基于钴元素纳米结构的磁特性

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摘 要

近年来，纳米颗粒已经成为物理，化学，工程和生物学中最重要的前沿技术之一。他们有很大的发展前景，在不久的将来将会有更多的突破，甚至将改变应用中技术进步的方向。纳米不仅意味着小规模，而且可以增强性能，高集成度和更少的能量消耗，这些属性正是行业的要求。例如，它们在磁数据存储，纳米传感器，生物医学诊断和治疗等领域中具有巨大的潜力。

但是，超顺磁性效应在应用方面对粒子的最小尺寸施加了阈值限制。一个克服这个极限的方法是通过耦合铁磁体（FM）颗粒到反铁磁（AF）介质获得交换各向异性。钴在铁磁元件中具有最高的磁各向异性能，这种属性使其更适合数据存储应用程序相对于铁和镍。

本课题主要包括通过惰性气体冷凝制得的铁磁性钴纳米颗粒与非磁性（如氧化硅）或反铁磁性（如铱锰合金）纳米薄膜的组合样品，利用MOKE和VSM测量其磁学性质，探究用MOKE定点测量被薄膜覆盖的纳米颗粒磁学性质的可能性。这些材料将有利于磁性数据存储并且可以帮助开发出新的永磁铁。

VSM的原理主要是，样品在以一定的频率在均匀磁场中振动，这会导致周围线圈内磁通量的变化，从而导致电压的变化，电压与磁化程度成正比，因此可以测出样品的磁化程度随磁场的变化的线图。

MOKE的原理主要是，当一个极化的电磁感应波从磁性材料的表面通过或反射时，它们将相互作用并以极性变化的形式反映出关于材料的磁学特性，磁光克尔仪器就是依据这种原理实现的。

在以往的实验中多用VSM（振动探针式磁强计）来测定纳米材料样品的性质，但是在铱锰薄膜上纳米颗粒被薄膜覆盖，虽然制备样品时需保持最上层覆盖的薄膜不能超过20nm，但是如果有时候薄膜厚度控制不好或者纳米颗粒太少VSM将探测不出纳米材料的性质。然而MOKE可以定点测量可以穿透薄膜并且更为敏感，因此更容易探测纳米颗粒。而且如果可以用MOKE代替VSM来测量，将会大大减小样品的尺寸。如果将此种材料应用到磁性存储材料纳米传感器等材料，将大大节约空间,效率提高。

关键词：钴纳米颗粒；振动探针式磁强计；磁光克尔效应MOKE；

Magnetic characterization of Co-based Nanoparticles

03013309 Cheng Ming

Supervised by Wang Mingchun Ulrich Herr

Abatract：

In recent years, nanoparticles (NPs) have become one of the most important and exciting forefronts in physics, chemistry, engineering and biology. They show great promise for providing us in the near future with many breakthroughs that will change the direction of technological advances in a wide range of applications. Nano does not only mean small scale, but also enhanced performance, high integration and less energy consumption. These properties are exactly what industry demands. As an example, NPs are attracting great attention due to their potential applications in areas such as magnetic data storage, nano-sensors, biomedical diagnoses and therapy.

However, the superparamagnetic effect imposes a threshold on the minimum size of the particle in terms of application. One way to overcome this limit is to obtain the exchange anisotropy by coupling the ferromagnetic (FM) particles to the antiferromagnetic (AF) medium. Cobalt has the highest magnetic anisotropy in ferromagnetic components, and this property makes it more suitable for data storage applications than iron and nickel.

This topic mainly includes the combination of ferromagnetic cobalt nanoparticles prepared by inert gas condensation and non-magnetic (such as silicon oxide) or antiferromagnetic (such as iridium manganese alloy) nano-film samples, using MOKE and VSM to measure its magnetic properties, The possibility of using MRKE to measure the magnetic properties of nanoparticles covered by the film is explored. These materials will facilitate magnetic data storage and can help develop new permanent magnets.
The principle of VSM is that the sample vibrates at a certain frequency in a uniform magnetic field, which results in a change in the magnetic flux in the surrounding coil, resulting in a voltage change that is proportional to the degree of magnetization. Then we can get the diagram for the degree of magnetization of the sample changing with the magnetic field.

The principle of MOKE is that when a polarized electromagnetic induction wave passes through or reflects from the surface of the magnetic material, they interact and reflect the magnetic properties of the material in the form of a polar change. The magneto-optical instrument is based on this principle.
In the past experiments, the properties of the nanomaterial samples were measured with the VSM (vibrating sample magnetometer), but the nanoparticles were covered with thin films on the iridium-manganese film, although the films with the uppermost layer required to prepare the samples could not exceed 20 nm. However, if sometimes the film thickness control is not good or the nanoparticles are too small, the VSM will not detect the properties of the nanomaterials. However, MOKE can point measurement can penetrate the film and more sensitive, so it is easier to detect nanoparticles. And if you can use MOKE instead of VSM to measure, will greatly reduce the size of the sample. If this material is applied to magnetic storage materials such as nano-sensors and other materials, will greatly save space and increase the efficiency.

Keywords: Co nanoparticles; VSM (vibrating sample magnetometer); Magneto-optic Kerr Effect

目 录

1. 绪论 8

2. 理论背景 9

2.1磁性材料 9

2.1.1 铁磁性材料 9

2.1.2反铁磁性材料 9

2.1.3 抗铁磁性材料 9

2.2 Stoner-Wohlfarth模型 10

2.3超顺磁极限 11

2.4 交换偏置 15

3. 实验方法 20

3.1样品制备方法 20

3.1.1磁控溅射技术 20

3.1.2输入气体冷凝 22

3.1.3 场退火和场冷却 23

3.2实验技术 23

3.2.1 振动样品磁强计 23

3.2.2磁光克尔效应 24

3.2.3锁相放大器原理 26

3.2.4 扫描电子显微镜 26

4. 实验结果 27

4.1 制备的样品 27

4.1.1 铜薄膜（用于校准） 27

4.1.2 铱锰薄膜（用于校准） 27

4.1.3 钴薄膜（用于测试MOKE仪器和VSM仪器） 28

4.1．4 钴纳米粒子嵌入到铜薄膜中 28

4.1．5 钴纳米粒子嵌入到铱锰薄膜中 28

4.2 薄膜厚度的校准 30

4.3 纳米粒子大小的测定 31

4.4 实验图线 33

4.4.1 钴薄膜校准实验仪器 33

4.4.2 钴纳米颗粒嵌入在铜薄膜中 35

4.4.3 钴纳米颗粒嵌入在铱锰薄膜中 38

5. 结论与展望 40

6. 致谢 41

7. 参考文献 41

1. 绪论

近年来，科学家在纳米科学和纳米技术方面取得了巨大的成功。纳米技术广泛的应用于设计，生产，检测和纳米尺寸的材料设备。纳米技术的进步促进了工具和设备的改进和在日常生活中的应用。在电气工程物理学中，纳米科学与纳米尺寸结构中的量子行为或电子行为密切相关。此外，在生物学和生物化学中还存在纳米尺寸的细胞成分和分子结构等。

为了研究铁磁体（FM）颗粒和反铁磁（AF）膜之间的交换各向异性，我们通常使用两种不同的方法用于合成纳米颗粒和薄膜的方法。其中，薄膜制备包括反铁磁（AF）薄膜，粘合层和保护层。我们使用不同类型的物理气相沉积技术：用于粘合层（例如，钽）和AF层（例如NiMn，IrMn）的磁控溅射;用于沉积保护盖层（主要是SiOx）的热蒸发。生产纳米颗粒最常用的方法是惰性气体冷凝，溶胶 - 凝胶和自组装方法。

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