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.

铁和硅是地壳中最丰富的两个元素。然而，这两种元素（FESI）中最简单的化合物具有奇异的电子和磁性，这些特性几十年来一直困惑研究人员。在低温下，它是一个非磁性半导体，间隙狭窄。在变暖时，大多数材料变得更难磁性：FESI变得更容易，并且变成了重型电子金属。尽管在超过四十年的实验中已知，但对此的适当理论描述仍未得到解决。当钴被替换为铁时，事物变得更加有趣。理论预测（对散装晶体的间接实验似乎证实），每个CO原子贡献一个电流的携带电子，以及一种电子旋转的磁性价值，表明具有完全极化的磁性半导体，而另外一个基于SI。的确，我们最近能够在商业硅晶片上制备这种材料的薄膜，这些材料似乎是表层：每个原子都与基板定义的晶格注册。自旋极化是所有自旋材料的关键值，随着极化的增加，所有自旋效应都会增长。因此，具有基于硅的高极化材料是一个非常诱人的前景。在我们项目的第一部分中，我们将确认薄膜的性质及其结构，磁性和电子特性。我们还将研究一种较简单，更快的方式，形成称为溅射的薄膜。然后，我们将继续对这种非凡材料的自旋极化进行第一个直接测量，此外，在技术上至关重要的薄膜形式的形式下，在Si晶圆上进行了磁性。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晦涩的效果：所谓的Dzyaloshinskii-Moriya相互作用。该术语不是在铁磁铁中通常的均匀状态，而是使旋转在螺旋中相互旋转。这可以在足够大的磁场中带到均匀的饱和状态，但是在途中，另一个在很大程度上被遗忘的理论物理学开始起作用。有一个由称为Skyrmions的磁涡旋的晶格形成的中间状态，这是一种拓扑结构，该拓扑结构首先发明了用于描述1960年代Pi-Meson的田地。去年显示（使用相关化合物的大块晶体，单硅酰胺），由于这种特殊的拓扑结构，这些旋转的磁性结构可以通过以电流密度流过电流密度的电流高约一百万倍，比在常规磁性材料中移动涡流所需的电流密度大约一百万倍。我们将在我们的硅化晶片样品中寻求这些磁性天际物体，并测量移动它们所需的当前密度。不幸的是，该材料仅在高于绝对零几十度的温度下具有磁性，并且在达到室温之前，所有磁性特性都会损失。然而，在元素周期表中用邻居代替硅，还可以将硅硅质铁转化为helimagnetic金属，完全更换将这种结构保存到零摄氏零几位的温度。我们将通过用钴掺杂该材料来完成我们的项目，并查看是否可以将临界温度推到室温以上，以进行技术有用的值。

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）

Temperature and magnetic-field driven dynamics in artificial magnetic square ice

DOI：
10.1117/12.2189320
发表时间：
2015-01-01
期刊：
SPINTRONICS VIII
影响因子：
0
作者：
Morley, Sophie A.;Stein, Aaron;Marrows, Christopher H.
通讯作者：
Marrows, Christopher H.

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