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

TL;DR

This paper presents a simple AC magnetometer using a self-oscillating LC circuit suitable for undergraduate labs, enabling practical learning of magnetic properties and demonstrating high stability and sensitivity, including detection of superconducting diamagnetism.

Contribution

Introduction of an accessible AC magnetometer based on a Colpitts oscillator for educational purposes, bridging the gap between theory and practical magnetism experiments.

Findings

Stable operation over 10 kHz to 10 MHz frequency range

Effective detection of superconducting diamagnetic signals

Suitable for undergraduate laboratory courses

Abstract

Understanding the magnetic properties of matter plays a key role in materials physics. However, university education on fundamental magnetism is 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 to 10 MHz and excellent performance to detect the diamagnetic signal from a superconductor at cryogenic temperature.