88 CHAPTER 9. MEASUREMENT TECHNIQUES
When we bring a sample having a magnetization M into the coil, we have
The corresponding flux change is
Combining Eqs. (9.3.1) and (9.3.2) leads to
This means that the output signal of the coil is proportional to the magnetization M but
independent of the magnetic field in which the size of M is to be determined.
In the VSM, the sample is subjected to a sinusoidal motion (frequency and the
corresponding voltage is induced in suitably located stationary pickup coils. The electrical
output signal of these latter coils has the samefrequency Its intensity is proportional to the
magnetic moment of the sample, the vibration amplitude, and the frequency A simplified
schematic representation of the VSM is given in Fig. 9.3.1. The sample to be measured
is centered in the region between the poles of a laboratory magnet, able to generate the
measuring field A thin vertical sample rod connects the sample holder with a transducer
assembly located above the magnet. The transducer converts a sinusoidal ac drive signal,
provided by an oscillator/amplifier circuit, into a sinusoidal vertical vibration of the sample
rod.The sample is thus subjected to a sinusoidal motion in the uniform magnetic field