Physics for Information Science: Unit III: Magnetic Properties of Materials
Spontaneous and Saturation Magnetisation
The molecular magnets in the ferromagnetic material is aligned in such a way that, they exhibit a magnetisation even in the absence of an external magnetic field.
SPONTANEOUS AND
SATURATION MAGNETISATION
The
molecular magnets in the ferromagnetic material is aligned in such a way that,
they exhibit a magnetisation even in the absence of an external magnetic field.
This is called Spontaneous magnetisation.
i.e.,
We know
He
=H+Hi
Here
H = 0, He = Hi
He
= λI [Since Hi = λI]
where
I is spontaneous magnetisation.
Temperature dependence of Spontaneous magnetisation
When
the external field is zero.
He
= λI …...(1)
From
the Langevin theory, we can write intensity of the magnetisation I as
I
= Is L (α) ……(2)
where
Is is saturation magnetisation.
For
ferromagnetics 
(or) 
…….(3)
By
comparing equation (1) and (3), we get
………(4)
We
know Is = Nμ ……(5)
Dividing
equation (4) by (5), we have
(or) we can write the above equation as
A
graph is plotted between I/Is as a function of T/Ɵ as shown in Fig.
3.11.
From
this graph we infer that,
(i)
When temperature is low, Weiss field overpowers the thermal energy and it gives
rise to maximum magnetisation.
i.e.,
I/Is = 1
(ii) When the temperature increased thermal
energy increases which randomises more and more of the parallel spins and at
curie temperature (T = Ɵ), all the parallel alignment of spins vanishes giving
rise to zero value of spontaneous magnetisation and the material is to highly
susceptible to get the external field. Thus, the substance become paramagnetic.
Physics for Information Science: Unit III: Magnetic Properties of Materials : Tag: : - Spontaneous and Saturation Magnetisation
Physics for Information Science: Unit III: Magnetic Properties of Materials
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Physics for Information Science
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