According to the physicist organization network report, British scientists observed the maximum atomic displacement in the thermal expansion of metal magnets. This discovery will play an important role in the development of future new materials such as high-efficiency sensors and refrigerants.
Under normal circumstances, most materials will deform slightly in the magnetic field. In a recent study, Alesand Bakza and his collaborators at the University of Cambridge in the United Kingdom discovered that a magnetic material containing manganese, CoMnSi, has a displacement of 2% between two adjacent atoms. The maximum displacement distance found in the magnet. Magnets have a strong magnetoelastic effect, and it is this mechanism that causes large displacements of atoms in certain materials.
Through a method called high-efficiency neutron diffraction combined with magnetic force measurement, scientists found in observation that changes in the magnetic field can cause a sudden increase in the magnetic properties of the material, called the variable magnetic transition stage. At this time, the magnetic change of the material comes from a strong magnetoelastic coupling between atoms. Magnetoelastic coupling as a precursor to the critical point of magnetization, strengthens the deformation effect, so there is a 2% "huge" change in the distance between manganese atoms during heating.
Physicist Carl Sandman of Imperial College London explained that in the magnetic field, driven by the exchange between two pairs of different manganese atoms, although the thermal expansion of the entire volume of the material is very small, it has a significant length in one axis The decrease is accompanied by an increase in temperature or magnetic field and positive thermal expansion in the other two axes. When the volume change of the material is small as a whole, the deformation will be large in one direction. In particular, textured materials will show greater deformation than other polycrystalline materials, and polycrystalline materials are more prone to "average" changes.
The researchers said that this discovery is helpful for research in many fields. Such as magnetic refrigeration materials and magnetostrictive materials, their response changes in the magnetic field can be used as sensors or actuators. And the researchers noticed that it may make the mixed material have the same large magnetoelastic effect.
Unlike gas volatile refrigeration, solid magnetic refrigerants are highly efficient room temperature refrigeration. Sandman said that changing the state of the material using a magnetic field can provide a cooling effect, which comes from the transformation of the solid form, rather than the refrigeration of the traditional compression refrigerator that evaporates liquid into gas. If in some materials with a harmonious lattice structure, the cooling effect of the magnetic refrigerant will usually be stronger.
The usual "magnetoelastic coupling" is mainly derived from rare earth compounds, and metal materials can only undergo large magnetoelastic coupling during the magnetic transition. Rare earths are used to make batteries and permanent magnets. Due to their key role in environmental protection technology, the demand for rare earths is increasing day by day. Therefore, this discovery also helps to reduce the demand for rare earth raw materials.
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