Direct Observation of Anapoles by Neutron Diffraction

Area of Science:

• Condensed Matter Physics
• Materials Science
• Neutron Scattering

Background:

• Magnetic neutron scattering is a key technique for probing magnetic structures.
• Electronic multipoles, such as dipoles, play a crucial role in material properties.
• Anapoles, a type of electronic multipole, possess unique polar and magnetic characteristics.

Purpose of the Study:

• To expand the scope of magnetic neutron scattering by observing novel electronic multipoles.
• To investigate the presence and characteristics of electronic Dirac dipoles (anapoles) in magnetic materials.
• To analyze the magnetic structure of a specific ferromagnet using neutron scattering.

Main Methods:

• Utilized magnetic neutron scattering to probe the magnetic structure of Sm_{0.976}Gd_{0.024}Al_{2}.
• Focused on basis-forbidden reflections, including the (2, 2, 2) reflection, to detect specific multipole orders.
• Measured magnetic amplitudes at selected reflections for detailed structural analysis.

Main Results:

• Observed electronic Dirac dipoles (anapoles) in a zero-magnetization ferromagnet, Sm_{0.976}Gd_{0.024}Al_{2}.
• These anapoles were found to be polar (parity odd) and magnetic (time odd).
• Measured magnetic amplitudes at four basis-forbidden reflections were in excellent agreement with calculations based on the appropriate magnetic space group.

Conclusions:

• The observation of electronic Dirac dipoles significantly expands the capabilities of magnetic neutron scattering.
• The results confirm the presence of anapoles in a zero-magnetization ferromagnet with a diamond-type structure.
• This study provides a foundation for exploring anapoles and other exotic electronic multipoles in magnetic materials.