Magnetic materials - a term commonly used for materials which exhibit strong magnetic properties, such as ferromagnetic or ferrimagnetic, further broadly classified as magnetically soft, hard, or semi-hard.1)
However, in general all materials are “magnetic” but they respond in various ways to magnetic field, depending on their atomic structure and ambient conditions, or at least do not significantly obstruct magnetic field. In that sense, even vacuum is “magnetic” because magnetic field can propagate through it and by definition its magnetic permeability $μ_0$ is a universal physical constant in the SI system of units.2)
On the other hand, antiferromagnetic materials have internally ordered magnetic structure, but such that does not produce large values of susceptibility (i.e. appears to be “non-magnetic”). Yet, these materials find use in special magnetic applications such as magnetoresistive sensors in magnetic hard drives.3)
Magnetic field can be completely expelled from a superconducting body (Meissner effect) but this happens due to the induced surface electric currents, rather than magnetic response as such. However, from the outside, type I superconductors behave as if they were perfect diamagnets, with permeability of zero (comparing to vacuum which has permeability of unity). 4)
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Magnetic properties of all pure chemical elements of practical importance were measured, with at least an order-of-magnitude accuracy (see the large illustration with the periodic table below). The elements can be broadly classified into diamagnetic and paramagnetic (weak magnetic properties) and ferromagnetic (strong magnetic properties). At room temperature only three elements are ferromagnetic: iron, cobalt, and nickel.
However, pure elements are rarely used because of their magnetic properties (but they can be used for other reasons, like for instance copper for making electric wires or noble gases for providing protective chemical atmosphere).
From engineering viewpoint, metal alloys and chemical compounds, even made from non-ferromagnetic elements, can exhibit very strong magnetic effects, which need to be tailored, by many means: chemical composition, mechanical forming, thermal processing (annealing), with or without magnetic field.
There are several ways in which materials can respond, and these different types of response are described by various types of magnetism:
A wide range of materials (both “magnetic” and “non-magnetic”) are widely used in engineering applications.
Soft magnetic materials (or rather “magnetically soft materials”) are used in energy generation and transformation, mechanical force generation, and signal processing such as sensing and transmission.
|Type of material||Main constituents||Comments|
|Pure iron||Fe||Saturation up to 2.15 T6), high cost, used in DC applications such as electromagnet or flux guides for permanent magnet circuits|
|Mild steel||Fe||Saturation up to 2.15 T, lowest cost, produced in very high volume, used in DC applications such as electromagnet, non-critical relay, or flux guides for permanent magnet circuits|
|Non-oriented electrical steel||Fe + Si||Saturation up to 2.15 T, higher cost, produced in thin sheets (<1 mm) in very high volume, used predominantly in motors and smaller generators and transfomers, mostly operating at mains frequency|
|Grain-oriented electrical steel||Fe + Si||Saturation up to 2.1 T, higher cost, produced in very high volume, used in power transformers, large generators and motors operating at mains frequency|
|Thin-gauge electrical steel||Fe + Si||Produced in thinner sheets (<0.25 mm) to suppress eddy currents, used in motors and generators operating at higher operating frequencies, e.g. in motors of electric vehicles|
|Fe-based amorphous tape||Fe + B||Saturation up to 1.75 T, higher cost, produced in high volume, used in power transformers and sensing applications. Higher permeability than electrical steels but very brittle (very thin ribbon (<0.05 mm) with amorphous structure|
|Soft ferrite||MnZn or NiZn||Saturation up to 0.5 T, medium cost, used typically for high-frequency applications, mechanically brittle and difficult to machine, produced through sintering|
|Iron and iron-alloy powder||Fe, Fe+Al||Saturation up to 1.5 T, medium cost, used typically for chokes in power supplies up to 100 kHz|
|Co-based amorphous tape||Co||Very high permeability, very expensive, used in pulse applications|
|Garnet, spinel and hexagonal ferrites||Various||Saturation up to 0.5 T, used in GHz applications|
This page is being edited and can be incomplete or incorrect.
For soft magnetic mateirals, the image below shows the summary of four types of characteristics: saturation, permeaiblity, frequency range, and cost.
Materials are classified as “semi-hard” mostly on the basis of their coercivity, with a range intermediate, between the soft (the lower the better) and hard (the higher the better).
However, from a wider perspective, it is the specific mode of use of a given material that defines the classification.9) There are three main types of applications for semi-hard magnetic materials: