What are the materials of permanent magnets?

Which magnetic material to choose for a permanent magnet?

There are five families of magnetic materials. In order of increasing magnetic strength, we find the types: Flexible, Ceramic, Alnico, Samarium Cobalt and Neodymium. The information below very briefly summarizes the properties of each type, to help you orient yourself in the exciting but complex world of permanent magnets.

A) Flexible permanent magnets

Soft magnets are made from a special variety of ferrite magnetic materials in most cases, and sometimes rare earths . These magnets are made by bonding ferrite or rare earth magnetic powders into various media, such as vinyl.

• The material: The material of the flexible magnets sport a white or brown color, similar to rubber. This inexpensive material can be bent, rolled, and twisted, and it's easy to cut with a craft knife or scissors. Magnetic strips and sheets are available with double-sided tape for easy application to products. Materials laminated with white vinyl can be printed using screen printing or digital printing techniques.
• Sizes and shapes: Rolls of magnetic sheets are typically 600mm wide and 30 meters long. The thickness varies between 0.5 and 1 mm.
• The different applications: labeling, signage, visual display, advertising, adhesion on office supplies, business cards, DIY projects, window dressing, etc. These are essentially visual applications.

B) Ceramic (or ferrite) magnets

Ceramic magnets are made of barium or strontium ferrite, the most commonly used and least expensive magnetic material available today.

• The Material: Moderately strong, with a deep magnetic field, and exhibiting good resistance to degaussing , ceramic magnets are popular for many consumer applications. This material is hard, brittle and anthracite in color.
• Sizes and shapes: Discs, rings, arcs and rectangular blocks.
• Applications: Commonly used for crafts, retainer latches, toys, motors, speakers, magnetic brakes, and a multitude of applications. It is a type of permanent magnet that has been produced for over 50 years and is found in a multitude of everyday and industrial uses. The magnetic field it emits is relatively weak but it is deep.

C) Alnico magnets

Alnico magnets are made of aluminum, nickel and cobalt, and have been popular since the 1930s. Alnico magnets are used primarily in technical applications, where high temperature resistance is paramount

• The material : Excellent for high temperature applications (up to 500°C), with high residual induction and the need for corrosion resistance. Cast alnico magnets can be made into relatively complex shapes.
• Sizes and shapes : Discs, rods, bars and other various shapes.
• Applications: Commonly used in meters and for specialized high temperature maintenance applications.

This type of magnet is rarely used, consumer and industrial applications are few, because its magnetic field is quite weak.

D) Samarium-cobalt (SmCo) magnets

Samarium-Cobalt magnets are a class of rare-earth magnetic materials that were developed in the early 1970s. Today, SmCo magnets are most often used in applications that require high temperatures and properties high magnetics .

• Material: High magnetic properties, very fragile, but can be used safely at temperatures up to 250°C.
• Dimensions and shapes: Discs, blocks and rings.
• Applications: Typically used for more technically advanced and high temperature applications.

The price is commensurate with the advantage of strong magnetic induction at high temperature .

E) Neodymium iron boron (NdFeB) magnets

Neodymium magnets are rare earth magnets with the highest magnetic properties . Comprised of neodymium, iron and boron , these powerful permanent magnets are the strongest class of magnetic materials available on the market today.

• Material: Not as brittle as SmCo, but should not be used at temperatures above 80°C, except in particular nuances. The material of neo magnets can corrode easily under certain conditions, so it is best to protect the surface with a zinc coating.
• Sizes and shapes: Discs, blocks, rings and rods.
• Applications: Ideal for industrial and non-technical applications such as holders, magnetic jewelry, clasps and more.

For each material that we have seen, there are dozens of shades (or grades) with more or less significant inductions and magnetic field depths. The choice of the shade is made according to your need for power or not.

MAGNET MATERIAL COMPARISON CHARTS.

WHICH PERMANENT MAGNET EMITS THE MOST POWERFUL MAGNETIC FIELD?

The magnets that deliver the strongest magnetic field to date are made from Rare Earths. Among the rare earths, extracted mainly in China, neodymium-iron-boron magnets are the most powerful. We naturally reason at room temperature, because neodymium (or NFB) quickly loses its power when the temperature becomes high. It can even permanently lose its magnetization, and we will therefore prefer Samarium Cobalt. There are curves which give the induction according to the temperature.

CRITERIA FOR CHOOSING A PERMANENT MAGNET?

Among the important criteria, here are the 3 main ones:

• the residual induction Br whose unit is the Gauss . This is an indication of the power the magnet is capable of achieving. As a reminder, 10000 Gauss = 1 Tesla. This induction is the most commonly exchanged information in the industrial world.
• The coercive force Hc whose unit is the Œrsteds. It is the force opposed to that of the magnet which would make it possible to demagnetize it definitively. The higher it is, the more the magnet is resistant to another magnet or electromagnet.
• The maximum energy produced BH Max whose unit is the Mega-Oersteds . It expresses the maximum energy (KJ) as a function of the volume of the magnet (m3).

Here are some notions of these 3 values ​​on 3 permanent magnet materials:

• Ferrite C1: Br=2200 Gauss / Hc=1900 Oersteds / BH Max= 1.1 MGoe
• SmCo 18: Br=8600 Gauss / Hc=7200 Oersteds / BH Max= 18 MGoe
• Neo N42: Br=13000 Gauss /Hc=12500 Oersteds /BH Max= 41 MGoe

With equal dimensions, this gives you an idea of ​​the difference in performance between two blocks of permanent magnets. The magnetic field will be clearly impacted, both in strength and in depth.

Conversely, with equal inductions, two types of magnets will have very different dimensions . Neodymium will be much more compact than ferrite.

CONCLUSION:

Depending on what you want to do, you are free to choose from these 5 subjects. Remember that neodymium is the most powerful but the most expensive , although its widespread use in recent years has reduced costs.

Ferrite, on the other hand, is the jack of all trades . It is average in everything, is offered at a low price which allows it to still be very present in industries.

Note that the performance advertised on paper is often optimistic compared to the real value of the chosen permanent magnet. Remember to measure the magnet, or even its magnetic circuit, with a gaussmeter or teslameter . We offer different models, classic or using a smartphone application.