The magnetic susceptibility of a ferromagnetic substance is

$A$ paramagnetic material has $10^{28} \text{ atoms/m}^3$. Its magnetic susceptibility at temperature $350 \text{ K}$ is $2.8 \times 10^{-4}$. Its susceptibility at $300 \text{ K}$ is

$A$ sensitive magnetic instrument can be shielded very effectively from outside magnetic fields by placing it inside a box of

What materials should be used to make permanent magnets?

The variation of magnetic susceptibility $(\chi )$ with temperature for a diamagnetic substance is best represented by:

The materials suitable for making electromagnets should have