What happens to the susceptibility of ferromagnetic substance if temperature is decreased ? a) Increases b) Decreases c) Remains same d) May increase or decrease

In ferromagnetic substances, susceptibility (χ) is strongly temperature-dependent due to the alignment of magnetic domains. As temperature decreases, thermal agitation reduces, allowing magnetic domains to align more easily with an external magnetic field. This increases the net magnetization and thus susceptibility increases.

Mathematically, susceptibility follows the Curie–Weiss law near the Curie temperature (T_C): $$\chi =\frac{C}{T-T_C}$$ where $C$ is the Curie constant. Below $T_C$, χ is high and increases further as $T\to 0$. Thus, susceptibility increases when temperature is decreased.

Answer: a) Increases