Thermomagnetic Analysis

Abstract

Abstract The most common method of measuring magnetic ordering temperatures is through the use of thermomagnetic analysis techniques. These techniques rely on methods previously described. In essence, thermomagnetic analysis involves sensitive measurement of a magnetic dipole moment in a zero or an applied field as a function of temperature. The components of the system therefore include an appropriate magnetometer. Superconducting quantum interference device (SQUID), vibrating‐sample, and Faraday‐balance magnetometers are commonly used in the field. Large axial fields can be applied using a superconducting solenoid; smaller axial fields can be applied using wound‐metal solenoids. Transverse fields can be applied using split‐coil superconducting solenoids or electromagnets. Measurement of the temperature dependence of magnetic properties requires careful design of the sample chamber and methods for heating and cooling, as well as accurate thermometry for monitoring temperature. Measurement of magnetic transitions of the types described in the other articles may entail the measurement of magnetic properties at temperatures ranging from cryogenic to ∼1100°C (the T c of elemental Co). The data illustrated in the figures in this article, probing magnetic phase transitions, were taken using either a SQUID magnetometer or a vibrating sample magnetometer. An abbreviated discussion of these systems is given. The principle of operation of a vibrating sample magnetometer (VSM) is based on placing a magnetic sample in a uniform magnetic field. The sample dipole moment is made to undergo a periodic sinusoidal motion at a fixed frequency using a transducer drive head to vibrate a sample rod. The term SQUID is an acronym for superconducting quantum interference device. The principles of operation of a typical SQUID magnetometer system for measuring a sample are briefly summarized.