Papers by Thomas Lottermoser
Applied Physics B, Aug 1, 2001
Ferroelectrics, 2002
ABSTRACT Theoretical aspects and experimental observations of nonlinear magnetoelectric phenomena... more ABSTRACT Theoretical aspects and experimental observations of nonlinear magnetoelectric phenomena concerning the optical second harmonic generation are discussed. The coexistence of ferroelectric and antiferromagnetic orders in the hexagonal manganites RMnO3 leads to a new contribution to the nonlinear polarisation. Polarisation selection rules of this contribution allow to determine the magnetic space groups of the hexagonal manganites. Spectroscopic study of second harmonic generation in magnetoelectric garnet films reveals the role of bismuth substitution in these compounds. A new magnetic-dipole mechanism based on magnetoelectric excitation of second harmonic generation in the centrosymmetric antiferromagnet NiO is experimentally studied. Multiphoton resonance gives rise to a high efficiency of this mechanism in NiO.
Applied Physics B, Mar 1, 1999
ijk and on their phase. One of the hexagonal manganites, YMnO3 is chosen to demonstrate in deta... more ijk and on their phase. One of the hexagonal manganites, YMnO3 is chosen to demonstrate in detail the experimental methods for obtaining this information. The interference of different contributions is utilized to study domain topography.
Physical Review Letters, Sep 4, 2001
In spite of the fact that inversion is a symmetry operation of both the crystalline and the magne... more In spite of the fact that inversion is a symmetry operation of both the crystalline and the magnetic lattice of NiO, second harmonic generation (SHG) has been observed below the Néel temperature. A spectroscopic study shows that the signal is due to combined magnetic-dipole and electric-dipole transitions between the ͑3d͒ 8 levels of the Ni 21 ion in the crystal field. The SHG is resonant in both the incoming and the outgoing light waves and thus greatly enhanced. A quadratic coupling of the nonlinear polarization to the order parameter was found. This allows the investigation of individual domains.
Nano Letters, Jul 20, 2023
arXiv (Cornell University), Apr 17, 2023
Mechanical pressure controls the structural, electric, and magnetic order in solid state systems,... more Mechanical pressure controls the structural, electric, and magnetic order in solid state systems, allowing to tailor and improve their physical properties. A well-established example is ferroelastic ferroelectrics, where the coupling between pressure and the primary symmetry breaking order parameter enables hysteretic switching of the strain state and ferroelectric domain engineering. Here, we study the pressure-driven response in a non-ferroelastic ferroelectric, ErMnO3, where the classical stress-strain coupling is absent, and the domain formation is governed by creation-annihilation processes of topological defects. By annealing ErMnO3 polycrystals under variable pressures in the MPa-regime, we transform non-ferroelastic vortex-like domains into stripe-like domains. The width of the stripe-like domains is determined by the applied pressure as we confirm by three-dimensional phase field simulations, showing that pressure leads to highly oriented layer-like periodic domains. Our work demonstrates the possibility to utilize mechanical pressure for domain engineering in non-ferroelastic ferroelectrics, providing a processing-accessible lever to control their dielectric, electromechanical, and piezoelectric response.
Proceedings of SPIE, Jul 12, 2002
The magnetic europium chalcogenide semiconductors EuTe and EuSe are investigated by the spectrosc... more The magnetic europium chalcogenide semiconductors EuTe and EuSe are investigated by the spectroscopy of second harmonic generation ͑SHG͒ in the vicinity of the optical band gap formed by transitions involving the 4f and 5d electronic orbitals of the magnetic Eu 2+ ions. In these materials with centrosymmetric crystal lattice the electric-dipole SHG process is symmetry forbidden so that no signal is observed in zero magnetic field. Signal appears, however, in applied magnetic field with the SHG intensity being proportional to the square of magnetization. The magnetic field and temperature dependencies of the induced SHG allow us to introduce a type of nonlinear optical susceptibility determined by the magnetic-dipole contribution in combination with a spontaneous or induced magnetization. The experimental results can be described qualitatively by a phenomenological model based on a symmetry analysis and are in good quantitative agreement with microscopic model calculations accounting for details of the electronic energy and spin structure.
Physical Review Materials
Using phase-field simulations, we show how interfaces acting on the geometric-improper ferroelect... more Using phase-field simulations, we show how interfaces acting on the geometric-improper ferroelectric polarization of hexagonal manganite and ferrite thin films can be used to control the formation of charged domain walls. We modify the Landau expansion of the free energy valid in bulk to emulate interface effects known from previous cross-sectional experiments, and we verify our model by comparing our results with images obtained in these experiments. We then show how the interface affects the orientation of ferroelectric domain walls in the fully three-dimensional case. Furthermore, we demonstrate that interface effects combined with an external electric field enable us to specifically choose the dominant domain-wall type (head-to-head, tail-to-tail, or neutral). We also find that an electric field can stabilize a novel domain-wall type which only emerges in the improper ferroelectric order but not in the primary structural distortion. Since the domain walls have a conductivity that is different from the interior of the domains, the influence of the interfaces of a thin film on the type and distribution of the walls gives us the possibility to control the transport properties of a material by appropriate thin-film engineering.
Science
The utility of ferroic materials is determined by the formation of domains and their poling behav... more The utility of ferroic materials is determined by the formation of domains and their poling behavior under externally applied fields. For multiferroics, which exhibit several types of ferroic order at once, it is also relevant how the domains of the coexisting ferroic states couple and what kind of functionality this might involve. In this work, we demonstrate the reversible transfer of a domain pattern between magnetization and electric-polarization space in the multiferroic Dy 0.7 Tb 0.3 FeO 3 . A magnetic field transfers a ferromagnetic domain pattern into an identical ferroelectric domain pattern while erasing it at its magnetic origin. Reverse transfer completes the cycle. To assess the generality of our experiment, we elaborate on its conceptual origin and aspects of application.
Nature Communications, 2021
Systems with long-range order like ferromagnetism or ferroelectricity exhibit uniform, yet differ... more Systems with long-range order like ferromagnetism or ferroelectricity exhibit uniform, yet differently oriented three-dimensional regions called domains that are separated by two-dimensional topological defects termed domain walls. A change of the ordered state across a domain wall can lead to local non-bulk physical properties such as enhanced conductance or the promotion of unusual phases. Although highly desirable, controlled transfer of these properties between the bulk and the spatially confined walls is usually not possible. Here, we demonstrate this crossover by confining multiferroic Dy0.7Tb0.3FeO3 domains into multiferroic domain walls at an identified location within a non-multiferroic environment. This process is fully reversible; an applied magnetic or electric field controls the transformation. Aside from expanding the concept of multiferroic order, such interconversion can be key to addressing antiferromagnetic domain structures and topological singularities.
Nature Communications, 2021
Systems with long-range order like ferromagnetism or ferroelectricity exhibit uniform, yet differ... more Systems with long-range order like ferromagnetism or ferroelectricity exhibit uniform, yet differently oriented three-dimensional regions called domains that are separated by two-dimensional topological defects termed domain walls. A change of the ordered state across a domain wall can lead to local non-bulk physical properties such as enhanced conductance or the promotion of unusual phases. Although highly desirable, controlled transfer of these properties between the bulk and the spatially confined walls is usually not possible. Here, we demonstrate this crossover by confining multiferroic Dy0.7Tb0.3FeO3 domains into multiferroic domain walls at an identified location within a non-multiferroic environment. This process is fully reversible; an applied magnetic or electric field controls the transformation. Aside from expanding the concept of multiferroic order, such interconversion can be key to addressing antiferromagnetic domain structures and topological singularities.
Journal of Physics D: Applied Physics, 2017
Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an ... more Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an incommensurate antiferromagnetic (AFM) structure at T-N approximate to 24 K. A weak ferroelectric or ...
Physical Review B, 2021
We resolve the domain-wall structure of the model antiferromagnet Cr 2 O 3 using nanoscale scanni... more We resolve the domain-wall structure of the model antiferromagnet Cr 2 O 3 using nanoscale scanning diamond magnetometry and second-harmonic-generation microscopy. We find that the 180 • domain walls are predominantly Bloch-like, and can coexist with Néel walls in crystals with significant in-plane anisotropy. In the latter case, Néel walls that run perpendicular to a magnetic easy axis acquire a well-defined chirality. We further report quantitative measurement of the domain-wall width and surface magnetization. Our results provide fundamental input and an experimental methodology for the understanding of domain walls in pure, intrinsic antiferromagnets, which is relevant to achieve electrical control of domain-wall motion in antiferromagnetic compounds.
Nature Reviews Materials, 2016
Materials with a coexistence of magnetic and ferroelectric order-multiferroicsprovide an efficien... more Materials with a coexistence of magnetic and ferroelectric order-multiferroicsprovide an efficient route for the control of magnetism by electric fields. The study of multiferroics dates back to the 1950s, but in recent years, key discoveries in theory, synthesis and characterization techniques have led to a new surge of interest in these materials. Different mechanisms, such as lone-pair, geometric, charge-ordering and spin-driven effects, can support multiferroicity. The general focus of the field is now shifting into neighbouring research areas, as we discuss in this Review. Multiferroic thin-film heterostructures, device architectures, and domain and interface effects are explored. The violation of spatial and inversion symmetry in multiferroic materials is a key feature because it determines their properties. Other aspects, such as the non-equilibrium dynamics of multiferroics, are underrated and should be included in the topics that will define the future of the field.
Nature Photonics, 2016
Laser-controlled writing and erasure of antiferromagnetic domains in multiferroic TbMnO3 using li... more Laser-controlled writing and erasure of antiferromagnetic domains in multiferroic TbMnO3 using light pulses of two different colours is demonstrated.
Physical Review Letters, 2009
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Papers by Thomas Lottermoser