Neutron and X-ray Scattering in Materials Science: Amorphous and Magnetic Materials
Sponsored by: TMS Functional Materials Division, TMS: Chemistry and Physics of Materials Committee
Program Organizers: Michael Manley, Oak Ridge National Laboratory; Chen Li, University of California-Riverside; Jennifer Niedziela, Oak Ridge National Lab; Hillary Smith, Swarthmore College

Monday 2:00 PM
March 20, 2023
Room: Aqua 311B
Location: Hilton

Session Chair: Michael Manley, Oak Ridge National Laboratory

2:00 PM  Invited
High-frequency Transverse Phonons in Metallic Glasses: Xiyang Li¹; Huaping Zhang²; Si Lan³; Doug Abernathy⁴; Maozhi Li²; Xun-li Wang¹; ¹City University of Hong Kong; ²Remin University; ³Nanjing University of Science and Technology; ⁴Oak Ridge National Laboratory
    Transverse phonons are an essential part of the dynamics spectra in glasses and liquids. Using inelastic neutron scattering and molecular dynamics (MD) simulations on a model Zr-Cu-Al metallic glass, we show that transverse phonons persist well into the high-frequency regime [1]. The MD simulations further revealed that the apparent peak width of the transverse phonons follows the static structure factor, indicating a close link between the phonon dynamics and the underlying disordered structure. The one-to-one correspondence was demonstrated numerically with empirical potentials for Zr-Cu-Al metallic glass as well as with a Lennard-Jones potential, suggesting that the correlation is a universal feature of glass. This remarkable correlation, which was found for the transverse but not longitudinal phonon branch, underscores the key role that transverse phonons hold for understanding the dynamics in disordered materials.

2:30 PM  Invited
In Situ Inelastic Neutron Scattering Measurements of Glassy Liquids: Hillary Smith¹; Marios Demetriou²; Brent Fultz³; ¹Swarthmore College; ²Glassimetal; ³Caltech
    Glasses transform from a stable glass to an undercooled liquid at the glass transition temperature far below their melting temperature. We have used in situ inelastic neutron scattering (INS) to measure the phonon density of states in a variety of glasses during continuous heating from the glass phase to an undercooled liquid, then into the crystalline phase. Time-resolved INS measurements are performed with event-mode data collection to assess the phonon entropy from the vibrational density of states in as little two minutes. The dynamics of the glass in its metastable liquid state are compared to its stable crystalline phase across the same temperature range to determine the excess vibrational entropy. We report measurements for a variety of glass types including metallic glasses, oxide glasses, molecular glasses, and chalcogenide glasses. Results will be considered in the context of a universal understanding of vibrational contributions to the thermodynamics of the glass transition.

3:00 PM
Inelastic Neutron Scattering Across the Melt: the Role of Vibrational Entropy in Latent Heat: Camille Bernal-Choban¹; Claire Saunders¹; Yang Shen¹; Stefan Haegeli Lohaus¹; Vladimir Ladygin¹; Shiva Mudide¹; Douglas Abernathy²; Brent Fultz¹; ¹California Institute of Technology; ²Oak Ridge National Laboratory
    Advances in neutron scattering continue to address long-standing questions in materials physics. One persisting challenge that can now be studied in-situ is the solid to liquid transition, specifically, what role atomic motion has in the entropy of fusion. Here, we performed inelastic neutron scattering measurements on powder samples of Ge, Sn, Pb, and Bi from ambient temperature to 200 K above each melting temperature. Analyses of the spectra, informed by MCViNE simulations and vibrational-transit theory, were used to obtain the vibrational densities of states for the solid and liquid phases of each element. Preliminary results show a distinct contribution of atomic motion for Ge, Sn, Bi, and Pb, ranging from over 50% to less than 5% of the entropy of fusion. The changes in diffusional and collective motions of atoms across the melt will also be discussed. This work is supported by DOE BES award No. DE-FG02-03ER46055.

3:20 PM
X-ray Free-electron Laser Heating of Water at Picosecond Time Scale: Eva Zarkadoula¹; Yuya Shinohara¹; Takeshi Egami²; ¹Oak Ridge National Laboratory; ²University of Tennessee / Oak Ridge National Laboratory
    Split-pulse X-ray photon correlation spectroscopy using X-ray free-electron laser is a promising tool to probe atomic dynamics in liquid and soft-matter in pico-second timescale, which has been accessible only by spectroscopy. However, sample heating by X-ray beam is a major obstacle for this technique. Using molecular dynamics and the two-temperature model we examine the atomic level response of water to X-ray laser pulse and compare with recent experiments. We investigate the effects of the sample heating and the heat dissipation on the structure and dynamics of water through the atomic density correlation and the dynamic structure factor. Our results indicate, in agreement with experiment, that, in addition to the beam energy, the time delay between the two pulses is a critical factor for obtaining reliable information on the atomic level dynamics of water. Work supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.

3:40 PM Break

3:55 PM
Use of Neutron and X-ray Total Scattering to Map Short-range Order and Improve Nucleation Modelling in Engineering Materials: Monika Rolinska¹; Joakim Odqvist¹; Peter Hedström¹; ¹KTH
    Neutron and X-ray total scattering enables study of short-range order interactions in materials. In engineering materials such as stainless steels and nickel-based superalloys, the initial short-range order will influence the ageing kinetics and thus also the lifetime of the component. For ferritic and duplex stainless steels it has been shown previously that an intermediate heat treatment above the miscibility gap, but below the conventional solution treatment temperature, affects the phase transformation kinetics at accelerated service conditions. This is linked to the initial short-range interactions, and has also been shown utilizing modelling on different scales. By mapping the short-range order above the miscibility gap using total scattering for different solution treatment temperatures for different systems, it is possible to obtain data which could improve both nucleation modelling and help to more accurately predict the phase transformation kinetics.

4:15 PM
Dynamic Imaging of Twin Formation in NiMnGa Based Magnetic Shape Memory Alloys under Cyclic Magnetic Field.: Saurabh Kabra¹; Anton Tremsin²; Winfried Kockelmann¹; ¹Science & Technology Facilities Council; ²University of California Berkley
    We have used time of flight neutron imaging to study the twin variant populations and twin formation/switching dynamics in a magnetic shape memory alloy, NiMnGa. These crystals produce huge elongation (up to 6%) upon the application of a magnetic field. The large elongation is a result of reorientation of twin-variants due to highly mobile twin boundaries. Time of flight allow us to discriminate neutron wavelengths which in turn gives us contrast between different variants in the single crystal due to differences in orientation. Using in situ magnetic field switching we continuously cycle the twins at a frequency between 1-10 Hz. By synchronizing the neutron detection events to the cyclic phenomenon in the shape memory crystal we have been able to image directly, the fast but repeatable twin switching events and the twin boundary motions. We present both the setup and initial results from our first experiments using this setup.

4:35 PM
Frustration-induced Diffusive Scattering Anomaly and Dimension Change in FeGe₂: Yaokun Su¹; Hillary Smith²; Matthew Stone³; Douglas Abernathy³; Mark Lumsden³; Carl Adams⁴; Chen Li¹; ¹University of California, Riverside; ²Swarthmore College; ³Oak Ridge National Laboratory; ⁴St. Francis Xavier University
    Magnetic frustration, arising from the competition of exchange interactions, has received great attention because of its relevance to exotic quantum phenomena in materials. In the current work, we report an unusual checkerboard-shaped scattering anomaly in FeGe₂, far from the known incommensurate magnetic satellite peaks, for the first time by inelastic neutron scattering. More surprisingly, such phenomenon appears as spin dynamics at low temperature, but it becomes prominent above Néel transition as elastic scattering. A new model Hamiltonian that includes an intraplane next-nearest neighbor was proposed and such anomaly is attributed to the near-perfect magnetic frustration and the emergence of unexpected two-dimensional magnetic order in the quasi-one-dimensional FeGe₂.

4:55 PM
Intriguing Magnetism of Topological Kagome Material TbMn6Sn6: Charles Mielke¹; Zurab Guguchia¹; ¹Paul Scherrer Institut
    Magnetic topological phases of quantum matter are an emerging frontier in physics and material science, of which kagome magnets appear as a highly promising platform. We explore magnetic correlations in the recently identified topological kagome system TbMn₆Sn₆ using muSR, combined with local field analysis and neutron diffraction. Our studies identify an out-of-plane ferrimagnetic structure with slow magnetic fluctuations which exhibit a critical slowing down below T^*_C1 ≅ 120 K and finally freeze into static patches with ideal out-of-plane order below T_C1 ≅ 20 K. The appearance of the static patches sets in at a similar temperature as the appearance of topological transport behaviors. We further show that a hydrostatic pressure of 2.1 GPa stabilizes the topological ferrimagnetic ground state, giving rise to a magnetically-induced topological system whose magnetism can be controlled through external control parameters. [1] C. Mielke III et al., Communications Physics 5, 107 (2022).