Diamagnetisme

An atom's net magnetic dipole moment is the vector sum of its orbital and the spin moment.

Materials consisting of atoms with paired electrons have zero net magnetic moments, and under an external magnetic field, moments opposite to the field are induced. Such materials are called diamagnets.

In an external magnetic field, an electron with angular velocity along the field direction experiences an inward Lorentz force, accelerating its motion. Thus, an additional current in the initial current direction induces a dipole moment opposite to the field direction.

Similarly, an electron with angular velocity opposite to the field experiences a deceleration due to the outward Lorentz force. The additional current is again clockwise, opposite to the initial current direction. The additional current results in a moment opposite to the field. 

Thus, the induced moment is always directed opposite to the external field.

When placed in an external magnetic field, diamagnetic materials repel the magnetic field, and the relative permeability of diamagnets is less than unity. Hence, the susceptibility is negative and temperature independent for diamagnets.