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Classification by susceptibility; ferro vs ferrimagnetic

Short answer

Magnetic materials are classified by susceptibility: diamagnetic (small negative), paramagnetic (small positive), ferromagnetic (very large positive), antiferromagnetic (small positive), ferrimagnetic (large positive). Ferromagnetic moments are parallel; ferrimagnetic moments are antiparallel but unequal, yielding net magnetization.

Classify magnetic materials based on their magnetic susceptibilities. What is the basic difference between ferromagnetic and ferrimagnetic material?

Magnetic susceptibility is χ=M/H\chi = M/H, the magnetization produced per unit applied field; μr=1+χ\mu_r = 1 + \chi. Based on the sign and size of χ\chi, magnetic materials are classified as follows.

Classχ\chi (typical)Temperature dependenceExamples
DiamagneticSmall, negative, ≈−10−5\approx -10^{-5}Independent of TTCu, Bi, Ag, water, graphite
ParamagneticSmall, positive, 10−510^{-5}–10−310^{-3}χ=C/T\chi = C/T (Curie)Al, Pt, O₂, Mn
FerromagneticVery large, positive, 10210^{2}–10510^{5}χ=C/(T−TC)\chi = C/(T - T_C) above TCT_CFe, Co, Ni
AntiferromagneticSmall, positive, 10−510^{-5}–10−310^{-3}Rises up to TNT_N, then C/(T+θ)C/(T + \theta)MnO, FeO, Cr
FerrimagneticLarge, positive, 1010–10410^{4}χ\chi falls above Curie/Néel temp.Fe₃O₄, ferrites
 1/chi
   ^        para    ferro      antiferro
   |       /        /          /
   |      /        /       \  /
   |     /        /         \/
   +----/--------/-----------+----> T
       0        Tc          TN

Brief description

  • Diamagnetic: no permanent atomic moment; induced moment opposes the field (Lenz's law); weakly repelled.
  • Paramagnetic: permanent but non-interacting moments; partly aligned by the field; weakly attracted.
  • Ferromagnetic: moments aligned parallel in domains by exchange interaction; very strong magnetization, hysteresis.
  • Antiferromagnetic: equal antiparallel moments cancel; weak response.
  • Ferrimagnetic: unequal antiparallel moments; net spontaneous magnetization.

Basic difference between ferromagnetic and ferrimagnetic materials

The basic difference is the arrangement of spins:

  • In a ferromagnetic material all neighbouring atomic moments are parallel, so the net magnetization is the full sum of the moments.
  • In a ferrimagnetic material the moments sit on two sublattices that are antiparallel but unequal, so the net magnetization is only their difference.
 Ferro:  ^  ^  ^  ^       Ferri:  ^  v  ^  v

Consequences: ferromagnets (metals) have higher saturation but low resistivity and high eddy loss; ferrimagnets (ceramic ferrites) have lower saturation but very high resistivity, so they are used at high frequencies.

✓ Answer checked by Claude Opus 5.5 (high effort)

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