Microwave101
Custom Search
 
 
 

Magnetic materials

Updated January 9, 2009

Click here to go to our main page on materials

Click here to go to a separate page on high-permeability materials

Click here to go to our page on permeability

Click here to go to our page on skin depth

The property that defines how a material responds to a magnetic field is its permeability. Permeability has a big effect on skin depth, metals with high permeability are poor conductors for RF signals.

The definition of permeability is the ratio of applied magnetic induction to the applied magnetic field:

R=B/H

(units are Gauss/Oersted)

Materials are divided into four categories, depending on their permeability.

Diamagnetic: R<1

Nonmagnetic: R=1 (air is a good example, but most metals are very close to nonmagnetic, close enough so you can round off R to 1.)

Paramagnetic: R>1

Ferromagnetic: R>>1

Material Type Relative permeability

Bismuth

Diamagnetic 0.99983
Silver Diamagnetic 0.99998
Copper Diamagnetic 0.999991
Lead Diamagnetic 0.999983
Water Diamagnetic 0.999991
Vacuum Nonmagnetic 1
Air Paramagnetic 1.0000004
Aluminum Paramagnetic 1.00002
Palladium Ferromagnetic 1.0008
Cobalt Ferromagnetic 250
Nickel Ferromagnetic 600
Mild Steel (0.2 C) Ferromagnetic 2,000
Iron (0.2 impurity) Ferromagnetic 5,000
Silicon Iron Ferromagnetic 7,000
Mumetal Ferromagnetic 100,000
Purified iron (0.05 impurity) Ferromagnetic 200,000
Supermalloy Ferromagnetic 1,000,000

Part of the table above came from Microwave Tubes by A.S.Gilmour. Order it from our book page!

Here's a table of Magnetic Susceptibilities of Paramagnetic and Diamagnetic Materials at 20°C on another web site, thanks to Faaron:

http://hyperphysics.phy-astr.gsu.edu/HBASE/tables/magprop.html

Note that the permeability of a material is not always a fixed bulk property, such as density. Permeability can be affected by how a material is treated, for example, the grain size of a metal can affect it.

Permeability of ferromagnetic materials can be quite nonlinear. Usually the values given in tables are for the maximum permeability, the slope at very low applied magnetic fields.

For these two reasons, you may very well see quite different relative permeability data for the same material, if you compare data from two suppliers or textbooks. Heck, you might even see two different numbers reported for the same material on this web site!

More to come!

 


 
everything RF

RF & MW Components

40,000+ Components
100+ Companies
Search by specification

www.everythingrf.com


You are visitor number 36857 to this page.

All content copyright P-N Designs, Inc.

Home | Virtual Lobby | Microwave Encyclopedia | Microwave Calculators | Unknown Editor | Acronym Dictionary
Message Boards | Cool Links | Microwave Mortuary | What's New? | Search Our Site | Download Area |Contact

P-N Design Services, Inc. - Tucson, Arizona
Webs with MOJO by PC Mojo - Cave Creek, AZ