19/20T超高场STM-MFM-AFM组合显微镜新镜体及其对磁场与电流调控庞磁阻薄膜的研究

Giant Magnetoresistive materials (GMR) of the multiplayer structure has been a great success in magnetic storage applications, and the CMR with more simple structure has a greater potential for magnetic storage applications, but it was almost cannot be applied because the critical field which is needed to produce magnetoresistance is too high. To find out the mechanism of CMR magnetoresistive behavior, we must find out the mechanism of the action of the injecting current and the microstructure and magnetic structure of the CMR, and how it was influenced by magnetic field. Actually, the injecting current indeed can change the and regulate the three elements which determine the properties of CMR: change the structure, change the electronic state and change the magnetic structure and behavior. In this project, Base on the 18T high magnetic field STM-MFM-AFM combo microscope(referred to SMA, I was a major biulder) which successfully constructed by ourelves, we will do substantial improvements for the core of the microscope and then make the SMA with atomic resolution imaging at 18T upgrade to 19-20T; the measurement method of the AFM/MFM was changed from frequency modulation non-contact measurement to "amplitude modulation non-contact measurement with feedback to steady amplitude and speed up" with high sensitivity and high stability which successfully developed by our group recently. The new SMA with more stable, more sophisticated, and higher magnetic field will be used to study the regulation of magnetic field and injection current(can be polarized by high magnetc field) of the micro-local magnetic structure and electronic state of the CMR of single crystal and thin film, revealing the regulation mechanism and potential applications of the thin film CMR.

多层结构的巨磁阻材料（GMR）已经在磁存储应用上获得了巨大的成功，而结构更简单的CMR具有更大的磁存储应用潜力，只是其产生磁阻效应的临界场太高而几乎得不到应用。要弄清CMR的磁阻行为机制，必须要弄清注入电流与CMR微观结构和磁结构的作用机制及其如何受磁场的影响。实际上，注入电流也确能改变和调制决定CMR物性的三要素：改变结构，改变电子态以及改变磁结构与行为。本项目将在我们自行研制成功的18T强磁场STM-MFM-AFM组合显微镜（简称SMA，我为主要建造人）基础上，对镜体部分做实质性改进，使原来的18T原子分辨率成像提升到19-20T；AFM/MFM测法也由调频非接触测量改为我组近期研制成功的高灵敏-高稳定的"反馈稳幅增速的调幅非接触测量"。更稳定、更精密、更高场的全新SMA将被应用于研究磁场与注入电流对庞磁阻单晶薄膜的微观局域磁结构与电子态的调控，揭示薄膜CMR的调控机理与应用潜力。

本项目是改进现有STM-MFM-AFM组合显微镜镜体使之能在19T及以上超高磁场中工作，并利用新镜体对磁场与电流调控庞磁阻薄膜进行局域显微成像的研究。本项目执行期间，我们先后研制出GeckoDrive、TunaDrive和SpiderDrive三种高度稳定、抗干扰的压电马达。利用GeckoDrive，我们研制出了高度稳定和抗干扰的STM及电化学STM；利用SpiderDrive，我们研制出了一款可植入18/20T超导磁体中的MFM，并利用该MFM对锰氧化物薄膜样品进行了大量的局域显微成像研究，上述工作发表在Ultramicroscopy，Review of Scientific Instruments等杂志上。特别是我们利用基于TunaDrive研制成功的STM在水冷磁体的大振动、高噪声的环境下获得了高达27T磁场下的清晰的原子图像，表明我们的新镜体完全可以在19T以上的磁场环境下工作，该工作发表在Nano Research上。我们利用基于SpiderDrive研制的MFM对LCMO/NGO的研究在实空间中观察到了相分离从电荷有序态到重现的完整过程，发现了丰富的相分离行为，该工作已经在Nature Communications上发表；在对PCMO/LSAT的局域显微成像研究过程中，我们也在实空间中观测了高场下反铁磁相的动态演变过程，这部分工作还在进行中。此外我们利用自制UHV-STM发现了下层原子散射表面电子的扫描隧道显微学证据，并提出了“集体干涉”理论模型，该工作发表在Carbon上。我们还发现外加偏置电压能精确控制石英音叉的本征频率在纳赫兹的量级进行迁移，这在超灵敏频率调制及高精度频率测量方面都有巨大的应用潜力，论文发表在Sensors上。

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