Picosecond Dynamics of Magnetic Exchange Springs

交换磁弹簧的皮秒动力学

基本信息

批准号：
EP/P02047X/1
负责人：
Robert Hicken
金额：
$ 81.86万
依托单位：
UNIVERSITY OF EXETER
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FP02047X%2F1
关键词：
Picosecond Dynamics Magnetic Exchange Springs

项目摘要

Ferromagnetic materials are found throughout the electromagnetic technology upon which modern life depends. They range from the bulk materials found in motors and dynamos to thin films used to store data in hard disk drives. Within a ferromagnet each atom has a magnetic moment, like planet earth, with north and south poles. The magnetic moments of adjacent atoms are forced to point in the same direction by the exchange interaction (EI), a purely quantum-mechanical effect, which is the most powerful force in magnetism, generating effective magnetic fields up to one hundred million times as strong as the earth's magnetic field.Our everyday experience is that some ferromagnets remain permanently magnetized while others do not. In the latter case, the magnetic moments have parallel alignment within microscopic regions known as domains, but different domains have magnetic moments pointing in different directions, so that there is no net magnetic moment overall. Neighbouring domains are separated by domain walls, about 10 nm (100 atomic diameters) wide, through which the orientation of the magnetic moments gradually rotates in a helical structure. The finite width of the domain wall is a consequence of the EI and the wall stores exchange energy like a spring. The proposed project is concerned with exchange spring (ES) structures that form through the thickness of multilayered thin films. Alternate layers are termed hard and soft because it is easier to form the helical structure in the latter. The helical structure is induced either by applying a magnetic field or by changing the relative alignment of the magnetic moments in different hard layers so as to twist the magnetic moments in the soft layers in between. By studying the form of the ES structure, and its response to external stimuli, we can obtain information about how the strength of the EI varies through the structure.The EI present in perfect crystals can already be calculated accurately. However, the magnetic materials used in the strongest permanent magnets, or as recording media in hard disk drives, are far from perfect and consist of nanoscale crystallites that interact with each other through the EI at their grain boundaries. Furthermore, the next generation of magnetic recording technology will use the combined influence of a magnetic field and a short laser pulse to switch the orientation of the magnetic moments so as to represent binary information. Rather little is known about the EI within the grain boundary regions, or how the EI is modified immediately after application of a laser pulse. The aim of this project is to use ES spring structures to obtain new information about the EI in such circumstances.State of the art thin film deposition will be used to fabricate ES structures in which the atomic scale structure can be carefully controlled so that the relationship between magnetic and structural properties can be better understood. Microwave radiation will be used to excite the ES so that magnetic moments oscillate with characteristic frequencies that allow the strength of the EI within different regions of the ES to be deduced. In particular, x-rays will be used to detect the motion, since by tuning the energy of the x-ray photons obtained from a synchrotron, the response of different atomic species can be separately determined, providing more detailed information of the mode of oscillation. Finally, the ES will be excited with an ultrafast laser pulse to soften the magnetic moments within one or more hard layer so that the ES can unwind. This unwinding motion will provide information about how the magnetic parameters of the material, including the EI, are modified by the laser pulse, and the conditions required for the magnetic moments of the hard layer to switch their orientation will be explored. The potential of ESs as laser assisted recording media will hence be determined.

在现代生活所依赖的整个电磁技术中都发现了铁磁材料。它们的范围从电动机和发电机中的散装材料到用于将数据存储在硬盘驱动器中的薄膜。在铁磁体中，每个原子都有一个磁性时刻，例如地球，北极和南极。相邻原子的磁矩被强迫通过交换相互作用（EI）指向相同的方向，这是一种纯机械效应，它是磁性中最强大的力量，产生有效的磁场，其有效磁场的强度是地球磁场的强度，我们的日常磁场是地球上的强度。我们的日常体验是，我们的一些铁磁铁仍然永久地磁性磁性，而另一些则无法。在后一种情况下，磁矩在被称为域的微观区域内具有平行对齐，但是不同的域具有指向不同方向的磁矩，因此总体上没有净磁矩。相邻的结构域被域宽约10 nm（100个原子直径）宽，磁矩的方向逐渐旋转在螺旋结构中。域壁的有限宽度是EI的结果，墙壁像弹簧一样存储交换能量。拟议的项目与通过多层薄膜的厚度形成的交换弹簧结构有关。替代层被称为硬和柔软，因为在后者中形成螺旋结构更容易。螺旋结构是通过施加磁场或通过在不同硬层中改变磁矩的相对对齐来诱导的，以便在之间的软层中扭动磁矩。通过研究ES结构的形式及其对外部刺激的反应，我们可以获取有关EI强度如何通过结构变化的信息。可以准确计算出完美晶体中的EI。但是，在最强的永久磁铁中使用的磁性材料，或用作硬盘驱动器中的记录介质，远非完美，由纳米级的结晶石组成，它们在其晶界通过EI相互相互作用。此外，下一代磁记录技术将利用磁场的综合影响和短激光脉冲来切换磁矩的方向，以表示二进制信息。关于晶界区域内的EI或在应用激光脉冲后立即修改EI的EI知之甚少。该项目的目的是使用ES弹簧结构在这种情况下获取有关EI的新信息。微波辐射将用于激发ES，以使磁矩具有特征性频率振荡，从而推导ES的不同区域内EI的强度。特别是，X射线将用于检测运动，因为通过调整从同步加速器获得的X射线光子的能量，可以分别确定不同原子物种的响应，从而提供更详细的振荡方式。最后，ES将使用超快激光脉冲激发，以软化一个或多个硬层内的磁矩，以便ES可以放松。这种放松的运动将提供有关如何通过激光脉冲修改材料（包括EI）的磁参数的信息，并将探索硬层磁矩所需的条件以切换其方向。因此，将确定ESS作为激光辅助记录媒体的潜力。

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）

Coherent transfer of spin angular momentum by evanescent spin waves within antiferromagnetic NiO

反铁磁 NiO 内渐逝自旋波的自旋角动量相干转移

DOI：
10.48550/arxiv.1912.05621
发表时间：
2019
期刊：
影响因子：
0
作者：
Dabrowski M
通讯作者：
Dabrowski M

Optically and Microwave-Induced Magnetization Precession in [Co/Pt]/NiFe Exchange Springs.

DOI：
10.1021/acsami.0c14058
发表时间：
2020-11
期刊：
ACS applied materials & interfaces
影响因子：
9.5
作者：
Maciej Da Browski;A. Frisk;D. M. Burn;D. G. Newman;C. Klewe;A. N’Diaye;P. Shafer;E. Arenholz;G. Bowden;T. Hesjedal;G. van der Laan;G. Hrkac;R. Hicken
通讯作者：
Maciej Da Browski;A. Frisk;D. M. Burn;D. G. Newman;C. Klewe;A. N’Diaye;P. Shafer;E. Arenholz;G. Bowden;T. Hesjedal;G. van der Laan;G. Hrkac;R. Hicken

Glancing-angle deposition of magnetic in-plane exchange springs

磁性面内交换弹簧的掠射角沉积