Anomalous hyperfine interaction in CoF(2) investigated by high resolution neutron spectroscopy

Area of Science:

• Condensed Matter Physics
• Materials Science
• Neutron Scattering

Background:

• Investigating low-energy excitations in magnetic materials is crucial for understanding phase transitions.
• Cobalt difluoride (CoF2) exhibits complex magnetic ordering, making it a candidate for studying fundamental magnetic phenomena.

Purpose of the Study:

• To probe the low-energy excitations in CoF2 using neutron spectroscopy.
• To characterize the behavior of these excitations as a function of temperature.
• To determine if these excitations can serve as an order parameter for the antiferromagnetic phase transition.

Main Methods:

• Utilized a high-resolution back-scattering neutron spectrometer to measure energy scans.
• Employed a CoF2 powder sample at various temperatures, including below and near the magnetic ordering temperature.
• Analyzed inelastic peak positions and intensities to extract physical parameters.

Main Results:

• Observed distinct inelastic peaks at approximately 0.728 µeV at low temperatures (3.46 K).
• These peaks shifted towards lower energies with increasing temperature, merging with the elastic peak at the magnetic ordering temperature (TN ≈ 37 K).
• The energy of these inelastic peaks was identified as originating from transitions within the hyperfine-split nuclear levels of 59Co isotopes.

Conclusions:

• The hyperfine splitting in CoF2 functions as an order parameter for the antiferromagnetic phase transition.
• The critical exponent (β = 0.313 ± 0.007) derived from this order parameter aligns with 3D Ising model predictions.
• The observed deviation from linear scaling in hyperfine splitting suggests the presence of an unquenched orbital moment in CoF2.