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Updated: May 25, 2026

High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
Published on: June 28, 2016
High-order Ho multipoles in HoB2C2 observed with soft resonant x-ray diffraction
A J Princep1, A M Mulders, E Schierle
1School of PEMS, UNSW, Canberra, ACT, 2600, Australia.
Soft resonant x-ray Bragg diffraction reveals dominant hexadecapole order in HoB2C2. Quadrupolar interactions are strong, but quadrupolar order requires a specific magnetic ground state for orbital lock-in.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Materials
Background:
- HoB2C2 exhibits a complex combined magnetic and orbitally ordered phase.
- Understanding the interplay of magnetic and quadrupolar moments is crucial for novel quantum materials.
Purpose of the Study:
- To investigate the Ho 4f multipole moments in the ordered phase of HoB2C2.
- To determine the contributions of various multipole moments (dipole to hexacontatetrapole) to the observed ordering.
- To elucidate the relationship between magnetic and quadrupolar ordering and their interactions.
Main Methods:
- Soft resonant x-ray Bragg diffraction (SRXD) at the Ho M4,5 edges.
- Analysis of energy and azimuthal angle dependence of scattered x-rays.
- Comparison with neutron diffraction and non-resonant x-ray diffraction data.
Main Results:
- Dominant hexadecapole (rank 4) order was identified in HoB2C2.
- Dipole and octupole magnetic terms have negligible influence.
- Magnetic and quadrupolar order parameters are distinct, with quadrupolar order increasing more sharply below the orbital ordering temperature.
- Quadrupolar interaction is strong, leading to orbital lock-in via a quasi-doublet ground state induced by magnetic order.
Conclusions:
- The study successfully characterized higher-order multipole moments in HoB2C2 using SRXD.
- Quadrupolar ordering is strongly influenced by the magnetic ground state, requiring specific conditions for orbital lock-in.
- SRXD provides distinct insights into magnetic and quadrupolar order parameters compared to other diffraction techniques.
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