Terms used in relation to permanent magnets (Part 2)

Term	Code	Unit	Explanation
Magnetic substance			A "Magnetic substance" means substances which can be magnetised by the effect of a magnetic field or magnet. Substances which magnetise strongly are called "Ferromagnetic substances", and are used as the material for permanent magnets, including iron and magnetite. However, substances which do not magnetise are called "Non-magnetic substances"; paper and plastic as typical examples, as well as metallic substances such as gold, silver, copper, aluminium, and magnesium.
Magnetic force line / magnetic flux			Imaginary lines representing the orientation of a magnetic field are called "Magnetic force lines". Magnetic force lines are expressed by lines originating from the N-pole and returning to the S-pole, and never cross each other. A bundle of magnetic force lines are called a "Magnetic flux".
Magnetic flux density	B	T (G)	The magnetic flux per unit area is called the "Magnetic flux density". The magnetic flux density represents the magnetic force at a point where a magnetic field exists. The unit representing magnetic flux density (B) is Tesla [T] in the SI system, and Gauss [G] in the CGS system.
Magnetic hysteresis curve			A magnetic hysteresis curve is a non-linear data aggregate or graph, which represents the tendency and distribution of magnetisation. The curve representing the relationship of an external magnetic field (H) with magnetisation (J) with the magnetic flux density (B) of a material is called the "Magnetic hysteresis curve (magnetisation curve)". Magnetic hysteresis curves may be classified into two types; a curve representing the relationship between the magnetisation of a material and the magnetic field (J-H curve), and the curve representing the relationship between the magnetic flux density and the magnetic field (B-H curve). The second quadrant in the graph of a magnetic hysteresis curve is called the "Demagnetisation curve", which is an important curve representing a material's characteristics.
Maximum energy product	Bhmax	J/m3 (GOe)	The maximum energy product is one of the characteristic values representing magnetic strength. The area of a rectangle (BxH) whose diagonals exist between the operating point and origin of the demagnetisation curve represented by the B-H curve is called the "Energy product", and the maximum value of an energy product is called the "Maximum energy product".
Remanent magnetic flux density	Br	T (G)	"Remanent magnetic flux density" is the magnetic density at the intersection of the vertical axis with the demagnetisation curve. Remanent magnetic flux density represents the magnetic flux density that a material can retain, even under the condition that a magnetic field is applied to such material to saturation, and then its magnetic field reduces to zero. Remanent magnetic flux density (Br) is dependent on materials, and referred to as one of characteristic values for measuring strength of magnetic force proper to materials.
Surface magnetic flux density	Bg	T (G)	"Surface magnetic flux density" is the magnetic flux density on the pole's surface of a magnet. For actual measurement, the surface magnetic flux density is determined as the value at a point which is slightly away from the pole's surface due to a mechanical reason of the measuring instrument. Surface magnetic flux density is useful for comparing different magnets, though it is difficult to determine a measurement point because surface magnetic flux density varies according to the magnet shape.
Coercive force	Hcb Hcj	A/m (Oe)	"Coercive force" is the intersection point of the transverse axis with the demagnetisation curve. Coercive force means the external magnetic force under the condition that the magnetic force of a material magnetised by applying a magnetic field to saturation is reduced to zero by applying a magnetic field whose direction is opposite to the magnetisation direction. The intersection point of the J-H curve with the transverse axis is represented by Hc (j or iHc), and the intersection point of the B-H curve with the transverse axis is represented by Hcb (bHc). Coercive force literally means the strength to retain the magnetic force, and is expressed as the characteristic value representing the characteristics of a material, as with remanent magnetic flux density. It is necessary to design a magnet carefully, using a material with a high remanent magnetic flux density and low coercive force, as it is highly dependent on the shape and temperature.
Permeance coefficient	Pc	Dimensionless	"Permeance coefficient" is the parameter determining where a magnet operates, and depends on the magnet's shape. A magnet always generates a magnetic field outside itself, and also generates a magnetic field in the opposite direction (demagnetising field) inside itself. A demagnetising field is an element which reduces the magnetic force, and depends on the magnet's shape. A permeance coefficient is defined by magnetic flux density against demagnetizing force. The shorter (thinner) the magnet is shaped in the magnetization direction in comparison with the surface area of the pole, the higher the demagnetizing field will become and the lower the permeance coefficient and magnetic force will become.
Curie temperature		K.℃	The "Curie temperature" or "Curie point", is the temperature at which a certain material completely loses its magnetic force due to the change of its crystalline structure due to an increase in temperature. Once a magnet reaches the Curie temperature, it cannot regain its magnetic force even if the temperature reduces to the ambient temperature.

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