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Materials World Network: Spin dynamics of the ferromagnet/antiferromagnet interface studied by time-resolved x-ray magnetic dichroism

材料世界网：通过时间分辨 X 射线磁二色性研究铁磁体/反铁磁体界面的自旋动力学

基本信息

批准号：
EP/J018767/1
负责人：
Robert Hicken
金额：
$ 45.85万
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：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ018767%2F1
关键词：
Materials World Network Spin dynamics

项目摘要

The field of spintronics aims to deliver new device function by controlling the motion of an electron through its magnetic moment, or "spin", as well as through its electric charge. The outstanding success of spintronics has been the use of Giant Magnetoresistance (GMR) in the spin-valve sensors used to read data from hard disk drives. The spin-valve consists of two ferromagnetic (F) layers separated by a non-magnetic layer. Each F layer has a magnetic moment that acts as a compass needle and reorients in response to an applied magnetic field, such as that generated by the bits of data stored on a hard disk. GMR occurs if the two compass needles change their relative orientation. If one of the compass needles is kept fixed while the other is free to reorient in the magnetic field then data can be read out as a change in the electrical resistance of the sensor.This project is concerned with the means by which one of the compass needles is fixed. The established method is to deposit an antiferromagnetic (AF) layer on the outside of one of the F layers. The F/AF interface generates a strong effective magnetic field that fixes the orientation of the F layer magnetization. This effect, known as "exchange bias", is widely used but poorly understood in detail. Within a F material each atom has a magnetic moment, and every such magnetic moment, or compass needle, is forced to align in the same direction by the powerful "exchange interaction". Within an AF material adjacent magnetic moments instead align anti-parallel to each other. At the F/AF interface the magnetic moments of the F become fixed relative to those in the interfacial AF layer. The AF material has no net magnetic moment, so is largely unaffected by applied magnetic fields, and its magnetism is more difficult to observe. Little is known about the magnetic moments (spins) of the AF at an F/AF interface, particularly when structural imperfections are present. Spin-valves are required to change their magnetic alignment on sub-nanosecond timescales, where the motion of the magnetic moments within the AF and their influence upon the F are completely unexplored.We will use synchrotron x-ray radiation to make the first measurements of the motion of the magnetic moments at the F/AF interface at GHz frequencies. In particular we will make use of the x-ray magnetic circular and linear dichroism effects, known as XMCD and XMLD respectively. The F/AF samples consist of atoms in which a nucleus is surrounded by filled and partially filled shells of electrons. The energy required to excite an electron from a filled to a partially filled shell has an energy that is specific to a particular atom, while the energy of the x-rays from the synchrotron can be tuned so as to study only that atom. The x-rays are produced in pulses of sub-nanosecond duration. By synchronizing the x-rays with a magnetic field that has a sinusoidal time variation, the instantaneous state of the sample may be determined at a given point in its cycle of oscillation. Specifically the XMCD and XMLD effects allow the magnetic state of the F and AF layers to be determined independently.We will use the Advanced Light Source (ALS) in Berkeley and the Diamond Light Source in the UK to apply this measurement technique to samples of the highest structural quality, fabricated by molecular beam epitaxy at the University of California, Berkeley. The GHz frequency dynamics of the F layer will first be characterized by time resolved magneto-optical measurements at Exeter. Both x-ray and magneto-optical measurements will be performed as a function of temperature so as to compare the response when the AF layer has different degrees of antiferromagnetic order. We will hence obtain much deeper insight into how the AF layer controls the response of the F layer to a high frequency magnetic field.

自旋电子学领域的目标是通过控制电子的磁矩或自旋以及通过电子的电荷来控制电子的运动，从而提供新的设备功能。自旋电子学的突出成功是在用于从硬盘驱动器读取数据的自旋阀传感器中使用了巨磁电阻(GMR)。自旋阀由两个被非磁性层隔开的铁磁性(F)层组成。每个F层都有一个磁矩，它充当指南针，并根据施加的磁场重新定向，例如存储在硬盘上的数据比特产生的磁场。如果两个指南针改变了它们的相对方向，就会发生GMR。如果一个指南针保持固定，而另一个可以在磁场中自由地重新定向，那么数据可以通过传感器的电阻变化来读出。这个项目涉及到一个指南针固定的方法。已建立的方法是在F层之一的外部沉积反铁磁性(AF)层。F/AF界面产生固定F层磁化方向的强有效磁场。这种被称为“交换偏差”的效应被广泛使用，但人们对它的详细了解却很少。在F材料中，每个原子都有一个磁矩，每个这样的磁矩，或罗盘指针，都被强大的“交换相互作用”强迫向同一方向排列。在AF材料中，相邻的磁矩彼此相反地反平行排列。在F/AF界面，F的磁矩相对于界面AF层的磁矩是固定的。AF材料没有净磁矩，因此在很大程度上不受外加磁场的影响，其磁性更难观察。关于AF在F/AF界面的磁矩(自旋)知之甚少，特别是当存在结构缺陷时。自旋阀需要在亚纳秒时间尺度上改变它们的磁排列，在这种时间尺度上，房颤内部的磁矩运动及其对F的影响是完全没有被探索的。我们将使用同步加速器x射线辐射在GHz频率下首次测量F/房颤界面上的磁矩运动。特别是，我们将利用x射线磁性圆形和线性二色性效应，分别称为XMCD和XMLD。F/AF样品由原子组成，其中原子核被填充和部分填充的电子壳层包围。激发电子从充满的壳层到部分充满的壳层所需的能量具有特定于特定原子的能量，而来自同步加速器的x射线的能量可以进行调节，以便只研究那个原子。X射线以亚纳秒持续时间的脉冲形式产生。通过使X射线与具有正弦时间变化的磁场同步，可以在其振荡周期中的给定点确定样品的瞬时状态。具体来说，XMCD和XMLD效应允许独立确定F层和AF层的磁状态。我们将使用伯克利的高级光源(ALS)和英国的钻石光源将这种测量技术应用于加州大学伯克利分校的分子束外延制造的最高结构质量的样品。F层的GHz频率动力学将首先通过埃克塞特的时间分辨磁光测量来表征。X射线和磁光测量都将作为温度的函数进行，以便比较当AF层具有不同程度的反铁磁有序时的响应。因此，我们将对AF层如何控制F层对高频磁场的响应有更深入的了解。