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Spin-Torque and Spin Polarisation in Epitaxial Magnetic Silicides

外延磁性硅化物中的自旋扭矩和自旋极化

基本信息

批准号：
EP/J007110/1
负责人：
Christopher Marrows
金额：
$ 59.6万
依托单位：
University of Leeds
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ007110%2F1
关键词：
Spin Torque Polarisation Epitaxial Magnetic

项目摘要

Iron and silicon are two of the most abundant elements in the earth's crust. Nevertheless, the simplest chemical compound of these two elements, iron monosilicide (FeSi), possesses bizarre electronic and magnetic properties that have confounded researchers for decades. At low temperatures it is a non-magnetic semiconductor with a narrow gap. On warming, most materials become harder to magnetise: FeSi becomes easier, and it transforms into a heavy electron metal. Although known experimentally for over four decades, the proper theoretical description of this is still not settled. When cobalt is substituted for iron things get even more interesting. Theory predicts (and indirect experiments on bulk crystals seem to confirm) that each Co atom contributes one current carrying electron, and also one electron spin's worth of magnetism, suggesting a perfectly polarised magnetic semiconductor - and what is more, one based on Si. Indeed, we have recently been able to prepare thin films of this material on commercial silicon wafer that appear to be epilayers: single crystals where every atom is in register with the lattice defined by the substrate. Spin polarisation is the key figure of merit for all spintronic materials, with all spintronic effects growing as the polarisation increases. Having a high polarisation material that is silicon-based is therefore a very tantalising prospect. In the first part of our project we will confirm the nature of our thin films and their structural, magnetic, and electronic properties. We will also investigate a simpler and quicker way of forming films known as sputtering. We will then go on to make the first direct measurements of the spin polarisation of this remarkable material, and moreover, do so in the technologically vital thin film form on Si wafer.The magnetism is truly remarkable in another way, however. The crystal structure of this material is very unusual in that it lacks mirror symmetry, and so an obscure effect that is suppressed in almost every other magnetic material comes into play: the so-called Dzyaloshinskii-Moriya interaction. Instead of the usual uniform state in a ferromagnet, this term causes the spins to spiral around each other in a helix. This can be brought to a uniform saturated state in a large enough magnetic field, but on the way another largely forgotten piece of theoretical physics comes into play. There is an intermediate state formed from a lattice of magnetic vortices called skyrmions, a topological structure first invented to describe fields of pi-mesons in the 1960s. Last year it was shown (using bulk crystals of a related compound, manganese monosilicide) that because of this special topology, these swirling magnetic structures can be set into motion by a current flowing through the crystal at a current density around one million times smaller than that needed to move a vortex in a conventional magnetic material. We shall seek these magnetic skyrmion objects in our silicide wafer samples and measure the current density needed to move them. Unfortunately, this material is only magnetic at temperatures a few tens of degrees above absolute zero, and all magnetic properties are lost well before room temperature is reached. Nevertheless, replacing silicon with its neighbour in the periodic table, germanium, can also transform iron silicide into a helimagnetic metal, with complete replacement preserving this structure up to a temperature a few degrees above zero Celsius. We shall complete our project by doping this material with cobalt and see if the critical temperature can be pushed above room temperature to technologically useful values.

铁和硅是地壳中含量最丰富的两种元素。尽管如此，这两种元素最简单的化合物--一硅化铁（FeSi）却具有奇异的电子和磁性，这让研究人员困惑了几十年。在低温下，它是一种具有窄隙的非磁性半导体。随着温度的升高，大多数材料变得更难磁化：FeSi变得更容易磁化，并转化为重电子金属。尽管四十多年来实验上已经知道了这一点，但对此的正确理论描述仍然没有确定。当钴取代铁时，事情变得更加有趣。理论预测（以及对大块晶体的间接实验似乎证实）每个Co原子贡献一个载流电子，以及一个电子自旋的磁性，这表明一个完美极化的磁性半导体-而且，一个基于Si的磁性半导体。事实上，我们最近已经能够在商业硅片上制备这种材料的薄膜，这些薄膜看起来像外延层：每个原子都与衬底定义的晶格对齐的单晶。自旋极化是所有自旋电子材料的关键品质因数，所有自旋电子效应随着极化的增加而增加。因此，具有硅基的高极化材料是非常诱人的前景。在我们项目的第一部分，我们将确认我们的薄膜的性质及其结构，磁性和电子特性。我们还将研究一种更简单、更快速的成膜方法，即溅射法。接下来，我们将对这种非凡材料的自旋极化进行首次直接测量，而且是在硅晶片上以技术上至关重要的薄膜形式进行测量。然而，磁性确实以另一种方式引人注目。这种材料的晶体结构非常不寻常，因为它缺乏镜像对称性，因此几乎所有其他磁性材料都抑制了一种模糊的效应：所谓的Dzyaloshinskiii-Moriya相互作用。与铁磁体通常的均匀状态不同，这一项导致自旋以螺旋形相互缠绕。这可以在足够大的磁场中达到均匀的饱和状态，但在此过程中，另一个基本上被遗忘的理论物理学开始发挥作用。有一种由磁涡旋晶格形成的中间态称为skyrmions，这是一种拓扑结构，最初是在20世纪60年代发明的，用于描述π介子场。去年的研究表明（使用相关化合物一硅化锰的大块晶体），由于这种特殊的拓扑结构，这些漩涡状的磁性结构可以通过流过晶体的电流来启动，电流密度比传统磁性材料中移动漩涡所需的电流密度小一百万倍。我们将在硅化物晶片样品中寻找这些磁性Skyrmion物体，并测量移动它们所需的电流密度。不幸的是，这种材料只有在绝对零度以上几十度的温度下才具有磁性，并且在达到室温之前，所有的磁性都消失了。然而，用元素周期表中的邻居锗取代硅，也可以将硅化铁转化为螺旋金属，完全取代可以将这种结构保持在零摄氏度以上几度的温度。我们将通过在这种材料中掺杂钴来完成我们的项目，看看临界温度是否可以被推到室温以上，达到技术上有用的值。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

DMI meter: Measuring the Dzyaloshinskii-Moriya interaction inversion in Pt/Co/Ir/Pt multilayers

DMI 计：测量 Pt/Co/Ir/Pt 多层膜中的 Dzyaloshinskii-Moriya 相互作用反演

DOI：
10.48550/arxiv.1402.5410
发表时间：
2014
期刊：
影响因子：
0
作者：
Hrabec A
通讯作者：
Hrabec A

Magnetic microscopy and topological stability of homochiral Néel domain walls in a Pt/Co/AlOx trilayer.

DOI：
10.1038/ncomms9957
发表时间：
2015-12-08
期刊：
Nature communications
影响因子：
16.6
作者：
Benitez MJ;Hrabec A;Mihai AP;Moore TA;Burnell G;McGrouther D;Marrows CH;McVitie S
通讯作者：
McVitie S

Dynamics of skyrmionic states in confined helimagnetic nanostructures