In order to obtain magnetorheological （MR） elastomers with high magnetorheological effect, a family of anisotropic rubber-based MR elastomers was developed using a new form of chemical modification. Three different ...In order to obtain magnetorheological （MR） elastomers with high magnetorheological effect, a family of anisotropic rubber-based MR elastomers was developed using a new form of chemical modification. Three different kinds of surfactants, i.e. anionic, nonionic and compound surfactants, were employed separately to modify iron particles. The MR effect was evaluated by measuring the dynamic shear modulus of MR elastomer with a magneto-combined dynamic mechanical analyzer. Results show that the relative MR effect can be up to 188% when the iron particles are modified with 15% Span 80. Besides the surface activity of Span 80, however, such high modifying effect is partly due to the plasticizing effect of Span 80. Compared with the single surfactant, the superior surface activity of compound surfactant makes the relative MR effect reach 77% at a low content of 0.4%. Scanning electron microscope observation shows that the modification of compound surfactant results in perfect compatibility between particles and rubber matrix and special self-assembled structure of particles. Such special structure has been proved beneficial to the improvement of the relative MR effect.展开更多
Magnetic topological quantum materials(TQMs) provide a fertile ground for the emergence of fascinating topological magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic(AFM) topological insu...Magnetic topological quantum materials(TQMs) provide a fertile ground for the emergence of fascinating topological magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic(AFM) topological insulator MnBi_(2)Te_(4) that could realize quantized anomalous Hall effect and axion insulator phase ignited intensive study on this family of TQM compounds. Here, we investigated the AFM compound Mn Bi4 Te7 where Bi_(2)Te_(3) and MnBi_(2)Te_(4) layers alternate to form a superlattice. Using spatial-and angleresolved photoemission spectroscopy, we identified ubiquitous(albeit termination dependent) topological electronic structures from both Bi_(2)Te_(3) and MnBi_(2)Te_(4) terminations. Unexpectedly, while the bulk bands show strong temperature dependence correlated with the AFM transition, the topological surface states with a diminishing gap show negligible temperature dependence across the AFM transition.Together with the results of its sister compound MnBi_(2)Te_(4), we illustrate important aspects of electronic structures and the effect of magnetic ordering in this family of magnetic TQMs.展开更多
FesoMn15-xCoxNi35 （x=0, 1, 3, 5, 7） alloys were prepared by arc melting under purified argon atmosphere. The ingots were homogenized at 930℃ for 90 h followed by water quenching. The crystal structure, magnetic pro...FesoMn15-xCoxNi35 （x=0, 1, 3, 5, 7） alloys were prepared by arc melting under purified argon atmosphere. The ingots were homogenized at 930℃ for 90 h followed by water quenching. The crystal structure, magnetic properties and magnetocaloric effects of the alloys were studied by X-ray diffraction （XRD） and MPMS-7-type SQUID. The results show that all samples still maintained a single γ-（Fe, Ni）-type phase structure. With the increase of the content of Co, the Curie temperatures of these alloys increased and exhibited a second-order magnetic transition from ferromagnetic （FM） to paramagnetic （PM） state near Curie temperature. The maximum magnetic entropy change and the relative cooling power of Fe50Mn10CosNi35 alloy was 2.55 J/kg.K and 181 J/kg, respectively, for an external field change of 5 T. Compared with rare earth metal Gd, FesoMnls-xCoxNi35 series of alloys have obvious advantage in resource price; their Curie temperatures can be tuned to near room temperature, maintain a relatively large magnetic entropy change at the same time and they are a type of potential magnetic refrigeration materials near room temperature.展开更多
基金ACKNOWLEDGMENTS This work was supported by the Natioal Natural Science Foundation of China （No.10672154） and the Specialized Research Fund for the Doctoral Program of Higher Education （No.20050358010）. The Scholarship BRJH funding of Chinese Academy of Sciences is also appreciated.
文摘In order to obtain magnetorheological （MR） elastomers with high magnetorheological effect, a family of anisotropic rubber-based MR elastomers was developed using a new form of chemical modification. Three different kinds of surfactants, i.e. anionic, nonionic and compound surfactants, were employed separately to modify iron particles. The MR effect was evaluated by measuring the dynamic shear modulus of MR elastomer with a magneto-combined dynamic mechanical analyzer. Results show that the relative MR effect can be up to 188% when the iron particles are modified with 15% Span 80. Besides the surface activity of Span 80, however, such high modifying effect is partly due to the plasticizing effect of Span 80. Compared with the single surfactant, the superior surface activity of compound surfactant makes the relative MR effect reach 77% at a low content of 0.4%. Scanning electron microscope observation shows that the modification of compound surfactant results in perfect compatibility between particles and rubber matrix and special self-assembled structure of particles. Such special structure has been proved beneficial to the improvement of the relative MR effect.
基金supported by the National Key Research and Development Program of China (2017YFA0305400, 2017YFA0304600, 2018YFA0307100, and 2018YFA0305603)the National Natural Science Foundation of China (11774190, 11674229, 11634009, 11774427, 51788104, and 11874035)+1 种基金EPSRC Platform Grant (EP/M020517/1)the support from the Shanghai Pujiang Program (17PJ1406200)。
文摘Magnetic topological quantum materials(TQMs) provide a fertile ground for the emergence of fascinating topological magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic(AFM) topological insulator MnBi_(2)Te_(4) that could realize quantized anomalous Hall effect and axion insulator phase ignited intensive study on this family of TQM compounds. Here, we investigated the AFM compound Mn Bi4 Te7 where Bi_(2)Te_(3) and MnBi_(2)Te_(4) layers alternate to form a superlattice. Using spatial-and angleresolved photoemission spectroscopy, we identified ubiquitous(albeit termination dependent) topological electronic structures from both Bi_(2)Te_(3) and MnBi_(2)Te_(4) terminations. Unexpectedly, while the bulk bands show strong temperature dependence correlated with the AFM transition, the topological surface states with a diminishing gap show negligible temperature dependence across the AFM transition.Together with the results of its sister compound MnBi_(2)Te_(4), we illustrate important aspects of electronic structures and the effect of magnetic ordering in this family of magnetic TQMs.
基金supported by the National Natural Science Foundation of China(Grant Nos.11032011 and 10872202)the Guangdong Provincial Science and Technology Program(Grant No.2010B050300008)+2 种基金the Guangzhou Municipal Science and Technology Program(Grant No.12F582080022)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry(Grant No.x2clB7120290)the Fundamental Research Funds for the Central Universities(Grant Nos.2012ZZ0013 and 2014ZZ0005)
文摘FesoMn15-xCoxNi35 （x=0, 1, 3, 5, 7） alloys were prepared by arc melting under purified argon atmosphere. The ingots were homogenized at 930℃ for 90 h followed by water quenching. The crystal structure, magnetic properties and magnetocaloric effects of the alloys were studied by X-ray diffraction （XRD） and MPMS-7-type SQUID. The results show that all samples still maintained a single γ-（Fe, Ni）-type phase structure. With the increase of the content of Co, the Curie temperatures of these alloys increased and exhibited a second-order magnetic transition from ferromagnetic （FM） to paramagnetic （PM） state near Curie temperature. The maximum magnetic entropy change and the relative cooling power of Fe50Mn10CosNi35 alloy was 2.55 J/kg.K and 181 J/kg, respectively, for an external field change of 5 T. Compared with rare earth metal Gd, FesoMnls-xCoxNi35 series of alloys have obvious advantage in resource price; their Curie temperatures can be tuned to near room temperature, maintain a relatively large magnetic entropy change at the same time and they are a type of potential magnetic refrigeration materials near room temperature.
