We report a systematic measurement of the electron-phonon thermalization timescales as a function of the sample base temperature in Ni using femtosecond electron diffraction. A strong temperature dependence has been observed in the vicinity of the Curie point. By assuming that ultrafast demagnetization completes well before the electron-phonon thermalization, this correlation between thermalization time and sample base temperature can be fit by a modified three temperature model describing the energy transfer among charge, spin and phonon subsystems. The results indicate that charges and spins can be characterized by a unified temperature during ultrafast lattice heating. *I was invited to be part of this research project as part of my Research Experience for Teachers program sponsored by The National High Magnetic Field Lab on the campus of Florida State University. I participated in the experimentation during the Summer of 2009. The paper on this experiement was published in Physical Review B 81, 220301 (R) (2010).
John E. Clark
Science Teacher, Deltona High School