Thermally Assisted All-Optical Helicity Dependent Magnetic Switching in Amorphous Fe100-xTbx Alloy Films
Thermally Assisted All-Optical Helicity Dependent Magnetic Switching in Amorphous Fe100-xTbx Alloy Films
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DOI：
10.1002/adma.201300176
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发表时间：
2013-06-11
影响因子：
29.4
通讯作者：
Bratschitsch, Rudolf
中科院分区：
文献类型：
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作者：
Hassdenteufel, Alexander;Hebler, Birgit;Bratschitsch, Rudolf
目前的海量数据存储依赖于切换小磁畴的能力。除了高存储密度外，短的开关时间[1]对于高效器件也很重要。在对镍的超快磁化动力学进行了开创性的实验之后，Stanciu等人最近证明，圆偏振飞秒激光脉冲不仅可以使亚铁磁GdFeCo退磁，而且可以在没有任何外部磁场的情况下将磁状态切换到相反的方向。[3]从那时起，理论和实验研究一直在努力深入了解这种新的光磁性。到目前为止，主要研究了光激励参数对全光开关（AOS）过程的影响，即脉冲啁啾，[4]脉冲宽度，[4，5]波长，[4，6]带宽，[4]脉冲重复率，[7]以及激光加热和圆偏振的组合。[6，7] Hohlfeld等人进行了一项温度依赖性研究。[8]和Vahaplar et al. [5，9]然而，这些测量仅给出了热辅助过程的一些提示。进行了时间分辨测量，[5，9]显示了对必要的阈值通量和磁补偿点以及开关速度的依赖性。Radu等人对GdFeCo化合物进行的元素特定研究[10]证明了每个磁性亚晶格（即Gd和Fe/Co）的激光诱导磁化动力学有两种不同的时间尺度[11]。这些研究中的绝大多数是在GdFeCo合金薄膜中进行的。[4-10发现替代的全光磁性材料是揭示AOS物理机制和发展技术应用的最紧迫和重要的挑战之一。沿着这条线的第一个实验是在（SmPr）FeO 3，[13，14] ErFeO 3，[15]和CoTb上进行的。[16]在这篇文章中，我们对非晶铁磁Fe 100-xTb x合金薄膜的AOS能力进行了全面的研究，其成分从19到38.5at.%不等。TB.特别关注的是在室温下的开关能力和AOS的合金系统的磁性能的链接。我们发现AOS只发生在22 - 34 at.%之间。TB.在此组成范围之外，观察到纯热退磁。AOS发生在磁补偿点的下方和上方。令人惊讶的是，我们发现AOS也发生在样品缺乏补偿温度（Tcomp）。AOS很容易在具有初始均匀或空间随机背景磁化的磁性薄膜中观察到。加热到居里温度与AOS有关。最重要的是，我们发现，样品的剩磁（MR）必须低于220 emu/cc的阈值AOS发生。图1a显示了本系统性研究的12个研究样本的M-T曲线。亚铁磁性稀土过渡金属（RE-TM）合金的特有之处在于，与TM相比，RE组分的磁化强度的温度依赖性更强。在具有高Tb含量（x≥ 28.0 at.%）的样品中，在低Tb含量（x≤ 22.0 at.%）的样品中，磁化强度主要由Tb磁矩决定，铁的时刻占上风。在中间组成范围（22.5≤ x≤ 27.5 at.%）中，存在净磁化消失的补偿温度。例如，对于24和27 at.%，Tcomp为218.5±1.0和345.5±1.0 K。TB，分别。在T= 300 K的温度下记录所有样品的M-H环（图S1，支持性信息）。从这些，再磁化（MR）和磁阻（HC）提取…
Present mass data storage relies on the ability to switch small magnetic domains. Besides high storage densities, short switching times [1] are important for efficient devices. After pioneering experiments on the ultrafast magnetization dynamics in nickel,[2] Stanciu et al. recently demonstrated that a circularly polarized femtosecond laser pulse not only demagnetizes the ferrimagnet GdFeCo, but also switches the magnetic state to the opposite direction without any external magnetic field.[3] Since then, theoretical and experimental investigations have strived to obtain a deeper insight into this new kind of opto-magnetism. Until now, the influence of the optical excitation parameters on the all-optical switching (AOS) process has mainly been investigated, ie, pulse chirp,[4] pulse duration,[4, 5] wavelength,[4, 6] bandwidth,[4] pulse repetition rate,[7] and the combination of laser heating and circular polarization.[6, 7] A temperature dependent study was performed by Hohlfeld et al.[8] and Vahaplar et al.[5, 9] However, these measurements give only some hints to a thermally assisted process. Time-resolved measurements were carried out,[5, 9] which show both a dependence on the necessary threshold fluence and the magnetic compensation point, as well as the switching speed. Element specific studies, performed by Radu et al. for GdFeCo compounds,[10] demonstrated two different timescales [11] for the laser induced magnetization dynamics for each of the magnetic sublattices, ie, Gd and Fe/Co. The overwhelming majority of these investigations were performed in GdFeCo alloy thin films.[4–10, 12] Discovery of alternative all-optical magnetic materials is one of the most pressing and important challenges for revealing the underlying physical mechanism of AOS and developing technological applications. First experiments along this line were performed on (SmPr) FeO 3,[13, 14] ErFeO 3,[15] and CoTb.[16]In this article, we present a comprehensive study on the AOS ability of amorphous ferrimagnetic Fe 100–xTb x alloy thin films with varying composition from 19 to 38.5 at.% Tb. Particular focus was put on the switching ability at room temperature and a link of AOS to the magnetic properties of the alloy system. We find that AOS only occurs between 22 and 34 at.% Tb. Outside this compositional range pure thermal demagnetization is observed. AOS occurs below and above the magnetic compensation point. Surprisingly, we find AOS to also take place in samples lacking a compensation temperature (Tcomp). AOS is readily observed in magnetic films with initially homogeneous or spatially random background magnetization. Heating to the Curie temperature is associated with AOS. Most importantly, we find that the sample remanent magnetization (MR) has to be below a threshold of 220 emu/cc for AOS to occur. Figure 1a shows M–T curves of a selection of the 12 investigated samples of this systematic study. Peculiar to ferrimagnetic rare earth transition metal (RE–TM) alloys is the stronger temperature dependence of the magnetization of the RE component as compared to the TM. In samples with high Tb content (x≥ 28.0 at.%), the magnetization is dominated by the Tb moment, in those with low Tb content (x≤ 22.0 at.%), the iron moment prevails. In the intermediate composition range (22.5≤ x≤ 27.5 at.%), a compensation temperature exists, where the net magnetization vanishes. For example, Tcomp is 218.5±1.0 and 345.5±1.0 K for 24 and 27 at.% Tb, respectively. M–H loops were recorded at a temperature of T= 300 K for all samples (Figure S1, Supporting Information). From these, the remanent magnetization (MR) and the coercitivity (HC) were extracted …