Magnetic Properties of Materials

Magnetic Properties of Materials

The response of a material to an external magnetic field is determined by its magnetic susceptibility ($\chi$) and relative permeability ($\mu_r$). These quantities allow us to classify materials into three main categories: diamagnetic, paramagnetic, and ferromagnetic.

Classification Based on Susceptibility ($\chi$)

• Diamagnetic: $\chi$ is negative and small in magnitude.
• Paramagnetic: $\chi$ is positive and small.
• Ferromagnetic: $\chi$ is positive and very large.

Classification Based on Relative Permeability ($\mu_r$)

Recall that $\mu_r = 1 + \chi$. This gives another way to classify materials:

• Diamagnetic: $\mu_r$ is slightly less than 1 ($0 \le \mu_r < 1$).
• Paramagnetic: $\mu_r$ is slightly greater than 1 ($1 < \mu_r < 1 + \varepsilon$), where $\varepsilon$ is a small positive number.
• Ferromagnetic: $\mu_r$ is much greater than 1 ($\mu_r \gg 1$). …