hystereesiskäyränä

Hystereesisäkäyrä, or hysteresis loop, is a graphical representation illustrating the relationship between a magnetic field and the magnetization of a ferromagnetic material. When a material is subjected to an increasing magnetic field, its magnetic domains align, leading to magnetization. As the external field is reduced, the magnetization does not necessarily return to zero along the same path. This phenomenon is known as hysteresis.

The hysteresis loop plots magnetic flux density (B) or magnetization (M) on the y-axis against magnetic field strength (H) on the x-axis. Starting from an unmagnetized state, as H increases, B also increases until it reaches saturation. When H is decreased, B decreases but lags behind H, retaining some residual magnetization even when H is zero. This residual magnetization is called retentivity. To reduce the magnetization to zero, a reverse magnetic field, known as coercivity, must be applied.

Further increasing H in the negative direction leads to negative saturation. As H is increased back towards positive values, the loop is completed. The area enclosed by the hysteresis loop represents the energy dissipated as heat within the material during each magnetization cycle, often referred to as hysteresis loss. The shape and size of the hysteresis loop depend on the material's properties. Soft magnetic materials have narrow loops and low coercivity, making them suitable for applications like transformers, while hard magnetic materials have wide loops and high coercivity, used in permanent magnets.