| Autor: |
Krycka KL; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America., Rhyne JJ; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America., Oberdick SD; Applied Physics, National Institute of Standards and Technology, Boulder, CO 80305, United States of America., Abdelgawad AM; Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, United States of America., Borchers JA; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America., Ijiri Y; Department of Physics and Astronomy, Oberlin College, Oberlin, OH 44074, United States of America., Majetich SA; Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, United States of America., Lynn JW; NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, United States of America. |
| Abstrakt: |
Inelastic neutron scattering is utilized to directly measure inter-nanoparticle spin waves, or magnons, which arise from the magnetic coupling between 8.4 nm ferrite nanoparticles that are self-assembled into a close-packed lattice, yet are physically separated by oleic acid surfactant. The resulting dispersion curve yields a physically-reasonable, non-negative energy gap only when the effective Q is reduced by the inter-particle spacing. This Q renormalization strongly indicates that the dispersion is a collective excitation between the nanoparticles, rather than originating from within individual nanoparticles. Additionally, the observed magnons are dispersive, respond to an applied magnetic field, and display the expected temperature-dependent Bose population factor. The experimental results are well explained by a limited parameter model which treats the three-dimensional ordered, magnetic nanoparticles as dipolar-coupled superspins. |
