Space between the poles of a magnet in which there exists a useablemagnetic field.
A magnet having apreferred direction of magnetic orientation, so that the magneticcharacteristics are optimum in one preferred direction.
Thecoercivity of a magnetic field is the intensity, or energy, required to reducethe magnetisation of a magnetised (to the point of saturation) object to zero.Essentially, it measures a magnetic material’s resistance to demagnetisation. The coercivity of magnetic materialis measured in Oersteds (Oe) – the higher the number,the greater the magnet’s resistance to demagnetisation.
The properties of all magnetic materials change when they areheated to a particular temperature. The Curie temperature (Tc), or Curie point,is the temperature at which the atomic structure of magnetic material ischanged and the object becomes demagnetised.Once heated to, or passed, the Curie point the magneticdomains of the material are released and become randomised and ‘self keepering’,resulting in permanent magnetic damage. As a result, the magnet will not emitany external magnetic fields.
Named after the famous German mathematician and physicistCarl Friedrich Gauss, the Gauss is a unit of measurement for magnetic fluxdensity. 1,000 Gauss is 1,000 lines of magnetism in each cm2 of polearea.
There are a number of different types of magnet, neodymium,samarium cobalt, ferrite and alnico, for example. Each type of magnet is manufactured in a number of differentgrades. The term grade defines the chemical characteristics of the material andits magnetic properties. Each grade of material, depending upon its coreelements and how it is manufactured will have different magnetic properties.You will find a list of magnet grades right here in our TechCentre.
A four quadrant graph, showing magnetising force relative toresultant magnetisation of a permanent magnet material as it is successivelymagnetised to its saturation point, then demagnetised, magnetised in thereverse polar direction and then finally re-magnetised. When the cycles are complete, this four quadrant graph willbe a closed loop which illustrates the magnetic characteristics of the magneticmaterial under test. Magnetically hard materials have a larger area inside theloop which denotes the level of magnetic energy. Magnetically soft materialslose magnetism when the magnetising field is removed and therefore these havevery small areas inside the loop. The second quadrant within the four quadrants(+X and -Y) is the most important of the four curves and is known as thedemagnetisation curve.
If the coercivity of a magnet is the force required to cancelout a saturated magnet’s magnetic field, theintrinsic coercivity is the force required to permanently demagnetise a magnet.Neodymium magnets have large differences between the coercivity and intrinsiccoercivity, therefore to permanently demagnetise a neodymium magnet takes muchmore energy than to just equalise (reduce to zero) a neodymium magnet’s magnetic field. Intrinsic coercivity is measured in kilo-Oersteds(kOe). Each grade of neodymium magnet has an associated intrinsiccoercive force, displayed on the ‘neodymium magnet grades’page of our TechCentre.
Partialdemagnetisation can be caused by exposure to high temperatures, externalmagnetic fields, shock or vibration. When exposed to certain conditions amagnet will regain any magnetism lost, however, in extreme situations themagnet will lose a percentage of its magnetism that won’t be recovered, known as irreversible losses. Anexample is exposing a magnet to temperatures exceeding its maximum operatingtemperature.
M-Hloop (Hysteresis loop)
Also known as the hysteresis loop, the M-H loop is a fourquadrant graph, showing magnetising force relative to resultant magnetisationof a permanent magnet material as it is successively magnetised to itssaturation point, then demagnetised, magnetised in the reverse polar directionand then finally re-magnetised.When the cycles are complete, this four quadrant graph willbe a closed loop which illustrates the magnetic characteristics of the magneticmaterial under test. Magnetically ‘hard’ materials have a large area inside theloop which denotes the level of magnetic energy. Magnetically ‘soft’ materials lose magnetism when themagnetising field is removed and therefore these have very small areas insidethe loop. The second quadrant within the four quadrants (+X and -Y) is the mostimportant of the four curves and is known as the demagnetisation curve.
Apermanent magnet is a solid material that produces its own consistent magneticfield because the material is magnetised. A permanent magnet is different to anelectromagnet as an electromagnet only acts as a magnet when an electriccurrent passes through its coils.
Remanenceis described as the magnetism that is left in a magnet, after the removal ofthe external magnetic force applied to magnetise it. When a material has beenmagnetised, it has remanence, as the magnetism has at some point been inducedby an external magnetic field.