Electricity and magnetism are closely related: Power lines generate a magnetic flux, rotating magnets in generator produce electricity. However, the phenomenon is far more complicated: electrical & magnetic properties of certain materials also are couple one another. Electrical properties of some crystals are often influenced by magnetic fields—and the other way around. In this case one speaks of a “magnetoelectric effect.” It plays a crucial technological role, for instance in certain sorts of sensors or in search for new concepts of data storage.
A special material was investigated that, 1st glance, no magnetoelectric effect would be expected in the least . But careful experiments have now shown that the effect are often observed in this material, it only works completely differently than usual. It are often controlled in highly sensitive way: Even small changes in direction of the magnetic flux can switch the electrical properties of material to a totally different state.
Symmetry controls the coupling
“Whether the electrical & magnetic properties of a crystal are coupled or not depends on the crystal’s internal symmetry,” says Prof. Andrei Pimenov from the Institute of Solid State Physics at TU Wien. “If the crystal features a high degree of symmetry, for instance , if one side of the crystal is the reflection of mirror of the opposite side, then for theoretical reasons there are often no magnetoelectric effect.”
This applies to the crystal, which has now been examined in detail—a so-called langasite made from lanthanum, gallium, silicon & oxygen, doped with holmium atoms. “The crystal structure is so symmetrical that it should actually not allow any magnetoelectric effect. And in this case of weak magnetic fields there’s indeed no coupling whatsoever with the electrical properties of the crystal,” says Andrei Pimenov. “But if we increase the strength of the magnetic flux, something remarkable happens: The holmium atoms change their quantum state & gain a moment of a magnet moment. This breaks the interior symmetry of the crystal.”
From a purely geometrical point of view, the crystal remains symmetrical, but the magnetism of the atoms has got to be taken under consideration also , and this is often what breaks the symmetry. Therefore the electrical polarization of the crystal are often changed with a magnetic flux . “Polarization is when the positive(+ve) & negative(-ve) charges within the crystal are displaced alittle bit, with reference to one another ,” explains Pimenov. “This would be easy to achieve with an electrical field—but thanks to the magnetoelectric effect, this is often also possible using magnetic flux .”
It’s not the strength, it is the direction
The stronger the magnetic flux , the stronger its effect on electrical polarization. “The relationship between polarization & magnetic flux strength is approximately linear, which is nothing unusual,” says Andrei Pimenov. “What is remarkable, however, is that the connection between polarization and therefore the direction of the magnetic flux is strongly non-linear. If you change the direction of the magnetic flux alittle bit, the polarization can completely tip over. this is often a new latest form of magnetoelectric effect, which wasn’t known before.” So alittle rotation may decide whether the magnetic flux can change the electrical polarization of the crystal or not.
Possibility for brand spanking new storage technologies
“The magnetoelectric effect will play an increasingly important role for various technological applications,” says Andrei Pimenov. “In a next step, we’ll try to attempt to change magnetic properties with an electrical field rather than changing electrical properties with a magnetic flux . in theory , this could be possible in just an equivalent way.”
If this succeeds, it might be a promising new thanks to store data in solids. “In magnetic memories like computer hard disks, magnetic fields are needed today,” Pimenov explains. “They are generated with magnetic coils, which needs a comparatively great amount of energy & time. If there have been an immediate way to switch the magnetic properties of a solid-state memory with an electrical field, this could be a breakthrough.”
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