AC magnetic measurements with a self-oscillating <i>LC</i> circuit and its application to university education

Understanding the magnetic properties of matter plays a key role in materials physics. However, university education on fundamental magnetism is often limited to a theoretical survey because of the lack of appropriate apparatus that can be applied for laboratory courses at the undergraduate level. In this work, we introduce an AC magnetometer based on the Colpitts self-oscillator with an inductor coil as a probe. We show that this type of self-oscillator can be adopted in a typical university laboratory course to learn the principles of magnetic measurement and to understand the fundamental magnetism of matter. We demonstrate the exceptional stability of the circuit with a working frequency range of 10 kHz–10 MHz and excellent performance to detect a diamagnetic signal from a superconductor at cryogenic temperatures.