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Measurements of critical slowing down in a 2-dimensional Ising system


Given that the dynamics, or time-evolution, of the ferromagnetic  properties of thin films has generated an enormous literature, it is  surprising that a fundamental dynamical property such as critical slowing  down near a phase transition has hardly been investigated experimentally.  In the context of ferromagnetism, critical slowing down refers to the  prediction that the relaxation of the magnetization toward equilibrium  occurs more and more slowly as the temperature, Tc, of a phase transition  is approached.  The relaxation time is predicted to scale as a power law  in (T-Tc)/Tc with dynamical exponent z, essentially because the size of  the magnetically correlated regions grow like a power law near Tc.  Although this theoretical description of a phase transition was worked out  starting in the 1960s, the measurement of the dynamical critical exponent  has proven to be very difficult, even for a conceptually simple system  like the two-dimensional Ising model. We have recently approached this  problem through the first studies of critical slowing down in ultrathin  ferromagnetic films.  By measuring the magnetic susceptibility of  Fe/W(110) near the Curie temperature, we are able to determine the dynamical critical exponent for the 2D Ising model in an internally  consistent manner.