The magnetic needle of a magnetic compass is made up of $\qquad$ .

Materials suitable for permanent magnets should have

The magnetic susceptibility is negative for

$A$ soft ferromagnetic material is placed in an external magnetic field. The magnetic domains:

$A$ paramagnetic sample shows a net magnetisation of $6 \, A/m$ when it is placed in an external magnetic field of $0.4 \, T$ at a temperature of $4 \, K$. When the sample is placed in an external magnetic field of $0.3 \, T$ at a temperature of $24 \, K$,then the magnetisation will be $...... \, A/m$.

When a magnetic substance is heated,then it