Perspective: Local ferromagnetic resonance measurement techniques: "Invited Review Article: Microwave spectroscopy based on scanning thermal microscopy: resolution in the nanometer range" [Rev. Sci. Instrum. 79, 041101 (2008)].
Perspective: Local ferromagnetic resonance measurement techniques: "Invited Review Article: Microwave spectroscopy based on scanning thermal microscopy: resolution in the nanometer range" [Rev. Sci. Instrum. 79, 041101 (2008)].
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观点：局域铁磁共振测量技术：“特邀评论文章：基于扫描热显微镜的微波光谱：纳米范围内的分辨率”[Rev.1]
DOI：
10.1063/1.2911921
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
C. Patton
中科院分区：
文献类型：
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作者：
N. Mo;C. Patton
根据Vonsovskii的说法，铁磁共振FMR是Arkad'yev在1911年发现的。FMR实验发现的标准引文是格里菲思，因为他观察到平面磁化电镀铁磁薄膜的相当宽的吸收轮廓和“异常”电子顺磁共振EPR场。一年后，Kittel通过考虑动态退磁场解释了反常FMR场。FMR与EPR不同，因为FMR场或频率由于静态和动态退磁场效应等而从纯电子自旋共振值的通常范围偏移相当大的量。测量铁磁电阻响应的传统方法是通过短路波导、微波谐振腔或带状线技术。人们通常用相对均匀的微波场激励FMR，并获得均匀模式或准均匀模式响应，其中所有旋进自旋以相同的标称幅度和相位被激励。尽管响应具有准均匀模式的性质，但大样本的实际功率吸收曲线通常取决于局部性质，这些性质可能包括非均匀微观结构以及局部磁矩、旋磁比、磁晶各向异性、阻尼和弛豫过程等的空间变化。许多工作人员还开发了各种“本地”FMR技术。局部FMR实验可以通过两种方式进行。在第一种方法中，在宽区域上激发样品，并且仅在样品的小区域上使用局部FMR探针进行检测。第二种方法利用局部激励和局部检测。局部FMR测量的第一个实际设置使用第二种方法，其中薄膜样品通过微波腔的小光圈被局部激发和检测。这种基本而简单的近场技术由Frait和Soohoo独立开发。从Frait和Soohoo的最初工作开始，本地FMR方法的工作不断发展。直到最近，这些主要集中在与近场光学相关的方法上，并且基于使用小探针。这些一般方法的非FMR相关综述见参考文献11。铁磁共振相关的引文包括工作与小型同轴回路铁磁共振探头和介质谐振器狭缝探头。这些方法代表了原始Frait/Soohoo方案在不同复杂程度上的相当直接的变化。这些方法从未能够实现低于约10米左右的空间分辨率。1988年，德国波鸿鲁尔大学的Pelzl提出了一种基于热效应的局部FMR新方法。这种方法导致了一个高度敏感和非常精细的规模FMR测量能力下降到10 nm左右。这种技术可以被称为“扫描热FMR显微镜”SThM。对于上面介绍的常规近场局部FMR方法，单个探针在磁响应的激发和检测中起双重作用。在SThM技术中，通常使用微波腔来激发壁装样品中的磁响应。然后使用热传感器通过壁中的小孔探测样品。热探头简单地测量局部温度的微小变化，该局部温度沿着由于FMR驱动的吸收功率引起的样品加热。参考文献16中描述的初始SThM系统基于光热调制方法。用40 Hz功率调制的He-Ne激光局部照射样品，光斑直径为180 m。调制引起样品磁化强度的局部变化，也是在40 Hz调制频率下。这又给出了FMR功率吸收的调制和相应的局部温度，然后通过锁定检测方法检测到局部温度。近年来，Meckenstock等人在这种基本的局部FMR热检测方法方面取得了相当大的进展。参考文献17描述了该方法的扩展，以在没有热调制的情况下直接检测。在这种情况下，标称分辨率约为100 nm。这些作者还开发了一种基于扫描热弹性显微镜SThEM的方法。在这种方法中，局部热弹性膨胀直接测量原子力显微镜AFM技术。这种方法的结合使人们能够将AFM领域的所有力量和进步带到局部FMR测量的桌子上。与以前的近场FMR显微镜相比，新的热技术提供了显着提高的空间分辨率。Meckenstock等人报道的SThEM空间分辨率在10 nm范围内。微波功率调制和锁相检测的使用提供了良好的灵敏度和高信噪比。科学文书审查79，040901 2008
According to Vonsovskii, ferromagnetic resonance FMR was unknowingly discovered by Arkad’yev in 1911. The standard citation for the experimental discovery of FMR is to Griffiths for his observation of the rather broad absorption profile and an “anomalous” electron paramagnetic resonance EPR field for in-plane magnetized electroplated ferromagnetic films. One year later, Kittel explained the anomalous FMR fields by taking the dynamic demagnetizing fields into account. FMR is distinct from EPR because the FMR field or frequency is shifted from the usual range of pure electron spin resonance values by substantial amounts because of both static and dynamic demagnetizing field effects, among others. The traditional approaches to the measurement of the FMR response are through shorted waveguide, microwave cavity, or stripline techniques. One usually excites the FMR with a relatively uniform microwave field and obtains a uniform-mode or quasi-uniform-mode response in which all of the precessing spins are excited at the same nominal amplitude and in phase. In spite of the quasi-uniform-mode nature of the response, the actual power absorption profile for a large sample often depends on the local properties that may include a nonuniform microstructure as well as spatial variations in the local magnetic moment, gyromagnetic ratio, magnetocrystalline anisotropy, damping and relaxation processes, and so on. From the late 1950s, various workers have also developed a variety of “local” FMR techniques. A local FMR experiment may be done in two ways. In the first, one excites the sample over a wide area and a local FMR probe is used for detection over a small region of the sample only. The second utilizes both local excitation and local detection. The first practical setup for local FMR measurements used the second approach, in which a thin film sample was excited and detected locally through a small iris of a microwave cavity. This basic and simple near field technique was developed independently by Frait and Soohoo. From the initial work by Frait and Soohoo, there has been evolving work on local FMR approaches. Until recently, these have focused mainly on methods related to near field optics and based on the use of small probes. See Ref. 11 for a non-FMR related review of these general approaches. FMR related citations include work with small coaxial loop FMR probes and dielectric resonator slit probes. These methods represent fairly straightforward variations of the original Frait/Soohoo schemes at different levels of sophistication. These approaches have never been able to achieve spatial resolutions below about 10 m or so. In 1988, a new approach to local FMR based on thermal effects was introduced by Pelzl at Ruhr University, Bochum, Germany. This method has led to a highly sensitive and very fine scale FMR measurement capability down to 10 nm or so. This technique may be termed “scanning thermal FMR microscopy” SThM . For the conventional near field local FMR methods introduced above, a single probe plays a dual role in both the excitation and detection of the magnetic response. In the SThM technique, a microwave cavity is often used to excite the magnetic response in a wall mounted sample. A thermal sensor is then used to probe the sample through a small hole in the wall. The thermal probe simply measures the small changes in the local temperature that go along with the sample heating due to the FMR driven absorbed power. The initial SThM system described in Ref. 16 was based on a photothermal modulation approach. The sample was locally illuminated by a 40 Hz power-modulated He–Ne laser with a 180 m diameter spot size. The modulation induces a localized change in the magnetization of the sample, also at the 40 Hz modulation frequency. This, in turn, gives a modulation in the FMR power absorption and the corresponding local temperature that is then detected by lock-in detection methods. In recent years, Meckenstock et al. have made considerable advances in this basic local FMR thermal detection approach. Reference 17 describes extensions of the method to direct detection without thermal modulation. The nominal resolution in this case was about 100 nm. These authors also developed a variation of the method based on scanning thermal-elastic microscopy SThEM . In this approach, the local thermal-elastic expansion is measured directly by atomic force microscopy AFM techniques. This marriage of methods allows one to bring all of the power and advances in the field of AFM to the table for local FMR measurements. Compared to the previous near field FMR microscopes, the new thermal techniques give a significantly improved spatial resolution. The reported SThEM spatial resolution by Meckenstock et al. was in the range of 10 nm. The use of microwave power modulation and lock-in detection gave good sensitivity and a high signal to noise ratio. REVIEW OF SCIENTIFIC INSTRUMENTS 79, 040901 2008