As a ferromagnetic material undergoes a hysteresis loop, its...

The magnetic susceptibility $\chi$ is defined as the ratio of magnetization $M$ to the magnetizing field intensity $H$, given by $\chi = \dfrac{M}{H}$.

At the point of retentivity on the hysteresis loop, $H = 0$ while $M \neq 0$. This gives $\chi = \dfrac{M}{0} \rightarrow \infty$. Thus, the susceptibility can be infinite.

At the point of coercivity, $M = 0$ while $H \neq 0$. This gives $\chi = \dfrac{0}{H} = 0$. Thus, the susceptibility can be zero.

In the regions of the loop where $M$ and $H$ have opposite signs (such as the second and fourth quadrants), the ratio $\dfrac{M}{H}$ is negative, meaning $\chi < 0$. Thus, the susceptibility can be negative.

Since $\chi$ varies continuously throughout the hysteresis loop, it does not maintain a fixed value.