When a cylindrical sample is placed coaxially in a periodically varying magnetic field the magnetisation in the sample also undergoes periodic variation. This variation is packed up by a coil placed coaxially with the sample.
For the uniform field H_a produced, the effective field H acting in the cylindrical sample will be
H = H_a-NM or H = H_a-NJ/μ₀ ————(1)
where M is magnetisation, N is normalised demagnetisation factor including 4π and J is the magnetic polarisation defined by
B = μ₀ H + J
with B = μH or μ₀ (H+M) as magnetic induction. The signal corresponding to the applied field, Ha can be written as
e1=C₁H_aH ————(2)
where C1 is a constant
Further the flux linked with pick coil of area AC due to sample of area A S will be
Φ = μ₀ A_C H + A_SJ
The signal l2 induced in the pick coil is proportional to dΦ/dt. This after integration gives
l₃ = C₃ Φ = C₃ μ₀ A_CH+C₃A_SJ ————(3)
Taking into consideration equation 1, 2 and 3 the electronic circuit is made to trace Hysteresis loop.