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Ferromagnetism is the phenomenon in which a substance, such as iron, becomes magnetized and remains magnetized in an external magnetic field for that period.
- It is the process through which some materials can form permanent magnets.
- Ferromagnetic materials are common metals that are strongly attracted to magnets due to their high magnetic permeability.
- These materials can be permanently magnetized if a strong magnetic field is provided.
- Metal ions of ferromagnetic materials, when grouped in small regions are known as solid-state domains.
- Ferromagnetism is associated with elements like cobalt, iron, nickel, and some alloys containing one or more of these elements.
- The most important requirement for a material to be ferromagnetic is its ions and atoms should possess permanent magnetic moments.
Read More: Permanent Magnets Vs Electromagnets
| Table of Contents |
Key Terms: Magnetism, Ferromagnetism, Magnets, Magnetic Effect, Magnetic Field, Permanent Magnets, Antiferromagnetism, Hysteresis Loop, Retentivity, Coercivity
What is Ferromagnetism?
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Ferromagnetism is a physical mechanism where certain materials attract each other, for example, iron. Some important characteristic properties are as follows:
- When ferromagnetic materials are put in a magnetic field, all the domains get oriented in the direction of the magnetic field which creates a powerful magnetic effect.
- When we withdraw the magnetic field, then those materials become permanent magnets.
- Ferromagnetism is the strongest form of magnetism among all other forms.
- It is also responsible for the widespread occurrence of magnetism in magnets that we experience in our everyday life.
Read also:
| Important Topics Related to Ferromagnetism | ||
|---|---|---|
| Bar Magnet | Magnetization and Magnetic Intensity | Magnetic Declination |
| Biot Savart’s Law | Earth’s Magnetic Field | Magnetic Pole |
| Paramagnetism | Magnetic Properties of Materials | Curie Constant |
What are Ferromagnetic Materials?
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The ferromagnetic materials and compounds that show spontaneous magnetization are tabulated below:
| Spontaneous magnetization (Curie temperature) | Ferromagnetic materials |
|---|---|
| 1043 | Fe |
| 1388 | Co |
| 587 | MnSb |
| 318 | MnAs |
| 627 | Ni |
| 292 | Gd |
| 88 | Dy |
Curie Temperature
The ferromagnetic property of materials is highly temperature-dependent.
- At high temperatures, the ferromagnetic materials become paramagnetic.
- The temperature at which this transition occurs is called as Curie Temperature.
- It is denoted by Tc. At Curie temperature, the magnetization saturation is neutral or zero.
- Curie Temperature is an important diagnostic property used to differentiate one mineral from another.
Examples of Ferromagnetism
- Rare earth magnets are also classified as ferromagnetic materials besides metallic alloys.
- Magnetite is a ferromagnetic material that is formed by the oxidation of iron into an oxide.
- A refrigerator magnet is another common example that is used to hold notes on a refrigerator door.
- Ferromagnets are also used is generators, hard drives, telephonic devices, and electronic motors.
Antiferromagnetism
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Antiferromagnetism is a type of magnetism in solids in which adjacent ions that act like tiny magnets spontaneously align themselves at relatively low temperatures into the opposite, antiparallel arrangements throughout the material in such a way that it exhibits almost no gross external magnetism.
Below is the table of Neel temperature of the antiferromagnetic substance.
| Temperature (K) | Antiferromagnetic Substance |
|---|---|
| 116 | Manganese Oxide |
| 61 | Manganese Fluoride |
| 311 | Chromium |
| 198 | Ferrous Oxide |
Read More: Lorentz Forces
Properties of Ferromagnetism
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Listed below are some important properties of ferromagnetic materials:
- A ferromagnetic material rod can quickly regain itself in the direction of the magnetic field.
- Ferromagnetic substances show permanent magnetism even in the absence of a magnetic field.
- When ferromagnetic substances are heated at high temperatures, the ferromagnetic substances get to transform into paramagnetic substances.
- Ferromagnetic materials have Permeability greater than 1.
- The mechanism of ferromagnetism is absent in gases and liquids.
- The intensity of magnetization (M), magnetic susceptibility (χm), relative permeability (µr), and magnetic flux density (B) of ferromagnetic material will be positive always.
Χm = M/H
µr = 1 + Χm
B = µ0(H + M)
Where
- µ0 → Magnetic permittivity of the free space.
- H → Applied magnetic field strength.
Hysteresis
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When the external magnetic field is eliminated, the ferromagnetic material does not get demagnetized fully.
- A magnetic field that is opposite in the direction is applied to bring it to zero.
- This property of retaining the magnetism even after removal of the magnetic field is called hysteresis.
- The hysteresis loop is a plot between the magnetic flux density which measures the magnetization, and the applied magnetic field intensity.
The hysteresis loop is given as follows:
Retentivity is the magnetic flux density that remains when the magnetization is reduced to zero. Coercivity is the strength that is applied to completely demagnetize the material.
Causes of Ferromagnetism
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Listed below are the primary causes for ferromagnetic property observed in materials:
- Ferromagnetism arises due to the interaction between the alignment of permanent dipoles in atoms and the neighboring atomic dipoles.
- Domains are oriented in the same direction in a ferromagnetic substance without the presence of an external magnetic field that exhibits a net magnetic moment.
- The neighboring domain magnetic moments are geared in opposite directions. So they cancel out each other and hence, the material's net magnetic moment is zero.
- Those domains align themselves in the direction of the external magnetic field.
- The material is strongly magnetized in this way in a parallel direction to the magnetizing field.
Read More: Magnetism & Gauss’s Law
Ferromagnetism: Advantages & Disadvantages
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Let us briefly look at the advantages and disadvantages of ferromagnetic materials.
Advantages
- Economical
- High operational temperatures
- Stable
- High electrical resistance margin
- High Rate of Permeability
Disadvantages
- Easily influenced by magnetic field
- Magnetization becomes unstable in the presence of weak magnetic field
Applications of Ferromagnetism
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There are numerous applications of Ferromagnetic materials for magnetic storage, electrical, and electromechanical equipment. Some of these are listed below:
- Permanent Magnets: Ferromagnetic materials are often used for making permanent magnets because their magnetization lasts longer.
- Transformer Core: Ferromagnetic materials are suitable for making the transformer core and choke which is subjected to very rapid cyclical changes because of its strong magnetic induction.
- Magnetic Tapes and Memory Store: It will serve the purpose of a memory storage unit as magnetization of a magnet depends on the magnetization field and the magnetization cycle it has undergone. Therefore, the magnetization cycles that it has undergone are recorded as the specimen's magnetization value.
Read More: The Bar Magnet
Things to Remember
- Ferromagnetism refers to a physical phenomenon in which certain materials like iron strongly attract each other.
- Ferromagnets occur in rare earth materials and gadolinium.
- Ferromagnetic substances show permanent magnetism even in the absence of a magnetic field.
- The main cause of ferromagnetism arises due to the interaction between the alignment of permanent dipoles in atoms and the neighboring atomic dipoles.
- There are numerous applications of Ferromagnetic materials for magnetic storage, electrical, and electromechanical equipment.
- Magnetite is a ferromagnetic material that is formed by the oxidation of iron into an oxide.
- Hysteresis Loop represents the magnetic nature of the ferromagnetic material when it is demagnetized.
Read More:
| Important Links Related to Chapter 5 : Magnetism and Matter | ||
|---|---|---|
| Magnetic Properties | Moving Charges & Magnetism | Einstein Field Equation |
| Magnetic Spectrum | Current Coil | Magnetometer |
| Magnetic Levitation Project | Curie Weiss Law | Bar Magnet as an Equivalent Solenoid |
| Inductance Formula | Faraday's Law | Moving Charges and Magnetism Important Questions |
Previous Year Questions
- Two parallel wires carry electric current in same direction. The wires..? [ KCET 1996]
- Resistance of an ideal ammeter is……? [ KCET 1996]
- If a current of 0.1 A is passed through the coil, what is the couple acting?[CBSE Class 12 ]
- The acceleration of the falling magnet is…..? [NEET]
- A bar magnet is equivalent to ........…?[KCET 2004]
- A metal ring is held horizontally and bar magnet is dropped through..? [NEET]
- The total charge, induced in a conducting loop when it is moved in magnetic field depend on? [NEET 1992]
- If a charge particle enters perpendicular in the uniform magnetic field, then……? [JIPMER 2016]
- Who invented the cyclotron?
- The magnetic susceptibility is negative for …….? [NEET 2016]
- Which of the following is a paramagnetic group? [JIPMER 2010]
- Nickel shows ferromagnetic property at room temperature?
- Two short bar magnets of length 1cm each have magnetic moments …? [JEE Main 2013]
- If a magnetic dipole of moment M situated in the direction of …?
- If the susceptibility of dia, para and ferro magnetic materials are …..?
- Materials suitable for permanent magnet, must have which of the following properties?
- At what temperature, the ferromagnetic substances become paramagnetic?
- a magnetic induction of strength at its centre is….?
- The ferromagnetic substance is converted into paramagnetic substances …? [JIPMER 1996]
- The relative permeability is represented by μr ……? [KCET 2001]
Sample Questions
Ques. Magnetic field lines are always nearly normal to the surface of a ferromagnet at every point. (This fact is analogous to the static electric field lines being normal to the surface of a conductor at every point.) Why? (2 marks)
Ans. It is because the permeability of those materials is greater than 1 so the field lines meet them normally.
μr >>1
Ques. Which metal should be used preferably to make permanent magnets? (2 marks)
Ans. Iron should be used to make permanent magnets as it is a ferromagnetic material.
Ques. What are ferromagnetic substances? (2 marks)
Ans. Ferromagnetic substances are those that can be permanently magnetized due to the existence of unpaired electrons, such as iron, cobalt, nickel, gadolinium, and CrO2.
Ques. What is ferromagnetism? (2 marks)
Ans. Ferromagnetism is a material characteristic that results in considerable magnetic permeability and, in many circumstances, significant magnetic coercivity, allowing the material to create a permanent magnet.
Ques. What are the examples of ferromagnetic materials? (2 marks)
Ans. Iron, cobalt, nickel, and other ferromagnetic elements are common examples. Furthermore, ferromagnetic materials include metallic alloys and rare earth magnets.
Ques. Is NaCl ferromagnetic? (1 mark)
Ans. NaCl is not ferromagnetic, it is diamagnetic.
Ques. What is meant by antiferromagnetism? (2 marks)
Ans. Antiferromagnetism is a type of magnetism in solids in which adjacent ions that act like tiny magnets spontaneously align themselves at relatively low temperatures into the opposite, antiparallel arrangements throughout the material in such a way that it exhibits almost no gross external magnetism.
Ques. What is the difference between ferromagnetism and antiferromagnetism? (2 marks)
Ans. The main difference between ferromagnetism and antiferromagnetism in the alignment of their magnetic moments. antiferromagnetic materials have antiparallel magnetic moments whereas Ferromagnetic materials have magnetic moments that align parallel to the applied magnetic field.
Ques. Name a few ferromagnetic materials. (2 marks)
Ans. These are some of the examples of ferromagnetic materials.
- Cobalt.
- Iron.
- Nickel.
- Gadolinium.
- Dysprosium.
- Permalloy.
- Awaruite.
- Wairakite.
Ques. How are ferromagnetic materials different from paramagnetic ones? (3 marks)
Ans. The main difference is in their alignment of magnetic moments.
Paramagnetic materials have a positive and small susceptibility to magnetic fields whereas Ferromagnetic materials have positive and large susceptibility to an external magnetic field. They can retain their magnetic properties after the removal of the external fields and exhibit a strong attraction to magnetic fields. Paramagnetic materials on the removal of the external field, lose their magnetism and therefore cannot be used to make permanent magnets.
Ques. What is Curie temperature? (3 marks)
Ans. A temperature over which the ferromagnetic material behaves as a paramagnetic material, is called curie temperature. This implies that if the temperature is rose above Curie temperature, ferromagnetic materials tend to lose their magnetic properties. Curie temperature is represented by TC.
Ethermal = kBT
Curie’s law is given by X =C/T
kB → Boltzmann constant
T → Temperature(Kelvin)
C → Curie Constant
Ques. What are the applications of ferromagnetism? (3 marks)
Ans. The applications of ferromagnetism are as follows:
- Permanent Magnets: Ferromagnetic materials are often used for making permanent magnets because their magnetization lasts longer.
- Transformer Core: Ferromagnetic materials are suitable for making the transformer core and choke which is subjected to very rapid cyclical changes because of its strong magnetic induction.
- Magnetic Tapes and Memory Store: It will serve the purpose of a memory storage unit as The magnetization of a magnet depends on the magnetization field and the magnetization cycle it has undergone. Therefore, the magnetization cycles that it has undergone are recorded as the specimen's magnetization value.
Ques. State the properties of ferromagnetism. (4 marks)
Ans. The properties of ferromagnetism are:
- A ferromagnetic material rod can quickly regain itself in the direction of the magnetic field.
- Ferromagnetic substances show permanent magnetism even in the absence of a magnetic field.
- When ferromagnetic substances are heated at high temperatures, the ferromagnetic substances get to transform into paramagnetic substances.
- ferromagnetic materials have Permeability greater than 1.
- The mechanism of ferromagnetism is absent in gases and liquids.
- The intensity of magnetization (M), magnetic susceptibility (χm), relative permeability (µr), and magnetic flux density (B) of ferromagnetic material will be positive always.
Ques. Explain the concept of the hysteresis loop. (4 marks)
Ans. The hysteresis loop is a loop that is formed by altering or changing the magnetizing force while measuring the material's magnetic flux simultaneously. It is formed When a ferromagnetic material is magnetized in one direction and then the removal of the imposed magnetizing field will not relax back to zero magnetization. The magnetic field in opposite direction needs to be null (zero).
Hysteresis is the property in which magnetization curve re-traceability is absent. It is a useful property as it can be used as a magnetic memory which is used in recording audiotapes and data is being stored through these on computer disks.
Ques. How are ferromagnetic,antiferromagnetic,paramagnetic and ferrimagnetic materials represented? (5 marks)
Ans. They are represented as below:
Ferromagnetic material
| ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ |
Anti-Ferromagnetic material
| ↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓ |
Ferrimagnetic material
| ↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓↑↓ |
Paramagnetic material
| ↑↓↑↑↓↑↑↓↑↑↓↑↑↓↑↑↓↑↑↓↑↑↓↑↑↓↑↑ |
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