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Hysteresis is a physics term that means, literally, to be late. It describes systems that do not directly follow the forces applied to them, but react slowly, or don't return completely to their original state: that is, systems whose states depend on their immediate history. For instance if you push on a piece of putty it will assume a new shape, and when you remove your hand it will not return to its original shape, or at least not entirely.

Hysteresis phenomena does not only show up in magnetical and ferromagnetical materials, but are present in the elastic and electromagnetic behavior of materials, in which a lag occurs between the application and the removal of a force or field and its subsequent effect. Electric hysteresis occurs when applying a varying electric field, and elastic hysteresis occurs in response to a varying force. Although the hysteresis loop depends on the material property behaviours, there is no complete theoretical description that explains the physical phenomenon.

The family of hysteresis loops, from the results of different applied varying voltages or forces, form a closed space in three dimensions, called the hysteroid.

Hysteresis was initially considered to be a dirty, unwanted, phenomena of materials. But its behaviour is now considered to be of very great importance in technology, and the property is for example used when constructing permanent memory.


The term is actually used almost entirely to describe an effect seen in magnetism, specifically in ferromagnetic materials. When an external magnetic field is applied to a ferromagnet, the ferromagnet "takes up" some of the external field. Even when the external field is removed, the magnet will retain some field, it has become magnetized.

A hysteresis loop occurs when an alternating magnetic field is applied to a ferromagnetic material. As the magnetic field increases, the magnetization also increases, but it has a lower value than the equilibrium magnetization. The magnetic field then reverses direction and starts to decrease - again the magnetization lags, this time staying above the equilibrium value. If the field is plotted against magnetization during this cycle, it will appear as a loop.

We sorely need a diagram here. Even a freehand sketch would be better than nothing.

This is a very important effect in many situations, notably magnetic tape and other related storage media like hard disks. In these materials it would seem obvious to have one polarity represent a bit, say north for 1 and south for 0. However if you want to change the storage from one to the other, the hysteresis effect requires you to know what was already there because the needed field will be different in every case.In order to avoid this problem, recording systems first overdrive the entire system into a known state, a process known as bias. Different materials require different biasing, which is why there is a selector for this on the front of most cassette recorders.

The term "hysteresis" is sometimes used in other fields, for example economics. In such cases it describes some sort of memory or lagging effect.

Liquid-solid phase transitions

Hysteresis is also a known phenomen in thermodynamics. Here the molecules change properties during heat transfer (via a potential field or a higher temperature increase) and it is this change that cause hysteresis.

The hysteresis effect can be used when wiring circuits with passive matrix addressing, used in nanoelectronics or electrochrome displays . In this scheme adjacent neighbouring components gets short-cutted and the hysteresis helps keeping the components into a particular state when changing the other components states, i.e. one can address all rows at the same time instead of do it individually.


When hysteresis occure with extensive and intensive variables, the work done on the system is the area under the hysteresis graph.

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What's Hysteresis?