Magnetization and magnetic susceptibility are the physical quantities that describe the response of a magnetic material to the application of an external magnetic field. Magnetic susceptibility χ is defined as the ratio between magnetization M and the intensity of the externally applied magnetic field B ,

These magnetic properties can be studied by determining the force on a magnetized sample of the material under study, or the magnetic induction or a perturbation of the field in the neighbourhood of the sample.

There is a generalized approach for the magnetic measurements techniques [1]. In an externally applied magnetic field, the material under study produces a force (F), or magnetic flux (ϕ), or an indirect signal (I). These phenomena are usually sensed by a detector, which results in output usually in the form of an electrical signal, either DC or AC. These techniques are in general termed magnetometry. The heart of a magnetometer is the detector, and it defines the principle involved in a particular type of magnetometer. A magnetic sample placed in a uniform magnetic field affects the magnetic flux distribution. This change can be sensed by a flux detector, which is usually in the form of a coil but can also be detected through a variety of sensors. On the other hand, a sample placed in a non-uniform magnetic field experiences a force, which can be detected by a force transducer. Such experimental techniques involving force or flux detections are classified as direct techniques, and they measure macroscopic or bulk magnetic properties of the material. These experimental techniques assume only the validity of Maxwell's electromagnetic equations and the thermodynamic equilibrium of the sample. The magnetic properties can also be measured by various indirect techniques, namely the Hall effect, magneto-optical Kerr/Faraday effects, NMR, FMR, M¨ossbauer, Neutron Scattering, μSR, and others, which take advantage of known relationships between the phenomenon detected and the microscopic magnetic properties of the specimen. In this chapter, we will focus on the direct techniques, and the indirect techniques will be the subject of later chapters in the book. It may be mentioned here that each magnetic measurement technique has distinct merits as well as limitations, and no single technique is universally applicable to study all types of magnetic phenomenon [1].