Evidence for a dynamic phase transition in[Co/Pt]3magnetic multilayers

Abstract

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(4Å)/Pt(7Å)] 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, σ 2 (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 σ 2 (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.

Effective field investigation of dynamic phase transitions for site diluted Ising ferromagnets driven by a periodically oscillating magnetic field

“…As an example, a DPT occurring in high frequency region is represented by Jiang et al [3] using the surface magneto-optical Kerr-effect technique for epitaxially grown ultrathin Co films on a Cu(001) surface. For a [Co(4A o )/Pt(7A o )] multilayer system with strong perpendicular anisotropy, an example of DPT is shown by Robb et al [4]. In this study, they found that the experimental nonequilibrium phase diagrams are found to strongly resemble the dynamic behavior calculated from simulations of a kinetic Ising model.…”

Driven-dissipative Ising model: Mean-field solution

“…One of the key results is the existence of a so-called dynamical phase transition, where the cycle-averaged magnetization becomes non-zero in a singular fashion. This has recently been supported by experimental evidence in the dynamics of thin ferromagnetic films [34].…”

Investigation of oscillation frequency and disorder induced dynamic phase transitions in a quenched-bond diluted Ising ferromagnet

“…On the experimental picture, it can be said that a great many of experimental studies have been devoted to DPTs and hysteresis behaviors of Co films on a Cu (001) surface [32], [Co(4A o )/Pt(7A o )] multi-layer system with strong perpendicular anisotropy [33], thin polycrystalline Ni 80 Fe 20 films [34], ultrathin ferromagnetic Fe/Au(001) films [35], epitaxial Fe/GaAs(001) thin films [36], epitaxial single ferromagnetic fcc NiFe(001), fcc Co(001), and fcc NiFe/Cu/Co(001) layers [37], Fe 0.42 Zn 0.58 F 2 [38], finemet thin films [39], and epitaxial Fe/GaAs(001) and Fe/InAs(001) ultrathin films [40]. After some detailed experimental investigations, it has been observed that experimental non-equilibrium dynamics of considered real magnetic systems strongly resemble the dynamic behav-ior predicted from theoretical calculations of a kinetic Ising model.…”