Magnetic Materials and Properties:

Diamagnetic Materials

• Shortcut Method: Diamagnetic materials have a relative permeability slightly less than 1 and a negative magnetic susceptibility that is very small $(μ_r < 1, χ_m < 0)$.

• Trick: Remember that diamagnetic materials weakly repel magnetic fields, so their relative permeability is less than 1.

Paramagnetic Materials

• Shortcut Method: Paramagnetic materials have a relative permeability slightly greater than 1 and a positive magnetic susceptibility that is very small $(μ_r > 1, χ_m > 0)$.

• Trick: Paramagnetic materials are weakly attracted to magnetic fields, so their relative permeability is slightly greater than 1.

Ferromagnetic Materials

• Shortcut Method: Ferromagnetic materials have a very high relative permeability, which can reach several thousand, and a very high positive magnetic susceptibility $(μ_r » 1, χ_m » 0)$. They also exhibit a Curie temperature, above which they lose their ferromagnetism and become paramagnetic $(T_c)$.

• Trick: Remember that ferromagnetic materials are strongly attracted to magnetic fields and can be permanently magnetized.

Magnetic Field of the Earth

• Shortcut Method: The magnetic field strength at the Earth’s surface is approximately 0.5 Gauss (50 μT), and it varies in strength and direction depending on location. The magnetic declination is the angle between the geographic North Pole and the magnetic North Pole, while the magnetic inclination (dip) is the angle between the magnetic field lines and the horizontal plane.

• Trick: Visualize the Earth’s magnetic field as a giant bar magnet with its poles near the geographic poles, but slightly offset.