Bisphenol F epoxy resin(EP)is often used in terminal current lead insulation of superconducting equipment because of its good insulation performance,high mechanical strength,good toughness at cryogenic temperatures,an...Bisphenol F epoxy resin(EP)is often used in terminal current lead insulation of superconducting equipment because of its good insulation performance,high mechanical strength,good toughness at cryogenic temperatures,and resistance to cold shock and heat shock.However,due to the wide temperature range of 80–300 K and the strong electric field,the EP-N_(2)interface is prone to surface flashover,resulting in terminal insulation failure.To improve the reliability of the current lead insulation,non-linear conductive EP/strontium titanate(SrTiO_(3))composites were prepared by modification with nano filling.The changes of dielectric,surface discharge,flashover,and trap distribution characteristics of composite materials were studied,and the mechanism of SrTiO_(3)on the surface flashover of composite materials was analysed.The results show that the conductivity of the composite increases with the rise of SrTiO_(3)filling content,and the amplitude of improvement is greater under the strong electric field,showing a more significant non-linearity.The composite has a lower trap energy level and a greater number of shallow traps compared to pure EP,which accelerates surface charge detrapping and reduces charge accumulation,effectively enhancing the discharge and surface flashover voltage of the composite.展开更多
The modulation of topological electronic state by an external magnetic field is highly desired for condensed-matter physics.Schemes to achieve this have been proposed theoretically,but few can be realized experimental...The modulation of topological electronic state by an external magnetic field is highly desired for condensed-matter physics.Schemes to achieve this have been proposed theoretically,but few can be realized experimentally.Here,combining transverse transport,theoretical calculations,and scanning tunneling microscopy/spectroscopy(STM/S)investigations,we provide an observation that the topological electronic state,accompanied by an emergent magneto-transport phenomenon,was modulated by applying magnetic field through induced non-collinear magnetism in the magnetic Weyl semimetal EuB6.A giant unconventional anomalous Hall effect(UAHE)is found during the magnetization re-orientation from easy axes to hard ones in magnetic field,with a UAHE peak around the low field of 5 kOe.展开更多
Ferromagnetic-structural transformation has been studied widely in MnCoGe-based materials. However, the magnetostructural transition(MST) from antiferromagnetic(AFM) orthorhombic phase to ferromagnetic(FM) hexagonal p...Ferromagnetic-structural transformation has been studied widely in MnCoGe-based materials. However, the magnetostructural transition(MST) from antiferromagnetic(AFM) orthorhombic phase to ferromagnetic(FM) hexagonal phase, which may lead to a large inverse magnetocaloric effect(MCE), has rarely been reported. Here, the introduction of Mn vacancy lowers the structural transition temperature while retains the AFM state in the orthorhombic phase, thus successfully realizing the AFM-FM MST in Mn0.95Co0.75Cu0.25Ge. Moreover, successive inverse and normal MCEs are observed around the first-order AFM-FM MST and the second-order FM-paramagnetic(PM) transition, respectively. A thermostat is proposed based on this special feature, which could release heat above the critical temperature while absorb heat below the critical temperature by simply applying the same magnetization/demagnetization cycles. This thermostat can be very useful in many applications where a constant temperature is required, such as cryostats and incubators.展开更多
Using spark plasma sintering （SPS）, Mn3Cu0.6Ge0.4N crystallites have been fabricated with different crystallite sizes, and their magnetic properties and thermal behaviors were systemically investigated. With decreas...Using spark plasma sintering （SPS）, Mn3Cu0.6Ge0.4N crystallites have been fabricated with different crystallite sizes, and their magnetic properties and thermal behaviors were systemically investigated. With decreasing crystallite size, the magnetic transition becomes increasingly slow, accompanied by broadening of the negative thermal expansion （NTE） operation-temperature window. The NTE operation-temperature window for the 12-nm crystallite sample reaches at 140 K, which is about 75% larger than that of the 74-nm crystallite sample. The magnetic properties and NTE operation-temperature window can be tuned by varying the crystallite size. This discovery will promote an even wider range of practical applications in precision devices.展开更多
基金National Natural Science Foundation of China,Grant/Award Numbers:51907047,52277143S&T Program of Hebei,Grant/Award Number:21567605HKey Laboratory of Special Machine and High Voltage Apparatus,Grant/Award Number:KFKT202207。
文摘Bisphenol F epoxy resin(EP)is often used in terminal current lead insulation of superconducting equipment because of its good insulation performance,high mechanical strength,good toughness at cryogenic temperatures,and resistance to cold shock and heat shock.However,due to the wide temperature range of 80–300 K and the strong electric field,the EP-N_(2)interface is prone to surface flashover,resulting in terminal insulation failure.To improve the reliability of the current lead insulation,non-linear conductive EP/strontium titanate(SrTiO_(3))composites were prepared by modification with nano filling.The changes of dielectric,surface discharge,flashover,and trap distribution characteristics of composite materials were studied,and the mechanism of SrTiO_(3)on the surface flashover of composite materials was analysed.The results show that the conductivity of the composite increases with the rise of SrTiO_(3)filling content,and the amplitude of improvement is greater under the strong electric field,showing a more significant non-linearity.The composite has a lower trap energy level and a greater number of shallow traps compared to pure EP,which accelerates surface charge detrapping and reduces charge accumulation,effectively enhancing the discharge and surface flashover voltage of the composite.
基金This work was supported by the National Key Basic Research Program of China(2021YFA0718700,2017YFA0302900,2017YFA0303003,2018YFB0704102,and 2018YFA0305800)the National Natural Science Foundation of China(11888101,11927808,11834016,11961141008,12174428,and 12274439)+4 种基金the Strategic Priority Research Program(B)of Chinese Academy of Sciences(XDB25000000,XDB33000000)CAS Interdisciplinary Innovation Team,Beijing Natural Science Foundation(Z190008)CAS through the Youth Innovation Promotion Association(2022YSBR-048)Key-Area Research and Development Program of Guangdong Province(2020B0101340002)the Center for Materials Genome.
基金supported by the National Key R&D Program of China(nos.2022YFA1403800,2022YFA1403400,2019YFA0704900)the Fundamental Science Center of the National Natural Science Foundation of China(no.52088101)+7 种基金the Synergetic Extreme Condition User Facility(SECUF)the Beijing Natural Science Foundation(no.Z190009)the National Natural Science Foundation of China(nos.11974394,12174426,12104280,and 12004416)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(XDB33000000)the Key Research Program of CAS(no.ZDRW-CN-2021-3)the CAS Project for Young Scientists in Basic Research(YSBR-003)the Scientific Instrument Developing Project of CAS(no.ZDKYYQ20210003)the Basic Research Plan of Shanxi Province(no.20210302124160).
文摘The modulation of topological electronic state by an external magnetic field is highly desired for condensed-matter physics.Schemes to achieve this have been proposed theoretically,but few can be realized experimentally.Here,combining transverse transport,theoretical calculations,and scanning tunneling microscopy/spectroscopy(STM/S)investigations,we provide an observation that the topological electronic state,accompanied by an emergent magneto-transport phenomenon,was modulated by applying magnetic field through induced non-collinear magnetism in the magnetic Weyl semimetal EuB6.A giant unconventional anomalous Hall effect(UAHE)is found during the magnetization re-orientation from easy axes to hard ones in magnetic field,with a UAHE peak around the low field of 5 kOe.
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFB0702704)the National Natural Science Foundation of China (Grant Nos. 51671022, and 51701130)+2 种基金the State Key Lab of Advanced Metals and Materials (Grant No. 2019-Z11)the Scientific and Technological Innovation Team Program of Foshan (Grant No. 2015IT100044)the Fundamental Research Funds for the Central Universities (Grant No. FRF-TP-18-014B1)
文摘Ferromagnetic-structural transformation has been studied widely in MnCoGe-based materials. However, the magnetostructural transition(MST) from antiferromagnetic(AFM) orthorhombic phase to ferromagnetic(FM) hexagonal phase, which may lead to a large inverse magnetocaloric effect(MCE), has rarely been reported. Here, the introduction of Mn vacancy lowers the structural transition temperature while retains the AFM state in the orthorhombic phase, thus successfully realizing the AFM-FM MST in Mn0.95Co0.75Cu0.25Ge. Moreover, successive inverse and normal MCEs are observed around the first-order AFM-FM MST and the second-order FM-paramagnetic(PM) transition, respectively. A thermostat is proposed based on this special feature, which could release heat above the critical temperature while absorb heat below the critical temperature by simply applying the same magnetization/demagnetization cycles. This thermostat can be very useful in many applications where a constant temperature is required, such as cryostats and incubators.
基金This work was supported by the National Natural Science Foundation of China （Nos. 51232004, 51377156, and 51401224）, the National Magnetic Confinement Fusion Science Program （No. 2015GB121001）, the fund of the State Key Laboratory of Technologies in Space Cryogenic Propellants （No. SKLTSCP1204）, and the Special Foundation of the Director Technical Institute of Physics and Chemistry, CAS.
文摘Using spark plasma sintering （SPS）, Mn3Cu0.6Ge0.4N crystallites have been fabricated with different crystallite sizes, and their magnetic properties and thermal behaviors were systemically investigated. With decreasing crystallite size, the magnetic transition becomes increasingly slow, accompanied by broadening of the negative thermal expansion （NTE） operation-temperature window. The NTE operation-temperature window for the 12-nm crystallite sample reaches at 140 K, which is about 75% larger than that of the 74-nm crystallite sample. The magnetic properties and NTE operation-temperature window can be tuned by varying the crystallite size. This discovery will promote an even wider range of practical applications in precision devices.
基金supported by the National Natural Science Foundation of China (21825102,22075014 and 22001014)the Fundamental Research Funds for the Central Universities,China(06500162 and 06500145)。
