Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO i...Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.展开更多
Graphene-reinforced Mg matrix composites suffer seriously from the weak Mg/graphene interfacial bonding.In this study,a first-principles study was performed to evaluate the feasibility of improving the Mg/graphene bon...Graphene-reinforced Mg matrix composites suffer seriously from the weak Mg/graphene interfacial bonding.In this study,a first-principles study was performed to evaluate the feasibility of improving the Mg/graphene bonding using an in-situ formed intermediate MgO layer.The calculated interface adhesion strengths suggested a relative ordering(from high to low)of Mg(0001)/MgO(11−1)>MgO(11−1)/graphene>Mg(0001)/graphene.The enhanced Mg/MgO/graphene interface bonding can be attributed to the newly formed strong ionic and covalent interactions at the Mg/MgO and the MgO/graphene interfaces,respectively,which replace the otherwise very weak van der Waals bonding between Mg and graphene.展开更多
The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3（110）interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n...The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3（110）interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n-type polar interface,the interface Ti3d electrons are the origin of the metallic and magnetic properties. Varying the thickness of Ba TiO3 may induce an insulator–metal transition, and the critical thickness is 4 unit cells. For the p-type polar interface, holes preferentially occupy the interface O 2p y state, resulting in a conducting interface. The unbalance of the spin splitting of the O 2p states in the interface Mg O layer leads to a magnetic moment of about 0.25μB per O atom at the interface.These results further demonstrate that other polar interfaces, besides LaAlO3/SrTiO3, can show a two-dimensional metallic behavior. It is helpful to fully understand the role of polar discontinuity on the properties of the interface, which widens the field of polar-nonpolar interfaces.展开更多
To study the influence of CoFeB/MgO interface on tunneling magnetoresistance （TMR）, different structures of magnetic tunnel junctions （MTJs） are successfully prepared by the magnetron sputtering technique and char...To study the influence of CoFeB/MgO interface on tunneling magnetoresistance （TMR）, different structures of magnetic tunnel junctions （MTJs） are successfully prepared by the magnetron sputtering technique and characterized by atomic force microscopy, a physical property measurement system, x-ray photoelectron spectroscopy, and transmission electron microscopy. The experimental results show that TMR of the CoFeB/Mg/MgO/CoFeB structure is evidently improved in comparison with the CoFeB/MgO/CoFeB structure because the inserted Mg layer prevents Fe-oxide formation at the CoFeB/MgO interface, which occurs in CoFeB/MgO/CoFeB MTJs. The inherent properties of the CoFeB/MgO/CoFeB, CoFeB/Fe-oxide/MgO/CoFeB and CoFeB/Mg/MgO/CoFeB MTJs are simulated by using the theories of density functions and non-equilibrium Green functions. The simulated results demonstrate that TMR of CoFeB/Fe-oxide/MgO/CoFeB MTJs is severely decreased and is only half the value of the CoFeB/Mg/MgO/CoFeB MTJs. Based on the experimental results and theoretical analysis, it is believed that in CoFeB/MgO/CoFeB MTJs, the interface oxidation of the CoFeB layer is the main reason to cause a remarkable reduction of TMR, and the inserted Mg layer may play an important role in protecting Fe atoms from oxidation, and then increasing TMR.展开更多
The dependence of perpendicular magnetic anisotropy （PMA） on the barrier layer MgO thickness in MgO/CoFeB /Ta multilayers is investigated. The results show that the strongest PMA occurs in a small window of about 2 ...The dependence of perpendicular magnetic anisotropy （PMA） on the barrier layer MgO thickness in MgO/CoFeB /Ta multilayers is investigated. The results show that the strongest PMA occurs in a small window of about 2 4nm with the increase of MgO thickness from 1-1Onto. The crystalline degree of MgO and the change of interatomic distance along the out-of-plane direction may be the main reasons for the change of PMA in these multilayers. Moreover, the roughnesses of 2- and 4-nm-thick MgO samples are 3.163 and 1.8 nm, respectively, and both the samples show PMA. These results could be used to tune the magnetic characteristic of the ultra thin CoFeB film for future applications in perpendicular magnetic devices.展开更多
Herein,we report a highly active K-added Ru/MgO catalyst for hydrogen storage into aromatic benzyltoluenes at low temperatures to advance liquid organic hydrogen carrier technology.The hydrogenation activity of Ru/K/M...Herein,we report a highly active K-added Ru/MgO catalyst for hydrogen storage into aromatic benzyltoluenes at low temperatures to advance liquid organic hydrogen carrier technology.The hydrogenation activity of Ru/K/MgO catalysts exhibits a volcano-shaped dependence on the K content at the maximum with 0.02 wt%.This is in good agreement with the strength and capacity of H_(2) adsorption derived from basicity,despite a gradual decrease in the textural property and the corresponding increase in the Ru particle size with increasing the K content.Density functional theory calculations show that heterolytic hydrogen adsorption properties(strength and polarization)are facilitated up to a specific density of K on the Ru–MgO interface and excessive K suppresses heterolytic H_(2) adsorption by direct interaction between K and hydrogen,assuring the hydrogenation activity and H_(2) adsorption capability of Ru/K/MgO catalysts.Hence,the Ru/K/MgO catalyst,when K is added in an optimal amount,is highly effective to accelerate hydrogen storage kinetics at low temperatures owing to the enhanced heterolytic H_(2) adsorption.展开更多
Interface enhanced superconductivity over 50 K has been discovered in monolayer Fe Se films grown on several TiO_2-terminated oxide substrates.Whether such phenomenon exists in other oxide substrates remains an extrem...Interface enhanced superconductivity over 50 K has been discovered in monolayer Fe Se films grown on several TiO_2-terminated oxide substrates.Whether such phenomenon exists in other oxide substrates remains an extremely interesting topic.Here we report enhanced superconductivity with an onset transition temperature of 18 K in monolayer Fe Se on Mg O(001) substrate by transport measurement.Scanning transmission electron microscopy investigation on the interface structure indicates that Fe Se films grow epitaxially on Mg O(001) and that overlayer Fe atoms diffuse into the top two layers of Mg O and substitute Mg atoms.Our density functional theory calculations reveal that this substitution promotes the charge transfer from the Mg O substrate to the Fe Se films,an essential process that also occurs in monolayer Fe Se on TiO_2-terminated oxides and contributes to the enhanced superconductivity therein.Our finding suggests that superconductivity enhancement in monolayer Fe Se films on oxides substrates is rather general as long as charge transfer is allowed at the interface,thus pointing out an explicit direction for searching for new high temperature superconductivity by interface engineering.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0400801)the National Natural Science Foundation of China(Grant Nos.61774128,61674124,11604275,11304257,and 61227009)+1 种基金the Natural Science Foundation of Fujian Province of China(Grant Nos.2017J01012,2014J01026,2016J01037,and 2015J01028)the Fundamental Research Funds for the Central Universities,China(Grant Nos.20720150027,20720160044,20720160122,20720170085,20720170012,and 20720150033)
文摘Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.
基金the financial supports from the National Natural Science Foundation of China(Nos.52061028,52061039,51971249,51761037)the Natural Science Foundation of Jiangxi Province,China(No.2020BABL204002)+1 种基金the Interdisciplinary Innovation Fund of Nanchang University(IIFNCU),China(No.9166-27060003-ZD05)the Innovative Funding for Graduate Students in Nanchang University,China(No.CX2019068).
文摘Graphene-reinforced Mg matrix composites suffer seriously from the weak Mg/graphene interfacial bonding.In this study,a first-principles study was performed to evaluate the feasibility of improving the Mg/graphene bonding using an in-situ formed intermediate MgO layer.The calculated interface adhesion strengths suggested a relative ordering(from high to low)of Mg(0001)/MgO(11−1)>MgO(11−1)/graphene>Mg(0001)/graphene.The enhanced Mg/MgO/graphene interface bonding can be attributed to the newly formed strong ionic and covalent interactions at the Mg/MgO and the MgO/graphene interfaces,respectively,which replace the otherwise very weak van der Waals bonding between Mg and graphene.
基金supported by the National Basic Research Program of China(Grant No.2013CB632506)the National Natural Science Foundation of China(Grant Nos.11374186,51231007,51202132,and 51102153)the Independent Innovation Foundation of Shandong University,China(Grant No.2012TS027)
文摘The first-principles calculations are employed to investigate the electrical properties of polar MgO/BaTiO3（110）interfaces. Both n-type and p-type polar interfaces show a two-dimensional metallic behavior. For the n-type polar interface,the interface Ti3d electrons are the origin of the metallic and magnetic properties. Varying the thickness of Ba TiO3 may induce an insulator–metal transition, and the critical thickness is 4 unit cells. For the p-type polar interface, holes preferentially occupy the interface O 2p y state, resulting in a conducting interface. The unbalance of the spin splitting of the O 2p states in the interface Mg O layer leads to a magnetic moment of about 0.25μB per O atom at the interface.These results further demonstrate that other polar interfaces, besides LaAlO3/SrTiO3, can show a two-dimensional metallic behavior. It is helpful to fully understand the role of polar discontinuity on the properties of the interface, which widens the field of polar-nonpolar interfaces.
基金Supported by the National Defense Advance Research Foundation under Grant No 9140A08XXXXXX0DZ106the Basic Research Program of Ministry of Education of China under Grant No JY10000925005+2 种基金the Scientific Research Program Funded by Shaanxi Provincial Education Department under Grant No 11JK0912the Scientific Research Foundation of Xi'an University of Science and Technology under Grant No 2010011the Doctoral Research Startup Fund of Xi'an University of Science and Technology under Grant No 2010QDJ029
文摘To study the influence of CoFeB/MgO interface on tunneling magnetoresistance （TMR）, different structures of magnetic tunnel junctions （MTJs） are successfully prepared by the magnetron sputtering technique and characterized by atomic force microscopy, a physical property measurement system, x-ray photoelectron spectroscopy, and transmission electron microscopy. The experimental results show that TMR of the CoFeB/Mg/MgO/CoFeB structure is evidently improved in comparison with the CoFeB/MgO/CoFeB structure because the inserted Mg layer prevents Fe-oxide formation at the CoFeB/MgO interface, which occurs in CoFeB/MgO/CoFeB MTJs. The inherent properties of the CoFeB/MgO/CoFeB, CoFeB/Fe-oxide/MgO/CoFeB and CoFeB/Mg/MgO/CoFeB MTJs are simulated by using the theories of density functions and non-equilibrium Green functions. The simulated results demonstrate that TMR of CoFeB/Fe-oxide/MgO/CoFeB MTJs is severely decreased and is only half the value of the CoFeB/Mg/MgO/CoFeB MTJs. Based on the experimental results and theoretical analysis, it is believed that in CoFeB/MgO/CoFeB MTJs, the interface oxidation of the CoFeB layer is the main reason to cause a remarkable reduction of TMR, and the inserted Mg layer may play an important role in protecting Fe atoms from oxidation, and then increasing TMR.
基金Supported by the National Basic Research Program of China under Grant No 2011CB921804the Beijing Key Subject Foundation of Condensed Matter Physics under Grant No 0114023
文摘The dependence of perpendicular magnetic anisotropy （PMA） on the barrier layer MgO thickness in MgO/CoFeB /Ta multilayers is investigated. The results show that the strongest PMA occurs in a small window of about 2 4nm with the increase of MgO thickness from 1-1Onto. The crystalline degree of MgO and the change of interatomic distance along the out-of-plane direction may be the main reasons for the change of PMA in these multilayers. Moreover, the roughnesses of 2- and 4-nm-thick MgO samples are 3.163 and 1.8 nm, respectively, and both the samples show PMA. These results could be used to tune the magnetic characteristic of the ultra thin CoFeB film for future applications in perpendicular magnetic devices.
基金financially supported by the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT,Republic of Korea(2019M3E6A1064908)the Ministry of Education,Republic of Korea(2016R1A6A1A03013422)。
文摘Herein,we report a highly active K-added Ru/MgO catalyst for hydrogen storage into aromatic benzyltoluenes at low temperatures to advance liquid organic hydrogen carrier technology.The hydrogenation activity of Ru/K/MgO catalysts exhibits a volcano-shaped dependence on the K content at the maximum with 0.02 wt%.This is in good agreement with the strength and capacity of H_(2) adsorption derived from basicity,despite a gradual decrease in the textural property and the corresponding increase in the Ru particle size with increasing the K content.Density functional theory calculations show that heterolytic hydrogen adsorption properties(strength and polarization)are facilitated up to a specific density of K on the Ru–MgO interface and excessive K suppresses heterolytic H_(2) adsorption by direct interaction between K and hydrogen,assuring the hydrogenation activity and H_(2) adsorption capability of Ru/K/MgO catalysts.Hence,the Ru/K/MgO catalyst,when K is added in an optimal amount,is highly effective to accelerate hydrogen storage kinetics at low temperatures owing to the enhanced heterolytic H_(2) adsorption.
基金supported by the National Natural Science Foundation of China(11574174,11774193,11790311,11404183,11474030,21573121 and 51421002)the National Basic Research Program of China(2015CB921000)+1 种基金the President Foundation of China Academy of Engineering Physics(YZJJLX2016010)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB07030200)
文摘Interface enhanced superconductivity over 50 K has been discovered in monolayer Fe Se films grown on several TiO_2-terminated oxide substrates.Whether such phenomenon exists in other oxide substrates remains an extremely interesting topic.Here we report enhanced superconductivity with an onset transition temperature of 18 K in monolayer Fe Se on Mg O(001) substrate by transport measurement.Scanning transmission electron microscopy investigation on the interface structure indicates that Fe Se films grow epitaxially on Mg O(001) and that overlayer Fe atoms diffuse into the top two layers of Mg O and substitute Mg atoms.Our density functional theory calculations reveal that this substitution promotes the charge transfer from the Mg O substrate to the Fe Se films,an essential process that also occurs in monolayer Fe Se on TiO_2-terminated oxides and contributes to the enhanced superconductivity therein.Our finding suggests that superconductivity enhancement in monolayer Fe Se films on oxides substrates is rather general as long as charge transfer is allowed at the interface,thus pointing out an explicit direction for searching for new high temperature superconductivity by interface engineering.
