Magnetic Measurements and Characterization

Abstract

IntroductionWhen characterizing the magnetic properties of iron oxides, whether they be geological or synthetic, there are four main factors that are of interest: (i) composition of the iron oxides; (ii) concentration in a bulk material; (iii) particle size distribution; and (iv) magnetic interaction between particles. These four factors are important because they govern the magnetic behavior that affects the usefulness of an iron oxide in any specific application. For example, composition can provide information about the provenance of the iron oxide minerals in a rock, sediment or soil, or the chemical stability of a synthesized nanoparticle. Particle size plays an important role in the magnetic properties of an iron oxide. Where some applications require superparamagnetic behavior, that is, only carries a high spontaneous magnetization in an applied field, others require that the material carry a stable remanent magnetization. Particle size is related to magnetic interaction between particles because interacting particles may behave collectively as a single larger particle.The magnetic properties that are most often used to characterize a material are susceptibility, saturation magnetization, coercivity, and Curie (T C ) or Néel (T N ) temperature. Remanent properties, that is, saturation remanent magnetization and remanent coercivity are also important in materials that can carry a permanent magnetization. This chapter focuses on methods that are commonly used to measure and characterize the magnetic properties of materials. First, the magnetic properties of the most common iron oxides and hydroxides are summarized; more detailed information on mineralogy, crystal structure, and magnetic properties can be found in several textbooks [1][2][3][4]. Methods for characterization can be divided into two types; those that measure induced magnetization, that is, measurements made in an applied field, and those that measure remanent magnetization, that is, in absence of an applied field. The latter are only useful for ferromagnetic materials that carry a permanent magnetization. The final section of this chapter reviews methods in interpreting magnetic properties alone or in combination.Iron Oxides: From Nature to Applications, First Edition. Edited by Damien Faivre.

Enhanced Methods to Estimate the Efficiency of Magnetic Nanoparticles in Imaging

“…For example, it has been shown that superparamagnetic behavior and high magnetic moment are desirable for both MRI and MPI [ 5 , 6 , 7 ]. The magnetic properties of a material will depend upon the particles’ chemical composition, size, shape and whether there is any magnetic interaction amongst the particles [ 3 , 8 ]. Chemical composition will determine to a large extent the saturation magnetization of a material.…”

Magnetic methods applied to the material, life, and environmental sciences

“…There is a broad palette of magnetic methods that help in identifying the composition, concentration and the effective particle size of ferromagnetic minerals [2]. Table 1 summarizes the information that some of these methods can provide.…”

“…In many applications, it is important to understand the way in which a magnetic particle responds to an external field. Composition, particle size, and degree of particle interaction all play a role in determining the efficiency of delivery, and usage; therefore, these properties need to be controlled in the synthesis of materials [2].…”