Antiferromagnetism , is the magnetic ordering of all the magnetic moments of a sample, in the same direction but in the opposite direction (in pairs, for example, or one subnet against another). An antiferromagnet is the material that can have antiferromagnetism.
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- 1 Explanation
- 2 Discovery
- 3 See also
- 4 Sources
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When the order of the magnetic moments is in the same direction but in opposite directions, for example in pairs, the so-called antiferromagnetism occurs. If the absolute value of the paired magnetic moments is the same, they are canceled and if they are different they are reduced. In ferromagnetic materials there is a temperature called Curie, above which they no longer have ferromagnetic properties. Antiferromagnetic materials also lose their properties by raising the temperature, now called Neel’s, which once overcome makes them paramagnetic, exhibiting a permanent magnetic moment in the absence of the applied external field. When we apply a magnetic field some of the moments are aligned parallel to it. By increasing the intensity, everyone’s alignment can be achieved.
The ferromagnetism occurs in ceramic materials where the magnetic moments of the ions are different offering different resistance to the alignment applying a magnetic field. As a result, a net magnetization is obtained. Magnetite exhibits ferrimagnetism, even though the interactions that give rise to the magnetic property are antiferromagnetic.
The visualization of the domains in an antiferromagnetic material was part of the conjecture until recently when it was agreed to examine the interior arrangement, thanks to the application of X-rays. The internal order of these materials is the size of the wavelength. X-ray, which means it is below 10 nanometers.
Therefore the antiferromagnetic interaction is the magnetic interaction that makes the magnetic moments tend to be arranged in the same direction and in the opposite direction, canceling them if they have the same absolute value, or reducing them if they are different. It has to spread throughout a solid to achieve antiferromagnetism. Like ferromagnetism, the antiferromagnetic interaction is destroyed at high temperature by the effect of entropy.
When the temperature above which antiferromagnetism is not appreciated is called the Neel temperature. Above this, the compounds are typically paramagnetic. Antiferromagnets are generally divided into magnetic domains. In each of these domains, all the magnetic moments are aligned.
At the boundaries between domains there is some potential energy, but the formation of domains is offset by the gain in entropy. By subjecting an antiferromagnetic material to an intense magnetic field, some of the magnetic moments align in parallel with it, even at the cost of aligning themselves parallel to their neighbors (overcoming the antiferromagnetic interaction).
Generally, a very strong magnetic field is required to align all the magnetic moments in the sample. These antiferromagnetic interactions can produce large magnetic moments, including magnetization. Ferromagnetism occurs in systems in which an antiferromagnetic interaction between magnetic moments of different magnitude implies a large resulting magnetic moment.
Magnetite is an extended solid that exhibits ferrimagnetism: it is a magnet, although the interactions are antiferromagnetic. Mn12 is a molecule that presents the same phenomenon: antiferromagnetic interactions carry a large magnetic moment of the ground state. On the other hand, spin edging systems with antiferromagnetic interactions show magnetization, due to small angular deviations from the alignment of the magnetic moments, not totally antiparallel.
Louis Eugène Néel ( 1904 – 2000 ), French physicist who made great contributions to magnetism. Following the work of Pierre-Ernest Weiss, who introduced the concept of molecular field and conceived the theory of ferromagnetism ( 1907 ), discovered the phenomenon of antiferromagnetism a early 1930s ; continued with a quantitative theory of ferrimagnetic fields ( 1947). He demonstrated the magnetic memory of rock deposits, which helps explain the physics of terrestrial magnetism. His work contributed to the advancement of techniques related to ferrites (such as electronics), as well as the knowledge of the most common magnetic materials used as insulators.