  A dynamic phase transition (DPT) with respect to the period P of an applied
alternating magnetic field has been observed previously in numerical
simulations of magnetic systems. However, experimental evidence for this DPT
has thus far been limited to qualitative observations of hysteresis loop
collapse in studies of hysteresis loop area scaling. Here, we present
significantly stronger evidence for the experimental observation of this DPT,
in a [Co(4 A)/Pt(7 A)]_3-multilayer system with strong perpendicular
anisotropy. We applied an out-of-plane, time-varying (sawtooth) field to the
[Co/Pt]_3 multilayer, in the presence of a small additional constant field,
H_b. We then measured the resulting out-of-plane magnetization time series to
produce nonequilibrium phase diagrams (NEPDs) of the cycle-averaged
magnetization, Q, and its variance, Var(Q), as functions of P and H_b. The
experimental NEPDs are found to strongly resemble those calculated from
simulations of a kinetic Ising model under analagous conditions. The similarity
of the experimental and simulated NEPDs, in particular the presence of a
localized peak in the variance Var(Q) in the experimental results, constitutes
strong evidence for the presence of this DPT in our magnetic multilayer
samples. Technical challenges related to the hysteretic nature and response
time of the electromagnet used to generate the time-varying applied field
precluded us from extracting meaningful critical scaling exponents from the
current data. However, based on our results, we propose refinements to the
experimental procedure which could potentially enable the determination of
critical exponents in the future.
