2D Power-Law Scaling Behavior of Barkhausen Avalanches

Sung-Chul Shin

Department of Physics and Center for Nanospinics of Spintronic Materials, KAIST, Daejeon 305-701, Korea

A ferromagnetic materials shows a sequence of discrete and jerky domain jumps, known as the Barkhausen effect. Recently, interest in the Barkhausen effect has grown as it is a good example exhibiting dynamical critical scaling behavior, evidenced by experimental observation of a power-law distribution of the Barkhausen jump size. So far, most studies have been carried out on 3D bulk samples by a classical inductive technique and very few experiments have been done on 2D systems mainly due to the low signal intensity of the inductive method. In this talk, we will present critical scaling behavior of Barkhausen avalanches of various 2D ferromagnetic thin films investigated via time-resolved magneto-optical microscopy, enabling to directly image Barkhausen avalanches at criticality.¹ A statistical analysis of the fluctuating size of Barkhausen jumps from numerous repetitive experiments shows a power-law scaling behavior in the 2D ferromagnetic systems. In 2D Co films. the critical exponent is found to be ~ 1.33 independent of a film thickness from 5-50 nm. Strikingly, the power-law distribution in 2D MnAs films is found that the critical exponent varies continuously from 1.32 to 1.04 as the temperature increases.² This is the first time to observe that the scaling behavior of the Barkhausen criticality of a given ferromagnetic film is experimentally tuneable by varying the temperature (not dimensionality). I will also discuss a universal scaling behavior of the first arrival time of a traveling magnetic domain wall into a finite space-time observation window, which can be explained by an unbiased 2D random-walking model.³

1. S.-C. Shin et al., J. Appl. Phys. (invited) 103, 07D907 (2008).
2. K.-S. Ryu et al., Nature Physics 3, 547 (2007).

3. M.-Y. Im et al., Phys. Rev. Lett., in press (2008).