a closed figure obtained by plotting magnetic flux density, B, against magnetizing field , H, when H increases and decreases
A plot of magnetizing force versus resultant magnetization (also called a B/H curve) of the material as it is successively magnetized to saturation, demagnetized, magnetized in the opposite direction and finally remagnetized. With continued recycles, this plot will be a closed loop which completely describes the characteristics of the magnetic material. The size and shape of this "loop" is important for both hard and soft materials. With soft materials, which are generally used in alternating circuits, the area inside this "loop" should be as thin as possible (it is a measure of energy loss). But with hard materials the "fatter" the loop, the stronger the magnet will be. The first quadrant of the loop (that is +X and +Y) is called the magnetization curve. It is of interest because it shows how much magnetizing force must be applied to saturate a magnet. The second quadrant (+X and -Y) is called the Demagnetization Curve.
A closed curve obtained for a material by plotting corresponding values of flux density for the ordinate and magnetizing force for the abscissa when the material is passing through a complete cycle between definite limits of either magnetizing force or flux density. If the material is not driven into saturation it is said to be on a minor loop.