The thermodynamic properties of Fe_(2)Ti_(3)O_(9) and Fe_(2)TiO_(5) were measured by means of the following solid state electrolyte cells:Pt,Fe+"FeO"||ZrO_(2)(CaO)||FeTiO_(3)+Fe_(2)Ti_(3)O_(9)+Fe_(2)O_(3),Pt...The thermodynamic properties of Fe_(2)Ti_(3)O_(9) and Fe_(2)TiO_(5) were measured by means of the following solid state electrolyte cells:Pt,Fe+"FeO"||ZrO_(2)(CaO)||FeTiO_(3)+Fe_(2)Ti_(3)O_(9)+Fe_(2)O_(3),Pt Pt,Fe+"FeOM"||ZrO_(2)(CaO)||FeTiO_(3)+Fe_(2)TiO_(5)+TiO_(2),Pt From the experimental data,the Gibbs energies of formation of Fe_(2)Ti_(3)O_(9) and Fe_(2)TiO_(5) were obtained:△G^(0)_(pr)(kJ·mol^(-1))=3459.7-0.847T,(1053K<T<1153K) △G^(0)_(pb)(kJ·mol^(-1))=-1700.2-0.465T,(1173K<T<1273K) Experimental results fit approximately to those of estimation.展开更多
Two-dimensional(2D)magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices.The study on its domain structure evolution with t...Two-dimensional(2D)magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices.The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism.Here,we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe_(3)GeTe_(2)(FGT)with a thickness range of 11.2-112 nm.Three types of domain structures and their corresponding hysteresis loops can be obtained.The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness,which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields.These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness.Our finding not only enriches the fundamental magnetism,but also paves a way towards spintronics based on 2D magnet.展开更多
Recently, two-dimensional van der Waals(vd W) magnetic heterostructures have attracted intensive attention since they can show remarkable properties due to the magnetic proximity effect. In this work, the spin-polariz...Recently, two-dimensional van der Waals(vd W) magnetic heterostructures have attracted intensive attention since they can show remarkable properties due to the magnetic proximity effect. In this work, the spin-polarized electronic structures of antimonene/Fe_(3)GeTe_(2)vdW heterostructures were investigated through the first-principles calculations. Owing to the magnetic proximity effect, the spin splitting appears at the conduction-band minimum(CBM) and the valence-band maximum(VBM) of the antimonene. A low-energy effective Hamiltonian was proposed to depict the spin splitting. It was found that the spin splitting can be modulated by means of applying an external electric field, changing interlayer distance or changing stacking configuration. The spin splitting energy at the CBM monotonously increases as the external electric field changes from-5 V/nm to 5 V/nm, while the spin splitting energy at the VBM almost remains the same. Meanwhile,as the interlayer distance increases, the spin splitting energies at the CBM and VBM both decrease. The different stacking configurations can also induce different spin splitting energies at the CBM and VBM. Our work demonstrates that the spin splitting of antimonene in this heterostructure is not singly dependent on the nearest Sb–Fe distance, which indicates that magnetic proximity effect in heterostructures may be modulated by multiple factors, such as hybridization of electronic states and the local electronic environment. The results enrich the fundamental understanding of the magnetic proximity effect in two-dimensional vdW heterostructures.展开更多
Hematite is an excellent catalyst for photoelectrochemical (PEC) water splitting but its performance has been highly limited by poor conductivity and high charge recombination.Here by a Zr-based treatment to create bu...Hematite is an excellent catalyst for photoelectrochemical (PEC) water splitting but its performance has been highly limited by poor conductivity and high charge recombination.Here by a Zr-based treatment to create bulk Fe_(2)ZrO_(5) in hematite and a F-based treatment to form an ultrathin surface FeF_(x) layer,the charge transfer can be highly improved and the charge recombination can be significantly suppressed.As a result,the FeF_(x) /Zr-Fe_(2)O_(3) photoanode presents an enhanced PEC performance with a photocurrent density of 2.43 m A/cm^(2)at 1.23 V vs.RHE,which is around 3 times higher than that of the pristine Fe_(2)O_(3) .The FeF_(x) /Zr-Fe_(2)O_(3) photoanode also shows a low onset potential of 0.77 V vs.RHE (100 mV lower than the pristine hematite).The performance is much higher than that of the sample treated by Zr or F alone,suggesting the synergistic effect between bulk Fe_(2)ZrO_(5) and surface FeF_(x) .By coupling with the FeNiOOH co-catalyst,the final photoanode can achieve a high photocurrent density of 2.81 mA/cm^(2) at 1.23 V vs.RHE.The novel design of Zr and F co-modified hematite can be used as a promising way to prepare efficient catalysts for solar water splitting.展开更多
Research interests in recent years have expanded into quantum materials that display novel magnetism incorporating strong correlations,topological effects,and dimensional crossovers.Fe_(3)GeTe_(2)represents such a two...Research interests in recent years have expanded into quantum materials that display novel magnetism incorporating strong correlations,topological effects,and dimensional crossovers.Fe_(3)GeTe_(2)represents such a twodimensional van der Waals platform exhibiting itinerant ferromagnetism with many intriguing properties.Up to date,most electronic transport studies on Fe_(3)GeTe_(2)have been limited to its anomalous Hall responses while the longitudinal counterpart(such as magnetoresistance)remains largely unexplored.Here,we report a few unusual transport behaviors on thin flakes of Fe_(3)GeTe_(2).Upon cooling to the base temperature,the sample develops a resistivity upturn that shows a crossover from a marginally-ln T to a-T^(1/2)dependence,followed by a lowertemperature deviation.Moreover,we observe a negative and non-saturating linear magnetoresistance when the magnetization is parallel or antiparallel to the external magnetic field.The slope of the linear magnetoresistance also shows a nonmonotonic temperature dependence.We deduce an anomalous contribution to the magnetoresistance at low temperatures with a scaling function proportional-HT^(1/2),as well as a temperature-independent linear term.Possible mechanisms that could account for our observations are discussed.展开更多
The magnetic properties of (Nd_(0.9)Dy_(0.1))_(16)Co_(5)Fe_(70)Nb_(2)B_(7) permanent magnetic alloy prepared by powder metallurgy are:Br=1.08T,_(1)H_(C)=1620kA/m,(BH)_(max)=208kJ/m^(3).The behaviour of Nb in this allo...The magnetic properties of (Nd_(0.9)Dy_(0.1))_(16)Co_(5)Fe_(70)Nb_(2)B_(7) permanent magnetic alloy prepared by powder metallurgy are:Br=1.08T,_(1)H_(C)=1620kA/m,(BH)_(max)=208kJ/m^(3).The behaviour of Nb in this alloy was studied by joint methods of dynamic observation by high voltage electron microscope(HVEM)and Mossbauer effects.With Nb and Co substituting parts of Fe and adding a little Dy,practical magnetic alloy with excellent properties can be obtained.The thermal stability of it is 80 ℃ higher than that of ternary Nd-Fe-13 magnet.The study shows that adding Nb into Nd-Fe-B can make the intrinsic coercivity appear peak value at about Nb=2%(in mole fraction).Nb mainly enters into Nd-rich and B-rich phases,a little into Nd_(2)Fe_(14)B phase.展开更多
Two-dimensional van der Waals(2D vdW)magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devic...Two-dimensional van der Waals(2D vdW)magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devices,and exploring various physical phenomena or technologies.Among them,Fe_(5)GeTe_(2)(F5GT)has ferromagnetic order close to room temperature,however the magnetic properties near its intrinsic transitions and F5GT-based 2D devices remain mostly unexplored.Here,we systematically demonstrate the peculiar magnetic properties of Fe_(5)GeTe_(2)nanoflakes near its intrinsic transition temperature(Tp)which is far lower than its Curie temperature(TC)of~265 K,and firstly discover anomalous magnetoresistance effect in F5GT homo-junctions by magneto-transport measurements.The strongest anomalous Hall effect occurs around Tp which is located in a temperature range from 130 to 160 K for the F5GT nanoflakes with different thicknesses.Furthermore,negative magnetoresistance(N-MR)and butterfly-shaped magnetoresistance(B-MR)are observed in F5GT homo-junction devices,and they appeared only in an intermediate temperature range from 110 to 160 K,noticeably showing the maxima near the T_(p)rather than the lowest temperature.Our experimental results clearly reveal the significant influence of intrinsic transitions on magnetic properties of F5GT and magnetoresistance effect in F5GT homo-junction devices,which imply a new strategy to achieve highperformance 2D spintronic devices by tuning intrinsic magnetic or structural transitions in 2D vdW magnets.展开更多
Magnetic tunnel junctions(MTJs),a prominent type of spintronic device based on the spin valve effect,have facilitated the development of numerous spintronic applications.The technical appeal for the next-generation MT...Magnetic tunnel junctions(MTJs),a prominent type of spintronic device based on the spin valve effect,have facilitated the development of numerous spintronic applications.The technical appeal for the next-generation MTJ devices has been proposed in two directions:improving device performance by utilizing advanced two-dimensional(2D)ferromagnetic materials or extending device functionalities by exploring the gate-tunable magnetic properties of ferromagnets.Based on the recent development of 2D magnets with the ease of external stimuli,such as electric field,due to their reduced dimensions,reliable prospects for gate-tunable MTJ devices can be achieved,shedding light on the great potential of next-generation MTJs with multiple functionalities for various application environments.While the electrical gate-tunable MTJ device is highly desirable for practical spintronic devices,it has not yet been demonstrated.Here,we demonstrate the experimental realization of a spin valve device by combining a vertical Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ with an electrolyte gate.The magnetoresistance ratio(MR ratio)of 36%for the intrinsic MTJ confirms the good performance of the device.By electrolyte gating,the tunneling MR ratio of Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ can be elevated 2.5 times,from 26%to 65%.Importantly,the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating,providing a promising method to control the magnetization configuration of the MTJ.Our work demonstrates a gate-tunable MTJ device toward the possibility for gate-controlled spintronic devices,paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications.展开更多
The unique crystal structure and multiple redox couples of iron titanate(Fe_(2)TiO_(5)) provide it a high theoretical capacity and good cycling stability when used as an electrode. In this study, the electrospinning m...The unique crystal structure and multiple redox couples of iron titanate(Fe_(2)TiO_(5)) provide it a high theoretical capacity and good cycling stability when used as an electrode. In this study, the electrospinning method is employed to synthesize one-dimensional(1 D) Fe_(2)TiO_(5) nanochains. The as-prepared Fe_(2)TiO_(5) nanochains exhibited superior specific capacity(500 mAh·g^(-1) at 0.10 A·g^(-1)),excellent rate performance(180 mAh·g^(-1) at 5.00 A·g^(-1)),and good cycling stability(retaining 100% of the initial specific capacity at a current density of 1.00 A·g^(-1) after1000 cycles). The as-assembled Fe_(2)TiO_(5)/SCCB lithiumion capacitor(LIC) also delivered a competitive energy density(137.8 Wh·kg^(-1))andpowerdensity(11,250 W·kg^(-1)). This study proves that the as-fabricated1 D Fe_(2)TiO_(5) nanochains are promising anode materials for high-performance LICs.展开更多
基金Supported by the National Natural Science Foundation of Chinathe Committee of Science and Technology of Liaoning Province and the State Education Committee of China。
文摘The thermodynamic properties of Fe_(2)Ti_(3)O_(9) and Fe_(2)TiO_(5) were measured by means of the following solid state electrolyte cells:Pt,Fe+"FeO"||ZrO_(2)(CaO)||FeTiO_(3)+Fe_(2)Ti_(3)O_(9)+Fe_(2)O_(3),Pt Pt,Fe+"FeOM"||ZrO_(2)(CaO)||FeTiO_(3)+Fe_(2)TiO_(5)+TiO_(2),Pt From the experimental data,the Gibbs energies of formation of Fe_(2)Ti_(3)O_(9) and Fe_(2)TiO_(5) were obtained:△G^(0)_(pr)(kJ·mol^(-1))=3459.7-0.847T,(1053K<T<1153K) △G^(0)_(pb)(kJ·mol^(-1))=-1700.2-0.465T,(1173K<T<1273K) Experimental results fit approximately to those of estimation.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0206202 and 2019YFA0308000)the National Natural Science Foundation of China(Grant Nos.51871130,62022089,and 11874405)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2019007)。
文摘Two-dimensional(2D)magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices.The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism.Here,we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe_(3)GeTe_(2)(FGT)with a thickness range of 11.2-112 nm.Three types of domain structures and their corresponding hysteresis loops can be obtained.The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness,which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields.These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness.Our finding not only enriches the fundamental magnetism,but also paves a way towards spintronics based on 2D magnet.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11774434, 11974431, and 11832019)supported by National Supercomputer Center in Guangzhou。
文摘Recently, two-dimensional van der Waals(vd W) magnetic heterostructures have attracted intensive attention since they can show remarkable properties due to the magnetic proximity effect. In this work, the spin-polarized electronic structures of antimonene/Fe_(3)GeTe_(2)vdW heterostructures were investigated through the first-principles calculations. Owing to the magnetic proximity effect, the spin splitting appears at the conduction-band minimum(CBM) and the valence-band maximum(VBM) of the antimonene. A low-energy effective Hamiltonian was proposed to depict the spin splitting. It was found that the spin splitting can be modulated by means of applying an external electric field, changing interlayer distance or changing stacking configuration. The spin splitting energy at the CBM monotonously increases as the external electric field changes from-5 V/nm to 5 V/nm, while the spin splitting energy at the VBM almost remains the same. Meanwhile,as the interlayer distance increases, the spin splitting energies at the CBM and VBM both decrease. The different stacking configurations can also induce different spin splitting energies at the CBM and VBM. Our work demonstrates that the spin splitting of antimonene in this heterostructure is not singly dependent on the nearest Sb–Fe distance, which indicates that magnetic proximity effect in heterostructures may be modulated by multiple factors, such as hybridization of electronic states and the local electronic environment. The results enrich the fundamental understanding of the magnetic proximity effect in two-dimensional vdW heterostructures.
基金supported by the National Key R&D Program of China (2020YFA0406103)the National Natural Science Foundation of China (U1932211)+1 种基金the Collaborative Innovation Center of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the 111 Project。
文摘Hematite is an excellent catalyst for photoelectrochemical (PEC) water splitting but its performance has been highly limited by poor conductivity and high charge recombination.Here by a Zr-based treatment to create bulk Fe_(2)ZrO_(5) in hematite and a F-based treatment to form an ultrathin surface FeF_(x) layer,the charge transfer can be highly improved and the charge recombination can be significantly suppressed.As a result,the FeF_(x) /Zr-Fe_(2)O_(3) photoanode presents an enhanced PEC performance with a photocurrent density of 2.43 m A/cm^(2)at 1.23 V vs.RHE,which is around 3 times higher than that of the pristine Fe_(2)O_(3) .The FeF_(x) /Zr-Fe_(2)O_(3) photoanode also shows a low onset potential of 0.77 V vs.RHE (100 mV lower than the pristine hematite).The performance is much higher than that of the sample treated by Zr or F alone,suggesting the synergistic effect between bulk Fe_(2)ZrO_(5) and surface FeF_(x) .By coupling with the FeNiOOH co-catalyst,the final photoanode can achieve a high photocurrent density of 2.81 mA/cm^(2) at 1.23 V vs.RHE.The novel design of Zr and F co-modified hematite can be used as a promising way to prepare efficient catalysts for solar water splitting.
基金supported by the National Natural Science Foundation of China(Grant Nos.12174439,11961141011,U2032204,and 12074039)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB28000000 and XDB33030000)。
文摘Research interests in recent years have expanded into quantum materials that display novel magnetism incorporating strong correlations,topological effects,and dimensional crossovers.Fe_(3)GeTe_(2)represents such a twodimensional van der Waals platform exhibiting itinerant ferromagnetism with many intriguing properties.Up to date,most electronic transport studies on Fe_(3)GeTe_(2)have been limited to its anomalous Hall responses while the longitudinal counterpart(such as magnetoresistance)remains largely unexplored.Here,we report a few unusual transport behaviors on thin flakes of Fe_(3)GeTe_(2).Upon cooling to the base temperature,the sample develops a resistivity upturn that shows a crossover from a marginally-ln T to a-T^(1/2)dependence,followed by a lowertemperature deviation.Moreover,we observe a negative and non-saturating linear magnetoresistance when the magnetization is parallel or antiparallel to the external magnetic field.The slope of the linear magnetoresistance also shows a nonmonotonic temperature dependence.We deduce an anomalous contribution to the magnetoresistance at low temperatures with a scaling function proportional-HT^(1/2),as well as a temperature-independent linear term.Possible mechanisms that could account for our observations are discussed.
基金Supported by the State Key Laboratory of Magnetism,Chinese Academy of Sciences。
文摘The magnetic properties of (Nd_(0.9)Dy_(0.1))_(16)Co_(5)Fe_(70)Nb_(2)B_(7) permanent magnetic alloy prepared by powder metallurgy are:Br=1.08T,_(1)H_(C)=1620kA/m,(BH)_(max)=208kJ/m^(3).The behaviour of Nb in this alloy was studied by joint methods of dynamic observation by high voltage electron microscope(HVEM)and Mossbauer effects.With Nb and Co substituting parts of Fe and adding a little Dy,practical magnetic alloy with excellent properties can be obtained.The thermal stability of it is 80 ℃ higher than that of ternary Nd-Fe-13 magnet.The study shows that adding Nb into Nd-Fe-B can make the intrinsic coercivity appear peak value at about Nb=2%(in mole fraction).Nb mainly enters into Nd-rich and B-rich phases,a little into Nd_(2)Fe_(14)B phase.
基金This work was financially supported by the National Key Research and Development Program of China(No.2022YFA1204004)the National Natural Science Foundation of China(Nos.52071026,52130103,51971026,and 52201288)+3 种基金the ISF-NSFC Joint Research Program(No.51961145305)the Beijing Natural Science Foundation Key Program(No.Z190007)the open research fund of Songshan Lake Materials Laboratory(No.2022SLABFN18)the Fundamental Research Funds for the Central Universities(No.06500140).
文摘Two-dimensional van der Waals(2D vdW)magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devices,and exploring various physical phenomena or technologies.Among them,Fe_(5)GeTe_(2)(F5GT)has ferromagnetic order close to room temperature,however the magnetic properties near its intrinsic transitions and F5GT-based 2D devices remain mostly unexplored.Here,we systematically demonstrate the peculiar magnetic properties of Fe_(5)GeTe_(2)nanoflakes near its intrinsic transition temperature(Tp)which is far lower than its Curie temperature(TC)of~265 K,and firstly discover anomalous magnetoresistance effect in F5GT homo-junctions by magneto-transport measurements.The strongest anomalous Hall effect occurs around Tp which is located in a temperature range from 130 to 160 K for the F5GT nanoflakes with different thicknesses.Furthermore,negative magnetoresistance(N-MR)and butterfly-shaped magnetoresistance(B-MR)are observed in F5GT homo-junction devices,and they appeared only in an intermediate temperature range from 110 to 160 K,noticeably showing the maxima near the T_(p)rather than the lowest temperature.Our experimental results clearly reveal the significant influence of intrinsic transitions on magnetic properties of F5GT and magnetoresistance effect in F5GT homo-junction devices,which imply a new strategy to achieve highperformance 2D spintronic devices by tuning intrinsic magnetic or structural transitions in 2D vdW magnets.
基金supported by the National Natural Sci-ence Foundation of China(91750101,21733001,52072168,51861145201)the National Key Basic Research Program of the Ministry of Science and Technology of China(2018YFA0306200,2021YFA1202901)+1 种基金the Fundamental Research Funds for the Central Universities(021314380078,021314380104,021314380147)Jiangsu Key Laboratory of Artificial Functional Materials.
文摘Magnetic tunnel junctions(MTJs),a prominent type of spintronic device based on the spin valve effect,have facilitated the development of numerous spintronic applications.The technical appeal for the next-generation MTJ devices has been proposed in two directions:improving device performance by utilizing advanced two-dimensional(2D)ferromagnetic materials or extending device functionalities by exploring the gate-tunable magnetic properties of ferromagnets.Based on the recent development of 2D magnets with the ease of external stimuli,such as electric field,due to their reduced dimensions,reliable prospects for gate-tunable MTJ devices can be achieved,shedding light on the great potential of next-generation MTJs with multiple functionalities for various application environments.While the electrical gate-tunable MTJ device is highly desirable for practical spintronic devices,it has not yet been demonstrated.Here,we demonstrate the experimental realization of a spin valve device by combining a vertical Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ with an electrolyte gate.The magnetoresistance ratio(MR ratio)of 36%for the intrinsic MTJ confirms the good performance of the device.By electrolyte gating,the tunneling MR ratio of Fe_(3)GeTe_(2)/h-BN/Fe_(3)GeTe_(2) MTJ can be elevated 2.5 times,from 26%to 65%.Importantly,the magnetic fields at which the magnetoresistance switches for the MTJ can be modulated by electrical gating,providing a promising method to control the magnetization configuration of the MTJ.Our work demonstrates a gate-tunable MTJ device toward the possibility for gate-controlled spintronic devices,paving the way for performing 2D magnetism manipulations and exploring innovative spintronic applications.
基金financially supported by the Natural Science Foundation of Jiangsu Province(No.BK20170549)the National Natural Science Foundation of China(No.21706103)+1 种基金the China Postdoctoral Science Foundation(No.2019T120393)the Postdoctoral Science Foundation of Jiangsu Province(No.2019K295)。
文摘The unique crystal structure and multiple redox couples of iron titanate(Fe_(2)TiO_(5)) provide it a high theoretical capacity and good cycling stability when used as an electrode. In this study, the electrospinning method is employed to synthesize one-dimensional(1 D) Fe_(2)TiO_(5) nanochains. The as-prepared Fe_(2)TiO_(5) nanochains exhibited superior specific capacity(500 mAh·g^(-1) at 0.10 A·g^(-1)),excellent rate performance(180 mAh·g^(-1) at 5.00 A·g^(-1)),and good cycling stability(retaining 100% of the initial specific capacity at a current density of 1.00 A·g^(-1) after1000 cycles). The as-assembled Fe_(2)TiO_(5)/SCCB lithiumion capacitor(LIC) also delivered a competitive energy density(137.8 Wh·kg^(-1))andpowerdensity(11,250 W·kg^(-1)). This study proves that the as-fabricated1 D Fe_(2)TiO_(5) nanochains are promising anode materials for high-performance LICs.
