and horseshoe magnets have to be taken care of to prevent them from loosing their magnetic properties.

The last type of permanent magnets, Ceramic or Ferrite magnets are the most popular today. They were first developed in the 1960's. These are fairly strong magnets but their magnetic strength varies greatly with variations in temperature.

Permanent Magnets can also be classified into Injection Molded and Flexible Magnets.

  1. 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.
  2. Flexible magnets are similar to injection molded magnets, using a flexible resin or binder such as vinyl, and produced in flat strips or sheets. These magnets are lower in magnetic strength but can be very flexible, depending on the binder used.
Shape & Configuration

Permanent magnets can be made into any shape imaginable. They can be made into round bars, rectangles, horseshoes, donuts, rings, disks, and other custom shapes. While the shape of the magnet is important aesthetically and sometimes for experimentation, how the magnet is magnetized is equally important. For example: A ring magnet can be magnetized South on the inside and North on the outside, or North on one edge and South on the other, or North on the top side and South on the bottom. Depending on the end usage, the shape and configuration vary.

Demagnetization

Permanent magnets can be demagnetized in the following ways:

  1. Heat - Heating a magnet until it is red hot makes it lose its magnetic properties.
  2. Contact with another Magnet - Stroking one magnet with another in a random fashion, will demagnetize the magnet being stroked.
  3. Hammering or jarring will loosen the magnet's atoms from their magnetic attraction.

Temporary Magnets

Temporary magnets are those that simply act like permanent magnets when they are within a strong magnetic field. Unlike permanent magnets however, they lose their magnetism when the field disappears. Paperclips, iron nails and other similar items are examples of temporary magnets. Temporary magnets are used in telephones and electric motors amongst other things.

Electromagnets

Electromagnet Had it not been for electromagnets we would have been deprived of many luxuries and necessities in life including computers, television and telephones. Electromagnets are extremely strong magnets. They are produced by placing a metal core (usually an iron alloy) inside a coil of wire carrying an electric current. The electricity in the current produces a magnetic field. The strength of the magnet is directly proportional to the strength of the current and the number of coils of wire its polarity depends on the direction of flow of current. While the current flows, the core behaves like a magnet. However, as soon as the current stops, the core is demagnetized.

Electromagnets are most useful when a magnet must be switched on and off as in large cranes used to lift cables and rods in construction.

Superconductors

These are the strongest magnets. They don't need a metal core at all, but are made of coils of wire made from special metal alloys which become superconductors when cooled to very low temperatures.