Magnetometry

Abstract

AbstractAll materials possess a magnetic moment; techniques for measuring that bulk macroscopic property are defined here as magnetometry. This article reviews the most common techniques for measuring the total magnetic moments of small samples (volume ≤1 cm3and/or mass ≤1 g). Several factors contribute to the bulk magnetic moment of a sample. Essentially all materials show weak diamagnetism from filled electronic core states of the atoms. Metallic materials show an additional contribution to their diamagnetism from the orbital motion of the otherwise degenerate spin‐up and spin‐down conduction electrons as well as Pauli paramagnetism from splitting of the conduction bands. The largest contribution to the magnetic moment of materials comes from unpaired localized spins of elemental constituents.It is important for many reasons to know a material's magnetic moment, a thermodynamic quantity. For strongly magnetic materials, it is probably the most useful and important physical property, determining their utility in applications. For magnetically ordered systems, magnetic moment measurements provide information about spin structure, anisotropy (in the case of nonpolycrystalline samples), and phase transitions. For paramagnetic systems, the total moment at high fields or the temperature dependence of the magnetic susceptibility can yield a measure of the moment per chemical constituent or magnetic impurity concentration, whether introduced purposefully or as impurities. The temperature dependence of the moment yields information on interactions between the paramagnetic ions or with the lattice. Certain features of the electronic structure of metallic materials can be determined from magnetic susceptibility, such as the density of states at the Fermi surface. For superconductors, high field magnetization can provide information about the critical field and critical current density.This article is restricted to the centimeter‐gram‐second (cgs) system of units for the magnetic moment, which is given in electromagnetic units (emu), where 1 emu = 10−3A‐m2.There are two direct techniques for measuring the magnetic moment of materials: one utilizes the detection of a change in magnetic flux produced by a sample, and the other utilizes the detection of a change in the force experienced by a sample.