Magnetodielectric detection of magnetic quadrupole order
Arrangement of Cu4O12 square cupolas in Ba(TiO)Cu4(PO4)4. © H.Ronnow/EPFL
EPFL scientists with colleagues around the world have demonstrated for the first time the magnetoelectric effect induced by a quadrupolar moments.
Recent extensive researches on magnetism and correlated electron systems have revealed that some vortex-like spin arrangements breaking space-inversion and/or time-reversal symmetries [e.g. magnetic toroidal, monopole, quadrupole moments, and magnetic skyrmion] give rise to emergent magnetoelectrical phenomena such as unconventional anomalous Hall effects and magnetoelectric (ME) effects. However, such vortex-like spin arrangements are rarely stabilized in real crystals. Although the ME activity has been theoretically predicted in the magnetic monopole and quadrupole moments, no concreate experimental demonstration has been reported to date because of a lack of appropriate materials.
A collaboration between Henrik Rønnow's lab at EPFL, Osaka University, Tokyo Institute of Technology, Paul Scherrer Institute, and Rutherford Appleton Laboratory, has now succeeded in demonstrating for the first time the ME effect induced by a quadrupolar moments. The work is published in Nature Communications.
The scientists propose a design idea for realizing the nanoscale vortex-like spin arrangements with ME activities, i.e., magnetic monopole and quadrupole moments, in a magnetic “square cupola” cluster. The square cupola is one of the Johnson solids (92 types in all) which are the mathematically-defined convex polyhedra having regular faces and equal edge lengths.
The team experimentally demonstrated that an antiferroic order of the vortex-like magnetic quadrupoles develops in the real material Ba(TiO)Cu4(PO4)4 comprising Cu4O12 square cupolas. Furthermore, the researchers observed clear magnetodielectric responses associated with the antiferroic quadrupole order — compelling experimental evidence for the design idea.
The present demonstration of the clear-cut design route based on a simple magnetic cluster opens a new stage of research on magnetism and correlated electron systems. It serves as a strategic guideline for the creation of ME active materials on the molecular level. Moreover, the nanometer-scale ME active spin vortex created by this method can potentially be used as a high-storage ME media, which contributes to future nanoscale spintronics. Thus, this work can encourage collaborative research between scientists in a wide variety of fields such as chemistry, solid-state physics, and mathematics for further development.
Reference
K. Kimura, P. Babkevich, M. Sera, M. Toyoda, K. Yamauchi, G. S. Tucker, J. Martius, T. Fennell, P. Manuel, D. D. Khalyavin, R. D. Johnson, T. Nakano, Y. Nozue, H. M. Rønnow, and T. Kimura. Magnetodielectric detection of magnetic quadrupole order in Ba(TiO)Cu4(PO4)4 with Cu4O12 square cupolas. Nature Communications 04 October 2016. DOI: 10.1038/NCOMMS13039