Novel exchange-coupled composite nanomagnets

尺寸在20纳米以下的定制磁岛的基本行为是一个值得关注的未知领域，因为纳米级有可能出现新的物理，并具有广泛应用的潜力，包括磁记录、传感器、磁性随机存取存储器和磁性振荡器。为此，我们将重点放在新型纳米级交换耦合复合(ECC)磁体上，该磁体包括硬磁和软磁两部分。我们的目的是获得对静态和动态行为的详细了解，从而使我们能够专门为磁数据存储定制磁性能，这需要高热稳定性、低开关场和窄开关场分布(SFD)。采用瑞士光源的极紫外光干涉光刻技术(EUV-IL)和最先进的电子束光刻技术，将制造出面密度为1TBit/in2及以上的ECC纳米磁岛阵列。在第一个例子中，我们将研究高各向异性的L10FePT合金膜与较软的FePt层相结合的ECC薄膜和纳米晶。然后我们还将探索更奇特的稀土-过渡金属(RE-TM)材料的潜力，即Fe1-xGdx。由于它们的非晶态性质，这些材料具有结构影响最小的优点，这一特性对于器件应用中的可重现磁化反转特别重要。此外，在Fe1-xGdx材料中，净饱和磁化强度与Gd含量有关，在补偿温度下为零，这导致了矫顽力的无限增加。FePt层和Fe1-xGdx层的结合将导致新的磁性行为。特别是，该系统可用于系统地研究饱和磁化强度和磁各向异性对ECC层叠中硬磁铁铂层的反转特性(切换场，SFD)的影响。为了了解磁性行为，特别是将SFD降到最低，需要对潜在的机制及其与材料微观结构的关系有一个详细的了解。因此，透射式电子显微镜将被用来确定单个磁岛的颗粒结构和结晶学，以及更先进的X射线和中子散射方法，这些信息将与磁性质相关联。我们的目的是能够通过修改种子层和加工条件来控制岛状颗粒结构。磁性和微结构信息都将被送入微磁模拟，这将给出对详细的自旋构型的重要理解，加强我们对静态和动态反转行为的理解，并阐明微结构对SFD的贡献。在动力学方面，我们打算进行测量和微磁模拟，以探索利用微波激励来逆转具有高磁各向异性材料的磁化强度的新的可能性。如果这在实验上是可以实现的，那么这种解决小但仍然热稳定的磁性纳米岛的创新方法可能会成为现实。这方面的实验工作是非常新的，我们倾向于通过通过铜带状线的脉冲和连续波电流来磁激励ECC岛。我们将使用各种技术来检测磁响应，包括扫描透射式X射线显微镜、MFM和霍尔测量。我们在这里申请三年的资金，致力于ECC磁性纳米岛阵列的这一高度热门领域的工作。

The fundamental behaviour of tailored magnetic islands with dimensions below 20 nm is an unchartered area deserving focus because of the possibility for new physics at the nanoscale and the potential for a wide range of applications including magnetic recording, sensors, magnetic RAM and magnetic oscillators. To this aim, we focus on novel nanoscale exchange-coupled com-posite (ECC) magnets incorporating a hard and a soft magnetic component. Our intention is to obtain a detailed understanding of both the static and dynamic behaviour, so allowing us to tailor the magnetic properties specifically for magnetic data storage, which requires high thermal stabil-ity, low switching fields and a narrow switching field distribution (SFD). Arrays of ECC nanoscale magnetic islands at areal densities of 1 Tbit/in2 and beyond will be fabricated with extreme ultraviolet interference lithography (EUV-IL) at the Swiss Light Source and state-of-the-art electron beam lithography. In the first instance, ECC thin films and nanois-lands combining high anisotropy films of L10 FePt alloys with softer FePt layers will be investi-gated. We will then also explore the potential of the more exotic rare earth–transition metal (RE-TM) materials, namely Fe1-xGdx. These materials have the advantage of minimal structural imper-fections due to their amorphous nature, a property particularly important for reproducible mag-netization reversal in device applications. In addition, in the Fe1-xGdx materials, the net saturation magnetization is dependent on the Gd content, being zero at the compensation temperature, which leads to an infinite increase in coercivity. The combination of FePt layers with the Fe1-xGdx layers will lead to novel magnetic behaviour. In particular, such a system can be used to study systematically the influence of the saturation magnetization and magnetic anisotropy on the re-versal characteristics (switching field, SFD) of the hard magnetic FePt layer in the ECC layer stack. In order to understand the magnetic behaviour, in particular to minimize the SFD, a de-tailed understanding of the underlying mechanisms and their relationship to the material micro-structure needs to be gained. Therefore, transmission electron microscopy (TEM) will be deployed to determine the grain structure and crystallography of individual magnetic islands, as well as more advanced x-ray and neutron scattering methods, and this information will be correlated with the magnetic properties. Our intention is then to be able to control the island grain structure by modification of the seed layers and processing conditions. Both the magnetic and microstructural information will be fed into micromagnetic simulations, which will give a vital understanding of the detailed spin configurations, strengthening our understanding of the static and dynamic re-versal behaviour, and elucidating the microstructural contribution to the SFD. In terms of the dynamics, we intend to undertake measurements and micromagnetic simulations to explore new possibilities of energy assisted reversal using microwave excitations to reverse the magnetization in materials with a high magnetic anisotropy. If this is realisable ex-perimentally, then this innovative approach of addressing small, but still thermally stable, mag-netic nanoislands could become a reality. Experimental work in this area is very new and we in-tend to magnetically excite the ECC islands by passing pulsed and continuous wave currents through a copper stripline. We will employ a variety of techniques to detect the magnetic response including scanning transmission x-ray microscopy, MFM and Hall measurements. We apply here for funding for three years to work on this highly topical area of arrays of ECC magnetic nanoislands.