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SOFT AND HARD MAGNETIC MATERIALS AND STONER-WOHLFARTH THEORY
NORASHIDA…
SOFT AND HARD MAGNETIC MATERIALS AND STONER-WOHLFARTH THEORY
NORASHIDA MOHD RAZALI,4SSCZ
INTRODUCTION
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:<3:hard --> low permeability (close to origin),high coercive force (Hc>1000 Oe), used for disk media/permanent magnet application.
:<3:soft -->high initial permeability,low coercivity(<100 Oe),for transformer/magnetic head application
STONER-WOHLFARTH THEORY
:smiley:simple analytical model describe hysteresis.
:smiley:uniform magnetized ellipsoid + uniaxial anisotropy/magneto-crystalline origin(SW particle) in field applied at θ to anisotropy axis.
:smiley: energy density;
:smiley:minimize Etotal --> 1/2 energy minima-hysteresis arise in field.
:smiley:Switching=irreversible jump from one minimum to another when d2E/d∅2= 0.
:smiley:loop shape=square when 𝛼=0, coercivity = anisotropy field
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:smiley:crude model for real polycrystalline magnet.
:smiley:remanence = 1/2 Ms,coercivity=0.482a
Henkel Plot
:smiley:2 remanence curves of non-interacting particle
:smiley:remanence of initial magnetization curve,Mr obtain by applied field,H to virgin state,reduce to 0.
:smiley:Mrd obtained in reverse field after saturation
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SOFT MAGNETIC MATERIALS
:speak_no_evil:easy to magnetize,demagnetized
:speak_no_evil:high frequency to applied ac
:speak_no_evil:low retentivity,low coercivity
:speak_no_evil:high permeability,high magnetic saturation
:speak_no_evil:low hysteresis losses-->less area of loop.
:speak_no_evil:used for transformer,inductance core(minimize energy dissipation)
:speak_no_evil:desirable in electromagnets.
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HARD MAGNETIC MATERIALS
:bear:permanent magnet material
:bear:retain magnetization,difficult to demagnetize.
:bear:high retentivity,high coercivity
:bear:high permeability,high magnetic saturation
:bear:high Tc,high hysteresis loop -->large area of loop
example:
Carbon steel,Tungsten steel,Al-Nico, etc...