Magnetic Effects of Current and Magnetism - Magnetic Properties of Materials (Dia, Para, Ferro)

Magnetization ($M$): It is the net magnetic moment per unit volume of the material, expressed as $M = \frac{m_{net}}{V}$. Its SI unit is $A/m$.

Magnetic Intensity ($H$): The external magnetic field that induces magnetism in a material. The relation between $B$, $H$, and $M$ is given by $B = \mu_0(H + M)$.

Magnetic Susceptibility ($\chi$): It measures how easily a substance can be magnetized. It is defined as the ratio of the intensity of magnetization to the magnetic intensity: $\chi = \frac{M}{H}$.

Relative Permeability ($\mu_r$): The ratio of the permeability of the medium to the permeability of free space. It is related to susceptibility by the equation $\mu_r = 1 + \chi$.

Diamagnetic Materials: These are substances that develop weak magnetization in a direction opposite to the external magnetic field. Their susceptibility $\chi$ is small and negative (e.g., $Bi$, $Cu$, $H_2O$).

Paramagnetic Materials: These substances develop weak magnetization in the same direction as the external field. Their susceptibility $\chi$ is small and positive (e.g., $Al$, $Na$, $O_2$).

Ferromagnetic Materials: These substances develop strong magnetization in the direction of the external field. They exhibit domain structure and have very large positive susceptibility $\chi$ (e.g., $Fe$, $Co$, $Ni$).

Curie's Law: For paramagnetic materials, the magnetic susceptibility is inversely proportional to the absolute temperature $T$, expressed as $\chi = \frac{C}{T}$, where $C$ is the Curie constant.

Curie Temperature ($T_C$): The temperature above which a ferromagnetic material transitions into a paramagnetic material. The susceptibility follows the Curie-Weiss Law: $\chi = \frac{C}{T - T_C}$ for $T > T_C$.

Hysteresis: The phenomenon where the magnetic induction $B$ lags behind the magnetizing field $H$. Key points include Retentivity (residual $B$ when $H=0$) and Coercivity (reverse $H$ needed to make $B=0$).