What is Magnetic property?

When a magnetic field is exerted on a particular material, the property shown by that material is expressed as magnetic property. Generally, the materials which exhibit magnetic characteristics are aluminum, nickel, dysprosium, cobalt, and many others. Some of the common magnetic properties of the material are listed below:

• Intensity of magnetisation
• Magnetic field or magnetic intensity
• Magnetic susceptibility
• Retentivity
• Coercivity

Intensity of magnetization

The intensity of magnetization is equivalent to the total dipole moment of certain material in a unit volume. If any material is placed under a magnetic field, the magnetic moments are positioned in a specific direction, and it will receive some amount of dipole moment. In the international standard system, the intensity of magnetization is measured in the units of Ampere per meter.

Magnetic intensity

The magnetic intensity is referred to as the capability of a magnetic field to magnetize the material medium. The magnetic intensity does get affected by variation in the nature of the medium. It is an external field that produces magnetic properties in a given material.

Magnetic susceptibility

Magnetic susceptibility can be explained as the quantity that indicates the correlation among magnetization present in a material and magnetic field intensity. It is denoted by the symbol $X_m$. The general relation of magnetic susceptibility is given by,

$X_m=\frac{I}{H}$

Here, I is the magnetization and H is the magnetic field intensity.

In the above relation, it is observed that the magnetic susceptibility relies on the intensity of magnetization as well as magnetic intensity, which means that it will alter with a variation in these magnetic quantities.

Retentivity

The property of a magnetic material to regain the magnetization is represented as retentivity. As compared to the temporary magnets, the retentivity is higher in permanent magnets. Materials and alloys having higher retentivity are ferromagnetic materials and Alnico.

Coercivity

Coercivity is one of the sensitive properties of a magnetic material that indicates the ability to withstand the magnetic field without getting demagnetized. Among several types of magnets, neodymium iron boron magnets have the greatest coercivity, and these magnets also contain the highest energy product.

Magnetism

Magnetism is expressed as the occurrence by which a given magnetic element applies force on other elements. Most of the elements cause magnetic moments that contribute to its magnetic characteristics as well as respond to a magnetic field.

The following are the basic types of magnetism.

• Diamagnetism
• Para-magnetism
• Ferromagnetism
• Ferrimagnetism
• Anti-ferro magnetism

Diamagnetism

Diamagnetism is a non-permanent weak type of magnetism that endures only in the existence of an external field. Diamagnetism is a negative magnetic effect because the outside magnetic field exerting on an atom deranged the orbiting electron and produced magnetic dipoles. These magnetic dipoles oppose the magnetic field. Some of the examples of diamagnetism are organic material, superconducting materials, and several others.

Below listed are some essential points related to diamagnetism.

• The magnitude of magnetic susceptibility is small or constant in diamagnetism.
• The sign of magnetic susceptibility is negative (-).
• The value of the magnetic moment is small.
• The direction of magnetization opposes the applied magnetic field's direction.
• At room temperature, copper, silver, silicon, and alumina are diamagnetic materials.

Para-magnetism

The para-magnetism is a slightly stronger type of magnetism as compared to diamagnetism. Para-magnetism is a positive magnetic effect because the magnetic dipoles are in the same direction as the magnetic field. When the temperature reduces, the para-magnetic effect increase because thermal disturbance sets up the direction of magnetic dipoles.

Below listed are some essential points related to para-magnetism.

• The magnitude of magnetic susceptibility is small or constant in diamagnetism.
• The sign of magnetic susceptibility is positive (+).
• Calcium, titanium, aluminum, and alloys of copper are para-magnetic materials.
• The paramagnetic effect will be lost if the applied magnetic field is removed.
• Alkali metals, earth elements, and transition metals are some examples.

The illustration of para-magnetic ordering is as follows:

Ferromagnetism

The ferromagnetic materials provide effective magnetic moments and do not rely on external magnetic field. In ferromagnetism, unpaired dipoles are formed because of the empty energy levels of atoms. In order to create permanent magnets, ferromagnetism property is utilized along with various alloys of neodymium and other elements.

Below listed are some important points related to ferromagnetism.

• The magnitude of magnetic susceptibility is a large or function of magnetic field strength in ferromagnetism.
• The sign of magnetic susceptibility is positive (+).
• Iron, cobalt, nickel, and gadolinium are ferromagnetic materials.
• Materials exhibiting ferromagnetism properties are transition metals and rare earth materials.

The illustration of ferromagnetic ordering is as follows:

Ferrimagnetism

Ferrimagnetism is described as the magnetic property that contains several magnetic moments but in opposite directions. In ferrimagnetic material, the magnetic moments are uneven, so spontaneous magnetization is possible. The structure of ferrimagnetic materials is quite similar to the crystal structure of iron oxides.

Below listed are some essential points related to ferrimagnetism.

• The magnitude of magnetic susceptibility is large.
• The sign of magnetic susceptibility is positive (+).
• Yttrium iron garnet (YIG), Nickle ferrite, and Barium ferrite are some examples of ferrimagnetic materials.
• Materials exhibiting ferrimagnetism properties are ceramic materials, ferrites, and chromite.

The illustration of ferrimagnetic ordering is as follows:

Anti-ferromagnetism

The magnetic dipole lines in anti-ferromagnetic materials oppose the orientation of a magnetic field, which produces 0 magnetizations. The anti-ferromagnetic materials achieve the highest susceptibility at some critical temperatures (Neel temperature). These are a subclass of ferromagnets, but they can be converted into para-magnetic by raising the temperature above a critical temperature.

Below listed are some important points related to anti-ferromagnetism.

• The magnitude of magnetic susceptibility is small or constant in anti-ferromagnetism.
• The sign of magnetic susceptibility is positive (+).
• Manganese, chromium, and alloys like iron manganese are anti-ferromagnetic materials.
• Anti-ferromagnetism property is shown by manganese oxide and salts of transition elements.

The illustration of antiferromagnetic ordering is as follows:

Hysteresis curve

The below schematic diagram is the hysteresis curve:

Some of the important points of the hysteresis curve are discussed below.

• In the curve, $B_r$ represents remanent induction, $H_C$ depicts coercivity, B is a magnetic field, and H is magnetic field intensity.
• When the magnetic saturation is achieved, the field will initiate to reduce until it reaches zero, resulting in residual magnetization called remanence.
• Hysteresis refers to the effect of retardation by material.
• In order to bring the magnetization to zero, the magnetic field strength is required, and it must be applied anti-parallel to the original magnetic field.

Common Mistakes

• Students commit mistakes while differentiating between ferromagnetism, anti-ferromagnetism, and ferrimagnetism. Actually, anti-ferromagnetism and ferrimagnetism are sub-parts of ferromagnetism.
• One of the significant confusion is between hard magnets and soft magnets related to hysteresis losses. The hysteresis losses in hard magnets are more in comparison to soft magnets.
• A misconception about the susceptibility of diamagnetic materials is that it does get affected by the changing the temperature. In actuality, susceptibility doesn't rely on temperature.

Context and Application

The topic magnetic properties of materials is very much significant in the several professional exams and courses for undergraduate, Diploma level, graduate, postgraduate. For example:

• Bachelors of Science in Physics
• Bachelors of Technology in Mechanical Engineering
• Bachelors of Technology in Civil Engineering
• Masters of Technology in Mechanical Engineering
• Doctor of Philosophy in Mechanical Engineering
• Diploma in Mechanical Engineering

Related concepts

• Magnetic properties of bar magnet
• Physical properties of material
• ferromagnetic materials
• Flux density and relative permeability
• Magnetic circuit
• Magnetic domains
• Magnetic flux density
• Magnetostriction
• Non magnetic properties

Practice problems

Q1. Which of the following material belongs to ferrimagnetic materials?

a. Alkali metals

b. Alkali non-metals

c. Ferrites

d. None of these

Correct answer: (c)

Q2. Identify the correct SI unit of magnetic field intensity?

a. Tesla

b. Weber per meter

c. Tesla per meter

d. Ampere per meter

Correct answer: (d)

Q3. Which of the following options is the correct source of magnetism?

a. Dipoles

b. Motion of charged particles

c. Magnetic domain

d. Electric field

Correct answer: (b)

Q4. In the coating of magnetic tapes which material is widely used?

a. Cobalt

b. Electromagnets

c. Ceramics

d. Alkali metals

Correct answer: (c)

Q5. Choose the correct option which represents the unit of magnetic flux density.

a. Weber per meter

b. Kilogram per meter cubed

c. Tesla

d. None of these

Correct answer: (c)