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The curves form a hysteresis loop. Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of the moment often form a loop or hysteresis curve, where there are ...
Magnetic hysteresis can be characterized in various ways. In general, the magnetic material is placed in a varying applied H field, as induced by an electromagnet, and the resulting magnetic flux density (B field) is measured, generally by the inductive electromotive force introduced on a pickup coil nearby the sample.
Usually only the hysteresis loop is plotted; the energy maxima are only of interest if the effect of thermal fluctuations is calculated. [1] The Stoner–Wohlfarth model is a classic example of magnetic hysteresis. The loop is symmetric (by a 180 ° rotation) about the origin and jumps occur at h = ± h s, where h s is known as the switching field.
Saturation is most clearly seen in the magnetization curve (also called BH curve or hysteresis curve) of a substance, as a bending to the right of the curve (see graph at right). As the H field increases, the B field approaches a maximum value asymptotically , the saturation level for the substance.
A family of hysteresis loops for grain-oriented electrical steel, a soft magnetic material. B R denotes retentivity and H C is the coercivity. The wider the outside loop is, the higher the coercivity. Movement on the loops is counterclockwise.
The downward curve after saturation, along with the lower return curve, form the main loop. The intercepts h c and m rs are the coercivity and saturation remanence . When ferrimagnets are exposed to an external magnetic field, they display what is called magnetic hysteresis , where magnetic behavior depends on the history of the magnet.
The hysteresis loop (P x versus E x) may be obtained from the free energy expansion by including the term −E x P x corresponding to the energy due to an external electric field E x interacting with the polarization P x, as follows:
The current is proportional to the magnetization of the sample - the greater the induced current, the greater the magnetization. As a result, typically a hysteresis curve will be recorded [5] and from there the magnetic properties of the sample can be deduced. The idea of vibrating sample came from D. O. Smith's [6] vibrating-coil magnetometer.