
Coercive Force 
Coercive force is the value of the external magnetic field that brings to zero the magnetization or magnetic flux density of a magnetic body. The external magnetic field is oriented in the opposite direction from the orientation of the of the magnetic body itself. The value of the external magnetic field when the magnetic polarization (or magnetization) and magnetic flux density of the magnetic body come to zero are written as HcJ and HcB to distinguish them, but when evaluating magnetic characteristics, normally the coercive force is expressed as HcJ. Coercive force is a measure of the stability of magnetization in the face of an external magnetic field or more simply the capacity to resist an external magnetic field. Material with high coercive force is called hard magnetic material and material with low coercive force is known as soft magnetic material. This is the most important characteristic for a permanent magnet material.
Maximum Energy Product
Maximum energy product is an index expressing the performance of a permanent magnet. The units are the joule per meter cubed [J/m3] in the SI system and the gauss oersted [GOe] in the CGS system. The maximum energy product is expressed as (BH)max. The product of H (taken as positive) and B at the point (H, B) on the B-H demagnetization curve is called the energy product and the maximum value of this product is the maximum energy product. This value serves as a yardstick for the maximum amount of magnetic flux taken out from the magnet per unit volume. When a magnetic circuit is designed to operate at the maximum energy product point, the magnet volume is reduced to its smallest value.
Magnetic Field
Magnetic field is the force operating on the magnetic charge. The symbol for the magnetic field is H and the units are the ampere/meter [A/m] for SI units and the oersted [Oe] for CGS units where 1 [A/m] = 4π•10-3 [Oe]. The Earth itself posses a magnetic field referred to as geomagnetism.
Magnetic Flux
Magnetic flux is the quantity of magnetic force lines and is analogous to current in an electric circuit. Flux is obtained by integrating the flux density over the surface area. The symbol for the magnetic flux is φ. The units are the weber [Wb] for the SI system and the Maxwell [Mx] for CGS units. 1 [Wb] = 108 [Mx].
Magnetic Flux Density
Magnetic flux density is the amount of magnetic flux per unit surface area. The units are the tesla [T] for SI units and the Gauss [G] for CGS units. The symbol for the magnetic flux density is B. The magnetic flux density within a magnetic body is the sum of the external magnetic field H and the magnetic body magnetic polarization J and in SI units is expressed as B=μ0H+J. 1 [T] = 104 [G].