Why are there only magnets that attract iron, but not gold, silver, or copper?

Magnets are one of the more common items in everyone’s daily life. It is estimated that many friends have had this question, that is why there are only magnets that can hold iron, but no magnets that can hold gold, silver, copper, and aluminum. , Magnetic silver, magnetic copper and magnetic aluminum? To solve this question, we need to briefly discuss the principle of magnetism.

Principle of magnetism

According to the different conditions under which magnetic objects generate magnetic fields, they can be divided into two categories, one is permanent magnetic objects, and the other is electromagnetic objects. The black magnets we usually see belong to permanent magnets; and the metal coils will show certain magnetism after being energized. After the current disappears, the magnetic field disappears, so this kind of object is electromagnetic. Also called soft magnetic.

Whether it is a permanent magnetic substance or an electromagnetic object, according to Maxwell's equation, the generation of a magnetic field is attributed to the movement of electric current, that is, electric field. This is well understood for electromagnetic objects. The flow of electric charges in a conductor generates an electric current, thus forming an electromagnetic field. For permanent magnets that are not energized, the generation of the magnetic field is essentially inseparable from the electric field. This electric field is composed of the atoms in the substance composed of the magnet, and the electrons outside the core are arranged regularly when they move around the nucleus at high speed. To.

It is undeniable that all substances in the world have magnetism, but the expression of magnetism is different. Generally speaking, it can be divided into three categories. One is paramagnetic substances, that is, objects under the action of an external magnetic field. It can generate the same additional magnetic field environment as the external magnetic field. Most substances have this property, such as transition metals, rare earth elements and their compounds, organic radicals, and oxygen. The second is the diamagnetic field material, that is, the object generates an additional magnetic field opposite to the external magnetic field under the action of an external magnetic field. For example, many metals such as copper and inert gases have such properties. The third type is ferromagnetic materials. Under the action of an external magnetic field, the same additional magnetic field as the external magnetic field is generated by paramagnetic materials, but the strength of this additional magnetic field is much greater, such as iron, cobalt, nickel and other metals.

For ferromagnetic substances, each magnet is composed of many small "separated regions", these small regions are called magnetic domains. When there is no external magnetic field, the atoms in each magnetic domain show a regular arrangement, but the atoms in each magnetic domain interact with each other, that is to say, the magnetic forces cancel each other out, and the whole does not exhibit magnetism. But if under the action of the external magnetic field (magnetization process), the arrangement direction of the atoms in these magnetic domains will be more vectorized, and they will be arranged along the magnetization direction, so that the magnetic moment direction of each magnetic domain is in line with the external magnetic field. If the direction is the same, the total magnetic moment of the magnet as a whole is not zero, and it shows magnetism to the outside.

The medium on which the magnetic force propagates

Up to now, scientists have summarized the interaction forces between matter and matter in the entire universe into four basic forms, namely gravity, electromagnetic force, strong interaction force and weak interaction force. Among them, electromagnetic force and gravity are ubiquitous in the macro, meso and micro worlds, but the larger the spatial scale, the more obvious the effect of gravity when interacting. The strong interaction force and the weak interaction force mainly reflect the force action mode at the microscopic atomic level.

Regardless of the force, the scientists determined that their "propagation" process must rely on the corresponding and special "space field", which requires specific microscopic particles to undertake transmission through their directional movement. Force field effect. According to the Standard Model of Particle Physics, up to now, scientists have discovered the elementary particles corresponding to electromagnetic force, strong interaction force, and weak interaction force. Electromagnetic force corresponds to photons, and strong interaction force corresponds to gluons. The weak interaction force corresponds to the W and Z bosons. At present, scientists have not discovered a clear transmission medium, and it is generally explained by hypothetical "gravitons".

Since magnetic force belongs to the category of electromagnetic force, the generation of magnetic field requires electromagnetic field as a medium environment, which means that photons, which carry the propagation of electromagnetic force, are also an important medium for the transmission of magnetic force. The reason why we cannot see the light in the magnetic field is because the frequency of the light corresponding to the photon that transmits the magnetic force is not within the range of visible light at all. At the same time, in order to better express the generation of magnetic force, scientists have introduced the concept of virtual photons, which is the constant exchange of virtual photons between charged particles, which triggers the transition of electronic energy levels and finally releases radiation of different frequencies. , Resulting in electromagnetic interaction force.

Why is there no magnetic gold, magnetic silver, magnetic copper, or magnetic aluminum?

According to the previous analysis of the material properties of the constituent materials, iron-cobalt-nickel is a ferromagnetic material, which is easily magnetized by an external magnetic field, and the additional magnetic field generated is strong, so permanent magnets can be manufactured. However, gold, silver, copper, and aluminum do not have the same magnetic domain microstructure in terms of microstructure as the external magnetic field environment, so it is difficult to be magnetized in the same direction, so it is impossible to make a magnet that attracts the corresponding metal. .

Strictly speaking, gold, silver, copper, and aluminum also have the "instinct" of magnetism. It is just the opposite of iron, cobalt and nickel. They are diamagnetic substances. Among the atoms that make up these substances, their electron shells are all electrons. Full", the total magnetic moment of the electron is zero. When affected by the external magnetic field environment, a certain amount of electron circulation can also be generated in the atom, but the direction of the magnetic moment generated by the circulation is opposite to the external magnetic field environment, and the displayed magnetic susceptibility is a very low value, only -10 The ^(-6) level is very weak, far from achieving the purpose of attracting or repelling the corresponding metal. This is why the magnetic gold, magnetic silver, magnetic copper, and magnetic aluminum cannot be manufactured.