Notes: Magnetic properties of materials
•Magnetism is inseparable from quantum mechanics.
•A classical system in thermal equilibrium cannot have a magnetic moment even in the
presence of an external magnetic field.
•The origins of the magnetic moment of an atom are: the spin of the electrons (spin
magnetic moment), the motion of the electrons around the nucleus and the variation of
the orbital angular momentum created by the application of a magnetic field (orbital
magnetic moment).
•Magnetic substances are classified into three categories: paramagnetic substances dia-
magnetic and ferromagnetic substances.
1 Paramagnetism:
•The atoms/ions of a paramagnetic substance have an individual magnetic moment.
•In the absence of an external magnetic field, the resulting magnetization −→
Mis zero.
•In the presence of an external magnetic field, the majority of the individual magnetic
moments orient towards the direction of −→
B, and the paramagnetic substance exhibits a
non-zero induced magnetization.
•Pierre Curie’s law is the first law that studies the magnetic susceptibility χas a function
of temperature T:χ=C
Twith χ > 0: the magnetic susceptibility and C: Curie constant.
•Magnetization and magnetic field are related by: −→
M=χ−→
B.
•The temperature promotes the disorder of individual magnetic moments.
•The increase of the external magnetic field allows to obtain the order of the individual
magnetic moments.
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