The microstructure change in thin NiFe/Cu/NiFe films during the magnetization process was observed by the Lorentz electronmicroscopy. TWo types of films were prepared: (1) one NiFe layer with anisotropy and the other ...The microstructure change in thin NiFe/Cu/NiFe films during the magnetization process was observed by the Lorentz electronmicroscopy. TWo types of films were prepared: (1) one NiFe layer with anisotropy and the other layer without, and (2) both NiFe layershave anisotropy normal each other. The domain wall migration and magnetization rotation processes in each of NiFe layers could be observed separately. The presence of magnetic anisotropy in the magnetic layer effectively controls the behavior of magnetic domains. Theinteraction between the two NiFe layers of the film could be observed not so strong in the present experiment.展开更多
The three-dimensional（3D） Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be v...The three-dimensional（3D） Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A3Bi（A = Na, K, Rb）. Here we report comprehensive high-resolution angle-resolved photoemission（ARPES） measurements on the two cleaved surfaces,（001） and（100）, of Na3Bi. On the（001） surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the kx–ky plane and by varying the photon energy to get access to different out-of-plane kzs. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the（100） surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the（100） plane. We directly observe two isolated 3D Dirac nodes on the（100） surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ~150 me V before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the3 D Dirac cones, on the possible formation of surface reconstruction of the（001） surface, and on the issue of basic Brillouin zone selection for the（100） surface.展开更多
文摘The microstructure change in thin NiFe/Cu/NiFe films during the magnetization process was observed by the Lorentz electronmicroscopy. TWo types of films were prepared: (1) one NiFe layer with anisotropy and the other layer without, and (2) both NiFe layershave anisotropy normal each other. The domain wall migration and magnetization rotation processes in each of NiFe layers could be observed separately. The presence of magnetic anisotropy in the magnetic layer effectively controls the behavior of magnetic domains. Theinteraction between the two NiFe layers of the film could be observed not so strong in the present experiment.
基金Project supported by the National Natural Science Foundation of China(Grant No.11574367)the National Basic Research Program of China(Grant Nos.2013CB921700,2013CB921904,and 2015CB921300)+2 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB07020300)The synchrotron radiation experiments have been done under the HiSOR Proposal numbers12-B-47 and 13-B-16
文摘The three-dimensional（3D） Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A3Bi（A = Na, K, Rb）. Here we report comprehensive high-resolution angle-resolved photoemission（ARPES） measurements on the two cleaved surfaces,（001） and（100）, of Na3Bi. On the（001） surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the kx–ky plane and by varying the photon energy to get access to different out-of-plane kzs. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the（100） surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the（100） plane. We directly observe two isolated 3D Dirac nodes on the（100） surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ~150 me V before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the3 D Dirac cones, on the possible formation of surface reconstruction of the（001） surface, and on the issue of basic Brillouin zone selection for the（100） surface.
