A series of trilayers of sputtered Fe/Si/Fe were grown to study the interface characteristics and magnetic coupling between ferromagnetic Fe layers (30 ? thick) for Si spacer thickness (tSi) ranging from 15 ? to 40 ?....A series of trilayers of sputtered Fe/Si/Fe were grown to study the interface characteristics and magnetic coupling between ferromagnetic Fe layers (30 ? thick) for Si spacer thickness (tSi) ranging from 15 ? to 40 ?. Grazing incidence x-ray diffraction, AFM, resistivity and x-ray photoelectron spectroscopy (XPS) meas-urements show substantial intermixing between the layers during deposition which results in trilayers of complicated structures for different sub-layer thicknesses. A systematic variation in silicide concentration across the interface is observed by XPS measurements. The Fe layers in the trilayers were observed to con-sist of Fe layers doped with Si, ferromagnetic Fe-Si silicide layers and nonmagnetic Fe-Si silicide interface layer, while the Si spacer was found to be Fe-Si compound layers with an additional amorphous Si (α-Si) sublayer for tSi≥ 30 ?. A strong anti-ferromagnetic (AF) coupling was observed in trilayers with iron silicide spacers, which disappeared if α-Si layers present in the spacers. The observed magnetization behaviour in each case is interpreted in terms of changes in interfacial structural and electronic properties due to variation in film thickness.展开更多
Highly pure red phosphors LiM(PO_(3))_(3):Eu^(3+)(M=Sr,Ca) doped with Eu^(3+)(1 mol%) were synthesized via solution combustion method and their crystal structure and luminescence dynamics were studied to explore its s...Highly pure red phosphors LiM(PO_(3))_(3):Eu^(3+)(M=Sr,Ca) doped with Eu^(3+)(1 mol%) were synthesized via solution combustion method and their crystal structure and luminescence dynamics were studied to explore its suitability in white light emitting diodes.The Rietveld refinement analysis of the powder Xray diffraction patterns reveals that the phosphors belong to the pure triclinic phase of LiSr(PO_(3))_(3) and LiCa(PO_(3)) with space group P-1(2).The scanning electron microscopy images showed the agglomerated morphology.The photoluminescence emission spectra under 393 nm show an orange band at 594 nm and a red band at 613 nm ascribed to ^(5)D_(0)→^(7)F_(1).^(5)D_(0)→^(7)F_(2) transitions of Eu^(3+)ion in both the phosphors.Moreover,the spectroscopic properties such as luminescence behaviour,and Stark splitting were used to examine the symmetry of Eu^(3+)ions in LiM(PO_(3))_(3):Es^(3+)(M=Sr,Ca) phosphors in terms of distortion induced upon doping.The Stark splitting shows that the actual site symmetry for Eu^(3+)ion was estimated to be D_(2) type for both phosphors.The photometric properties of LiCa(PO_(3))_(3):Eu^(3+)such as Commission International de l'Eclairage coordinates(x=0.64,y=0.36) near to the standard one(red),high color purity(95%) and higher brightness reveal that the phosphor has the capability of acting as a red component in n-UV white light emitting diodes.展开更多
The height of total entropy(S)for a magnetic refrigerant material is essentially concerned with the magnetic and structural transitions.However,the participation of such transitions in layered materials is not well un...The height of total entropy(S)for a magnetic refrigerant material is essentially concerned with the magnetic and structural transitions.However,the participation of such transitions in layered materials is not well understood.Therefore,the purpose of this work is to investigate the interplay between double layer lattice with their single perovskite counterpart,to achieve optimal magnetocaloric performance.A series of self-doped Pr_(1.4+x)Sr_(1.6-x)Mn_(2)O_(7)(0.0≤x≤0.5)Ruddlesden-Popper(R-P)perovskite have been prepared through the solid-state sintering method.With increasing the Pr-stoichiometry,the lattice faults have increased and the double layer lattice dramatically disintegrates into single perovskite structure.Due to the reduction of bilayer R-P phase into single perovskite the spin crossover occurs from weak bilayer(T=304 K)interactions towards the strong three-dimensional(T=308 K)interactions respectively.This series consistently develops thermomagnetic irreversibility in zero-field cooled(ZFC)-field cooled(FC)magnetization,which is indicative of a spin-glass state.The glassy nature has been ascribed collectively to the lattice strain produced because of dislocations and to an antiferromagnetic phase segregated at the surface.The maximum value of temperature average entropy change(TEC)and adiabatic temperature(ΔT)has enhanced nearly by 4 folds from 0.53 J kg^(-1)K^(-1),0.59 K(for x=0.0)up to 1.85 J kg^(-1)K^(-1),10 K(for x=0.5)at 2.5 T,respectively.Additionally,the room temperature relative cooling power has improved from 26.94 J/kg up to 77.84 J/kg with an applied field of 2.5 T.Our findings in this work suggest that the controlled reduction of double layer lattice into single perovskite and/or existence of both phases simultaneously in bilayer R-P manganites may be very effective in obtaining the desirable characteristics of magnetocaloric effects.展开更多
文摘A series of trilayers of sputtered Fe/Si/Fe were grown to study the interface characteristics and magnetic coupling between ferromagnetic Fe layers (30 ? thick) for Si spacer thickness (tSi) ranging from 15 ? to 40 ?. Grazing incidence x-ray diffraction, AFM, resistivity and x-ray photoelectron spectroscopy (XPS) meas-urements show substantial intermixing between the layers during deposition which results in trilayers of complicated structures for different sub-layer thicknesses. A systematic variation in silicide concentration across the interface is observed by XPS measurements. The Fe layers in the trilayers were observed to con-sist of Fe layers doped with Si, ferromagnetic Fe-Si silicide layers and nonmagnetic Fe-Si silicide interface layer, while the Si spacer was found to be Fe-Si compound layers with an additional amorphous Si (α-Si) sublayer for tSi≥ 30 ?. A strong anti-ferromagnetic (AF) coupling was observed in trilayers with iron silicide spacers, which disappeared if α-Si layers present in the spacers. The observed magnetization behaviour in each case is interpreted in terms of changes in interfacial structural and electronic properties due to variation in film thickness.
基金Defence Research and Development Organization (DRDO),Govt.of India for financial support under DIA -KCOE (Kalam Centre of Excellence) reference no.KCST-SS02/2020。
文摘Highly pure red phosphors LiM(PO_(3))_(3):Eu^(3+)(M=Sr,Ca) doped with Eu^(3+)(1 mol%) were synthesized via solution combustion method and their crystal structure and luminescence dynamics were studied to explore its suitability in white light emitting diodes.The Rietveld refinement analysis of the powder Xray diffraction patterns reveals that the phosphors belong to the pure triclinic phase of LiSr(PO_(3))_(3) and LiCa(PO_(3)) with space group P-1(2).The scanning electron microscopy images showed the agglomerated morphology.The photoluminescence emission spectra under 393 nm show an orange band at 594 nm and a red band at 613 nm ascribed to ^(5)D_(0)→^(7)F_(1).^(5)D_(0)→^(7)F_(2) transitions of Eu^(3+)ion in both the phosphors.Moreover,the spectroscopic properties such as luminescence behaviour,and Stark splitting were used to examine the symmetry of Eu^(3+)ions in LiM(PO_(3))_(3):Es^(3+)(M=Sr,Ca) phosphors in terms of distortion induced upon doping.The Stark splitting shows that the actual site symmetry for Eu^(3+)ion was estimated to be D_(2) type for both phosphors.The photometric properties of LiCa(PO_(3))_(3):Eu^(3+)such as Commission International de l'Eclairage coordinates(x=0.64,y=0.36) near to the standard one(red),high color purity(95%) and higher brightness reveal that the phosphor has the capability of acting as a red component in n-UV white light emitting diodes.
基金the National Research Foundation of Korea grant the Korean government(No.2018R1D1A1B07046937)。
文摘The height of total entropy(S)for a magnetic refrigerant material is essentially concerned with the magnetic and structural transitions.However,the participation of such transitions in layered materials is not well understood.Therefore,the purpose of this work is to investigate the interplay between double layer lattice with their single perovskite counterpart,to achieve optimal magnetocaloric performance.A series of self-doped Pr_(1.4+x)Sr_(1.6-x)Mn_(2)O_(7)(0.0≤x≤0.5)Ruddlesden-Popper(R-P)perovskite have been prepared through the solid-state sintering method.With increasing the Pr-stoichiometry,the lattice faults have increased and the double layer lattice dramatically disintegrates into single perovskite structure.Due to the reduction of bilayer R-P phase into single perovskite the spin crossover occurs from weak bilayer(T=304 K)interactions towards the strong three-dimensional(T=308 K)interactions respectively.This series consistently develops thermomagnetic irreversibility in zero-field cooled(ZFC)-field cooled(FC)magnetization,which is indicative of a spin-glass state.The glassy nature has been ascribed collectively to the lattice strain produced because of dislocations and to an antiferromagnetic phase segregated at the surface.The maximum value of temperature average entropy change(TEC)and adiabatic temperature(ΔT)has enhanced nearly by 4 folds from 0.53 J kg^(-1)K^(-1),0.59 K(for x=0.0)up to 1.85 J kg^(-1)K^(-1),10 K(for x=0.5)at 2.5 T,respectively.Additionally,the room temperature relative cooling power has improved from 26.94 J/kg up to 77.84 J/kg with an applied field of 2.5 T.Our findings in this work suggest that the controlled reduction of double layer lattice into single perovskite and/or existence of both phases simultaneously in bilayer R-P manganites may be very effective in obtaining the desirable characteristics of magnetocaloric effects.
