Domain wall dynamics and Barkhausen jumps in thin-film permalloy microstructures

Abstract

Domain wall jump-amplitude and velocity distributions associated with Barkhausen jumps in a 300-Å-thick thin-film permalloy and a 200ϫ 200 ͑m͒ 2 ϫ 220-Å-thick permalloy sample microstructrue are measured using a high-speed magneto-optic Kerr effect polarimeter. The jump-amplitude and velocity distributions are obtained for applied-field sweep rates from 0.9 Oe/ s to 6.3ϫ 10 4 Oe/ s. The velocity distributions exhibit statistical properties consistent with the stochastic description of field-driven domain wall motion developed by ABBM ͓B. Alessandro, C. Beatrice, G. Bertotti, and A. Montorsi, J. Appl. Phys. 68, 2901 ͑1990͔͒. Averaged velocity distributions exhibit the expected increase of dynamic coercivity as the sweep rate is increased, and the maximum domain wall velocity measured as a function of the applied field at the stochastic depinning threshold is shown to be governed by the mobility limit imposed by local spin damping. The averaged velocity ͗͑H − H 0 ͒͘ obtained from the distributions is observed to depart from the commonly accepted lineardependence model, especially at higher drive-field sweep rates. This departure is interpreted as an indication of a sweep-rate-dependent mobility. Sweep-rate-dependent jump-amplitude distributions P͑⌬M͒ versus ⌬M are obtained from the Barkhausen effect data. These distributions exhibit power-law behavior with a sharp cutoff at large values of ⌬M. Attempts to reconcile the measured jump-amplitude distributions and sweep-ratedependent exponents with various models of universal scaling are described. Power-law fits to P͑⌬M͒ distributions measured to optimize temporal resolution ͑required for the velocity-distribution studies͒ yield a sweeprate-dependent exponent that varies from ␤ = 1.45± 0.05 to ␤ = 1.0 as dH / dt is varied from 25 Oe/ s to 6.3 ϫ 10 4 Oe/ s. This range of sweep-rate-dependent ␤ agrees with the ABBM model and is consistent with the sweep-rate dependence exponent rule that predicts linear sweep-rate scaling for the adiabatic value ␤ =3/2 ͓R. A. White and K. A. Dahmen, Phys. Rev. Lett. 91, 085702 ͑2003͔͒. Additional experiments on both 300-Å-thick continuous films and the same microstructures optimized for ⌬M sensitivity yield a more accurate value of ␤ ͑␤ = 1.33± 0.01͒, which corresponds to a CZDS model ͑␤ =4/3͒ ͓C. Cizeau, S. Zapperi, G. Durin, and H. E. Stanley, Phys. Rev. Lett. 79, 4669 ͑1997͒; Phys. Rev. B 58, 6353 ͑1998͔͒. Adiabatic limit values of ␤ determined from all of the experiments are definitively outside the range ␤ ϳ 1.0 for self-organized criticality in a two-dimensional system ͓P. Bak, C. Tang, and K. Wiesenfeld, Phys. Rev. Lett. 59, 381 ͑1987͔͒, and also appear to be inconsistent with experimental results for 900 Å Fe films on MgO in which ␤ = 1.1 was obtained from rescaled P͑⌬M͒ distributions ͓E. Puppin, Phys. Rev. Lett. 84, 5415 ͑2000͔͒. The sweep-rate dependence of ␤ determined in a system that manifests an adiabatic limit of ␤ that is not equal to 3 / 2 also violates the model of White and Dahman that prohibits sweep-rate-dependent s...

Single domain wall dynamics in thin magnetic wires

“…Such a value corresponds well to the one found in [9,11]. Different temperature dependence than Co 68 Mn 7 Si 15 B 10 microwire could be explained by the different pinning mechanism in the both samples (compare H sw $ f(T) given in Fig.…”

“…This adiabatic motion is thus characterized by intermittent jumps from defect to defect governed (at a local position) by a generalized Eq. (2) [11,12] …”

Temperature Dependence of the Magnetic Hysteresis Curves in Magnetic Multilayers

“…The steps of the external magnetic eld, ΔH, are related to the coercivity. As described in our previous paper 5) , the physical cause of the coercivity is related to the delay of the response of the Barkhausen jump [15][16][17][18][19] by the applied magnetic eld. From the temperature dependence of the step of the effective magnetic eld that was introduced by eq.…”

The Barkhausen Effects and Nano-System Magnetizations in Fe

“…The Bohr magneton: ® B = eh/4³m = 9.274 © 10 ¹24 [Am 2 ] becomes the element of these magnetic dipole moments, where constants are e = 1.602 © 10 16 [C], h = 6.626 © 10…”

“…Realistic magnetizations are cleared by the use of the large scale computing resources, where exact results have not been produced till in these days. 16) Nevertheless, the correct theory already existed, the first stage studies of these in a century ago could not correctly discuss the magnetizations because of very few computing resources.…”