Engr. Abbas Abbasi Behavior of Ferromagnetic Materials Saturation and Hysteresis

Ferromagnetic Material A material whose permeability is very much larger than 1 (from 60 to several thousand times ), and which exhibits hysteresis phenomena Material that acquires strong magnetism when placed in an external magnetic field. Examples are iron, cobalt, nickel, and their alloys.

MMF (DC ) Vs Flux Curve If MMF (Ni) is increased flux also increases There comes a stage when increase in MMF does not produce corresponding increase in flux The plot above is known as “Magnetization curve” of the core

Saturation Saturation Region Unsaturated region

B-H Curve

B-H Curve and Permeability (µ) Permeability is the slope of the “Magnetization curve” Constant permeability Low and unstable permeability

MMF (AC ) Vs Flux Curve F φ

Hysteresis Loop

Magnetic Domains (Reason for hysteresis) Within the metals there are very small regions called domains In each domain atoms are aligned, with their magnetic fields pointing in the same direction (acting like a small magnet) These tiny domains are oriented randomly in the metal When external fields are applied, energy is required to align these domains in the direction of the main field These energy losses are called hysteresis losses (core losses) When all the domain have been aligned, the stage is called saturation