CMR材料的高密存储应用至今仍因低场MR弱而受阻。近期研究倾向拔高相分离对MR的决定作用，特别是CMR膜与衬底对称失配产生的各向异性应力可增强相分离竞争并导致低场MR、多重金属-绝缘转变和各向异性磁阻等重要效应，是重要突破口，故结构上微观的相分离的局域行为研究就成关键。该局域研究很少，体现本项目的重要。但有难度，因其最佳厚度仅25nm，磁信号太弱。我们最早在Science上揭示MFM是CMR膜局域研究有力手段，后又发表CMR膜中存在相分离的MFM图像。去年我们潜心研制出新原理的高Q调幅MFM，便在60nm对称失配CMR膜中获得高清晰"磁单畴"相分离图像且行为丰富。本项目以20T磁体中的该MFM研究相分离更强的<40nm超薄对称失配CMR高品质单晶膜中的微观磁结构，其形成和受磁场、温度、光照等调控的局域机制，从微观上弄清其低场MR特性和戏剧性输运行为，特别关注可能的超低场CMR局域及其成因。

The next generation high density storage application of manganese oxide colossal magneto-resistive (CMR) material still does not come true due to its low magneto-resistance (MR) in low magnetic field. Recent studies tend to enhance the decision role of phase separation on the origin of CMR effect. So, the local (microscopic) behavior research of the microscopically structured phase separation becomes particularly important. Especially, very recent studies show that the anisotropic strains in the CMR film induced by the lattice symmetry mismatch between the CMR film and its substrate will greatly enhance the phase competition / separation in the film and result in relatively high MR in low field. This is a major breakthrough and the clarification of its local phase separation behavior and mechanism becomes the key to the understanding of low-field high MR effect. This research is rarely seen, implying that this project is important. But, such research is difficult because the optimal thickness of the symmetry mismatch CMR film is about 20-30nm, which is too thin to produce sufficiently strong local magnetic signal. I was the first author of a Science paper which indicated that the magnetic force microscope (MFM) was a power tool in the studies of local magnetic structures of CMR thin films and later further published the MFM images of local phase separations in CMR thin films (cited 140 times). Last year, we invented and implemented a new principle high sensitivity "high Q factor amplitude modulated MFM", from which we immediately obtained high quality "single domain" phase separation MFM images of a 60 nm thick symmetry mismatch CMR film. These single domains also showed rich behaviors. In this project, we will utilize this MFM (installed in a 20T ultra-strong Oxford superconducting magnet) to systematically study the local phase separation structures and behaviors of high quality "thinner than 40 nm ultra-thin" symmetry mismatch CMR films grown by pulsed laser deposition (PLD), including their responses to the changes of temperature, external magnetic field and light etc. The goal is to microscopically clarify the low field MR characteristics and the dramatic macroscopic transport behaviors of this type CMR films. Particular attention will be paid to the possible ultra-low field high MR locals and the reasons.