The enhancement technique is basically the measurement of the ac susceptibility in the presence of a second biasing field ͑pulsed dc or ac͒. This useful technique will be adopted for modification of the ac susceptometer. A proportional integral derivative controller, commonly used in temperature controllers, and a voltage to current converter with variable gain and sign, play special roles in this measurement technique. A second sinusoidal ac field ͑in addition to the measuring field͒ is used

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... the biasing field. The technique is a very useful one to obtain quantitative information about domain wall pinning, domain contribution to magnetization, etc. in the magnetic systems.