Magnetism:
The attraction or Repulsion force exerted by magnets when they are brought nearby is called magnetism. Every substance is made up of small particles called atoms which are further made of electrons, protons, and neutrons. In short, they carry electric charges. When these charges move, they cause magnetism.
Types of Magnetism:
- Diamagnetism
- Paramagnetism
- Ferromagnetism
- Antiferromagnetism
- Ferrimagnetism
Diamagnetism:
Diamagnetism is the weakest form of magnetism that arises
only in the presence external field. It is caused due to a change in the orbital motion of electrons when a magnetic field is applied. There are no magnetic dipoles in the absence of a magnetic
field. When a magnetic field is applied, the dipole moments align themselves opposite to the direction of the applied magnetic field. The magnetic susceptibility, 𝛘m (μr – 1) is negative i.e. B in a
diamagnetic material is less than that of a vacuum.
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| Diamagnetism |
Paramagnetism:
Paramagnetism is caused by the incomplete cancellation of magnetic moments between electron pairs. In paramagnetic materials, it exists without the application of any external magnetic field. However, the magnetic moments are randomly aligned, which causes no net magnetization without any external magnetic field. On application of an external magnetic field, all the dipole moments get aligned in the direction of the field. The magnetic susceptibility is small but positive. i.e. B in a
paramagnetic material is slightly greater than that of a vacuum.
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| Paramagnetism |
Ferromagnetism:
Certain materials possess permanent magnetic moments even when no external magnetic field is applied. This phenomenon is known as
ferromagnetism. Permanent magnetic moments in ferromagnetic materials
arise due to uncancelled electron spins by their
electron structure. The coupling interactions of electron spins of adjacent atoms
cause the alignment of moments with one another. The origin of this coupling is attributed to the electron
structure. Ferromagnetic materials like Fe (26 – [Ar] 4s²3d⁶)
have incompletely filled d orbitals and hence unpaired electron
spins.
Antiferromagnetism:
If the coupling of electron spins results in anti-parallel
alignment, then spins will cancel each other and no net
magnetic moment will arise. This is known as antiferromagnetism. MnO is one such
example. In MnO, O²⁻ ions have no net magnetic moments and the
spin moments of Mn²⁺ ions are aligned anti-parallel to each
other in adjacent atoms.
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| Antiferromagnetism |
Ferrimagnetism:
Certain ionic solids having a general formula MFe₂O₄ where
M is any metal, show permanent magnetism, termed
ferrimagnetism, due to partial cancellation of spin moments.In Fe₃O₄, Fe ions can exist in both 2+ and 3+ states as
Fe²⁺O²⁻ (Fe³⁺)₂(O²⁻)₃ in 1:2 ratio. The antiparallel coupling
between Fe³⁺ (Half in A sites and half in B) moments cancels
each other. Fe²⁺ moments align themselves in the same direction which causes a net magnetic moment.
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| Ferrimagnetism |