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The former - the paramagnetic effect is determined by the inherent magnetic moment (total magnetic moment) of atoms (molecules). And the inherent magnetic moment can be zero, why? Think about it, there are actually two spin directions for electrons: up and down. In most substances, the number of electrons with upward and downward rotation is almost the same, and the spin magnetic moments they generate cancel out each other. Moreover, the orbital magnetic moments of electrons also cancel out each other due to different "revolution" directions, so only a small part or even zero of the inherent magnetic moment remains.

The latter, the diamagnetic effect, is determined by the orbital magnetic moment of the electron, which can also be said to be determined by the orbital magnetic moment of all electrons in the atom. Under the action of an external magnetic field, this magnetic moment will never be zero because the atom will have electrons. This means that no matter what medium is placed in a magnetic field, it will produce a diamagnetic effect!

For paramagnetic matter, its inherent magnetic moment is not zero, so the magnetization of its internal atoms (molecules) is achieved by the combination of paramagnetic and diamagnetic effects. However, the paramagnetic effect is much stronger than the diamagnetic effect, so it generally shows paramagnetism.

The inherent magnetic moment of the substance itself is zero, which means that the magnetism of the atoms or molecules that make up the substance is zero, so it naturally has no magnetism.

The inherent magnetic moment of matter itself is not zero, such as iron, which has many magnetic chips (small magnetic needles) inside. However, due to the disorderly arrangement of many magnetic chips on macroscopic objects, they cancel out each other and make themselves non magnetic.

As mentioned above, with the increase of temperature, ferromagnetic material can become paramagnetic due to the role of magnetic chips. When the temperature reaches the Curie temperature, thermal motion makes it impossible for the magnetic moments to be arranged in parallel, disrupting the arrangement of electron spins. This means that the spontaneous magnetization zone is gone, and the electron spins become disorderly, canceling each other out and becoming paramagnetic. As a result, ferromagnetism disappears.