Discovery of the Origin of the Giant Magnetostriction Effect

Giant Magnetostriction and Large Piezoelectric Effect Are Based on Similar Principles

2010.05.11

National Institute for Materials Science

Dr. Xiaobing Ren, Group Leader of the Ferroic Physics Group, Sensor Materials Center, National Institute for Materials Science , and Dr. Sen Yang, Research Fellow of the same group, together with Dr. Keisuke Kobayashi, Station Leader of the NIMS Beamline Station, and others discovered a structural “morphotropic phase boundary” accompanied by magnetism in a ferromagnetic material, and also found a giant magnetostriction effect (giant magnetostriction) 100 times that of iron with the boundary composition.

Abstract

  1. Dr. Xiaobing Ren, Group Leader of the Ferroic Physics Group, Sensor Materials Center, National Institute for Materials Science (NIMS; President: Sukekatsu Ushioda), and Dr. Sen Yang, Research Fellow of the same group, together with Dr. Keisuke Kobayashi, Station Leader of the NIMS Beamline Station, and others discovered a structural “morphotropic phase boundary” accompanied by magnetism in a ferromagnetic material, and also found a giant magnetostriction effect (giant magnetostriction) 100 times that of iron with the boundary composition. These discoveries clarified the mechanism of the giant magnetostriction effect, which had been unknown for 30 years, and overturned the accepted view in the field of magnetism that “crystal structure does not depend on magnetic state.” As a result, it can now be understood that the giant magnetostriction effect and the high piezoelectric effect in ferroelectric materials have the same origin.
  2. All ferroelectric materials, beginning with iron, display a magnetostriction effect, in which the material expands or contracts when subjected to a magnetic field. If this effect is sufficiently large, application to many type of sensors and actuators can be expected. However, practical application is difficult, as virtually all ferroelectric materials have a weak level of magnetostriction on an order from only 1/1,000,000 to 1/100,000. On the other hand, a giant magnetostrictive effect 100 times greater than ordinary magnetostriction was discovered in the magnetostrictive material Terfernol-D, which was discovered 30 years ago, but the principle of that effect was not well understood. Consequently, there were no guidelines for obtaining the giant magnetostriction effect, and the search for other giant magnetostrictive materials depended on empirical methods.
  3. Using a high angular resolution powder X-ray diffraction device at the Synchrotron Radiation Facility (SPring-8), the team led by Dr. Ren discovered that the magnetically heterogeneous phase boundary of a ferromagnetic material is simultaneously a structurally heterogeneous phase boundary, in other words, a “morphotropic phase boundary.” This discovery was a world’s first. In addition to overturning the commonsense view in the field of magnetism that “crystal structure does not depend on magnetic state,” this discovery also makes it possible to understand that the “ferromagnetic morphotropic phase boundary” is identical with the “ferroelectric morphotropic phase boundary” which can be seen in ferroelectrics. Furthermore, the NIMS team also discovered a giant magnetostriction effect 100 times larger than the magnetostriction effect in iron in the phase boundary composition of the rare earth ferromagnetic alloy TbCO2-DyCO2. This showed substantially the same phenomenon as the maximum piezoelectric effect in the phase boundary composition of ferroelectrics. From this research, the origin of the giant magnetostriction effect can be interpreted as “magnetic/lattice instability in the morphotropic phase boundary,” and can be understood in a similar manner to the large piezoelectric effect in the ferroelectric/piezoelectric material PZT and similar substances.
  4. Based on these research results, guidelines can be proposed for the search for new giant magnetostrictive materials (and in particular, low cost giant magnetostrictive materials) using this new knowledge in the future. Thus, this work is expected to contribute to the development and practical application of giant magnetostrictive materials.
  5. The results of this research are scheduled for publication in the Journal of the American Physical Society, Physical Review Letters, in the near future.