Jan Schultheiß

• Dragland, Ruben Skjelstad; Schultheiß, Jan; Ushakov, I. N.; Proksch, R. & Meier, Dennis (2026). Interferometric Vector Piezoresponse Force Microscopy for Simultaneous Ferroelectric Domain and Crystallographic Orientation Mapping in Uniaxial Ferroelectric Polycrystals. Small. ISSN 1613-6810. doi: 10.1002/smll.75372.
• Belrhiti‐Nejjar, Rachid; Zahn, Manuel Peter; Limelette, Patrice; Haas, Max; Féger, Lucile & Monot‐Laffez, Isabelle [Vis alle 11 forfattere av denne artikkelen] (2025). Domain‐Wall Driven Suppression of Thermal Conductivity in a Ferroelectric Polycrystal. Advanced Science. 12(38). doi: 10.1002/advs.202506931. Fulltekst i vitenarkiv Vis sammendrag

  Abstract A common strategy for reducing the thermal conductivity of polycrystalline systems is to increase the number of grain boundaries. Indeed, grain boundaries enhance the probability of phonon scattering events, which has been applied to control the thermal transport in a wide range of materials, including hard metals, diamond, oxides, and two‐dimensional (2D) systems such as graphene. Here, the opposite behavior in improper ferroelectric ErMnO 3 polycrystals is reported, where the thermal conductivity decreases with increasing grain size. This unusual relationship between heat transport and microstructure is attributed to phonon scattering at ferroelectric domain walls. The domain walls are more densely packed in larger grains, leading to an inversion of the classical grain‐boundary‐dominated transport behavior. The findings open additional avenues for microstructural engineering of materials for thermoelectric and thermal management applications, enabling simultaneous control over mechanical, electronic, and thermal properties.

• Zahn, Manuel Peter; Müller, Aaron Merlin; Kelley, Kyle P.; Neumayer, Sabine; Kalinin, Sergei V. & Kézsmarki, István [Vis alle 11 forfattere av denne artikkelen] (2025). Reversible long-range domain wall motion in an improper ferroelectric. Nature Communications. 16(1). doi: 10.1038/s41467-025-57062-8. Fulltekst i vitenarkiv
• Dragland, Ruben Skjelstad; Mejía, Catalina Salazar; Hansen, Ingvild; Hamasaki, Yosuke; Panduro, Elvia Anabela Chavez & Ehara, Yoshitaka [Vis alle 9 forfattere av denne artikkelen] (2025). Relation between 4f-magnetism and the low-temperature magnetocaloric effect in multiferroic hexagonal manganites. Communications Materials. 6(1). doi: 10.1038/s43246-025-00813-3. Fulltekst i vitenarkiv
• Wolk, Katharina; Dragland, Ruben Skjelstad; Panduro, Elvia Anabela Chavez; Hjelmstad, Michael E.; Richarz, Leonie & Yan, Zewu [Vis alle 11 forfattere av denne artikkelen] (2024). Coexistence of multi-scale domains in ferroelectric polycrystals with non-uniform grain-size distributions. Matter. ISSN 2590-2393. 7(9), s. 3097–3106. doi: 10.1016/j.matt.2024.04.041. Fulltekst i vitenarkiv Vis sammendrag

  Engineering of ferroelectric domain structures enables direct control over the switching dynamics and is crucial for tuning the functional properties of ferroelectrics for various applications, ranging from capacitors to future nanoelectronics. Here, we investigate the domain formation in poly- and single-crystalline improper ferroelectric hexagonal DyMnO3. We show that a non-uniform grain-size distribution in the polycrystal facilitates the coexistence of multi-scale domains, varying by up to one order of magnitude in size. This unusual domain structure originates from an inverted domain-size/grain-size dependence that is intrinsic to the hexagonal manganite polycrystals, expanding previous studies toward non-uniform grain-size distributions. Our results demonstrate that the micrometer-sized grains in DyMnO3 represent individual ferroelectric units with a characteristic domain structure, giving a new dimension to domain engineering in ferroelectric polycrystals with non-uniform microstructures.

• Schultheiss, Jan Erich; Puntigam, L.; Winkler, M.; Krohns, S.; Meier, Dennis & Das, H. [Vis alle 8 forfattere av denne artikkelen] (2024). Magnetoelectric coupling at the domain level in polycrystalline hexagonal ErMnO<inf>3</inf>. Applied Physics Letters. ISSN 0003-6951. 124(25). doi: 10.1063/5.0209216. Fulltekst i vitenarkiv Vis sammendrag

  We explore the impact of a magnetic field on the ferroelectric domain pattern in polycrystalline hexagonal ErMnO3 at cryogenic temperatures. Utilizing piezoelectric force microscopy measurements at 1.65 K, we observe modifications of the topologically protected ferroelectric domain structure induced by the magnetic field. These alterations likely result from strain induced by the magnetic field, facilitated by intergranular coupling in polycrystalline multiferroic ErMnO3. Our findings give insights into the interplay between electric and magnetic properties at the domain scale and represent a so far unexplored pathway for manipulating topologically protected ferroelectric vortex patterns in hexagonal manganites.

• Zhou, Lima; Puntigam, Lukas; Lunkenheimer, Peter; Bourret, Edith; Yan, Zewu & Kézsmárki, István [Vis alle 10 forfattere av denne artikkelen] (2024). Post-synthesis tuning of dielectric constant via ferroelectric domain wall engineering. Matter. ISSN 2590-2393. 7(9), s. 2996–3006. doi: 10.1016/j.matt.2024.04.024. Fulltekst i vitenarkiv Vis sammendrag

  A promising mechanism for achieving colossal dielectric constants involves the use of insulating internal barrier layers, such as insulating domain walls in ferroelectrics. A key advantage of domain walls, compared to other stationary interfaces, is their mobility, offering the potential for post-synthesis adjustment of the dielectric constant. In this work, we demonstrate that altering the domain wall density enables the tuning of the dielectric constant in our template material, i.e., hexagonal ErMnO3 single crystals. Through microscopy and macroscopic dielectric spectroscopy, we quantify changes in domain wall density and correlated these with changes in dielectric constant within a single sample. Analysis of the dielectric data suggests that the insulating domain walls act as “ideal” capacitors connected in series. Our approach to engineering the domain wall density can be readily extended to other control methods, e.g., electric fields or mechanical stresses, providing a degree of flexibility to in situ tune the dielectric constant.

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• Dragland, Ruben Skjelstad; Wolk, Katharina; Panduro, Elvia Anabela Chavez; Richarz, Leonie Caroline; Yan, Zewu & Bourret, Edith [Vis alle 10 forfattere av denne artikkelen] (2024). Ferroelectric Domains in DyMnO3 Polycrystals with Inhomogeneous Grain-size Distribution. Fulltekst i vitenarkiv
• Dragland, Ruben Skjelstad; Wolk, Katharina; Panduro, Elvia Anabela Chavez; Hunnestad, Kasper Aas; Schultheiss, Jan Erich & Meier, Dennis (2024). Domain Size Engineering by Grain Scaling in Polycrystalline Hexagonal DyMnO3. Fulltekst i vitenarkiv
• Dragland, Ruben Skjelstad; Wolk, Katharina; Panduro, Elvia Anabela Chavez; Hunnestad, Kasper Aas; Schultheiss, Jan Erich & Meier, Dennis (2023). Non-uniform Grain Size Effects on Ferroelectric Domain Scaling in DyMnO3. Fulltekst i vitenarkiv

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