There are hysteresis magnetic, ferroelectric, dynamic, elastic. It is also found in biology, soil science, economics. Moreover, the essence of this definition is almost the same. But the article will focus on the magnetic, you will learn more about this phenomenon, what it depends on and when it manifests itself. This phenomenon is studied in universities with a technical focus, it is not included in the school curriculum, so not everyone knows about it.
Hysteresis magnetic
This is an irreversible and ambiguous dependence of the magnetization index of a substance (and these are, as a rule, magnetically ordered ferromagnets) on an external magnetic field. In this case, the field is constantly changing - decreasing or increasing. The general reason for the existence of hysteresis is the presence of an unstable state and a stable state at the minimum of the thermodynamic potential, and there are also irreversible transitions between them. Hysteresis is also a manifestation of a first-order magnetic orientational phase transition. With them, transitions from one phase to another occur due to metastable states. The characteristic is a graph, which is called the "hysteresis loop". Sometimes it is also called the "magnetization curve".
Hysteresis loop
On the graph of M versus H you can see:
- From the zero state, at which M=0 and H=0, with an increase in H, M also grows.
- When the field increases, the magnetization becomes almost constant and equal to the saturation value.
- When H decreases, the opposite change occurs, but when H=0, the magnetization M will not be equal to zero. This change can be seen from the demagnetization curve. And when H=0, M takes on a value equal to the residual magnetization.
- As H increases in the range –Hm… +Hm, the magnetization changes along the third curve.
- All three curves describing the processes are connected and form a kind of loop. It is she who describes the phenomenon of hysteresis - the processes of magnetization and demagnetization.
Magnetization energy
A loop is considered asymmetric in the case when the maxima of the H1 field, which are applied in the reverse and forward directions, are not the same. A loop has been described above, which is characteristic of a slow magnetization reversal process. With them, quasi-equilibrium relationships between the values of H and M are preserved. It is necessary to pay attention to the fact thatthat during magnetization or demagnetization, M lags behind H. And this leads to the fact that all the energy that is acquired by the ferromagnetic material during magnetization is not completely transferred during the demagnetization cycle. And this difference goes all into the heating of the ferromagnet. And the magnetic hysteresis loop turns out to be asymmetric in this case.
Loop Shape
The shape of the loop depends on many parameters - magnetization, field strength, the presence of losses, etc. The chemical composition of the ferromagnet, its structural state, temperature, the nature and distribution of defects, the presence of processing (thermal, thermomagnetic, mechanical). Therefore, the hysteresis of ferromagnets can be changed by subjecting the materials to mechanical processing. This changes all the characteristics of the material.
Hysteresis loss
During the dynamic remagnetization of a ferromagnet by an alternating magnetic field, losses are observed. Moreover, they make up only a small fraction of the total magnetic losses. If the loops have the same height (the same maximum value of magnetization M), the dynamic type loop is wider than the static one. This is due to the fact that new losses are added to all losses. These are dynamic losses, they are usually associated with eddy current, magnetic viscosity. In sum, quite significant hysteresis losses are obtained.
Single-domain ferromagnets
BIf the particles have different sizes, the process of rotation takes place. This happens because the formation of new domains is unfavorable from the energy point of view. But the process of particle rotation is hindered by anisotropy (magnetic). It can have a different origin - be formed in the crystal itself, arise due to elastic stress, etc.). But it is precisely with the help of this anisotropy that the magnetization is held by the internal field. It is also called the effective magnetic anisotropy field. And magnetic hysteresis arises due to the fact that the magnetization changes in two directions - forward and reverse. During the remagnetization of single-domain ferromagnets, several jumps occur. The magnetization vector M turns towards the field H. Moreover, the turn can be uniform or non-uniform.
Multi-domain ferromagnets
In them, the magnetization curve is built in a similar way, but the processes are different. During magnetization reversal, the domain boundaries shift. Therefore, one of the causes of hysteresis may be the delay in boundary shifts, as well as irreversible jumps. Sometimes (if ferromagnets have a fairly large field), the magnetic hysteresis is determined by the delay in growth and the formation of magnetization reversal nuclei. It is from these nuclei that the domain structure of ferromagnetic substances is formed.
Hysteresis theory
It should be taken into account that the phenomenon of magnetic hysteresis also occurs when the field H rotates, and not only when it changes in sign andsize. This is called the hysteresis of the magnetic rotation and corresponds to a change in the direction of the magnetization M with a change in the direction of the field H. The occurrence of the hysteresis of the magnetic rotation is also observed when the sample is rotated relative to the fixed field H.
The magnetization curve also characterizes the magnetic structure of the domain. The structure changes during the passage of magnetization and magnetization reversal processes. The changes depend on how far the domain boundaries are shifted and on the effects of an external magnetic field. Absolutely everything that can delay all the processes described above puts ferromagnets into an unstable state and causes magnetic hysteresis to occur.
It should be taken into account that the hysteresis depends on many parameters. The magnetization changes under the influence of external factors - temperature, elastic stress, therefore, hysteresis occurs. In this case, a hysteresis appears not only in the magnetization, but also in all those properties on which it depends. As can be seen from here, the phenomenon of hysteresis can be observed not only during the magnetization of the material, but also during other physical processes associated directly or indirectly with it.
