Asymmetric magnetic disorder observed in thermally activated magnetization reversal of exchange-biased IrMn/CoFe films

Lee, Hun-Sung; Ryu, Kwang-Su; You, Chun‐Yeol; Jeon, Kun-Rok; Yang, See‐Hun; Parkin, Stuart S. P.; Shin, Sung‐Chul

doi:10.1016/j.jmmm.2012.07.038

Cited by 8 publications

(4 citation statements)

References 33 publications

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“…As mentioned earlier, there is considerable interest in the experimental investigations of Barkhausen noise in thin films and samples of different thickness, e.g. [7,[9][10][11][12][13][14][15][16]. The behaviour of Barkhausen avalanches observed in these systems depends on the sample composition, driving mode, and the segment of the hysteresis loop where the analysed signal originates, as well as the sample thickness.…”

Section: Discussionmentioning

confidence: 99%

“…The underlying magnetisationreversal processes in these disordered ferromagnetic materials typically exhibit domain nucleation and domain-wall propagation under slow driving by the external field [4,5]. Hence, there is an increased interest in the experimental investigations of the Barkhausen noise (BHN) accompanying the magnetisation reversal along the hysteresis loop in nanowires [6], thin films [7][8][9][10][11][12][13][14], and systems with a finite thickness [15,16]. On the other hand, theoretical and numerical investigations of the impact of the specific sample shape on the magnetisation reversal processes are still in their infancy [17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

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The critical Barkhausen avalanches in thin random-field ferromagnets with an open boundary

Tadić

Mijatović

Janićević

et al. 2019

Sci Rep

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The interplay between the critical fluctuations and the sample geometry is investigated numerically using thin random-field ferromagnets exhibiting the field-driven magnetisation reversal on the hysteresis loop. The system is studied along the theoretical critical line in the plane of random-field disorder and thickness. The thickness is varied to consider samples of various geometry between a two-dimensional plane and a complete three-dimensional lattice with an open boundary in the direction of the growing thickness. We perform a multi-fractal analysis of the Barkhausen noise signals and scaling of the critical avalanches of the domain wall motion. Our results reveal that, for sufficiently small thickness, the sample geometry profoundly affects the dynamics by modifying the spectral segments that represent small fluctuations and promoting the time-scale dependent multi-fractality. Meanwhile, the avalanche distributions display two distinct power-law regions, in contrast to those in the two-dimensional limit, and the average avalanche shapes are asymmetric. With increasing thickness, the scaling characteristics and the multi-fractal spectrum in thicker samples gradually approach the hysteresis loop criticality in three-dimensional systems. Thin ferromagnetic films are growing in importance technologically, and our results illustrate some new features of the domain wall dynamics induced by magnetisation reversal in these systems.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The critical Barkhausen avalanches in thin random-field ferromagnets with an open boundary

Tadić

Mijatović

Janićević

et al. 2019

Sci Rep

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“…Disordered ferromagnetic films exhibiting criticality at the hysteresis loop [4,11,[16][17][18] are conveniently modeled by two-dimensional random-field Ising model (2D-RFIM) [19][20][21], as described in Section II. Besides, these model systems are also of high importance for theoretical considerations for the following reasons.…”

Section: Introductionmentioning

confidence: 99%

Dynamical implications of sample shape for avalanches in 2-dimensional random-field Ising model with saw-tooth domain wall

Tadić

2018

Physica A: Statistical Mechanics and its Applications

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We study dynamics of a built-in domain wall (DW) in 2-dimensional disordered ferromagnets with different sample shapes using random-field Ising model on a square lattice rotated by 45 degrees. The saw-tooth DW of the length L x is created along one side and swept through the sample by slow ramping of the external field until the complete magnetisation reversal and the wall annihilation at the open top boundary at a distance L y . By fixing the number of spins N = L x × L y = 10 6 and the random-field distribution at a value above the critical disorder, we vary the ratio of the DW length to the annihilation distance in the range L x /L y ∈ [1/16, 16]. The periodic boundary conditions are applied in the y-direction so that these ratios comprise different samples, i.e., surfaces of cylinders with the changing perimeter L x and height L y . We analyse the avalanches of the DW slips between following field updates, and the multifractal structure of the magnetisation fluctuation time series. Our main findings are that the domain-wall lengths materialised in different sample shapes have an impact on the dynamics at all scales. Moreover, the domain-wall motion at the beginning of the hysteresis loop (HLB) probes the disorder effects resulting in the fluctuations that are significantly different from the large avalanches in the central part of the loop (HLC), where the strong fields dominate. Specifically, the fluctuations in HLB exhibit a wide multi-fractal spectrum, which shifts towards higher values of the exponents when the DW length is reduced. The distributions of the avalanches in this segments of the loops obey power-law decay and the exponential cutoffs with the exponents firmly in the mean-field universality class for long DW. In contrast, the avalanches in the HLC obey Tsallis density distribution with the power-law tails which indicate the new categories of the scale invariant behaviour for different ratios L x /L y . The large fluctuations in the HLC, on the other hand, have a rather narrow spectrum which is less sensitive to the length of the wall. These findings shed light to the dynamical criticality of the random-field Ising model at its lower critical dimension; they can be relevant to applications of the dynamics of injected domain walls in two-dimensional nanowires and ferromagnetic films.

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“…In our samples, asymmetries of the MHLs are evident in figure 1 (for example, the descending curve in the 180 • MHL for t AF = 15 nm is sharper than the ascending curve). Asymmetric magnetization and domain behaviour in exchange bias has been the subject of other works [42][43][44][45][46] and has often been explained as differences in the reversal behaviour along and against the exchange bias vector. Microscopy studies of the magnetic microstructures in these cases have shown rapid domain wall motion along one field direction resulting in an abrupt change in magnetization, while the opposite branch of the magnetization loop is divided into a rotational part, followed by partial switches, and finally, domain wall motion [42,43], thus explaining the sharp transition along one direction and more gradual curve along the other.…”

Section: Resultsmentioning

confidence: 99%

Critical curves in NiFe/FeMn bilayers with varying antiferromagnetic layer thickness

Adams¹,

Cimpoesu²,

Benit³

et al. 2021

J. Phys. D: Appl. Phys.

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The effect of antiferromagnetic (AF) layer thickness on exchange bias was studied in a series of NiFe(50 nm)/FeMn(t) bilayers through both irreversible and reversible experiments at room temperature. The exchange bias was evaluated in the sample plane both through measurement of the major hysteresis loops and probing the reversible susceptibility. The critical curve was constructed to map the angular dependence of the magnetization switching and exchange bias, which is found to evolve as a function of AF layer thickness. Ferromagnetic resonance absorption was measured at several frequencies and angles, and angular-dependent absorption curves were plotted. A comparison is made between the recorded exchange bias using the three methods. The measurements reported are supported by simulations under a generalized Stoner–Wohlfarth model, and general limitations of the experiment are discussed.

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Asymmetric magnetic disorder observed in thermally activated magnetization reversal of exchange-biased IrMn/CoFe films

Cited by 8 publications

References 33 publications

The critical Barkhausen avalanches in thin random-field ferromagnets with an open boundary

The critical Barkhausen avalanches in thin random-field ferromagnets with an open boundary

Dynamical implications of sample shape for avalanches in 2-dimensional random-field Ising model with saw-tooth domain wall

Critical curves in NiFe/FeMn bilayers with varying antiferromagnetic layer thickness

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