X-ray magnetic holography in reflection geometry

近年来，X射线磁全息术作为一种无透镜纳米成像的补充技术引起了人们的兴趣，它可以用来对连续和结构薄膜中的磁化区进行成像。全息术的关键在于，磁化的成像不仅可以在剩余状态下进行(如使用例如PEEM和MFM的磁区表征的典型)，而且可以在整个外加磁场范围内进行。这对于研究磁态的演化，从而探索磁体的一系列本征性质是一个很大的优势。由于实验的性质，这是在传输几何学中进行的，然而，成像仅限于磁化的“面外”分量。如果磁化是面内的，就像通常的薄膜结构的情况一样，由于XMCD效应的消失，成像被抑制。在这个项目中，我们打算通过提出一种新的反射几何来克服X射线磁性全息术的局限性，这种几何结构允许我们对具有面内磁化的样品成像。为了实现这个几何体，我们将修改样本的结构，以适应散射反射率实验。特别是，我们将在传输实验中引入反射式‘Pins’，作为参考‘孔’。反光针和物体都将被放置在透明的SIN膜上，以便将来自背景的散射降至最低。作为本实验的一部分，它还打算探索一种新的样品设计，其中通过FIB研磨去除被观测对象的周围背景。这将有助于显著提高预期的信噪比。使用SXRMS全息术的另一个好处是元素的选择性。可以对包括相同宏观体积的不同材料进行成像。例如，在多层系统(如具有两个不同磁层的GMR器件)的情况下，可以同时获得几个层的成像，从而提供了研究相邻层中不同磁矩的关系的机会。

In recent years X-ray magnetic holography has attracted interest as a complementary technique for lensless nanoscopic imaging of magnetisation domains in continuous and structured thin films. Essential for the holography is that the imaging of the magnetisation can be performed not only in the remanent state (as is typical for domain characterization using e.g. PEEM and MFM), but also over the full range of the applied field. This has been a great advantage in the opportunity to study the evolution of the magnetic states and thus to explore a range of the intrinsic properties of magnets. Due to the nature of the experiment, which is performed in transmission geometry, imaging is however limited only to 'out-of-plane' components of the magnetization. If the magnetization is in-plane, as is normally the case for thin film structures, the imaging is inhibited due to the vanishing XMCD effect. This restricts the application of the technique to only a single geometry.In this project we intend to overcome the limitation of x-ray magnetic holography by proposing a novel 'reflection' geometry of the technique, which allows us to image samples that have 'in-plane' magnetization. To implement this geometry we will modify the structure of the sample that will suit the scattering reflectivity experiments. In particular, we will introduce reflective 'pins', which will serve as reference 'holes' in the transmission experiment. Both reflective pins and the object will be placed on a transparent SiN membrane to allow the scattering from the background to be minimised. As part of this experiment it is also intended to explore a new design of the sample, in which the surrounding background of the observed object is removed by FIB milling. This will help significantly to improve the expected signal/noise intensity ratio. An added bonus of using SXRMS holography is the element selectivity. The imaging can be performed for different materials comprising the same macroscopic volume. For instance, in the case of a multilayered system (such as GMR devices with two different magnetic layers) the imaging can be obtained simultaneously for several layers, hence giving the opportunity to study the relation of the different magnetic moments in neighbouring layers.