The product of magnetic susceptibility ($\chi$) and absolute temperature (T) is constant for a

According to Curie's law, the magnetic susceptibility ($\chi$) of a paramagnetic substance is inversely proportional to its absolute temperature ($T$).

$\chi \propto \dfrac{1}{T}$

$\chi = \dfrac{C}{T}$

$\chi T = C$

where $C$ is Curie's constant. Thus, the product of magnetic susceptibility and absolute temperature is constant for a paramagnetic substance.

For diamagnetic substances, susceptibility is independent of temperature. For ferromagnetic substances, susceptibility follows the Curie-Weiss law ($\chi = \dfrac{C}{T - T_c}$) above the Curie temperature.

Answer: paramagnetic substance.