Soft and Hard Magnetic Materials
and Stoner-Wohlfarth theory
Soft and Hard
Magnetic Materials
Hard Magnetic Materials
Stoner-Wahlfarth
Model
Soft Magnetic Materials
Ferromagnetic materials divided into two: soft and hard magnetic materials
Typical hysteresis loop when magnetic field applied on ferromagnetic materials
Hard magnetic materials show low initial permeability and high coercive force
Soft magnetic materials have high initial permeability ans low coercive forc
Magnetization reversal behavior would be different since both ferromagnetic materials have different magnetic parameters associate with their hysteresis
Simple analytical model describing hysteresis
Consider a uniformly magnetized ellipsoid with uniaxial anisotropy of shape of magneto-crystalline origin in a field at an angle, theta to the anisotropy axis
Easy to magnetize and demagnetize
Favor rapid switching of magnetism to applied ac field due to high frequency
Low retentivity
Low coercivity
High permeability
High magnetic saturation
Lesser area of hysteresis loop, thus low hysteresis losses
Desirable for electromagnets
Used for transformer and inductance core to minimize energy dissipation
Examples: FeSi alloy/ FeNi alloy
High permeability
High magnetic saturation
High coercivity
High curie point/temperature
High retentivity
Larger area of hysteresis loop, thus high hysteresis losses
Can retain magnetization and hard to demagnetize
Also called permanent magnet materials
Examples: carbon steel, tungsten steel, AlNiCo
Hysteresis arises in the field range where two minima are present
Typical hysteresis loop for Stoner-Wahlfarth
An array of non-interacting magnetic particles with a random distribution of anisotropy axes is a crude model for a real polycrystalline magnet
Hankel plot, relation between two remenence curves for system of non-interacting particles was pointed by Wohlfarth. The remanence of the initial magnetization curve is obtained by applying a field to the virgin state and reducing it to zero