Phonons, which are quasi-particles associated with sounds or lattice vibrations, have long been thought to possess negligible magnetic moments. However, a recent experiment carried out by researchers at Nanjing University and the Chinese Academy of Sciences has challenged this belief. Their study, published in Nature Physics, revealed the existence of giant phonon magnetic moments in Fe2Mo3O8, a polar antiferromagnet. This groundbreaking discovery has opened up new possibilities for understanding the interplay between magnetism and phonons.
The main objective of the study conducted by the researchers was to gain a deeper understanding of the relationship between phonons and magnetism. By focusing on the antiferromagnet Fe2Mo3O8, they aimed to establish a direct link between lattice vibrations and magnetic processes, providing opportunities for phononic control of magnetic dynamics and the development of novel spin information devices.
To achieve their research goals, the team utilized two key techniques: magneto-Raman spectroscopy and inelastic neutron scattering. These methods allowed them to investigate the phononic nature of low-lying excitations in Fe2Mo3O8 single crystals. By measuring the phonon frequency shift under magnetic fields, they were able to determine the phonon magnetic moments (PMM) using the phonon Zeeman effect.
The researchers made an unexpected discovery during their experiments. They found that the phonon magnetic moments in Fe2Mo3O8 were significantly enhanced near the boundaries between the antiferromagnetic and paramagnetic phases. This enhancement was unique and had not been observed in previous studies.
The study was a collaboration between Prof. Yuan Wan’s team at the Chinese Academy of Sciences and Prof. Jinsheng Wen’s lab at Nanjing University. Prof. Wan’s group conducted a symmetry analysis to formulate a minimal model that explained the fundamental physics underlying the experiment, while Prof. Wen was responsible for synthesizing the sample and collecting the neutron measurements.
The most remarkable finding of the study was the detection of a sixfold enhancement in the phonon magnetic moment in Fe2Mo3O8. This enhancement resulted from a 600% ferrimagnetic fluctuation near the magnetic transition. These findings suggest that the phonon magnetic moment could surpass the magnetic moment of an electron or a magnon mode and even diverge with the magnetic susceptibility.
Implications for Future Research
The discovery of giant phonon magnetic moments in Fe2Mo3O8 opens up new avenues for further research. The experimental findings, together with the theoretical microscopic model proposed by the researchers, could lead to exciting discoveries about the interplay between magnetism and phonons. Future studies could explore non-equilibrium regimes, such as investigating chiral phonons-driven magnetic dynamics or transient ferromagnetism.
The study conducted by researchers at Nanjing University and the Chinese Academy of Sciences has unveiled an unprecedented phenomenon: giant phonon magnetic moments in Fe2Mo3O8. This breakthrough discovery challenges the conventional belief that phonons possess negligible magnetic moments. The findings open up exciting possibilities for further research in understanding magnetism and phonons, paving the way for potential advancements in phononic control of magnetic dynamics and the development of novel spin information devices.
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