# Magnet Glossary

 Air Gap A non-magnetic discontinuity in a ferro-magnetic circuit. For example, the space between the poles of a magnet, although filled with brass or wood or any other non-magnetic material, is nevertheless called an air gap. Amorphous Refers to magnetic materials that are metallurgically non-crystalline in nature. Anisotropic Having properties which are dependent upon direction within the material. See also, "isotropic" and "grain oriented". Anneal A high-temperature conditioning of magnetic material to relieve the stresses introduced when the material was formed. To prevent oxidation, the anneal is usually performed in a vacuum or inert gas atmosphere. AWG American Wire Gauge A gauging system used to size magnet wire. B - Magnetic Induction The magnetic field induced by a field strength, H. It is the vector sum, of each point within the substance, of the magnetic field strength and resultant intrinsic induction. Magnetic induction is the flux per unit area normal to the direction of the magnetic path. Bd - Remanent Induction Any magnetic induction that remains in a magnetic material after removal of an applied saturating magnetic field, Hs. (Bd is the magnetic induction at any point on the demagnetization curve; measured in gauss or tesla.) Bd x Hd - Energy Product Indicates the energy that a magnetic material can supply to an external magnetic circuit when operating at the Bd, Hd point on its demagnetization curve; measured in megaGauss-Oersteds (MGOe) or kiloJoules per cubic meter (kJ/m3). Bd/Hd - Slope Of The Operating Line The ratio of the remanent induction, Bd, to a demagnetizing force, Hd. It is also referred to as the permeance coefficient, shear line, load line and unit permeance. Bg - Magnetic Induction In The Air Gap The average value of magnetic induction over the area of the air gap, Ag; or it is the magnetic induction measured at a specific point within the air gap; measured in Gauss. BH Loop A hysteresis loop of four quadrants. In practice, usually only the first and second or, more typically, only the second quadrant is shown. BHmax - Maximum Energy Product The maximum product of (Bd x Hd) which can be obtained on the demagnetization curve, i.e. in the second quadrant of the hysteresis loop. Bi (or J) - Intrinsic Induction The contribution of the magnetic material to the total magnetic induction, B. It is the vector difference between the magnetic induction in the material and the magnetic induction that would exist in a vacuum under the same field strength, H. This relation is expressed by the equation: Bi = B - Hem where; Bi = intrinsic induction in gauss (or tesla); B = magnetic induction in gauss (or tesla); Hem = field strength in oersteds (or kA/m). Bis (or Js) - Saturation Intrinsic Induction The maximum intrinsic induction possible in a material. Br - Residual Induction (or Flux Density) The magnetic induction corresponding to zero magnetizing force in a magnetic material after saturation in a closed circuit; measured in gauss or tesla. CGS System Centimeter-Gram-Second system, the oldest system of units and the one used for presenting powder core data. Only the units for magnetizing force, magnetic flux density, length, mass and time are utilized. Closed Circuit Condition Exists when the external flux path of a permanent magnet is confined within high permeability material. Coercive Force, Hc The value of demagnetizing force that reduces residual induction to zero. Measure of how permanent a magnet is; permanent magnets have a high coercivity. The intensity of a magnetic field needed to demagnetize a substance.The maximum coercive force, as measured on a saturated magnet, is proportional to the remanent flux density. See "flux density." It is expressed in oersteds or kiloAmps per meter (kA/m). Coercivity, Hci or iHc The resistance of a magnetic material to demagnetization. It is equal to the value of H where the intrinsic curve intersects the H axis in the second quadrant of the hysteresis loop. It is expressed in oersteds or kiloAmps per meter (kA/m). Curie Temperature, Tc The temperatures above which ferromagnetic materials become paramagnetic, losing substantially all of their permanent magnetic properties. The materials will no longer have magnetic attraction, but will remain attracted to other magnets . Demagnetization Curve That portion of the hysteresis loop which lies between the residual induction point, Br, and the coercive force point, Hc (normal curve) or Hci (intrinsic curve). The coordinates Bd and Hd designate points on the normal curve. Demagnetized A material condition where a ringing AC field has reduced the remanent induction to or near zero. A ringing AC field is a continually decreasing sinusoidal field. A pulsed DC field can be used to achieve gross demagnetization, but with much effort and with residual local magnetization. Eddy Currents Circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields, creating an opposing force to the magnetic flux. Eddy currents can be harnessed to perform useful work (such as dampening of movement), or may be unwanted consequences of certain designs, which should be accounted for of minimized. Electromagnet A magnet formed by current flowing through a conductor. The electrical conductor may be wire, copper plate or strips of foil and may exist with a permeable material such as steel to conduct the field to desired areas. The magnetic field exists only so long as current flows through the coil. Energy Product The energy that a magnetic material can supply to an external magnetic circuit when operating at a point on its demagnetization curve; measured in megaGauss-Oersteds (MGOe). See also BHmax. Ferrites A soft ferrite material that has lower permeability with very low eddy-current loss. The common ferrites are nickel-zinc, manganese-zinc and magnesium-zinc ferrite. Ferromagnetism Ferromagnetic materials have atomic fields that align themselves parallel with externally applied fields creating a total magnetic field much greater than the applied field. Ferromagnetic materials have permeability's much greater than 1. Above the Curie temperature, the ferromagnetic materials become paramagnetic. Flux In magnetics, the magnetic field Flux implies flow, which is not the case in magnetics. That is, no one has measured a magnetic "flow". Flux is represented conceptually as "magnetic lines of force". Flux density is measured in gauss or tesla. Fluxmeter An instrument that measures the change of flux linkage with a search coil. The current in the search coil caused by relative motion with the magnet is integrated (totalized). Using a calibrated coil allows calculation of field and magnet properties. Gauss The unit of magnetic induction, B, in the CGS electromagnetic system. The flux density of the earth's magnetic field at the surface is about 1 gauss. One gauss is equal to one maxwell per square centimeter or 10-4 tesla. Gauss Rating alone is not enough to indicate the strength of a magnet. The Gauss Rating is a unit of measurement that relates to the strength of a magnet and is connected with the density of lines of magnetic force coming from a magnet. However, the pulling power or strength of a magnet is also related to the actual physical size of a magnet. Larger magnets have more mass than smaller magnets and so can store a greater amount of magnetic energy. So you could have a magnet with a very high gauss rating which will in fact have less overall strength that a much bigger magnet with a lower gauss rating. To complicated things further, gauss magnetic strength is often misquoted or exaggerated. One common misunderstanding is the difference between two different ways of measuring strength: he Manufactures Rating and the actual Surface Gauss Rating of a magnet. The Manufacturers Rating (Magnetic Remanence (Br)) of the magnetic material is a property of the magnet when measured in the manufactures original magnetising equipment, in what's called a closed circuit. It indicates the magnetic field strength remaining inside the magnet and represents a grade of magnetic material (N48 ~ 13,800 gauss; N45 ~ 13,300 gauss and N40 ~ 13,000 gauss). This measurement is much higher than the surface gauss reading. The Surface Gauss Rating represents the magnetic flux density generated outside the magnet body. Gaussmeter An instrument that measures the instantaneous value of magnetic induction, B. Its principle of operation is usually based on one of the following: the Hall effect, nuclear magnetic resonance (NMR), or the rotating coil principle. Hc - Coercive Force Equal to the demagnetizing force required to reduce residual induction, Br, to zero; measured in oersteds (or kA/m). The material characteristic of coercivity is taken as the maximum coercivity -- that value of H required to reduce the residual induction to zero after the material has been saturated (fully magnetized). Hci - Intrinsic Coercive Force Indicates a material's resistance to demagnetization. It is equal to the demagnetizing force which reduces the intrinsic induction, Bi, in the material to zero; measured in oersteds (or kA/m). As for coercivity, the maximum value of intrinsic coercivity is obtained after the material has been saturated (fully magnetized). Hd The value of H corresponding to the remanent induction, Bd; measured in oersteds (or kA/m). See also BdHd. Hm Common symbol for maximum applied magnetizing force. Hs - Net Effective Magnetizing Force The magnetizing force required in the material, to magnetize to saturation; measured in oersteds (or kA/m). Hysteresis and Hysteresis Loss Hysteresis is the tendency of a magnetic material to retain its magnetization. Hysteresis causes the graph of magnetic flux density versus magnetizing force to form a loop rather than a line. The area of the loop represents the difference between energy stored and energy released per unit volume of material per cycle. This difference is called hysteresis loss. It is one of two major loss mechanisms in inductor cores; the other is eddy current loss. Hysteresis loss is measured at low frequency to distinguish it from eddy current loss. Hysteresis Loop A closed curve obtained for a material by plotting (usually to rectangular coordinates) corresponding values of magnetic induction, B, for ordinate and magnetizing force, H, for abscissa when the material is passing through a complete cycle between definite limits of either magnetizing force, H or magnetic induction, B. If the material is not "driven" to saturation, it is said to be on a minor loop. Hysteresis, Magnetic The property of a magnetic material by virtue of which the magnetic induction for a given magnetizing force depends upon the previous conditions of magnetization. Hysteresisgraph An instrument that draws hysteresis loops. Also called permeameter. Isotropic Having magnetic properties that are independent of the magnet orientation. Most magnetic materials are anisotropic as cast or powdered: each crystallite has a preferred direction of magnetic orientation. If the particles are not physically oriented during manufacture of the magnet, this results in a random arrangement of the particles and magnetic domains and produces isotropic magnet properties. Conversely, orienting the material during processing results in an anisotropic magnet. Keeper A piece(s)of soft iron that is placed on or between the pole faces of a permanent magnet to decrease the reluctance of the air gap and thereby reduce the flux leakage from the magnet. They are usually installed to resist demagnetization for Alnico magnets/assemblies. Not needed for Neodymium and other modern magnets. KiloGauss 1 kiloGauss is equal to 1,000 Gauss. Knee (of the demagnetization curve) In the second and fourth quadrants of the hysteresis loop, some materials such as ferrite and rare earth magnets exhibit a distinct "knee" or rapid change in slope of the intrinsic curve. The location of the knee is of interest to designers. If the magnet operates below the knee, irreversible loss of magnetic output occurs. Lodestone Naturally magnetic rock is made up of the mineral magnetite, which itself is primarily composed of iron oxide Magnetic Circuit The combination of magnet, permeable flux carriers and air gaps through or around which the magnetic flux path passes. Magnetic Circuit The combination of magnet, permeable flux carriers and air gaps through or around which the magnetic flux path passes. Magnetic Energy The product of the flux density (B) in a magnetic circuit and the (de)magnetizing force (H) required to reach that flux density. Magnetic Path The route magnetic flux follows in a magnetic circuit. Magnetization N Rating Neodymium magnets are graded by the magnetic material they are made from. In general, the higher the grade of material, the stronger the magnet. Neodymium magnets currently range in commercial grades from N27 to N54. The theoretical limit for Neodymium magnets is grade N64. The grade of most of our stock magnets is N48. Poles, North and South Magnetic The north pole of a magnet, or compass, is attracted toward the north geographic pole of the earth (which is actually, by definition, a magnetic south pole), and the south pole of a magnet is attracted toward the south geographic pole of the earth. The letter "N", and the other pole by the letter "S" designate the north-seeking pole of a compass or of a magnet. The N (north) pole of the magnet will attract the S (south) pole of another magnet: unlike poles attract. Remanence The magnetic induction remaining in a material when the magnetizing force has been reduced to zero. Also called "remanent induction". Residual Flux The flux that remains in a core when the applied MMF is returned to a value of zero. Return Path A magnet typically forms only part of the magnetic circuit. Soft magnetic materials such as steels are used to carry the magnetic flux to the gap or working region for interaction with other components. This conductor of magnetic flux is referred to as the return path. It is usually designed to minimize fringing and leakage flux. Sintered Magnets Magnets produced from a compacted powder, which is then subjected to a heat operation where the full density and magnetic orientation is achieved Stabilization A treatment of a magnetic material designed to increase the permanency (stability) of its magnetic properties or condition in an application by causing the loss prior to or during installation or assembly, but prior to testing and use. Tc - Curie Temperature The transition temperature above which a material loses its (ferro) magnet properties. Most references state that the ferromagnetic material becomes paramagnetic (weakly magnetic). Temperature Coefficient A factor that describes the reversible change in a magnetic property with a change in temperature. The magnetic property spontaneously returns when the temperature is cycled to its original point so long as a limit condition is not exceeded - see note below. It usually is expressed as the percentage change per unit of temperature over a specified temperature range. Note: above (or below) a critical temperature, dependent upon the material and its magnetic characteristics and magnetic circuit, an irreversible loss may take place, which is recovered when the magnet is re-saturated. Temperature Stabilization After manufacture, many types of hard and soft magnetic materials can be thermally cycled to make them less sensitive to subsequent temperature extremes. Tesla MKSA (SI) unit for magnetic flux density, defined by Faraday's Law. A Tesla represents a volt-second per square meter per turn. One Tesla equals 10,000 Gauss. Tmax - Maximum Service Temperature The maximum temperature to which the magnet may be exposed with no significant long-range instability or structural changes. A proposed magnetic definition is that the hysteresis normal curve is substantially a straight line in the second quadrant up to the Tmax temperature and becomes curved above Tmax. Weber The practical unit of magnetic flux. It is the amount of magnetic flux which, when linked at a uniform rate with a single-turn electric circuit during an interval of 1 second, will induce in this circuit an electromotive force of 1 volt. 1 Weber = 108 Maxwells.