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Magnetic Materials

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All materials are magnetic in the sense that they respond to an applied magnetic field. In most cases this response is linear and small. Magnetic materials also exhibit chaotic and soliton phenomena associated with nonlinear systems.

Magnetism and magnetic materials have been used for many decades in many modern medical applications and several new applications are being developed in part because of the availability of superior electromagnets, superconducting magnets and permanent magnets.

Definition

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Magnetic materials are among the most exotic classes of materials and are especially important in today' rapidly advancing technology and telecommunication era.

The soft magnetic material is more a technical term than a scientific one. The word "soft" means temporary in the sense that the ferromagnetism emerges only when a magnetic field is applied. In contrast, hard or permanent magnets display ferromagnetism in the absence of an external field.

All magnetic elements in purest form are soft, whereas magnetic solid solutions and compounds can be either soft or hard, depending on the composition and metallurgical treatments.

Some examples of magnetic materials are listed below.

Compound/Element Formula
Cerium Ce
Chromium (III) oxide Cr2O3
Cobalt (II) oxide CoO
Erbium Er
Erbium oxideEr2O3
GadoliniumGd
Iron (II) oxideFeO
NeodymiumNd
PraseodymiumPr
SamariumSm
TerbiumTb
Vanadium oxideV2O3

Properties

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Materials may show various kinds of magnetic behavior. Two of the simpler kinds are diamagnetic behavior and paramagnetic behavior. The interaction of a material with the external magnetic field in both cases is usually quite weak that is usually small. Materials may also show complex magnetic behavior. Some materials may show magnetic saturation and high value of the magnetic field when acted upon by an external magnetic field. These materials show ferromagnetic or ferrimagnetic behavior.

1. Diamagnetic property


This property arises due to the orbital motion of electrons. It is induced effect which comes about due to the precession of the orbital angular momentum vector when a magnetic field is applied.

2. Paramagnetic property


The paramagnetic property of materials arises when there is a permanent magnetic moment associated with atoms or ions. All magnetic moments of atoms however do not align in the direction of the applied magnetic field due to the presence of thermal energy trying to randomize the magnetic moments.

Types

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The various different types of magnetic materials are traditionally classified according to their bulk susceptibility. The first group of materials for which magnetic moment is small and negative. These materials are called diamagnetic their magnetic response opposes the magnetic field. Examples of diamagnets are copper, silver, gold bismuth and beryllium. Superconductors form another special group of diamagnets for which magnetic moment is -1.

A second group of materials for which magnetic moment is small and positive are paramagnets. The magnetization of paramagnets is weak but aligned parallel with the direction of the magnetic field. Examples of paramagnets are aluminum, platinum and manganese.

The most widely recognized magnetic materials are the ferromagnetic solids for which the susceptibility is positive, much greater than 1, and typically can have magnetic moments 50 to 10000. Examples of these materials are iron, cobalt and nickel and several rare earth metals and their alloys.

Soft Magnetic Materials

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Soft magnetic materials are mainly utilized in in applications in which magnetic materials are needed to amplify the flux generated by an electrical current. The principal characteristics of soft magnetic materials are remanence, coercivity, maximum and initial values of permeability, saturation value of flux density B and coercive force. Properties of different soft magnetic materials present a set of first quardrant hysteresis loops called demagnetization cures.

Soft iron is utilized in the form of solid bars, sheets and most recently as a powder.Powder metal soft magnetic materials also can be used in their sintered form. Sintered soft magnetic materials are most commonly used as pure iron, phosphorus iron, silicon iron and nickel iron forms. There are a number of technical and economic advantages for using sintered powder soft magnetic material.
  1. Wide range of materials available to designer
  2. The possibility of obtaining complex and varied shapes
  3. Process repeatability easily controlled by statistical methods
  4. Tolerance reliability
  5. Present magnetic characteristics close to fully dense materials.

Hard Magnetic Materials

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Hard magnetic materials are used as generators of the magnetic field. Hard magnetic materials have both high residual induction and high coercivity. The magnet quality depends not only on remanence coercive force and the maximum energy product but also on its temperature dependence corrosion resistance, resistivity, brittleness and cost. Hard magnetic materials include ferrite ceramic magnets.

The properties of different hard magnetic materials including magnetic and temperature performance of different families of hard magnetic materials including magnetic and temperature performance of different families of hard magnet materials.

Non Magnetic Materials

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Substances that are not attracted by a magnet even from a very close distance are called non-magnetic substances. The term magnetic materials refer to ferromagnetic materials which exhibit high induction under magnetic field. Other materials such as paramagnetic materials and diamagnetic materials have very little magnetic induction under the magnetic field and are considered non magnetic materials.

Today magnetic materials are indispensable materials supporting our civilization. Almost every electric appliance in a home uses some form of magnetic materials. The major applications of magnetic materials are permanent magnets, soft magnetic materials, magnetic sensors, magnetic recording materials.
The magnetic materials list is given below.

Types of material Magnetic material
Composition
Ferrite
Ferrite
Manganese-zinc ferrite
Nickel-zinc ferrite
Strontium ferrite
Cobalt ferrite
Barium ferrite
40% $Fe_{2}O_{3}$, 40MnO, 20 CdO
$Mn_{2}Zn_{(1-2)}Fe_{2}O_{4}$
$Ni_{2}Zn_{(1-2)}Fe_{2}O_{4}$
$SrFe_{12}O_{19} (SrO.6Fe_{2}.O_{5})$
$CoFe_{2}O_{4} (CoO.Fe_{2}O_{3})$
$BaFe_{12}O_{19} (BaO.6Fe_{2}O_{3})$
Alloys
Alnico
Comol
Hipernom (Ni-Mo alloy)
Iron-silicon magnet alloy
Magnet steel
Chromindur
Silmanal
Platinax
Bismanol
Cobalt-platinum alloy
Chromium-manganes-antimonide
Ultra-mag
Vectolite
Magnadur
Lodex
Rare earth magnet
Awaruite
Wairauite
35% cobalt,34% iron,15 Nickel, 7% aluminum, 5% titanium and 4% copper
17% Molybdenum, 12% cobal, 71% iron
79% nickel, 4% molybdenum and balance iron
Iron with 1-5% silicon
Iron with carbon and chromium content
28% chromium, 15% cobalt and iron
6.75% silver, 8.8 manganese, and 4.45 aluminium
76.7% platinum and 23.3 cobalt
Bismuth-manganese alloy with 20.8% manganese
Cobalt-platinum alloy
CrxMn2xSb
Pt-Co magnet material
Ferric and ferrous oxide with cobalt; $BaO(Fe_{2}O_{3})_{6}$
Iron-cobalt with lead powder
Samarium-cobalt, cesium-cobalt, Neodymium-iron-boron magnet
$Ni_{3}Fe$
CoFe
Metallic oxide Magnetite
Ulvospinel
Hematite
Ilmenite
Maghemite
Jacobsite
$Fe_{3}O_{4}$
$Fe_{2}TiO_{2}$
$\alpha Fe_{2}O_{3}$
$FeTiO_{2}$
$\beta Fe_{2}O_{3}$
$MnFe_{2}O_{4}$
Metallic sulfide Pyrhotite
Greigite
Troilite
$Fe_{7}S_{8}$
$Fe_{3}S_{4}$
FeS

Metallic oxyhudroxides Goethite
Lepidocrocite
Feroxyhyte
$\alpha FeOOH$
$\beta FeOOH$
$\delta FeOOH$
Metals Iron
Nickel
Cobalt
Fe
Ni
Co
Table: List of magnetic materials
  1. Magnetic materials are used in mariners (direction finding) compass has a magnetic needle in it.
  2. Magnetic materials are used to make certain type of toys. They are used in kitchens as knife holders or in workshops as tool holders.
  3. Many doors or boxes and purses have magnetic latches. For example, the refrigerator door is held closed by a magnet.