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Determination of intrinsic damping of perpendicularly magnetized ultrathin films from time-resolved precessional magnetization measurements

机译：通过时间分辨进动磁化测量确定垂直磁化超薄膜的固有阻尼

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摘要

Magnetization dynamics are strongly influenced by damping, namely, the loss of spin angular momentum from the magnetic system to the lattice. An "effective" damping constant α_(eff) is often determined experimentally from the spectral linewidth of the free induction decay of the magnetization after the system is excited to its nonequilibrium state. Such an α_(eff), however, reflects both intrinsic damping as well as inhomogeneous broadening that arises, for example, from spatial variations of the anisotropy field. In this paper, we compare measurements of the magnetization dynamics in ultrathin nonepitaxial films having perpendicular magnetic anisotropy using two different techniques, time-resolved magneto-optical Kerr effect (TRMOKE) and hybrid optical-electrical ferromagnetic resonance (OFMR). By using an external magnetic field that is applied at very small angles to the film plane in the TRMOKE studies, we develop an explicit closed-form analytical expression for the TRMOKE spectral linewidth and show how this can be used to reliably extract the intrinsic Gilbert damping constant. The damping constant determined in this way is in excellent agreement with that determined from the OFMR method on the same samples. Our studies indicate that the asymptotic high-field approach that is often used in the TRMOKE method to distinguish the intrinsic damping from the effective damping may result in significant error, because such high external magnetic fields are required to make this approach valid that they are out of reach. The error becomes larger at lower intrinsic damping constants and thus may account for the anomalously high damping constants that are often reported in TRMOKE studies. In conventional ferromagnetic resonance (FMR) studies, inhomogeneous contributions can be readily distinguished from intrinsic damping contributions by studying the magnetic field dependence of the FMR linewidth. Using an analogous approach, we show how reliable values of the intrinsic damping can be extracted from TRMOKE in two distinct magnetic systems with significant perpendicular magnetic anisotropy: ultrathin CoFeB layers and Co/Ni/Co trilayers.
机译：磁化动力学受到阻尼的强烈影响，即从磁系统到晶格的自旋角动量的损失。通常在系统被激发到其非平衡状态后，根据磁化强度的自由感应衰减的谱线宽度，通过实验确定“有效”阻尼常数α_（eff）。然而，这样的α_（eff）既反映了固有阻尼，又反映了例如由各向异性场的空间变化引起的不均匀加宽。在本文中，我们使用时间分辨磁光克尔效应（TRMOKE）和混合光电铁磁谐振（OFMR）这两种不同的技术，比较了具有垂直磁各向异性的超薄非外延薄膜的磁化动力学测量。通过在TRMOKE研究中使用以很小的角度施加到薄膜平面的外部磁场，我们为TRMOKE谱线宽开发了一个显式的闭式解析表达式，并展示了如何将其可靠地用于提取固有吉尔伯特阻尼不变。以这种方式确定的阻尼常数与通过OFMR方法确定的相同样品具有极好的一致性。我们的研究表明，TRMOKE方法中经常使用的渐进高场方法将固有阻尼与有效阻尼区分开可能会导致显着误差，因为需要如此高的外部磁场才能使这种方法有效，以确保它们不存在触手可及。当固有阻尼常数较低时，误差会变大，因此可能会解释TRMOKE研究中经常报告的异常高的阻尼常数。在常规的铁磁共振（FMR）研究中，通过研究FMR线宽对磁场的依赖性，可以很容易地将非均匀贡献与固有阻尼贡献区分开。使用类似的方法，我们展示了如何在两个具有显着垂直磁各向异性的不同磁系统中从TRMOKE提取本征阻尼的可靠值：超薄CoFeB层和Co / Ni / Co三层。

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  • 来源
    《Physical review》 |2015年第22期|224402.1-224402.9|共9页
  • 作者

    Amir Capua; See-hun Yang; Timothy Phung; Stuart S. P. Parkin;

  • 作者单位

    IBM Research Division, Almaden Research Center, 650 Harry Rd., San Jose, California 95120, USA;

    IBM Research Division, Almaden Research Center, 650 Harry Rd., San Jose, California 95120, USA;

    IBM Research Division, Almaden Research Center, 650 Harry Rd., San Jose, California 95120, USA;

    IBM Research Division, Almaden Research Center, 650 Harry Rd., San Jose, California 95120, USA,Max Planck Institute for Microstructure Physics, Halle (Saale), D-06120, Germany;

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