arXiv subjects

Ingrid Hallsteinsen

Publications and source records attributed to Ingrid Hallsteinsen.

7 recordsLinked to original sources

arXiv2026

Tailoring Emergent Magnetic Moment in La$_{0.7}$Sr$_{0.3}$MnO$_3$-Bi$_2$Te$_3$ Heterostructures via Interfacial Reconstructions

We report emergent magnetic behavior in heterostructures composed of (111)-oriented La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) and (00$l$)-oriented Bi$_2$Te$_3$ (BT), controlled by interfacial reconstructions. When BT is deposited directly onto LSMO, an intermediate interfacial layer forms between the two materials. Polarized Neutron Reflectometry modeling reveals that this reconstructed region stabilizes a secondary magnetically ordered phase that is coupled to the underlying ferromagnetic LSMO layer. As a consequence, the heterostructures exhibit unconventional self-crossing magnetic hysteresis loops at room temperature, characterized by a reversal of the net magnetization at low applied fields. In contrast, the introduction of a tellurium seed layer results in a sharper LSMO-BT interface, while preserving the anomalous hysteresis behavior and enhancing the saturation magnetization. Element-specific X-ray absorption spectroscopy suggests that the emergent magnetic phase originates from the chemical reconstruction of manganese species. These results demonstrate that interface engineering in magnetic oxide-topological insulator heterostructures provides a pathway to control emergent magnetic coupling and emergent magnetic states in oxide-topological insulator heterostructures.

cond-mat.mtrl-sci↗

arXiv2026

Electronic Structure and Resonant Circular Dichroism of La$_{0.7}$Sr$_{0.3}$MnO$_3$ from Soft X-ray Angle-Resolved Photoemission

Coupling between spin, orbital, charge, and lattice degrees of freedom in transition-metal oxides produces a variety of electronic and magnetic phenomena of importance for future technologies. Here, we explore the electronic band structure of a (111)-oriented La0.7Sr0.3MnO3 thin film through soft X-ray angle-resolved photoemission spectroscopy (ARPES). The measurements agree with the electronic band structure calculated with density functional theory using Hubbard U correction. Furthermore, we probe the circular dichroism in ARPES, and observe a pronounced momentum- resolved magnetic circular dichroism in resonant photoemission from the Mn L-edge. The approach combines the momentum- and spin-selectivity of ARPES and X-ray magnetic circular dichroism, respectively, which could provide a useful approach for the study of unconventional magnetism.

cond-mat.str-el↗

arXiv2025

Anisotropic Strain Engineering in La0.7Sr0.3MnO3/LaFeO3 Superlattice: Structural Relaxation and Domain Formation

Anisotropic strain engineering in epitaxial oxide films provides new opportunities to control the antiferromagnetic and structural properties crucial for advancements of antiferromagnetic spintronics. Here we report on a (La0.7Sr0.3MnO3/LaFeO3)4 superlattice grown on (101)o DyScO3 substrate which imposes significant anisotropic in-plane strain. Reciprocal space mapping reveals selective strain relaxation along the tensile in-plane [010]o axis, while compression along the perpendicular in-plane [-101]o axis remains strained. Scanning precession electron diffraction and higher-order Laue zone analysis show that the relaxation is accommodated by structural domain formation in the LaFeO3 layers, initiating from the second bilayer and propagating out-of-plane. These domains minimise structural defects and correlate with the substrate step edges. X-ray magnetic dichroism measurements reveal bulk-like in-plane antiferromagnetic order with polydomain signature as previously reported. Our findings reveal the presence of structural domains coexisting with antiferromagnetic polydomain states, showing a strain-domain-magnetism relationship that provides insights for applications of strain engineering in spintronics applications.

cond-mat.mtrl-sci↗

arXiv2020

Effect of strain on magnetic and orbital ordering of LaSrCrO$_3$/LaSrMnO$_3$ heterostructures

We investigate the effect of strain and film thickness on the orbital and magnetic properties of LaSrCrO$_3$ (LSCO)/LaSrMnO$_3$ (LSMO) heterostructures using bulk magnetometry, soft X-ray magnetic spectroscopy, first-principles density functional theory, high-resolution electron microscopy and X-ray diffraction. We observe an anti-parallel ordering of the magnetic moments between the ferromagnetic LSMO layers and the LSCO spacers leading to a strain-independent ferromagnetic ground state of the LSCO/LSMO heterostructures for LSMO layers as thin as 2 unit cells. As the LSMO thickness is increased, a net ferromagnetic state is maintained, however, the average magnetic moment per Mn is found to be dependent on the magnitude of the substrate-induced strain. The differences in the magnetic responses are related to preferential occupation of the Mn $x^2-y^2$ (in-plane) d-orbitals for tensile strain and $3z^2-r^2$ (out-of-plane) orbitals under compressive strain leading to competing ferromagnetic and anti-ferromagnetic exchange interactions within the LSMO layers. These results underscore the relative contributions of orbital, structural and spin degree of freedom and their tunability in atomically-thin crystalline complex oxide layers.

cond-mat.mtrl-sci↗

arXiv2018

3D sub-nanoscale imaging of unit cell doubling due to octahedral tilting and cation modulation in strained perovskite thin films

Determining the 3-dimensional crystallography of a material with sub-nanometre resolution is essential to understanding strain effects in epitaxial thin films. A new scanning transmission electron microscopy imaging technique is demonstrated that visualises the presence and strength of atomic movements leading to a period doubling of the unit cell along the beam direction, using the intensity in an extra Laue zone ring in the back focal plane recorded using a pixelated detector method. This method is used together with conventional atomic resolution imaging in the plane perpendicular to the beam direction to gain information about the 3D crystal structure in an epitaxial thin film of LaFeO3 sandwiched between a substrate of (111) SrTiO3 and a top layer of La0.7Sr0.3MnO3. It is found that a hitherto unreported structure of LaFeO3 is formed under the unusual combination of compressive strain and (111) growth, which is triclinic with a periodicity doubling from primitive perovskite along one of the three <110> directions lying in the growth plane. This results from a combination of La-site modulation along the beam direction, and modulation of oxygen positions resulting from octahedral tilting. This transition to the period-doubled cell is suppressed near both the substrate and near the La0.7Sr0.3MnO3 top layer due to the clamping of the octahedral tilting by the absence of tilting in the substrate and due to an incompatible tilt pattern being present in the La0.7Sr0.3MnO3 layer. This work shows a rapid and easy way of scanning for such transitions in thin films or other systems where disorder-order transitions or domain structures may be present and does not require the use of atomic resolution imaging, and could be done on any scanning TEM instrument equipped with a suitable camera.

cond-mat.mtrl-sci↗

arXiv2016

Assessing electron beam sensitivity for SrTiO$_3$ and La$_{0.7}$Sr$_{0.3}$MnO$_3$ using electron energy loss spectroscopy

Thresholds for beam damage have been assessed for La$_{0.7}$Sr$_{0.3}$MnO$_3$ and SrTiO$_3$ as a function of electron probe current and exposure time at 80 and 200 kV acceleration voltage. The materials were exposed to an intense electron probe by aberration corrected scanning transmission electron microscopy (STEM) with simultaneous acquisition of electron energy loss spectroscopy (EELS) data. Electron beam damage was identified by changes of the core loss fine structure after quantification by a refined and improved model based approach. At 200 kV acceleration voltage, damage in SrTiO$_3$ was identified by changes both in the EEL fine structure and by contrast changes in the STEM images. However, the changes in the STEM image contrast as introduced by minor damage can be difficult to detect under several common experimental conditions. No damage was observed in SrTiO$_3$ at 80 kV acceleration voltage, independent of probe current and exposure time. In La$_{0.7}$Sr$_{0.3}$MnO$_3$, beam damage was observed at both 80 and 200 kV acceleration voltages. This damage was observed by large changes in the EEL fine structure, but not by any detectable changes in the STEM images. The typical method to validate if damage has been introduced during acquisitions is to compare STEM images prior to and after spectroscopy. Quantifications in this work show that this method possibly can result in misinterpretation of beam damage as changes of material properties.

cond-mat.mtrl-sci↗

arXiv2016

Thickness and temperature dependence of the magnetodynamic damping of pulsed laser deposited $\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ on (111)-oriented SrTi$\text{O}_3$

We have investigated the magnetodynamic properties of $\text{La}_{0.7}\text{Sr}_{0.3}\text{MnO}_3$ (LSMO) films of thickness 10, 15 and 30 nm grown on (111)-oriented SrTi$\text{O}_3$ (STO) substrates by pulsed laser deposition. Ferromagnetic resonance (FMR) experiments were performed in the temperature range 100--300 K, and the magnetodynamic damping parameter $α$ was extracted as a function of both film thickness and temperature. We found that the damping is lowest for the intermediate film thickness of 15 nm with $α\approx 2 \cdot 10^{-3}$, where $α$ is relatively constant as a function of temperature well below the Curie temperature of the respective films.

cond-mat.mes-hall↗