Filters

2016 - 20202

More filters

2019 - 20202
Reset filters

Settings

DDC: 620 × Subject: grain boundaries ×

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Influencing Martensitic Transition in Epitaxial Ni-Mn-Ga-Co Films with Large Angle Grain Boundaries
    (Basel : MDPI, 2020) Lünser, Klara; Diestel, Anett; Nielsch, Kornelius; Fähler, Sebastian
    Magnetocaloric materials based on field-induced first order transformations such as Ni-Mn-Ga-Co are promising for more environmentally friendly cooling. Due to the underlying martensitic transformation, a large hysteresis can occur, which in turn reduces the efficiency of a cooling cycle. Here, we analyse the influence of the film microstructure on the thermal hysteresis and focus especially on large angle grain boundaries. We control the microstructure and grain boundary density by depositing films with local epitaxy on different substrates: Single crystalline MgO(0 0 1), MgO(1 1 0) and Al2O3(0 0 0 1). By combining local electron backscatter diffraction (EBSD) and global texture measurements with thermomagnetic measurements, we correlate a smaller hysteresis with the presence of grain boundaries. In films with grain boundaries, the hysteresis is decreased by about 30% compared to single crystalline films. Nevertheless, a large grain boundary density leads to a broadened transition. To explain this behaviour, we discuss the influence of grain boundaries on the martensitic transformation. While grain boundaries act as nucleation sites, they also lead to different strains in the material, which gives rise to various transition temperatures inside one film. We can show that a thoughtful design of the grain boundary microstructure is an important step to optimize the hysteresis.
  • Thumbnail Image
    Item
    Toward edges-rich MoS2 layers via chemical liquid exfoliation triggering distinctive magnetism
    (Milton Park : Taylor & Francis, 2016) Gao, Guanhui; Chen, Chi; Xie, Xiaobin; Su, Yantao; Kang, Shendong; Zhu, Guichi; Gao, Duyang; Eckert, Jürgen; Trampert, Achim; Cai, Lintao
    The magnetic function of layered molybdenum disulfide (MoS2) has been investigated via simulation, but few reliable experimental results have been explored. Herein, we developed edges-rich structural MoS2 nanosheets via liquid phase exfoliation approach, triggering exceptional ferromagnetism. The magnetic measurements revealed the clear ferromagnetic property of layered MoS2, compared to the pristine MoS2 in bulk exhibiting diamagnetism. The existence of ferromagnetism mostly was attributed to the presence of grain boundaries with abundant irregular edges confirmed by the transmission electron microscopy, magnetic force microscopy and X-ray photoelectron spectroscopy, which experimentally provided reliable evidences on irregular edges-rich states engineering ferromagnetism to clarify theoretical calculation.