New measurement technique reveals unexpected properties of magnetic material
Temperature is an important material property well familiar to all of us. The physical background of temperature of any material is the vibration of its constituents, for example atoms or molecules. The larger the vibrations the hotter is the temperature of the material. These vibrations are called phonons and they are important to understand phenomena such as thermal conductivity in solids or liquids. In addition, in magnetic materials there are magnons, vibrations of the magnetization. Like the phonons, the magnon population increases with increasing temperature of the magnetic system. A measure of the magnon population is called the magnon temperature. Magnons and phonons interact in magnetic materials whereby the strength of the interaction depends on the material.
Researchers of the group of Professor Burkard Hillebrands at the University of Kaiserslautern (Physics Department, State Research Center OPTIMAS and Graduate School of Excellence MAINZ) have developed a new technique to measure the magnon temperature. They are using an instrument called Brillouin light scattering spectrometer which is observing the shift in the frequency of the laser light (see picture). This technique was now utilized for the first time to measure the magnon temperature and, thus, investigate the interaction of magnons and phonons. The investigations revealed that the interaction of magnons and phonons is much stronger than previously thought.
The new application of the measurement technique and the results of this study will have important implications for the field of spin caloritronics. In fact, the experimental findings challenge contemporary theories in the field and suggest new directions for further investigations. In the new research field of spin caloritronics scientists are exploiting the potential of magnon phonon interactions for future applications in magnetic memory and magnetic sensor devices.
The work of the team from Oxford, Kiew and Kaiserslautern has recently been published in the prestigious scientific journal “Physical Review Letters”:
Direct measurement of magnon temperature: new insight into magnon-phonon coupling in magnetic insulators; M. Agrawal, V.I. Vasyuchka, A.A. Serga, A.D. Karenowska, G.A. Melkov, B. Hillebrands; Phys. Rev. Lett.111, 107204 (2013)
For more information, please contact Prof. Dr. Burkard Hillebrands:
hilleb(at)physik.uni-kl.de, Phone +49 (0) 631 205-4228 / -2202