Nanum Nanotechnology: Remanence, Saturantion and Coercivity study of several ferrites

First the teory (from wikipedia.org):

Remanence:

Remanence or remanent magnetization is the magnetization left behind in a permanent magnet after an external magnetic field is removed. It is also the measure of that magnetization. Colloquially, when a magnet is "magnetized" it has remanence. It is also the magnetic memory in magnetic storage and the source of information on the past Earth's field in paleomagnetism.

The equivalent term residual magnetization is generally used in engineering applications. In transformers, electric motors and generators a large residual magnetization is desirable (see also electrical steel). In many other applications it is an unwanted contamination, for example a magnetization remaining in an electromagnet after the current in the coil is turned off. Where it is unwanted, it can be removed by degaussing.

Sometimes the term retentivity is used for remanence measured in units of magnetic flux density.

Saturation remanence:

The default definition for remanence is the magnetization remaining in zero field after a large magnetic field is applied (enough to achieve saturation). A magnetic hysteresis loop is measured using instruments such as a vibrating sample magnetometer and the zero-field intercept is a measure of the remanence. In physics this measure is converted to an average magnetization (the total magnetic moment divided by the volume of the sample) and denoted in equations as Mr. If it must be distinguished from other kinds of remanence it is called the saturation remanence or saturation isothermal remanence (SIRM) and denoted by Mrs.

In engineering applications the residual magnetization is often measured using a B-H Analyzer, which measures the response to an AC magnetic field. This is represented by a flux density BR. This value of remanence is one of the most important parameters characterizing permanent magnets; it measures the strongest magnetic field they can produce. Neodymium magnets, for example, have a remanence approximately equal to 1.3 teslas.

Magnetic saturation:

Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetizing field H cannot increase the magnetization of the material further, so the total magnetic field B levels off. It is a characteristic particularly of ferromagnetic materials, such as iron, nickel, cobalt and their alloys.

Coercivity:

In materials science, the coercivity, also called the coercive field or coercive force, of a ferromagnetic material is the intensity of the applied magnetic field required to reduce the magnetization of that material to zero after the magnetization of the sample has been driven to saturation. Coercivity is usually measured in oersted or ampere/meter units and is denoted HC.

Coercivity measures the resistance of a ferromagnetic material to becoming demagnetized. Coercivity can be measured using a B-H Analyzer or magnetometer.

Materials with high coercivity are called hard ferromagnetic materials, and are used to make permanent magnets. Permanent magnets find application in electric motors, magnetic recording media (e.g. hard drives, floppy disks, or magnetic tape) and magnetic separation.

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