High-field cantilever magnetometry as a tool for the determination of the magnetocrystalline anisotropy of single crystals

Abstract

Cantilever torque magnetometry is utilized widely in physics and material science for the determination of magnetic properties of thin films and semiconductors. Here, we report on its first application in rock magnetism, namely the determination of K 1 and K 2 of single crystal octahedra of natural magnetite. The design of cantilever magnetometers allows optimization for the specific research question at hand. For the present study, a cantilever magnetometer was used that enables measurement of samples with a volume up to 64 mm 3. It can be inserted into an electromagnet with a maximum field of 2 T. The cantilever spring is suitable for torque values ranging from 7.5 × 10 − 7 N·m to 5 × 10 − 6 N·m. The torque is detected capacitively; the measured capacitance is converted into torque by using a calibrated feedback coil. The magnetometer allows in-situ rotation of the sample in both directions and is, therefore, also suitable to analyze rotational hysteresis effects. The evaluation of the magnetite anisotropy constants involved Fourier analysis of the torque signal on the magnetite crystals' (001) and (110) planes. The absolute anisotropy constant has been computed using the extrapolation-to-infinite-field method. The value of K 1 at room temperature is determined at − 1.28 × 10 4 [J m − 3] (± 0.13, i.e. 10%) and that of K 2 at − 2.8 × 10 3 [J m − 3] (± 0.1, i.e. 2%). These values concur with earlier determinations that could not provide an instrumental error, in contrast with this work. The cantilever magnetometer performs four times faster than other torque magnetometers used for rock magnetic studies. This makes the instrument also suitable for magnetic fabric analysis.