Magnetic hysteresis

Magnetic hysteresis is the complete cycle of magnetic material magnetization and demagnetization.

Magnetic materials are magnetized by bringing the external magnetic field to the maximum possible value, subsequently reducing the external magnetic field until it is zero, thus generating a permanent material magnetization.

The magnetic hysteresis phenomena (and the material magnetic properties) are detected by the hysteresis curve trend that illustrates the magnetic density flux B and the magnetic polarization J as a function of the magnetizing force H.

This can be represented with a coordinate system that can be placed in four quadrants:

Magnetic hysteresis

The first quadrant shows the behavior of the material at the beginning of its magnetization.

By applying an external magnetic field, the magnetic dipole is initially positioned parallel to it, and then steadily increases in alignment with the magnetic force.

The second quadrant shows us the magnetic material demagnetization, the most important process for permanent magnets because it detects their most important properties. The second quadrant is in fact present on the various materials technical data sheets and it is also used for design and sizing activities (for example electrical machines that use magnets).

Subsequently, by increasing the magnetic force, you obtain an increasing elementary magnets alignment in opposition to the initial magnetization (quadrant 3). This process continues until a complete saturation level is reached, which involves a magnetic material polarity inversion.

At this point it is possible to carry out a demagnetization (fourth quadrant) and subsequently a magnetization (first quadrant) in the same way of the initial direction, by reversing again the external magnetic field polarity.

The ferromagnetic materials hysteresis curve is symmetrical to the origin of the coordinates axis.

Each magnetic material has different hysteresis curves depending on its properties and the magnetization.

For more information about Garnet’s magnets, visit the magnets section on our website.

For further information consult the article Technical properties of the main magnetic materials: Neodymium, Samarium Cobalt, Alnico and Ferrite.