scholarly journals Microstructural Changes Influencing the Magnetoresistive Behavior of Bulk Nanocrystalline Materials

2020 ◽  
Vol 10 (15) ◽  
pp. 5094
Author(s):  
Stefan Wurster ◽  
Martin Stückler ◽  
Lukas Weissitsch ◽  
Timo Müller ◽  
Andrea Bachmaier
Keyword(s):  
Nanocrystalline Materials ◽  
Giant Magnetoresistance ◽  
Room Temperature ◽  
Annealing Temperature ◽  
High Pressure Torsion ◽  
Ex Situ ◽  
Thermal Treatments ◽  
Synchrotron Diffraction ◽  
Bulk Nanocrystalline

Bulk nanocrystalline materials of small and medium ferromagnetic content were produced using severe plastic deformation by high-pressure torsion at room temperature. Giant magnetoresistive behavior was found for as-deformed materials, which was further improved by adjusting the microstructure with thermal treatments. The adequate range of annealing temperatures was assessed with in-situ synchrotron diffraction measurements. Thermally treated Cu–Co materials show larger giant magnetoresistance after annealing for 1 h at 300 °C, while for Cu-Fe this annealing temperature is too high and decreases the magnetoresistive properties. The improvement of magnetoresistivity by thermal treatments is discussed with respect to the microstructural evolution as observed by electron microscopy and ex-situ synchrotron diffraction measurements.

Mechanical Properties of Nanocrystalline Materials Produced by In Situ Consolidation Ball Milling

2008 ◽  
Vol 579 ◽  
pp. 15-28 ◽  
Author(s):  
Carl C. Koch ◽  
Khaled M. Youssef ◽  
Ron O. Scattergood
Keyword(s):  
Mechanical Properties ◽  
Ball Milling ◽  
Nanocrystalline Materials ◽  
Preparation Method ◽  
High Strength ◽  
Al Alloys ◽  
Ductile Metals ◽  
Cu Alloys ◽  
Bulk Nanocrystalline

This paper reviews a method, “in situ consolidation ball milling” that provides artifactfree bulk nanocrystalline samples for several ductile metals such as Zn, Al and Al alloys, and Cu and Cu alloys. The preparation method is described in this paper and examples of the mechanical behavior of nanocrystalline materials made by this technique are given. It is found that in such artifact-free metals, combinations of both high strength and good ductility are possible.

Deformation Twins Formed in Nanocrystalline Materials

2006 ◽  
Vol 503-504 ◽  
pp. 125-132 ◽  
Author(s):  
Yuntian T. Zhu
Keyword(s):  
Grain Boundaries ◽  
Nanocrystalline Materials ◽  
Partial Dislocation ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Nucleation And Growth ◽  
Analytical Models ◽  
Partial Dislocations ◽  
Deformation Twins ◽  
Low Strain Rate

Deformation twins have been oberved in nanocrystalline (NC) Al synthsized by cryogenic ball-milling and in NC Cu processed by high-pressure torsion under room temperature and at a very low strain rate. They were found formed by partial dislocations emitted from grain boundaries. This paper first reviews experimental evidences on deformation twinning and partial dislocation emissions from grain boundaries, and then discusses recent analytical models on the nucleation and growth of deformation twins. These models are compared with experimental results to establish their validity and limitations.

scholarly journals Ion-Irradiation-Induced Amorphization Of Cadmium Niobate Pyrochlore

2000 ◽  
Vol 650 ◽  
Author(s):  
A. Meldrum ◽  
K. Beaty ◽  
L. A. Boatner ◽  
C. W. White
Keyword(s):  
Electron Microscope ◽  
Ambient Temperature ◽  
Transmission Electron Microscope ◽  
Room Temperature ◽  
Ion Irradiation ◽  
Ex Situ ◽  
Temperature Dependent ◽  
Transmission Electron ◽  
Ion Energies

ABSTRACTIrradiation-induced amorphization of Cd2Nb2O7 pyrochlore was investigated by means of in-situ temperature-dependent ion-irradiation experiments in a transmission electron microscope, combined with ex-situ ion-implantation (at ambient temperature) and RBS/channeling analysis. The in-situ experiments were performed using Ne or Xe ions with energies of 280 and 1200 keV, respectively. For the bulk implantation experiments, the incident ion energies were 70 keV (Ne+) and 320 keV (Xe2+). The critical amorphization temperature for Cd2Nb2O7 is ∼480 K (280 keV Ne+) or ∼620 K (1200 keV Xe2+). The dose for in-situ amorphization at room temperature is 0.22 dpa for Xe2+, but is 0.65 dpa for Ne+ irradiation. Both types of experiments suggest a cascade overlap mechanism of amorphization. The results were analyzed in light of available models for the crystalline-to-amorphous transformation and were compared to previous ionirradiation experiments on other pyrochlore compositions.

Phase Transformations in Sol-Gel PZT Thin Films

2000 ◽  
Vol 623 ◽  
Author(s):  
D.P. Eakin ◽  
M.G. Norton ◽  
D.F. Bahr
Keyword(s):  
Thin Films ◽  
Heat Treatment ◽  
Room Temperature ◽  
Structural Changes ◽  
Sol Gel ◽  
Ex Situ ◽  
Ambient Conditions ◽  
Crystalline Films ◽  
In Situ Heating

AbstractThin films of PZT were deposited onto platinized and bare single crystal NaCl using spin coating and sol-gel precursors. These films were then analyzed using in situ heating in a transmission electron microscope. The results of in situ heating are compared with those of an ex situ heat treatment in a standard furnace, mimicking the heat treatment given to entire wafers of these materials for use in MEMS and ferroelectric applications. Films are shown to transform from amorphous to nanocrystalline over the course of days when held at room temperature. While chemical variations are found between films crystallized in ambient conditions and films crystallized in the vacuum conditions of the microscope, the resulting crystal structures appear to be insensitive to these differences. Significant changes in crystal structure are found at 500°C, primarily the change from largely amorphous to the beginnings of clearly crystalline films. Crystallization does occur over the course of weeks at room temperature in these films. Structural changes are more modest in these films when heated in the TEM then those observed on actual wafers. The presence of Pt significantly influences both the resulting structure and morphology in both in situ and ex situ heated films. Without Pt present, the films appear to form small, 10 nm grains consisting of both cubic and tetragonal phases, whereas in the case of the Pt larger, 100 nm grains of a tetragonal phase are formed.

Deformation-Induced Nanocrystallization in Al-Rich Metallic Glasses

2006 ◽  
Vol 114 ◽  
pp. 123-132 ◽  
Author(s):  
Nancy Boucharat ◽  
Rainer J. Hebert ◽  
Harald Rösner ◽  
Gerhard Wilde
Keyword(s):  
Metallic Glasses ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
In Situ Tem ◽  
Number Density ◽  
High Number Density ◽  
Glass Forming ◽  
Processing Strategies ◽  
Improved Performance

Deformation-induced nanocrystallization has been investigated in a marginally Al88Y7Fe5 glass forming alloy. Conventional calorimetry and microstructural analyses of materials that have been subjected to high pressure torsion straining (HPT) at room temperature indicate the development of an extremely high number density of small Al nanocrystals. The nanocrystals appear to be distributed homogeneously throughout the sample without any evidence of strong coarsening. Moreover, the comparison between nanocrystallization caused by the application of either HPT, cold-rolling or in-situ TEM tensile straining yielded the identification of the probable mechanisms underlying the formation of nanocrystals. These results form the basis for the development of advanced processing strategies for producing new nanostructures with high nanocrystal number densities which allow increased stability and improved performance.

Texture Evolution of Magnesium Single Crystals Deformed by High-Pressure Torsion

2008 ◽  
Vol 584-586 ◽  
pp. 263-268 ◽  
Author(s):  
Bartlomiej J. Bonarski ◽  
Erhard Schafler ◽  
Borys Mikułowski ◽  
Michael Zehetbauer
Keyword(s):  
High Pressure ◽  
Single Crystals ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Texture Evolution ◽  
In Situ Stress ◽  
Higher Symmetry ◽  
Strain Measurements ◽  
X Ray

Single crystals of technical purity Magnesium (99.8 wt.%) of initial orientations [ ] 2 1 10 and [ ] 2 2 11 were subjected to HPT deformation at room temperature up to strains of 10. The microstructural evolution has been analyzed by X-ray microtexture investigations and by in-situ stress-strain measurements. The results can be described in terms of shear arising from HPT deformation and - with higher strains - in terms of recrystallization. In crystals with hard orientation[ ] 2 2 11 , these features occur at smaller strains than in crystals with soft orientation [ ] 2 1 10 , i.e. with higher symmetry. In general, the observed textures and strength variations are much stronger than those reported for fcc HPT deformed metals.

Influence of annealing temperature on the properties of TiO2 films annealed by ex situ and in situ TEM

2012 ◽  
Vol 27 (6) ◽  
pp. 1014-1019 ◽  
Author(s):  
Tangchao Peng ◽  
Xiangheng Xiao ◽  
Feng Ren ◽  
Jinxia Xu ◽  
Xiaodong Zhou ◽  
...  
Keyword(s):  
Annealing Temperature ◽  
Ex Situ ◽  
In Situ Tem ◽  
Tio2 Films

Growth of CoSi2/Si Multilayer Structures

1988 ◽  
Vol 116 ◽  
Author(s):  
T. L. Ljni ◽  
P. J. Grunthaner ◽  
F. D. Schowengerdt ◽  
R W. Fathauer ◽  
J. H. Mazur ◽  
...  
Keyword(s):  
Electron Spectroscopy ◽  
Auger Electron ◽  
Room Temperature ◽  
Annealing Temperature ◽  
Multilayer Structures ◽  
Stoichiometric Ratio ◽  
Critical Temperatures ◽  
Amorphous Si ◽  
Minimum Yield

AbstractGrowth techniques for very thin CoSi2 and Si layers for multilayer applications have been studied. CoSi2 layers without observable pinholes are grown by atechnique utilizing the room-temperature codeposition of Co and Si in stoichiometric ratio with a Si cap, followed by annealing. The crystallinity of the resulting CoSI2 layers annealed at various temperatures was studied by in-situ Rutherford backscattering channeling spectroscopy. The channeling minimum yield decreases with increasing annealing temperature, and drops sharply at ~ 570ºC. Si overgrowth was studied on CoSi2 by a Si template technique, which utilizes the deposition of a thin amorphous Si layer followed by annealing prior to the growth of the bulk of the Si layer. The effect of Si thickness and annealing temperature on Islanding of the Si overlayer was studied by Auger electron spectroscopy. Critical temperatures for a numberof Si thicknesses were identified, above which islanding of these layers occurs.

MAGNETORESISTANCE IN NANO-SCALE NiO-CONTAINING Co/Cu/Co SPIN VALVES

2005 ◽  
Vol 19 (15n17) ◽  
pp. 2574-2579 ◽  
Author(s):  
A. M. ZHANG ◽  
X. S. WU ◽  
L. SUN ◽  
A. HU
Keyword(s):  
Room Temperature ◽  
Annealing Temperature ◽  
Growth Parameters ◽  
Coupling Effect ◽  
Spin Valve ◽  
Interface Roughness ◽  
Spin Valves ◽  
X Ray ◽  
X Ray Scattering

A series of NiO -containing Co/Cu/Co spin valves with the thickness Co of 5 nm and Cu of 2 nm were fabricated by magnetron sputtering technique with different growth parameters. NiO layer with the thickness of 40 nm is used as a coupling layer. Magnetoresistance (MR) of the spin valve with NiO layer under the bottom of Co/Cu/Co (BSV) is larger than that of the spin valve with NiO layer at the top of Co/Cu/Co (TSV) at room temperature. The MR values can be improved with decreasing the sputtering rate of copper layer. The studies by in-situ grazing incident X-ray scattering on the annealing temperature dependence of MR show that the decrease of the interface roughness between Co and NiO may increase the MR value, while the decrease of the coupling effect between NiO and Co decreases the MR value.

Surface Morphologies and Interfaces of TiSi2 Formed from UHV Deposited Ti on Si

1989 ◽  
Vol 160 ◽  
Author(s):  
Hyeongtag Jeon ◽  
R. J. Nemanich ◽  
J.W. Honeycutt ◽  
G. A. Rozgonyi
Keyword(s):  
Room Temperature ◽  
Ex Situ ◽  
Island Formation ◽  
Surface And Interface ◽  
Angle Measurements ◽  
Contact Angle Measurements ◽  
Liquid Model ◽  
Surface Morphologies ◽  
Substrate Temperatures

AbstractThe island formation of TiSi2 and the surface morphologies and interfaces of TiSi2 on Si have been examined and related to the surface and the interface energies. Ti (200Å and 400Å) films were deposited on clean, reconstructed Si(100) and Si(111) substrates at room temperature and also at high substrate temperatures (500°C~800°C). The TiSi2 formation process is monitored with in-situ LEED and AES and the surface morphologies and interfaces are examined with ex-situ SEM and TEM. For annealing to temperatures such that the C54 phase forms, the results indicate island formation with clean reconstructed substrate regions between the islands. The TiSi2 islands show different morphology on the (100) and (111) oriented substrates. The mechanism of TiSi2 island formation is described in terms of a liquid-liquid model, and the surface and interface energies for the TiSi2 island are determined from contact angle measurements.

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