Why can't magnets be adsorbed on some metal surfaces?

Why can't magnets be adsorbed on some metal surfaces?

The premise that a magnet can be adsorbed on a metal surface is that the metal can be "magnetized".

What is magnetic moment?

The nucleus is composed of protons and neutrons, and the outer layer has electrons moving around the nucleus quickly. Magnetism is formed in the way electrons rotate around the nucleus and its rotation. Magnetism is not only formed by the revolution and rotation of electrons around the nucleus. What's more important is that the eccentricity of the circumstance forms magnetism, that is, the eccentricity of electron movement shows positive and negative polarity, and then magnetism is formed. It will also react with each other, and then mix together, showing the "magnetic moment" of the nucleus.

What kind of metal can be magnetized?

Magnetization is to make the magnetic pitch direction of the magnetic domains in the magnetic material become consistent. There are magnetic moments in the nucleus of a metal atom and the spin of its peripheral electrons, as well as the movement of electrons in orbit. The vector sum of the various magnetic moments in the atom is the net magnetic moment, or atomic magnetic moment.

If the orientation of the various magnetic moments in the atom is roughly the same, that is, the order of the atomic magnetic moment is very high, then a strong magnetic field will be generated from this, and this substance is a magnet. For metals such as iron, cobalt, and nickel, their magnetic moments will not completely cancel out, and there is a certain net magnetic moment. As a result, these metals will be magnetized into magnets in the magnetic field generated by the original magnet, and they will attract each other with the original magnet through electromagnetic force. The magnetic moments of other metal atoms are almost completely cancelled out, so they will not be magnetized, so they will not be attracted by the magnet.

That is to say, when a magnet is close to some metals, its original messy magnetic moment sequence will be magnetized, showing magnetism, but the magnetic moment of some metals is still messy and cannot be magnetized. This is why the magnetism of the magnet is affected by temperature, because the temperature affects the movement of electrons, which leads to the disorder of the magnetic moment, which manifests as the disappearance or weakening of magnetism.

Therefore, some doors and windows in life can be adsorbed and some cannot be adsorbed, depending on whether the alloy contains ferromagnetic substances.

How many kinds of magnetism are there? According to the adsorption capacity can be roughly divided into the following categories.

Diamagnetism

Diamagnetism means that the magnetic moments of electrons in the atoms of some substances cancel each other out, and the total magnetic moment is zero. All organic compounds are diamagnetic substances.

Paramagnetism 

Refers to the magnetic properties of a material that responds weakly to a magnetic field. The magnetic moment can take any direction in the magnetic field. All the atoms or ions in these materials produce very small magnetic moments under the action of a magnetic field. For example, many transition metals: copper, silver, gold, zinc, cadmium, and mercury are not easily adsorbed by magnets.

Ferromagnetic

Refers to the magnetic moments of adjacent atoms or ions in a substance that are roughly aligned in the same direction in certain regions due to their interactions. When the applied magnetic field increases, the alignment degree of the combined magnetic moments of these regions will increase accordingly The phenomenon of reaching a certain limit value. That is, in the absence of an external magnetic field, ferromagnets can also exhibit magnetism. Only four metal elements are ferromagnetic above room temperature, namely iron, cobalt, nickel and gadolinium.

Antiferromagnetic

Inside the antiferromagnetic substance, the spins of adjacent valence electrons tend to be opposite. The net magnetic moment of this substance is zero and no magnetic field is generated. This kind of substance is relatively uncommon, and most antiferromagnetic substances only exist in low temperature conditions. If the temperature exceeds the Néel temperature, it usually becomes paramagnetic. For example, chromium, manganese, light lanthanides.

Ferrimagnetism

The main magnetic phenomenon is the material made of ferrimagnetic substance, called ferrimagnetic material. When an external magnetic field is applied, the change of its magnetization with the external magnetic field is similar to that of a ferromagnetic substance. Ferrites are mostly ferrimagnetic.

Superparamagnetic

Refers to a ferromagnetic substance with a single domain structure when the particle is smaller than the critical size. When the temperature is lower than the Curie temperature and higher than the block temperature, it exhibits paramagnetic characteristics, but under the action of an external magnetic field, its paramagnetic susceptibility is much higher than that of general paramagnetic materials, which is called superparamagnetism. When the external magnetic field is removed, the residual magnetism disappears quickly. This effect is common when the magnetic particles in the storage disk are extremely small, and will become extremely unstable under the influence of temperature, causing "thermal agitation", resulting in the loss of stored data.