Coherent and incoherent ultrafast magnetization dynamics in 3d ferromagnets driven by extreme terahertz fields
Coherent and incoherent ultrafast magnetization dynamics in 3d ferromagnets driven by extreme terahertz fields
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DOI：
10.1103/physrevb.98.014405
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发表时间：
2018-07-03
影响因子：
3.7
通讯作者：
Hauri, Christoph P.
中科院分区：
文献类型：
--
作者：
Shalaby, Mostafa;Donges, Andreas;Hauri, Christoph P.
磁性材料中的超快自旋动力学通常与近红外飞秒激光脉冲对电子系统的超快加热有关，因此只能间接和非选择性地访问自旋顺序。在这里，我们通过极强的太赫兹脉冲来探索铁磁体中的自旋动力学，因为在这些低频下，磁场提供了一种直接和选择性的途径来相干地控制磁化。我们发现，在低场下，观测到的非共振激发的自旋进动与太赫兹磁场锁相。在极值太赫兹场下，由于能量的吸收，相干自旋动力学与超快的非相干磁猝灭相缠绕。这种退磁是在单次曝光时发生的。在太赫兹泵浦通量约为100mJ/cm(2)的情况下，磁性被永久地改变。我们得出的结论是，磁化转换是不可能达到的。我们的原子自旋动力学模拟很好地解释了测量到的磁化响应。我们发现了由THz激光与电子电荷耦合驱动的退磁，这表明非导电材料可以实现相干的THz磁化反转。
Ultrafast spin dynamics in magnetic materials is generally associated with ultrafast heating of the electronic system by a near infrared femtosecond laser pulse, thus offering only an indirect and nonselective access to the spin order. Here we explore spin dynamics in ferromagnets by means of extremely intense THz pulses, as at these low frequencies the magnetic field provides a direct and selective route to coherently control the magnetization. We find that, at low fields, the observed off-resonantly excited spin precession is phase locked to the THz magnetic field. At extreme THz fields, the coherent spin dynamics become convoluted with an ultrafast incoherent magnetic quenching due to the absorbed energy. This demagnetization takes place upon a single shot exposure. The magnetic properties are found to be permanently modified above a THz pump fluence of approximate to 100 mJ/cm(2). We conclude that magnetization switching cannot be reached. Our atomistic spin-dynamics simulations excellently explain the measured magnetization response. We find that demagnetization driven by THz laser-field coupling to electron charges occurs, suggesting nonconducting materials for achieving coherent THz-magnetization reversal.