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arXiv · 2402.18436

Magnetization fluctuations and magnetic aftereffect probed via the anomalous Hall effect

Nadine Nabben·Giacomo Sala·Ulrich Nowak·Matthias Krüger·Sebastian T. B. Goennenwein
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Abstract

Taking advantage of the anomalous Hall effect, we electrically probe low-frequency magnetization fluctuations at room temperature in a thin ferromagnetic Pt/Co/AlO$_x$ layer stack with perpendicular magnetic anisotropy. We observe a strong enhancement of the Hall voltage fluctuations within the hysteretic region of the magnetization loop. Analyzing both the temporal evolution of the anomalous Hall voltage and its frequency-dependent noise power density, we identify two types of magnetic noise: abrupt changes in the magnetic domain configuration, evident as Barkhausen-like steps in the Hall voltage time trace, yield a noise power density spectrum scaling with frequency as $1/f^{\beta}$ with $\beta\approx 1.9$. In contrast, quasi-stationary magnetization configurations are connected with a magnetic noise power density with an exponent $\beta\approx 0.9$. The observation of Barkausen steps and relaxation effects shows that the magnetic system is in a non-stationary state in the hysteresis region, such that the fluctuation-dissipation theorem cannot be expected to hold. However, the time-dependent change in the Hall voltage for constant magnetic field strength resembles the integrated noise power.

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Nadine Nabben, Giacomo Sala, Ulrich Nowak, Matthias Krüger, Sebastian T. B. Goennenwein. 2024-02-28. Magnetization fluctuations and magnetic aftereffect probed via the anomalous Hall effect. https://arxiv.org/abs/2402.18436

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