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| Computer simulations reveal faults in rare earth material. Credit: Thomas Schrefl. Click to enlarge. |
Researchers at St. Pölten University of Applied Sciences in Austria have shown that rare earth permanent magnets may contain local deformations in the crystal lattice of the material, resulting in a weakening of the magnetic force of the material in these areas. This could be avoided by optimizing the material structure, the researchers said, which would save resources by reducing the amount of rare earth elements required for applications.
The team presented the results of its high-end computer simulations, carried out as part of a Special Research Program funded by the Austrian Science Fund FWF, in an invited presentation at the annual meeting of the The Minerals, Metals & Materials Society (TMS 2011) in San Diego, California.
The rare earths have many unique physical and chemical properties
which make them important, if not critical, components in a variety of
energy technologies, noted Karl Gschneidner from Iowa State University in a separate presentation at TMS 2011. In the transportation sector La is used in batteries; Ce in gasoline cracking catalysts and in three-way catalytic converters; Nd in electric motors; Y as an oxygen sensor to control lean/rich fuel mixtures and as an oxidation resistant coating in aircraft turbine engines; and
Y, Gd, Lu as the hosts and Eu, Tb, Dy and Er as the activators in phosphors
for display units. In the energy generating and transmission sectors: Nd
in Nd-Fe-B permanent magnets for wind generators; and Y in YBa2Cu3O7
superconductors in both wind generators and electrical transmission lines.
The team at St. Pölten University studied the exact structure of neodymium-iron-boron (Nd-Fe-B) magnets.
Our simulations show disturbances in the crystalline structure in neodymium magnets. Such disturbances cause the magnetizing direction to change in these areas. In a so-called anisotropic magnet, like the neodymium magnet, in which all parts must have the same magnetizing direction, this phenomenon weakens the magnet.
—Prof. Thomas Schrefl
The team’s simulations show that such disturbances in the junctions between individual material grains occur when three different grains meet. In these triple junctions, a non-magnetic enclosure is formed and the crystal lattice near the enclosure is disturbed. In the same region, a high demagnetizing field weakens the magnet further.
The influence of disturbances on the magnet’s behaviour were found in multiscale simulations that take into account several different dimensions—from the atomistic to the visible range. Conventional simulations were unable to cover this range of size until now. It was the combination of individual numerical computational methods, such as fast boundary element methods and tensor grid methods for computing the magnetic fields, which made it possible, FWF said. The development was achieved by Prof. Schrefl’s team as part of the Special Research Program ViCoM – Vienna Computational Materials Laboratory.
The FWF-funded Special Research Program includes 12 project groups with more than 50 scientists working on describing material properties.
Resources
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Thomas Schrefl; Simon Bance; Harald Oezelt; Gino Hrkac. Modeling of Magnetization Reversal in Nd-Fe-B Based Sintered Magnets (TMS2011)
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Karl Gschneidner. The Rare Earth Contributions to Global Energy Solutions (TMS 2011)