Theory-of-Ferromagnet

Domain Theory of Ferromagnetism

Ferromagnetic Substances

The substances in which atoms cooperate with each other in such a way that they exhibit a strong magnetic effect and are strongly attracted by magnetic fields are called ferromagnetic substances. For example, Nickle, Cobalt, Alnico, etc.

Domains:

The small magnetized regions in a ferromagnetic substance are called domains.

In 1907 A.D., Weiss proposed domain theory to describe the ferromagnetic phenomenon in materials. According to this theory, a solitary crystal of ferromagnetic strong consists of a lot of tiny areas, and each region is automatically allured to saturation level called a domain. The dimension of the domain might vary from 10 − 6 to the entire volume of the crystal.

The spin magnetic moments of whole atoms restricted within a domain are oriented in a certain direction. The directions of magnetizations of various domains of the sampling are random to make sure that the resultant of magnetizations of all domains in the material is zero in the absence of an applied magnetic field.

Domains Ferromagnetism

These domains arise since the energy is not minimum when a large sampling has a uniform magnetization. When the external magnetic field is applied, these domains align in the direction of the applied field and the specimen shows magnetization and also becomes a magnet.

In the presence of the weak external field, the magnetization in the material takes place mostly by the process of domain growing, however, in the strong magnetic field the material is magnetized primarily by the procedure of domain placement.

When the field is removed, the domains orientation does not recover its initial positions, and also thus the product is not completely demagnetized, yet some residual magnetism remains in it.

Domains in Soft Magnetic Material

In soft materials, domains can easily be oriented on applying an external magnetic field and on removing the field, also return to the original position. Iron is the best example.

Further Reading:  Law of Conservation of Momentum
Domains in Hard Magnetic Material

In hard substances, domains cannot be easily oriented on applying the external magnetic field. Steel is a good example of hard magnetic material. The domain in the steel can be aligned by a very strong external magnetic field, but once oriented, retain their positions.

Effect of Temperature

Thermal vibrations tend to disturb the orderliness of the domains. Ferromagnetic substances preserve the orderliness at an ordinary temperature which begins to lose their orderliness due to an increase in temperature, this process starts at a certain temperature.

Curie Temperature

The temperature above which a ferromagnetic substance becomes paramagnetic is called curie temperature. The Curie temperature for iron is about 750 ᵒC.

MCQs

  • 1. What are ferromagnetic substances characterized by?
    • A) Weak magnetic effect
    • B) No response to magnetic fields
    • C) Strong magnetic effect
    • D) Resistance to temperature changes
    • Answer: C) Strong magnetic effect
  • 2. What are the small magnetized regions in a ferromagnetic substance called?
    • A) Domains
    • B) Particles
    • C) Nuclei
    • D) Electrons
    • Answer: A) Domains
  • 3. Who proposed the domain theory to describe ferromagnetic phenomenon?
    • A) Albert Einstein
    • B) Max Planck
    • C) Pierre Curie
    • D) Pierre-Ernest Weiss
    • Answer: D) Pierre-Ernest Weiss
  • 4. What happens to the domains of a ferromagnetic material when an external magnetic field is applied?
    • A) They disappear
    • B) They align in the direction of the field
    • C) They shrink in size
    • D) They rotate randomly
    • Answer: B) They align in the direction of the field
  • 5. Which type of magnetic material exhibits easy reorientation of domains upon the removal of an external magnetic field?
    • A) Hard magnetic material
    • B) Soft magnetic material
    • C) Ferromagnetic material
    • D) Paramagnetic material
    • Answer: B) Soft magnetic material
  • 6. What happens to the domains in hard magnetic materials when subjected to a strong external magnetic field?
    • A) They disappear
    • B) They align permanently
    • C) They become randomly oriented
    • D) They shrink in size
    • Answer: B) They align permanently
  • 7. At what temperature do ferromagnetic substances begin to lose their orderliness?
    • A) Absolute zero
    • B) 100°C
    • C) The Curie temperature
    • D) 750°C
    • Answer: C) The Curie temperature
  • 8. What effect do thermal vibrations have on the orderliness of domains in ferromagnetic substances?
    • A) They enhance orderliness
    • B) They have no effect
    • C) They cause disorderliness
    • D) They induce a paramagnetic effect
    • Answer: C) They cause disorderliness
  • 9. Which substance has a Curie temperature of approximately 750°C?
    • A) Cobalt
    • B) Iron
    • C) Nickel
    • D) Alnico
    • Answer: B) Iron
  • 10. What is the primary characteristic of ferromagnetic substances?
    • A) Weak magnetization
    • B) Random domain orientation
    • C) Strong attraction by magnetic fields
    • D) Low resistance to temperature changes
    • Answer: C) Strong attraction by magnetic fields
  • 11. What is the primary characteristic of domains in ferromagnetic substances?
    • A) They are aligned in the absence of an external field
    • B) They disappear in the presence of an external field
    • C) They are unaffected by thermal vibrations
    • D) They are randomly oriented
    • Answer: A) They are aligned in the absence of an external field
  • 12. What happens to the domains of a ferromagnetic material when subjected to a weak external magnetic field?
    • A) They disappear
    • B) They shrink in size
    • C) They align partially
    • D) They rotate randomly
    • Answer: C) They align partially
  • 13. Which type of magnetic material retains residual magnetism after the removal of an external magnetic field?
    • A) Diamagnetic material
    • B) Paramagnetic material
    • C) Soft magnetic material
    • D) Hard magnetic material
    • Answer: D) Hard magnetic material
  • 14. What is the primary factor determining the behavior of domains in ferromagnetic substances?
    • A) Mass of the substance
    • B) Shape of the substance
    • C) Atomic structure of the substance
    • D) Temperature of the substance
    • Answer: D) Temperature of the substance
  • 15. What is the primary function of domains in ferromagnetic substances?
    • A) To resist external magnetic fields
    • B) To align randomly
    • C) To enhance thermal conductivity
    • D) To minimize energy by magnetization
    • Answer: D) To minimize energy by magnetization
Further Reading:  Modulation: Definition, Types, & Importance of Modulation

 

Frequently Asked Questions (FAQs) about Domain Theory of Ferromagnetism:

  1. What are ferromagnetic substances, and how are they characterized?
    • Ferromagnetic substances are materials that exhibit a strong magnetic effect and are strongly attracted by magnetic fields. They are characterized by their ability to become magnetized in the presence of an external magnetic field.
  2. What are domains, and how do they contribute to ferromagnetism?
    • Domains are small magnetized regions within a ferromagnetic material where the magnetic moments of atoms are aligned in a certain direction. These domains contribute to ferromagnetism by collectively aligning in the direction of an external magnetic field, resulting in magnetization of the material.
  3. Who proposed the domain theory of ferromagnetism, and when?
    • The domain theory of ferromagnetism was proposed by Pierre-Ernest Weiss in 1907. This theory describes how ferromagnetic materials consist of numerous small domains, each with its own magnetic orientation.
  4. What happens to domains in the presence of an external magnetic field?
    • When an external magnetic field is applied, the domains within a ferromagnetic material align themselves in the direction of the field, resulting in overall magnetization of the material.
  5. How do soft magnetic materials differ from hard magnetic materials in terms of domain orientation?
    • In soft magnetic materials, domains can easily be oriented in the direction of an external magnetic field and return to their original positions upon field removal. In contrast, hard magnetic materials have domains that resist reorientation and retain their alignment even after the external field is removed.
  6. What effect does temperature have on ferromagnetic materials and their domains?
    • Temperature can disrupt the orderliness of domains in ferromagnetic materials due to thermal vibrations. As temperature increases, ferromagnetic substances begin to lose their orderliness, leading to reduced magnetization.
  7. What is the Curie temperature, and how does it relate to ferromagnetism?
    • The Curie temperature is the temperature above which a ferromagnetic substance becomes paramagnetic, losing its ferromagnetic properties. For example, iron has a Curie temperature of about 750°C, beyond which it becomes paramagnetic.
Further Reading:  Galvanometer - Construction, Working, and Applications of Galvanometer