hysteresiskäyrässä

Hysteresiskäyrä, often translated as hysteresis loop or curve, is a graphical representation illustrating the relationship between a magnetic field and the magnetic flux density in a ferromagnetic material. This phenomenon occurs because the magnetization of the material does not change instantaneously with the applied magnetic field. Instead, it lags behind, creating a loop when the magnetic field is varied cyclically.

When an unmagnetized ferromagnetic material is subjected to an increasing magnetic field, the magnetic domains within the material align, leading to an increase in magnetic flux density. This initial increase is represented by the lower portion of the hysteresis loop. As the magnetic field continues to increase, the material eventually reaches saturation, where all magnetic domains are aligned.

When the applied magnetic field is then decreased, the magnetic flux density does not follow the same path back. A residual magnetic flux density, known as remanence, remains even when the applied field is reduced to zero. To bring the magnetic flux density back to zero, a reverse magnetic field, called the coercive force, must be applied. This lagging effect is the essence of hysteresis.

Further increasing the magnetic field in the reverse direction leads to saturation in the opposite direction. When the field is then reduced and reversed again, another loop is traced. The area enclosed by the hysteresis loop is proportional to the energy lost per unit volume of the material during each magnetization cycle. This energy loss is typically dissipated as heat and is an important consideration in the design of magnetic devices, such as transformers and electromagnets. Different ferromagnetic materials exhibit different hysteresis loop shapes, which are indicative of their magnetic properties and suitability for various applications.