The matter which can used to make something is known as material. It may include raw and processed material, assemblies, fuels, small tools and other accessories which may be consumed directly or indirectly.
Some common examples of materials are metal, adhesive, bio polymers, plastics, glass, wood, textiles and recycled material. Some mechanical, physical and chemical properties of materials are as follow.
- Mechanical properties: Strength, Toughness, Hardness, Ductility, Elasticity, Fatigue and Creep
- Chemical properties: Oxidation, Corrosion, Flammability, Toxicity
- Physical properties: Density, Specific heat, Melting and boiling point, Thermal expansion and conductivity, Electrical and magnetic properties
On the basis of the behavior of material towards magnet they can be classified in two types.
- Magnetic Materials: These materials are attracted by magnetic field. Iron, nickel and cobalt objects such as iron nail, key, metal spade, needle and metal door handle are magnetic in nature.
- Non-Magnetic Materials: These materials are not attracted towards magnet. For example; wood, rubber, plastics, coins, leather and feather are non-magnetic in nature.
Materials which are capable to being magnet in magnetic field are called as magnetic materials. Metals like iron, nickel, cobalt and their compounds and alloys are magnetic in nature. Magnetic materials can be classified in two types.
- Soft magnetic materials: These materials do not have permanent magnetism and lose their magnetism quickly in the absence of magnetic field. They form temporary magnets and also known as electromagnet. The best examples of soft magnet are iron-silicon alloys, nickel-iron alloy and iron.
- Hard magnetic materials: These magnetic materials retain their magnetism in absence of magnetic field and also known as permanent magnets. Alloys composed of iron, cobalt and aluminum are generally acted as hard magnetic materials.
- The most common magnetic materials are metallic, metallic oxide and ceramics. Metallic materials like laminated steel, iron powder are works well in mains power transformers.
- The iron powder is insulated by acid treatment which produces an oxide layer on the outer surface and insulates each iron particle from the next. This powder can mixed with other non-magnetic materials to from useful shapes or ring core.
- Magnetic materials which are composed of metallic oxides are known as ferrite. These are ceramics and also known as rare earth types. They are stable, highly resistance and permanent magnets.
- Generally ferrite contains around 50% of iron oxide with other metals like manganese, zinc etc.
- The metallic oxides of manganese (Mn) and zinc (Zn) are used for lower frequency work due to their high permeability and low bulk resistivity.
- The other example of ferrite has nickel and zinc oxide composition which has low permeability and high bulk resistivity.
On the basis of response in magnetic field, magnetic material can be classified in five types.
- Diamagnetic materials: These materials have a weak, negative susceptibility to magnetic fields, thus slightly repelled by a magnetic field. Diamagnetic materials do not retain the magnetic properties in the absence of magnetic field. Such type of materials have all paired electrons, hence there is no permanent net magnetic moment per atom. Most common examples of diamagnetic material are copper, silver, and gold.
- Paramagnetism: They have a small, positive susceptibility to magnetic fields and slightly attracted by a magnetic field. Like diamagnetic materials, they also lose their magnetic properties in the absence of magnetic field. Magnesium, molybdenum, lithium, and tantalum are examples of paramagnetic materials. They have some randomly arranged unpaired electrons hence show some magnetic moment.
Some examples of paramagnetic materials are as follow.
- Ferromagnetism: They have a large, positive susceptibility to an external magnetic field and exhibit a strong attraction to magnetic fields. They are permanent magnet after removal of magnetic field also. Because of the presence of magnetic domains, they get their strong magnetic properties.
- Ferrimagnetism: In such materials, the electron spins are orientated anti parallel to one another but, due to an inequality in the number of spins in each orientation, there exists an overall magnetic moment.
- Antiferromagnetism: They have unpaired electrons which are line up opposite of one another and have a zero magnetic moment.
The magnetic properties of a material can be analyzed by using some properties like magnetic susceptibility (χ) which is a ratio of magnetization (M) to magnetic field (H). The value of magnetic susceptibility for various magnetic materials is as follow.
In general, metals like iron, chromium, aluminum, uranium, platinum, copper, cobalt and nickel are magnetic in nature. Their metallic compounds and alloys with various metals are also magnetic in nature. Some magnetic materials with their compositions are as follow.
Non-magnetic materials are not affected by external magnetic field and show net zero magnetic moment due to random alignment of magnetic field of individual atoms. Wood, plastics, rubber, glass are common examples of non-magnetic materials. Some metals like gold, platinum, aluminum are also non-magnetic in nature but can be magnetized under certain conditions of temperature. Some alloys of titanium, manganese and chromium are also non-magnetic in nature and widely used in drill collar.