# Determination of Magnetic Susceptibility by Faraday's Method

In this method, a very small volume of the magnetic sample is packed in a quartz ampoule and suspended from a sensitive balance is placed in a region of fairly strong magnetic field. In this situation, the product H(dH/dx), where dH/dx is the field gradient, is constant over the volume of the sample. The whole set-up is housed in an enclosure which can be flushed with nitrogen or helium. The ampoule has an internal diameter of ~1 mm and the balance used is a quartz fibre torsion balance. The region of uniform H(dH/dx) is determined by placing a small volume of a calibrant of mass m and of known magnetic susceptibility at different point along the field. The value of H(dH/dx) is obtained from the relation:

dF = mχ_{g}H(dH/dx) -----Equation:1

or, H(dH/dx) = dF/mχ_{g} -----Equation:2

Where dF is the force experienced by the sample due to the magnetic field and is measured using a cathetometer. With the help of the measurements first with calibrant and then with the sample, we can write the relation-

χ_{s} = χ_{c}d_{s}/d_{c} m_{c}/m_{s} -----Equation:3

Here χ_{s} and χ_{c} are the gram susceptibilities of the sample and calibrant, m_{s} m_{c} are the respective masses and d_{s} and d_{c} are the respective deflections at constant H(dH/dx).

In the above equation:3, all the parameters on the right hand side are known, and hence gram susceptibility χ_{s} of sample can be calculated easily.

## Advantages of Faraday's Method

✍︎ It requires small amount of sample compared to Goy method.

✍︎ Good sensitivity is additional advantage of this technique.

## Disadvantages of Faraday's Method

✍︎ Delicate equipment, fragile suspension devices, constructional difficulty, inconvenient solution measurements and small weight changes are some of the disadvantages of this technique.

Source: R.C.Maurya Inorganic Chemistry

### Determination of Magnetic Susceptibility by Gouy Method

### Determination of Magnetic Susceptibility by NMR Method

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