Physics for Information Science: Unit III: Magnetic Properties of Materials
Magnetic Moment of a Ferrite Molecule
Bohr Magneton
The orbital magnetic moment and the spin magnetic moment of an electron in an atom can be expressed in terms of smallest atomic unit of magnetic moment called Bohr magneton.
MAGNETIC
MOMENT OF A FERRITE MOLECULE
Bohr Magneton
The
orbital magnetic moment and the spin magnetic moment of an electron in an atom
can be expressed in terms of smallest atomic unit of magnetic moment called
Bohr magneton.
1
Bohr Magneton = eћ/2m ⇒
μB⇒ 9.27 × 10-24
Am2
Saturation
magnetization of a ferrite molecule can be calculated from the number of
unpaired spins of Fe2+ and Fe3+
Let
us consider an example of Ferrite say Ferrous ferrite having the formula
Fe2+
Fe3+ O4 for calculating the magnetic moment.
In
Ferrous ferrite we have two types of ions viz. Fe2+ and Fe3+
(i)
Here Fe2+ ions has six electrons in 3d shell. Out of 6 electrons two
electrons are paired with each other and hence left with 4 unpaired electrons
as shown in fig. 3.35 (a).
The
Fe2+ gives rise to 4 Bohr magneton.
(ii)
Fe3+ ions has five electrons in 3d shell and hence all these 5 are
unpaired electrons as shown in fig. 3.35 (b)
The
Fe3+ gives rise to 5 Bohr magneton.
Since
we have two Fe3+, totally, the Fe2+ gives rise to 2×5 =
10 Bohr magnetons.
Total
magnetization of Fe2++ Fe3+ = 4+ 10 = 14 Bohr magneton.
(i.e.,) 14 μB.
Theoretically
we get 14 μB but experimetally the total magnetic moment got is only 4.08 μB.
The reason for this discrepancy is as follows:
If
all the spins are aligned parallel then we will get the total magnetisation as
14μB. But in ferrites half of the magnetic spins of Fe23+
ions are parallel to one direction and the remaining half of Fe23+
ions are parallel in opposite direction as shown in Fig. 3.35 (c) and hence
they cancel each other. Therefore, the net magnetic moment is only due to Fe2+
ions alone (i.e.,) hence we get the total magnetisation as 4uB, which has a
good agreement with the experiment value i:e., 4.08 μB.
Similarly
we can calculate the total magnetic moment of any ferrite molecule with respect
to the number of unpaired electrons in the divalent metal ions.
Physics for Information Science: Unit III: Magnetic Properties of Materials : Tag: : Bohr Magneton - Magnetic Moment of a Ferrite Molecule
Physics for Information Science: Unit III: Magnetic Properties of Materials
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