Unconventional Spin Relaxation Involving Localized Vibrational Modes in Ho Single-Atom Magnets

Area of Science:

• Condensed Matter Physics
• Quantum Magnetism
• Surface Science

Background:

• Understanding spin relaxation in single-atom magnets is crucial for developing quantum technologies.
• Holmium (Ho) atoms on MgO/Ag(100) surfaces present a unique system for studying magnetic properties at the atomic scale.

Purpose of the Study:

• To investigate the spin relaxation dynamics of Ho single atom magnets on a MgO/Ag(100) surface.
• To determine the influence of temperature and magnetic field on spin relaxation.
• To elucidate the underlying mechanisms responsible for observed relaxation behaviors.

Main Methods:

• Experimental measurements of spin relaxation as a function of temperature and magnetic field.
• Theoretical calculations using density functional theory (DFT).

Main Results:

• Ho single atom magnets demonstrate thermally activated spin relaxation at low magnetic fields.
• Relaxation times exceed 1000 seconds up to 30 K and 8 T, contrasting with faster relaxation in single molecule magnets and bulk impurities at high fields.
• A two-phonon Raman process, activated by local vibrations, was identified as the dominant relaxation mechanism, showing a peak near zero field and suppression at higher fields.

Conclusions:

• Local vibrations play a critical role in the spin relaxation of axially coordinated Ho atoms.
• The observed unconventional magnetic field dependence of relaxation is attributed to a field-suppressed two-phonon Raman process.
• This study highlights the importance of lattice dynamics in controlling magnetic properties at the single-atom level.