Question -
Answer -
(i) Ferromagnetism
(ii)Paramagnetism
(iii)Ferrimagnetism
(iv)Antiferromagnetism
(v)12-16 and 13-15 group compounds.
Answer
(i) Ferromagnetism: The substancesthat are strongly attracted by a magnetic field are called ferromagneticsubstances. Ferromagnetic substances can be permanently magnetised even in theabsence of a magnetic field. Some examples of ferromagnetic substances areiron, cobalt, nickel, gadolinium, and CrO2.
In solid state, themetal ions of ferromagnetic substances are grouped together into small regionscalled domains and each domain acts as a tiny magnet. In an un-magnetised pieceof a ferromagnetic substance, the domains are randomly-oriented and so, theirmagnetic moments get cancelled. However, when the substance is placed in amagnetic field, all the domains get oriented in the direction of the magneticfield. As a result, a strong magnetic effect is produced. This ordering ofdomains persists even after the removal of the magnetic field. Thus, theferromagnetic substance becomes a permanent magnet.
Schematic alignment of magnetic moments in ferromagnetic substances
(ii) Paramagnetism: The substances that are attracted by a magnetic field arecalled paramagnetic substances. Some examples of paramagnetic substances are O2,Cu2t, Fe3t, and Cr3t.
Paramagnetic substances get magnetised in amagnetic field in the same direction, but lose magnetism when the magneticfield is removed. To undergo paramagnetism, a substance must have one or moreunpaired electrons. This is because the unpaired electrons are attracted by amagnetic field, thereby causing paramagnetism.
(iii) Ferrimagnetism: The substances in which the magnetic moments of the domainsare aligned in parallel and anti-parallel directions, in unequal numbers, aresaid to have ferrimagnetism. Examples include Fe3O4 (magnetite),ferrites such as MgFe2O4 and ZnFe2O4.
Ferrimagnetic substances are weakly attracted bya magnetic field as compared to ferromagnetic substances. On heating, thesesubstances become paramagnetic.
Schematic alignment of magnetic moments in ferrimagnetic substances
(iv) Antiferromagnetism: Antiferromagneticsubstanceshave domain structures similar to ferromagnetic substances, but areoppositely-oriented. The oppositely-oriented domains cancel out each other’smagnetic moments.
Schematic alignment ofmagnetic moments in antiferromagnetic substances
(v) 12-16 and 13-15group compounds: The 12-16 groupcompounds are prepared by combining group 12 and group 16 elements and the13-15 group compounds are prepared by combining group 13 and group15 elements.These compounds are prepared to stimulate average valence of four as in Ge orSi. Indium (III) antimonide (IrSb), aluminium phosphide (AlP), and galliumarsenide (GaAS) are typical compounds of groups 13-15. GaAs semiconductors havea very fast response time and have revolutionised the designing ofsemiconductor devices. Examples of group 12-16 compounds include zinc sulphide(ZnS), cadmium sulphide (CdS), cadmium selenide (CdSe), and mercury (II) telluride(HgTe). The bonds in these compounds are not perfectly covalent. The ioniccharacter of the bonds depends on the electronegativities of the two elements.