GeMn granular thin films are a unique and promising material for spintronics applications due to large positive magnetoresistance (MR). Previous studies on GeMn have suggested that the large MR is related to nanospinodal decomposition of GeMn into Mn-rich ferromagnetic nanoparticles and Mn-poor paramagnetic matrix. However, its microscopic origin of the MR has not been clarified yet. Here, using X-ray magnetic circular dichroism (XMCD), which is extremely sensitive to the local magnetic state of each atom, we investigate the magnetic properties of the nanoparticles and the matrix in GeMn separately. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo spin-disorder magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.
A phenomenological model for magnetoresistance in granular polycrystalline colossal magnetoresistive materials: the role of spin polarised tunnelling at the grain boundaries
已经观察到，在磁致电阻（CMR）材料的块状和多晶薄膜中，与单晶或低于铁磁转变温度Tc的单晶膜相比，磁阻遵循不同的行为。在本文中，我们发展了一个唯象模型来解释磁场依赖的电阻在颗粒CMR材料考虑到自旋极化隧道在晶界。该模型已被拟合到两个系统，即La 0.55 Ho 0.15 Sr 0.3 MnO 3和La 1.8 Y 0.5 Ca 0.7 Mn 2 O 7。从拟合的结果中，我们已经分离出，在La 0.55Ho 0.15Sr 0.3MnO 3，来自自旋极化隧道在晶界的磁电阻的晶粒间的贡献的内在贡献。结果表明，La_（0.55）Ho_（0.15）Sr_（0.3）MnO_3的本征磁电阻效应随温度的变化符合双交换模型的预测.
Enhancement of giant magnetoresistance effect in the Ruddlesden-Popper phase Sr3Fe2-xCoxO7-d: Predominant role of oxygen nonstoichiometry and magnetic phase separation
Magnetoresistive behaviour of ternary Cu-based materials processed by high-pressure torsion
采用高压扭转对三元铜基材料（CuFeCo和CuFeNi）进行剧烈塑性形变，制备了具有纳米晶结构的块体样品。其目标是生产具有颗粒巨磁阻效应的材料，需要铁和铁磁材料之间的界面。这两个三元系统的磁效应，发现充分的后续退火有积极的影响。的变形状态，以及热处理后的显微组织变化，使用扫描电子显微镜和X射线衍射测量进行了研究。从电子显微镜推断，观察到的单相结构的所有变形样品，表明形成过饱和固溶体。然而，从颗粒状巨磁阻效应的存在来判断，必须存在小的铁磁颗粒。Cu 62 Fe 19 Ni 19在400 °C下退火1 h后，室温电阻率下降最大（1790 kA/m时为2.45%）。结合经典的微观结构研究和磁性测量的结果，深入了解铁磁颗粒的演变是可以访问的。
