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From iron to chromium: Which elements exhibit strong magnetism at room temperature?
The magnetic structure in a magnetic material refers to the ordered arrangement of magnetic spins within an ordered crystal lattice. This area of research is a branch of solid-state physics. Not all solid materials are magnetic. In fact, most materials are non-magnetic in the absence of an external magnetic field. This is due to the Pauli exclusion principle, which causes the spins of electrons to cancel each other out, keeping the charge density of the material uniform. .
However, in certain circumstances, the material's electrons spontaneously break this symmetry and exhibit strong magnetic behavior.
When the material is in its ground state, ferromagnetism is its most prominent feature. In this state, the spins of all electrons are aligned in the same direction, producing a macroscopic magnetization. For example, typically, there are more electrons with a spin quantum number called "up" than with "down", and this asymmetry provides a stable overall magnetic field for the material.
Antiferromagnetism, in contrast, is a relatively simple magnetic structure in which electron spins point alternately up and down, ultimately leading to the cancellation of the macroscopic magnetization. Therefore, understanding these fundamental magnetic structures is crucial for in-depth studies of the magnetic properties of materials.
In more complex magnetic structures, such as magnetic frustration, the directions of local spins can form three-dimensional arrangements, leading to more diverse magnetic behaviors.
In addition to the basic magnetic structure, the effect of temperature changes on magnetic materials cannot be ignored. In the Stoner magnetic mode, the mean-field interaction of electrons leads to a uniform decrease in the local magnetization as the temperature increases. In contrast, in the case of local magnetic moments, the electronic states are confined to specific atoms and their interaction range is shorter. Therefore, understanding the magnetic behavior of materials at different temperatures is an important direction for further research.
Observing these magnetic structures involves evaluating the magnetic throughput over temperature and the magnitude of the external magnetic field. The use of neutron diffraction technology can help scientists obtain three-dimensional images of spin arrangements. Neutrons reveal the magnetic structure of a material by the way they scatter off atomic nuclei. In the temperature range above the magnetic transition point, the material exhibits paramagnetic behavior, but once the temperature drops below this point, the intensity of neutron scattering will change.
In addition, as the spins are ordered, new Bragg reflections emerge, a manifestation of the formation of a superstructure.
In the study of magnetic elements, only iron, cobalt and nickel show spontaneous strong magnetism at room temperature, and their Curie temperatures are all higher than room temperature (Tc > 298K). Barium cobalt zirconium exhibits spontaneous magnetization at 293 K, close to room temperature, and is occasionally considered a fourth strongly magnetic element. Thorium and cerium are paramagnetic at room temperature, but become gyromagnetic below their Neel temperature and eventually ferromagnetic below their Curie temperature, but their magnetic behavior is often more complex.
More complex magnetic structures, such as the antiferromagnetism of iron and other transition metals such as nickel and cobalt, also change with temperature. Other elements, such as lithium, molybdenum, and chromium, exhibit more complex antiferromagnetic arrangements, but their specific spin relationships and stability are still under investigation.
It is worth noting that in some elements, such as copper and silver, the magnetism mainly comes from their nuclear magnetic moment, which is a weak magnetic property, resulting in their switching temperature close to absolute zero.
With the progress of materials science, various new technologies such as transformer technology have emerged, which allow us to study magnetic structures more deeply without having to rely on neutron sources or synchrotron radiation sources. Such research is not only of great significance for the understanding of materials, but also helpful for the design of future electronic devices or magnetic components.
However, will these complex magnetic structures have a more profound impact on future technological development?
