Neutron diffraction; A Primer

Dronskowski, R.*; Brckel, T.*; Kohlmann, H.*; Avdeev, M.*; Houben, A.*; Meven, M.*; Hofmann, M.*; Kamiyama, Takashi*; Zobel, M.*; Schweika, W.*; et al.

Zeitschrift fr Kristallographie; Crystalline Materials, 239(5-6), p.139 - 166, 2024/06

https://doi.org/10.1515/zkri-2024-0001

Because of the neutron's special properties, neutron diffraction may be considered one of the most powerful techniques for structure determination of crystalline and related matter. Neutrons can be released from nuclear fission, from spallation processes, and also from low-energy nuclear reactions, and they can then be used in powder, time-of-flight, texture, single crystal, and other techniques, all of which are perfectly suited to clarify crystal and magnetic structures. With high neutron flux and sufficient brilliance, neutron diffraction also excels for diffuse scattering, for in situ and operando studies as well as for high-pressure experiments of today's materials. In this primer, we summarize the current state of neutron diffraction (and how it came to be), but also look at recent advances and new ideas, e.g., the design of new instruments, and what follows from that.

Composition dependence of bulk properties in the Co-intercalated transition metal dichalcogenide CoTaS

Park, P.*; Cho, W.*; Kim, C.*; An, Y.*; Avdeev, M.*; Iida, Kazuki*; Kajimoto, Ryoichi; Park, J.-G.*

Physical Review B, 109(6), p.L060403_1 - L060403_7, 2024/02

https://doi.org/10.1103/PhysRevB.109.L060403

Pressure-modulated magnetism and negative thermal expansion in the HoFe intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; Kato, Kenichi*; Hattori, Takanori; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

https://doi.org/10.1021/acs.chemmater.3c00158

Hydrostatic and chemical pressure are efficient stimuli to alter the crystal structure and are commonly used for tuning electronic and magnetic properties in materials science. However, chemical pressure is difficult to quantify and a clear correspondence between these two types of pressure is still lacking. Here, we study intermetallic candidates for a permanent magnet with a negative thermal expansion (NTE). Based on in situ synchrotron X-ray diffraction, negative chemical pressure is revealed in HoFe on Al doping and quantitatively evaluated by using temperature and pressure dependence of unit cell volume. A combination of magnetization and neutron diffraction measurements also allowed one to compare the effect of chemical pressure on magnetic ordering with that of hydrostatic pressure. Intriguingly, pressure can be used to control suppression and enhancement of NTE. Electronic structure calculations indicate that pressure affected the top of the majority band with respect to the Fermi level, which has implications for the magnetic stability, which in turn plays a critical role in modulating magnetism and NTE. This work presents a good example of understanding the effect of pressure and utilizing it to control properties of functional materials.

Ultralow thermal conductivity from transverse acoustic phonon suppression in distorted crystalline -MgAgSb

Li, X.*; Liu, P.-F.*; Zhao, E.*; Zhang, Z.*; Guide, T.*; Le, M. D.*; Avdeev, M.*; Ikeda, Kazutaka*; Otomo, Toshiya*; Kofu, Maiko; et al.

Nature Communications (Internet), 11, p.942_1 - 942_9, 2020/02

https://doi.org/10.1038/s41467-020-14772-5

In high-performance thermoelectric materials, there are two main low thermal conductivity mechanisms: the phonon anharmonic and phonon scattering resulting from the dynamic disorder, which have been successfully revealed by inelastic neutron scattering. Using neutron scattering and ab initio calculations, we report here a mechanism of static local structure distortion combined with phonon-anharmonic-induced ultralow lattice thermal conductivity in -MgAgSb. Since the transverse acoustic phonons are almost fully scattered by the intrinsic distorted rocksalt sublattice in this compound, the heat is mainly transported by the longitudinal acoustic phonons. The ultralow thermal conductivity in -MgAgSb is attributed to its atomic dynamics being altered by the structure distortion, which presents a possible microscopic route to enhance the performance of similar thermoelectric materials.

Block magnetism coupled with local distortion in the iron-based spin-ladder compound BaFeSe

Nambu, Yusuke*; Ogushi, Kenya*; Suzuki, Shumpei*; Du, F.*; Avdeev, M.*; Uwatoko, Yoshiya*; Munakata, Koji*; Fukazawa, Hiroshi; Chi, S.*; Ueda, Yutaka*; et al.

Physical Review B, 85(6), p.064413_1 - 064413_5, 2012/02

https://doi.org/10.1103/PhysRevB.85.064413

Magnetism in the insulating BaFeSe was examined through susceptibility, specific heat, resistivity and neutron diffraction measurements. After formation of a short-range magnetic correlation, a long-range ordering was observed below 255 K. The transition is obscured by bulk properties. Magnetic moments are arranged to form a Fe ferromagnetic unit, and each Fe stacks antiferromagnetically. This block magnetism is of the third type among magnetic structures of ferrous materials. The magnetic ordering drives unusually large distortion via magnetoelastic coupling.