Advertisements
Advertisements
Question
What happens to a ferromagnetic material when its temperature increases above curie temperature?
Advertisements
Solution
A ferromagnetic material is made up of small regions known as domains. The atomic magnetic moments of nearest-neighbour atoms interact strongly within each domain via exchange interaction, a quantum mechanical phenomenon, and align parallel to each other even in the absence of an external magnetic field. As a result, a domain is spontaneously magnetised to saturation.
Only up to a specific temperature does the material keep its domain structure. When heated, the increased thermal agitation opposes spontaneous domain magnetization. Finally, at a critical temperature known as the Curie point or Curie temperature, thermal agitation overcomes the exchange forces and maintains the atomic magnetic moments randomly oriented. As a result, the material becomes paramagnetic above the Curie point. The ferromagnetic to paramagnetic transition is a transition from order to disorder. The material becomes ferromagnetic again when cooled below the Curie point.
RELATED QUESTIONS
Distinguish between ‘paramagnetic’ and ‘ferromagnetic’ substances.
Which of the following substances is ductile?
Show diagrammatically the behaviour of magnetic field lines in the presence of (i) paramagnetic and (ii) diamagnetic substances. How does one explain this distinguishing feature?
Distinguish between diamagnetic and paramagnetic substances.
The magnetic susceptibility of annealed iron at saturation is 4224. Find the permeability of
annealed iron at saturation. (μ0 = 4Π × 10−7 SI unit)
Explain Curie’s law for a paramagnetic substance.
Which of the following substances are diamagnetic?
Bi, Al, Na, Cu, Ca and Ni
The relative magnetic permeability of a magnetic material is 800. Identify the nature of magnetic material and state its two properties.
Draw magnetic field line when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field line due to the substances?
Choose the correct option:
A rectangular magnet suspended freely has a period of oscillation equal to T. Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely. Its period of oscillation is T′, the ratio of T′/T is ______.
A paramagnetic gas has 2.0 × 1026 atoms/m with atomic magnetic dipole moment of 1.5 × 10−23 A m2 each. The gas is at 27°C.
- Find the maximum magnetization intensity of this sample.
- If the gas in this problem is kept in a uniform magnetic field of 3 T, is it possible to achieve saturation magnetization? Why?
The susceptibility of a paramagnetic material is χ at 27° C. At what temperature its susceptibility be χ/3?
A rod of magnetic material of cross-section 0.25 cm2 is placed in a magnetizing field of intensity 4000 A/m-1. The magnetic flux passing through the rod is 25 × 10-6 Wb. Find out
(a) relative permeability
(b) magnetic susceptibility and
(c) magnetisation of the rod.
Two identical bar magnets each of magnetic moment M, separated by some distance are kept perpendicular to each other. The magnetic induction at a point at the same distance d from the centre of magnets, is (µ0 = permeability of free space)
A domain in a ferromagnetic substance is in the form of a cube of side 1 µm. If it contains 8 × 1010 atoms and each atomic dipole has a dipole moment of 9 × 10-24 Am2 then the magnetisation of the domain is ______.
For a paramagnetic substance, the magnetic susceptibility is ______.
The susceptibility of a magnetic material is positive and small. The material is ______.
Relative permittivity and permeability of a material are `epsilon_"r"` and `µ_"r"` respectively. Which of the following values of these quantities are allowed for a diamagnetic material?
The magnetic property of magnetic substance is associated with ____________.
Above the curie temperature the susceptibility of ferromagnetic substance varies ____________.
A small quantity of paramagnetic liquid is taken in a watch - glass and kept on two dissimilar magnetic poles. The liquid ____________.
Which graph shows the variation of magnetic susceptibility (`chi`) with magnetizing field (H) for a paramagnetic substance?
Why is diamagnetism, in contrast, almost independent of temperature?
Would the maximum possible magnetisation of a paramagnetic sample be of the same order of magnitude as the magnetisation of a ferromagnet?
Explain qualitatively on the basis of domain picture the irreversibility in the magnetisation curve of a ferromagnet.
A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnetic field B in the core for a magnetising current of 1.2 A?
The coercivity of a small magnet where the ferromagnet gets demagnetized is 3 × 103 Am–1. The current required to be passed in a solenoid of length 10 cm and number of turns 100, so that the magnet gets demagnetized when inside the solenoid, is ______.
The magnetic susceptibility is negative for ______.
Metals getting magnetised by orientation of atomic magnetic moments in external magnetic field are called ______.
Earth's magnetic field analyses has a horizontal component except at:-
If a charged particle at rest experience no electromagnetic force
The universal property of all substances is ______.
S is the surface of a lump of magnetic material.
- Lines of B are necessarily continuous across S.
- Some lines of B must be discontinuous across S.
- Lines of H are necessarily continuous across S.
- Lines of H cannot all be continuous across S.
Essential difference between electrostatic shielding by a conducting shell and magnetostatic shielding is due to ______.
- electrostatic field lines can end on charges and conductors have free charges.
- lines of B can also end but conductors cannot end them.
- lines of B cannot end on any material and perfect shielding is not possible.
- shells of high permeability materials can be used to divert lines of B from the interior region.
Explain quantitatively the order of magnitude difference between the diamagnetic susceptibility of N2 (~5 × 10–9) (at STP) and Cu (~10–5).
If the magnetizing field on a ferromagnetic material is increased, its permeability ______.
Which of the following has a permeability less than that of free space?
Which of the following cannot modify an external magnetic field as shown in the figure?
The relative magnetic permeability of a substance X is slightly less than unity and that of substance Y is slightly more than unity, then ______.
What is magnetic hysterisis?
State the dimensions of magnetization.
Magnetic susceptibility of a diamagnetic substance ______.
Match List-I with List-II.
| List-I (Material) | List-II (Susceptibility) | ||
| A. | Diamagnetic | I. | χ = 0 |
| B. | Ferromagnetic | II. | 0 > χ ≥ −1 |
| C. | Paramagnetic | III. | χ >> 1 |
| D. | Non-magnetic | IV. | 0 < χ < ε |
Choose the correct answer from the options given below:
