General existence and determination of conjugate fields in dynamically ordered magnetic systems

Metamagnetic fluctuation characteristics near dynamic phase transitions

We experimentally explore the magnetization dynamics of thin ferromagnetic Co films with uniaxial in-plane anisotropy near the dynamic phase transition (DPT) and, in particular, we study the temporal characteristics of anomalous metamagnetic fluctuations that occur in its vicinity, and for which no thermodynamic equivalent exists. For this purpose, we measure the real-time evolution of magnetization trajectories in the relevant dynamic phase space, conduct a Fourier analysis of these experimental results and compare it to a model, in which the fluctuating metamagnetic behavior occurs in a purely random manner, following individual state probability distributions. We find excellent quantitative agreement in between our experimental results and the random state model, clearly indicating that multiperiod time-correlations of magnetic states are not relevant in our DPT system, not even for the occurrence of the anomalous metamagnetic fluctuations that are nonetheless associated with nonperiodic magnetic state evolutions.

Experimental Observation of Critical Scaling in Magnetic Dynamic Phase Transitions

We explore the critical behavior of dynamic phase transitions in ultrathin uniaxial Co films. Our data demonstrate the occurrence of critical fluctuations, which define the critical regime, and in which we conduct a scaling analysis of the dynamic order parameter Q, utilizing a dynamic analog to the Arrott-Noakes equation of state. Our results show dynamic critical exponents that agree with the 2D Ising model as theoretically predicted. However, equilibrium critical exponents of our sample agree with the 3D Ising model. We argue that these differences between dynamic and thermodynamic behavior are due to fundamentally different length scales at which dimensional crossovers occur.