[論文レビュー] Antiferromagnetic Barkhausen noise induced by weak random-field disorder

Bosiljka Tadić|arXiv (Cornell University)|Feb 16, 2026

Theoretical and Computational Physics被引用数 0

ひとこと要約

This study numerically analyzes field-driven magnetisation reversal in a 3D antiferromagnetic Ising model with weak random-field disorder, revealing antiferromagnetic Barkhausen noise, plateau-based hysteresis structure, and disorder-dependent multifractal avalanche dynamics.

ABSTRACT

This study numerically investigates magnetisation reversal processes driven by an external magnetic field in three-dimensional antiferromagnetic spin models with weak random field disorder. Considering an extremely weak disorder and low temperature, we observe a step-wise hysteresis loop and the appearance of short magnetisation bursts of a characteristic triangular shape; the number of bursts increases with disorder, indicative of Barkhausen-type noise. These phenomena are attributed to the simultaneous reversal at a given external field of segments composed of spins with identical neighbourhoods. A local random field orients one or more spin neighbours, resulting in small, ferromagnetic-like clusters distributed throughout the system. As disorder increases, these clusters may merge to form a labyrinthine structure within the antiferromagnetic background, facilitating brief avalanche propagation. The results demonstrate that, compared with familiar random-field ferromagnets, the observed antiferromagnetic Barkhausen noise and the related avalanche sequence have a profoundly different structure, organised into peaks associated with the transition between magnetisation plateaus. They exhibit prominent cyclical trends and disorder-dependent multifractal fluctuations, with the singularity spectrum quantifying the degree of disorder. The activity avalanches exhibit scale invariance resembling that recently found in experiments with disordered ferr extit{i}magnets and martensites, as well as in quantum Barkhausen noise, which are associated with active geometric regions rather than individual-spin dynamics. The observed scaling behaviour is interpreted in terms of self-organised critical dynamics.

研究の動機と目的

• Investigate how weak random-field disorder affects hysteresis and magnetisation reversal in 3D antiferromagnets.
• Characterise Barkhausen-type noise and avalanche structures arising during field-driven reversals.
• Determine how disorder strength alters hysteresis loops, bursts, and avalanche statistics.
• Compare antiferromagnetic Barkhausen noise with known ferromagnetic random-field systems and identify unique scaling features.

提案手法

• Model is a 3D cubic lattice of Ising spins with antiferromagnetic nearest-neighbour coupling and quenched Gaussian random fields h_i with zero mean and variance f^2.
• Dynamics mimic zero-temperature, adiabatic driving with external field H_t ramped slowly to trace a hysteresis loop.
• Spins flip with probability p (0<p<1) to account for finite-temperature/ frustration effects; p=0.95 unless specified.
• Avalanche metrics: size S and duration T computed from sequences of spin flips between consecutive field updates.
• AF-BHN is the time series n_t of spin flips; avalanches are segments between zero-current baselines; analysis includes cyclic trend extraction and multifractal analysis.
• Multifractal analysis employs detrended fluctuation functions F_q(n) to obtain H(q) and the singularity spectrum Ψ(α) via Legendre transform.

実験結果

リサーチクエスチョン

• RQ1 弱いランダム場雑音を増加させると、反強磁性ヒステリシスループの形状と磁化のプラトーの出現はどのように変化するか？
• RQ2 弱く乱れた反強磁性体における Barkhausen 型ノイズとアベランチの構造と確率分布はどうなり、これを既知の磁性RFIM結果と比較できるか？
• RQ3 AF-BHNのバーストは循環的トレンドと多重フラクタルゆらぎを示すか、これらを用いて乱雑さの強さを定量化できるか？
• RQ4 この反強磁性系におけるアベランチサイズ分布のスケーリング形とカットオフは何であり、自己組織化臨界ダイナミクスを示すか？

主な発見

• 弱いランダム場雑音は、反強磁性系において磁化プラトーとバーストを伴う段階的ヒステーシスを生み出し、純粋な反強磁性体の鋭いステップとは異なる。
• バーストは短く三角形状のイベントとして現れ、各ヒステリシス枝で7つの明確なピークに組織され、各ピークは裏返した隣接スピンの数と特定される。
• 乱雑さが増すとバーストが多くなり、迷路のようなクラスター構造が生じ、反転が遅くなる一方でプラトー間の転換が広がる。
• アベランチサイズ分布は低乱雑さ領域で、肩と伸長指数切断を伴う二段階の勾配を示し、指数は τ_s ≈ 1.09 および τ_T ≈ 1.15、より高い乱雑さで異なるスケーリングを示す。
• アベランチ列は循環的傾向と多重フラクタル特徴を示し、特異性スペクトル Ψ(α) は乱雑さの増加とともに広がり、より対称になる。
• スケーリング形 P(S,f) ≈ (R/⟨S⟩) P̃(S/⟨S⟩) は、従来のRFIM Ferromagnets とは異なる、乱雑さ依存の準平均場様の自己組織化臨界ダイナミクスを示唆する。
• 強い乱雑さはアベランチ間のスケール差を小さくし、乱雑さが制御する多重フラクタルゆらぎと、プラトー転移に結びつく峰状活性を示す。