解锁稀土磁体中的超快自旋动力学
Unlocking ultrafast spin dynamics in a rare-earth magnet
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中文总结 AI 辅助
研究稀土磁体中光驱动磁化动力学速度受限问题，通过对亚铁磁性钆铁石榴石进行飞秒泵浦-探测磁光光谱实验，利用选择性光激发局域磁态，实现Gd子晶格超快退磁，揭示超快磁响应受材料属性和光激发路径影响。
中文摘要 AI 辅助
光驱动磁化动力学的速度从根本上取决于角动量在电子、自旋和晶格自由度之间转移的效率。在稀土磁体中，此过程通常较慢，因为光激发主要作用于巡游电子，而磁矩存在于局域4f态。本文表明对局域磁态的选择性光激发可克服这一限制。利用亚铁磁性钆铁石榴石的飞秒泵浦-探测磁光光谱，共振激发Gd3+在4.65 eV的4f内跃迁，解析了反铁磁耦合的Gd和Fe子晶格随后动力学。直接激发4f流形诱导Gd子晶格超快退磁，特征时间为38 fs，比元素钆快两个数量级，甚至比同一材料中Fe子晶格响应还快。非共振激发则强烈抑制Gd动力学加速，而Fe响应基本不变。这些结果表明稀土系统的超快磁响应不仅受固有材料属性支配，还受光激发路径影响。因此，选择性访问局域磁态为工程化角动量流和控制远离平衡态的磁性提供了强大的光子手段。
英文摘要
The speed of optically driven magnetization dynamics is fundamentally determined by how efficiently angular momentum can be transferred between electronic, spin and lattice degrees of freedom. In rare-earth magnets, this process is typically slow because optical excitation primarily addresses itinerant electrons, whereas the magnetic moment resides in localized 4f states. Here we show that selective optical excitation of localized magnetic states can overcome this limitation. Using femtosecond pump-probe magneto-optical spectroscopy of ferrimagnetic gadolinium iron garnet, we resonantly excite an intra-4f transition of Gd3+ at 4.65 eV and resolve the ensuing dynamics of the antiferromagnetically coupled Gd and Fe sublattices. Direct excitation of the 4f manifold induces an ultrafast demagnetization of the Gd sublattice with a characteristic time of 38 fs, more than two orders of magnitude faster than in elemental gadolinium and even faster than the response of the Fe sublattice in the same material. By contrast, off-resonant excitation strongly suppresses the acceleration of the Gd dynamics while leaving the Fe response largely unchanged. These results demonstrate that the ultrafast magnetic response of rare-earth systems is governed not only by intrinsic material properties but also by the optical excitation pathway. Selective access to localized magnetic states therefore provides a powerful photonic handle for engineering angular-momentum flow and controlling magnetism far from equilibrium.
