Dynamic Critical Phenomena and Universal Behavior of Soft Modes in Low-Dimensional Periodic Magnetic Systems - Presentazione poster by R. Zivieri - Conferenza internazionale

Since the pioneering work of Halperin and Hohenberg [1] on the generalization of scaling laws to dynamical properties of critical phenomena, the critical behavior of dynamic excitations in physical systems has been investigated as a function of temperature. In this study a quantitative formulation of the dynamic critical phenomena of soft modes in periodic and low-dimensional magnetic systems is given by investigating as a function of the external magnetic field H at fixed temperature. In these systems, whose geometries are in the nanometric range, the frequency curvature of the two lowest soft modes, namely the end mode (EM) and the fundamental (F) mode, as a function of H in the vicinity of the critical field Hc is expressed via dynamic critical exponents. The critical phase transitions are characterized by the following universal quantities: a) the ratio between the critical field and the aspect ratio; (b) the ratio between the dynamic critical exponents of the EM and F mode frequencies [2]. This behavior has been found according to micromagnetic simulations based on the dynamical matrix method (DMM) applied to different types of low-dimensional periodic systems. Some numerical results for a critical phase transition corresponding to the rotation of the static magnetization M from the hard to the easy axis with decreasing H for 2D antidot lattices (ADLs) with different hole diameters have been performed [2]. For these low-dimensional periodic systems: a) the ratio hc/r (with hc= Hc/4π M and r =d/s with d the hole diameter and s the hole separation) is 0.04; (b) the ratio between the dynamic critical exponents of the F mode and the EM frequencies is 0.4 confirming the universal behavior. References: [1] B.I. Halperin and P.C. Hohenberg, Phys. Rev. Lett. 19, 700 (1967). [2] R. Zivieri et al., J. Phys. Cond. Matter 25, 336002 (2013)