Magnet Materials


Magnet Materials

 

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Contents

  • 1.0 Magnet Materials
  • 2.0 Material Comparisons
  • 3.0 Magnetic Strength
  • 4.0 Magnetic Ratings
  • 5.0 Magnetic Properties
  • 6.0 Maximum Operating Temperatures

1.0 Which Magnet Materials Are Available?

You have five options when it comes to magnetic materials. In order to increase magnetic strength, these are the Flexible, Ceramic and Alnico types. Below is a summary of the properties for each type, to help you choose what you may need.

Flexible Magnets

Flexible magnets can be described as a special type of rare-earth or ferrite magnet materials. They are made by binding rare-earth or ferrite magnet powders in a variety carriers such as vinyl.

  • Characteristics: Flexible magnet material is like rubber, and either white or dark brown in color. This cheap material is easy to bend, coil, twist, and cut with a knife and scissors. Magnetic sheets and magnetic strips can be applied to products with double-sided adhesive tape. Material laminated with white vinyl can have digital or silk printing imprinted.
  • Dimensions and shapes: The typical thickness of magnetic strips is 1/16″. Magnetic sheeting rolls are typically 24″ wide, 100′ long, and the typical thickness ranges between 0.02″ and 0.03″.
  • Applications: Labeling, signage, visual display, premiums and adhering office supplies. Business cards. Window treatments.

Ceramic Magnets

Ceramic (ferrite magnets) are made of barium and strontium ferrite. They are the most popular, low-cost magnet material today.

  • Ceramic magnets have many desirable characteristics. They are magnetically strong and resist demagnetization well. This material is hard and brittle and dark grey in color.
  • Sizes and shapes: Discs are a variety of shapes, including rings, blocks, discs, and arc segments.
  • Applications Commonly used to make crafts, hold latches, toys and motors.

Alnico Magnets

Alnico magnets, which are composed of cobalt, nickel, and aluminum, have been in use since the 1930’s. Alnico magnets are used primarily in technical applications, where temperature stability is critical. (top)

  • Characteristics: Excellent for high temperature applications up to 1,000degF, high residual induction, and corrosion resistant. You can also make cast alnico magnets in complex shapes.
  • Sizes and shapes: Rods, rods, bars and horseshoes.
  • Applications Commonly used for Meters and high-temperature applications.

Samarium Cobalt(SmCo) Magnets

Samarium Cobalt Magnets are a group of rare-earth magnet materials. They were first introduced in the 1970’s. SmCo magnets are used most frequently in applications that require high temperatures and magnetic properties. (top)

  • Characteristics: High magnetic properties, very brittle, but can be safely used at temperatures up to 500degF.
  • Sizes and shapes: Blocks, discs, and rings.
  • Applications : Is used primarily for high-temperature and more technical applications.

Neodymium Iron Boron (NdFeB) Magnets

Rare-earth magnets with the best magnetic properties are called Neodymium magnets. These strong permanent magnets, which are made up of neodymium and iron, are the strongest class of magnet materials currently available.

  • Characteristics: Not as brittle as SmCo, but should not be used at temperatures above 300degF, without special design considerations. The surface of neo magnet material can corrode under certain conditions. It is best to protect it by coating or plating.
  • Sizes and shapes: Discs/blocks, rings, rings, and rods.
  • Applications These are ideal for industrial and non-technical uses such as holding magnetic jewelry, clasps, and many other things.

There are different grades within each family, in addition to the ones mentioned above. The grade isn’t very important for most non-technical purposes. MagnetShop.com shows magnets that are economical and suitable for general purposes. (top)

2.0 Material Comparisons

Magnet Material Comparison

Relative cost by weight / Relative cost By BHmax

Weight by BHmax

Maximum Operating Temperature / Difficulty to Use

3.0 What are the strongest magnets in the world?

Rare Earths magnets are today’s strongest. The strongest magnets of the Rare Earths are the Neodymium Iron-Boron types. Samarium Cobalt magnets are stronger than Neodymium Iron-Boron ones at higher temperatures (around 200 degrees C or above), depending on the magnetic circuit. (top)

4.0 How are magnets rated

  1. Residual induction (given symbol Br and measured using Gauss). This indicates how strong the magnet can be.
  2. Coercive force (given symbol Hc and measured in Oersteds). This indicates how difficult it can be to demagnetize the magnet.
  3. Maximum Energy Product (given symbol BHmax and measured in Gauss–Oersteds). This indicates how much magnet material is needed to project a certain level of magnetic flux. (top)

5.0 What properties are common magnet materials?

These are the three most important characteristics of magnets that are used in the majority of magnet materials today.

How can I use this information?

You can calculate the amount of magnetic flux that different materials will project at a distance by using a magnet size. This information can also be used to compare materials.

Example: What is the flux requirement for a Neo 35 project compared to a Ceramic 5 project of the same size at a distance?

Divide the Br. of Neo 35 by Br. of Ceramic 5, (12,300/3.950) to get 3.1. The Neo 35 would provide you with 3.1 times as much flux at the same distance as a Ceramic 5. This information can be used to determine the required magnet volume for different magnet materials. (top)

Example: At a given distance, what volume of a Ceramic 5 magnet would produce the same flux as a Neo35 magnet?

Divide the BHmax for Neo 35 by the BHmax for Ceramic 5, (35/3.6), to get 9.7. To get the same flux, the Ceramic 5 magnet must have a volume 9.7 times the Neo 35 magnet’s.

6.0 What is the recommended operating temperature for different magnet materials?

The magnetic circuit in which the magnet is operating will determine the maximum temperature at which a magnet can be used effectively. Below are the maximum operating temperatures for different classes of magnet materials. To ensure that the magnet does not become demagnetized at temperatures close to those shown, it may be necessary to pay special attention. (top)


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