A5024145949- Metallic Glasses and Amorphous Alloys
- Material Dynamics and Properties
- Theoretical and Computational Physics
- Magnetic and transport properties of perovskites and related materials
- Glass properties and applications
- Magnetic properties of thin films
- Advanced Condensed Matter Physics
- Rare-earth and actinide compounds
- nanoparticles nucleation surface interactions
- Magnetic Properties of Alloys
- Electronic and Structural Properties of Oxides
- Phase-change materials and chalcogenides
- Physics of Superconductivity and Magnetism
- Magnetic Properties and Applications
- Solidification and crystal growth phenomena
- ZnO doping and properties
- Thermodynamic and Structural Properties of Metals and Alloys
- High-pressure geophysics and materials
- Surface Roughness and Optical Measurements
- Intermetallics and Advanced Alloy Properties
- Semiconductor materials and devices
- Force Microscopy Techniques and Applications
- Metal and Thin Film Mechanics
- Shape Memory Alloy Transformations
- Copper Interconnects and Reliability
University of Göttingen
2016-2025
California Institute of Technology
1987-2025
Universitätsmedizin Göttingen
2007-2023
University College London
2018
University of Florida
2009
University of Augsburg
1992-2001
Augsburg University
1990-2000
Siemens (Germany)
1992-1996
The Aerospace Corporation
1988
At room temperature a large magnetoresistance, \ensuremath{\Delta}R/R(H=0), of 60% has been observed in thin magnetic films perovskitelike La-Ba-Mn-O. The were grown epitaxially on ${\mathrm{SrTiO}}_{3}$ substrates by off-axis laser deposition. In the as-deposited state, Curie and saturation magnetization considerably lower compared to bulk samples, but increased subsequent heat treatment. samples show drop resistivity at transition, existence polarons seems dominate electric transport this region.
Room temperature (${T}_{R}$) elastic constants and compressive yield strengths of $\ensuremath{\sim}30$ metallic glasses reveal an average shear limit ${\ensuremath{\gamma}}_{C}=0.0267\ifmmode\pm\else\textpm\fi{}0.0020$, where ${\ensuremath{\tau}}_{Y}={\ensuremath{\gamma}}_{C}G$ is the maximum resolved stress at yielding, $G$ modulus. The ${\ensuremath{\gamma}}_{C}$ values for individual are correlated with $t={T}_{R}/{T}_{g}$, a single glass follows same correlation (vs $t=T/{T}_{g}$). A...
Noncrystalline metallic hydrides can be formed from certain crystalline Zr3Rh intermetallic phases by hydrogenation. X-ray diffraction patterns, density measurements, and superconducting properties confirmed the transition to amorphous phase this solid state reaction. The explained in terms of a ‘‘chemical frustration’’ effect.
Metallic glasses, combining metallic bonding and disordered atomic structures, are at the cutting edge of materials research. Recent advances in this field have revealed that many key questions glassy physics inherently connected to one important relaxation mode: so-called secondary (β) relaxation. Here, we review features β relaxations their relations other processes properties. Special emphasis is put on current roles future promise understanding glass transition phenomenon, mechanical...
Abstract Focusing on metallic glasses as model systems, we review the features and mechanisms of β-relaxations, which are intrinsic universal to supercooled liquids glasses, demonstrate their importance in understanding many crucial unresolved issues glassy physics materials science, including glass transition phenomena, mechanical properties, shear-banding dynamics deformation mechanisms, diffusion breakdown Stokes–Einstein relation well crystallization stability glasses. We illustrate that...
Abstract Melting is well understood in terms of the Lindemann criterion, which essentially states that crystalline materials melt when thermal vibrations their atoms become so vigorous they shake themselves free binding forces. This picture does not necessarily have to hold for glasses, where nature solid–liquid cross-over highly debated. The criterion implies expansion coefficients crystals are inversely proportional melting temperatures. Here we find that, contrast, coefficient glasses...
Using molecular dynamics simulations with a many-body force field, we studied the deformation of single crystal Ni and NiCu random alloy nanowires subjected to uniform strain rates but kept at 300 K. For all rates, nanowire is elastic up $7.5%$ yield stress 5.5 GPa, far above that bulk Ni. At high find for both systems crystalline phase transforms continuously an amorphous phase, exhibiting dramatic change in atomic short-range order near vanishing tetragonal shear constant perpendicular...
Calorimetric measurements of the glass transition are presented for metallic glasses, ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$, and organic polymers with cooling heating rates ranging over more than three orders magnitude. Fits onset temperatures to a Vogel-Fulcher-type equation give divergence significantly above values obtained Vogel-Fulcher fits viscosity. The width extrapolates sharp step at finite rate, which is close range where data were taken. results suggest that becomes independent...
The configurational properties associated with the transition from anelasticity to plasticity in a transiently deforming metallic glass-forming liquid are studied. data reveal that underlying kinetics for flow can be separated into reversible and irreversible hopping across energy landscape, identified beta alpha relaxation processes, respectively. A critical stress characterizing is recognized as an effective Eshelby "backstress," revealing link between apparent "confinement stress" of...
Metallic-glass formation by solid-state reactions has been observed in multilayer Zr-Co diffusion couples and studied cross-sectional transmission electron microscopy. Planar growth of a Corich amorphous phase proceeds from each interface the unreacted sample, thus consuming Co layers at higher rate. Further annealing results eventually reaction Co-rich glassy with remaining Zr. Because high diffusivity phase, Kirkendall voids are formed during this homogenizing process lined up periodicity...
The development of metal alloys that form glasses at modest cooling rates has stimulated broad scientific and technological interest. However, intervening crystallization the liquid in even most robust bulk metallic glass-formers is orders magnitude faster than many common polymers silicate glass-forming liquids. Crystallization limits experimental studies undercooled hampers efforts to plastically process glasses. We have developed a method rapidly uniformly heat glass 10(6) kelvin per...
In multicomponent metallic glasses, we demonstrate that diffusion and secondary (β) relaxation are closely related. The motion of the smallest constituting atoms takes place within temperature time regimes where β relaxations activated, and, in particular, two processes have similar activation energies. We suggest cooperative stringlike atomic plays an important role both processes. This finding provides additional insights into structural origin as well mechanisms diffusions glasses.
Cu1−xCox alloys with x=0.1 and x=0.2 have been prepared by conventional melt spinning. The rapid solidification process results in an extended solubility of Co Cu although some precipitates already during quenching. In the as-quenched ribbons, magnetoresistance (MR) is only order 1.5%. It increases dramatically controlled nucleation growth from supersaturated matrix. highest MR 11% at 300 K occurs for Cu90Co10 after aging about 440 °C when clusters are superparamagnetic. Saturation possible...
A new metallic glass, which was created by vapour deposition at an appropriately high substrate temperature, shows exceptional thermal stability, and enhanced glass transition temperature elastic modulus. Comparing this material with other organic glasses prepared similar routes known as ultrastable demonstrates the formation of glassy materials correlates to important concept fragility.
The Johari-Goldstein secondary (β) relaxations are an intrinsic feature of supercooled liquids and glasses. They crucial to many properties glassy materials, but the underlying mechanisms still not established. In a model metallic glass, we study atomic rearrangements by molecular dynamics simulations at time scales up microseconds. We find that distributions single-particle displacements exhibit multiple peaks, whose positions quantitatively match pair distribution function. These...
We present experimental evidence on the physical origin of a magnetic dead layer (MDL) in manganite nanoparticles. The studied nanoparticles constitute wall La0.67Sr0.33MnO3 and La0.67Ca0.33MnO3 nanotubes. Magnetic properties analysis high resolution transmission electron microscopy show shell approximately 2 nm thickness with different from core. In this atoms are noncrystalline array that perfectly explains 50% reduction magnetization compared to bulk. Moreover, we internal structure MDL...
Significance Bulk metallic glasses are the most promising materials in many technological applications thanks to their mechanical properties. The stability and thermoelasticity of supercooled liquid metals is encoded temperature dependence viscosity at glass transition: fragility. Although with colloidal it has been possible explain fragility terms softness (or its inverse, steepness) microscopic interparticle potential, same could not be done due complex interatomic interaction. Here we...
Two dimensional mapping of structural properties near a single shear band in Zr-based bulk metallic glass reveals the presence hardness and modulus reductions at micrometer length scale. The isolated had carried all macroscopic plastic strain material shear-band exhibits variations both along normal to plane. Analyzing nanoindentation data indicates that long range internal stresses are primary cause spatially varying structure. results demonstrate nano-scale defect may have signature.