1301.4885 (V. Lopez-Flores et al.)

Role of critical spin fluctuations in ultrafast demagnetization of
transition-metal rare-earth alloys    [PDF]

V. Lopez-Flores, V. Halte, C Stamm, N. Pontius, M. Hehn, E. Otero, E. Beaurepaire, C. Boeglin

Ultrafast magnetization dynamics induced by femtosecond laser pulses have been measured in ferrimagnetic Co0.8Gd0.2, Co.74Tb.26 and Co.86Tb.14 alloys. Using X-ray magnetic circular dichroism at the Co L3, Tb M5 and Gd M5 edges we demonstrate for the first time that the demagnetization dynamics are composition and element dependent. We show that a thermalization time as fast as 280 is observed for the rare-earth when pumped toward the compensation temperature, where the magnetic moments of the two sublattices compensate, and it is limited to 500 fs when pumped toward the Curie temperature (Tc). We propose critical spin fluctuations in the vicinity of TC as the mechanism which reduces the demagnetization rates of the 4f electrons in transition-metal rare-earth alloys.

View original: http://arxiv.org/abs/1301.4885