Magnetic hysteresis

This curve increases rapidly at first and then approaches an asymptote called magnetic saturation.

At zero field strength, the magnetization is offset from the origin by an amount called the remanence.

[1]: Chapter 15 Magnetic hysteresis loops are not exclusive to materials with ferromagnetic ordering.

The magnetization can also change by addition or subtraction of domains (called nucleation and denucleation).

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.

The obtained incremental formulation is variationally consistent, i.e., all internal variables follow from the minimization of a thermodynamic potential.

Micromagnetics simulations attempt to capture and explain in detail the space and time aspects of interacting magnetic domains, often based on the Landau-Lifshitz-Gilbert equation.

Toy models such as the Ising model can help explain qualitative and thermodynamic aspects of hysteresis (such as the Curie point phase transition to paramagnetic behaviour), though they are not used to describe real magnets.

Many of these make use of their ability to retain a memory, for example magnetic tape, hard disks, and credit cards.

In these applications, hard magnets (high coercivity) like iron are desirable so the memory is not easily erased.

Magnetic hysteresis material (soft nickel-iron rods) has been used in damping the angular motion of satellites in low Earth orbit since the dawn of the space age.