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首页> 外文期刊>Physical Review X >Broadband Spectroscopy of Thermodynamic Magnetization Fluctuations through a Ferromagnetic Spin-Reorientation Transition
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Broadband Spectroscopy of Thermodynamic Magnetization Fluctuations through a Ferromagnetic Spin-Reorientation Transition

机译：通过铁磁旋转重新定向过渡的热力学磁化波动的宽带光谱

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We use scanning optical magnetometry to study the broadband frequency spectra of spontaneous magnetization fluctuations, or “magnetization noise,” in an archetypal ferromagnetic film that can be smoothly tuned through a spin-reorientation transition (SRT). The SRT is achieved by laterally varying the magnetic anisotropy across an ultrathin Pt / Co / Pt trilayer, from the perpendicular to in-plane direction, via graded Ar + irradiation. In regions exhibiting perpendicular anisotropy, the power spectrum of the magnetization noise S ( ν ) exhibits a remarkably robust ν ? 3 / 2 power law over frequencies ν from 1?kHz to 1?MHz. As the SRT region is traversed, however, S ( ν ) spectra develop a steadily increasing critical frequency ν 0 , below which the noise power is spectrally flat, indicating an evolving low-frequency cutoff for magnetization fluctuations. The magnetization noise depends strongly on applied in- and out-of-plane magnetic fields, revealing local anisotropies and also a field-induced emergence of fluctuations in otherwise stable ferromagnetic films. Finally, we demonstrate that higher-order correlators can be computed from the noise. These results highlight broadband spectroscopy of thermodynamic fluctuations as a powerful tool to characterize the interplay between thermal and magnetic energy scales, and as a means of characterizing phase transitions in ferromagnets.
机译：我们使用扫描光磁测度法研究自发磁化波动的宽带频谱，或者在型原型铁磁膜中的“磁化噪声”，其可以通过自旋重新定向转换（SRT）平稳调整。通过梯度AR +照射通过垂直于面内方向横向地改变超薄Pt / Co / Pt三层磁各向异性的磁各向异性来实现SRT。在表现出垂直各向异性的区域中，磁化噪声S（ν）的功率谱表现出非常坚固的ν？ 3/2电力法通过1？kHz到1？MHz的3/2电力法。然而，随着SRT区域的遍历，S（ν）光谱显影稳定增加的临界频率ν0，下面噪声功率是光谱扁平的，表示用于磁化波动的不断变化的低频截止。磁化噪声强烈取决于施加的和外平面磁场，揭示局部各向同性，以及诸如稳定的铁磁膜中的场诱导的波动出现。最后，我们证明可以从噪声计算更高阶的相关器。这些结果突出了热力学波动作为一种强大的工具，以表征热电能和磁能尺度之间的相互作用，以及作为铁圆形仪中相位过渡的手段。

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