3.6 Magnetic Properties

  d and f Block Elements

• Permagnetic substances is one which is weakly attracted in magnetic field.

• Damagnetic substances is one which is repelled by a magnetic field.

• The paramagnetic behaviour is possible due to the presence of one or more single filled atomic orbitals whereas diamagnetic behaviour is due to the presence of paired electrons.

• Most of the transition metals and ions have unpaired electrons in $(n-1) d$ orbitals and they are paramagnetic in nature.

• Due to increase in unpaired electrons in $d$-orbital from one to five magnetic moment and paramagnetic nature increases.

• The metals like $Fe$, $Co$ and $Ni$ are highly paramagnetic and used in pemanent magnets are called ferromagnetic.

• The alloy Alnico $Al$ (12%), $Ni$ (20%), $Co$ (50%) and $Fe$ (10%) is used in permanent magnet.

• Magnetic character is expressed in terms of magnetic moment arises from spin of electrons.

• Magnetic moment is expressed in Bh or magneton (B.M.). $$1B.M. = \frac{{eh}}{{4\pi MC}}$$ when $h$ = the plancks constant, $e$ = electronic charge, $c$ = velocity of light and $m$ = mass of electron.

• Effective magnetic moment $(M_{eff})$ of paramagnetic substance is $$M_{eff}=\sqrt {n(n + 2)} $$ $n$ = the no. of unpaired electrons and B.M. is bhor magneton.