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Magnetic field-induced changes in the electrical resistance of materials reveal insights into the fundamental properties governing their electronic and magnetic behavior. Various classes of magnetoresistance have been realized, including giant, colossal, and extraordinary magnetoresistance, each with distinct physical origins. In recent years, extreme magnetoresistance (XMR) has been observed in topological and non-topological materials displaying a non-saturating magnetoresistance reaching 10 3 −10 8 % in magnetic fields up to 60 T. XMR is often intimately linked to a gapless band structure with steep bands and charge compensation. Here, we show that a linear XMR of 80,000% at 15 T and 2 K emerges at the high-mobility interface between the large band-gap oxides γ-Al 2 O 3 and SrTiO 3 . Despite the chemically and electronically very dissimilar environment, the temperature/field phase diagrams of γ-Al 2 O 3 /SrTiO 3 bear a striking resemblance to XMR semimetals. By comparing magnetotransport, microscopic current imaging, and momentum-resolved band structures, we conclude that the XMR in γ-Al 2 O 3 /SrTiO 3 is not strongly linked to the band structure, but arises from weak disorder enforcing a squeezed guiding center motion of electrons. We also present a dynamic XMR self-enhancement through an autonomous redistribution of quasi-mobile oxygen vacancies. Our findings shed new light on XMR and introduce tunability using dynamic defect engineering. Extreme magnetoresistance is characterized by a large and non-saturating magnetoresistance. Typically, it is observed in materials with compensated bandstructures, however, here, Christensen et al demonstrate a large and non-saturating magnetoresistance in a γAl2O3/SrTiO3 heterostructure, which is related to disorder, rather than the materials bandstructure.

Ferromagnetism is observed at ferroelastic domain walls in strontium titanate and its heterostructures with other oxides. Applying strain can reverse the magnetism. This suggests the possibility of device engineering using domain walls.

Two-dimensional electron gases (2DEGs) formed at the interface of insulating complex oxides promise the development of all-oxide electronic devices. These 2DEGs involve many-body interactions that give rise to a variety of physical phenomena such as superconductivity, magnetism, tunable metal–insulator transitions and phase separation. Increasing the mobility of the 2DEG, however, remains a major challenge. Here, we show that the electron mobility is enhanced by more than two orders of magnitude by inserting a single-unit-cell insulating layer of polar La 1− x Sr x MnO 3 ( x = 0, 1/8, and 1/3) at the interface between disordered LaAlO 3 and crystalline SrTiO 3 produced at room temperature. Resonant X-ray spectroscopy and transmission electron microscopy show that the manganite layer undergoes unambiguous electronic reconstruction, leading to modulation doping of such atomically engineered complex oxide heterointerfaces. At low temperatures, the modulation-doped 2DEG exhibits Shubnikov–de Haas oscillations and fingerprints of the quantum Hall effect, demonstrating unprecedented high mobility and low electron density. The insertion of La 1− x Sr x MnO 3 in the interface between LaAlO 3 and SrTiO 3 enhances the electron mobility due to charge-transfer-induced modulation doping. Shubnikov–de Haas oscillations and fingerprints of the quantum Hall effect are observed.

The discovery of two-dimensional electron gases at the heterointerface between two insulating perovskite-type oxides, such as LaAlO 3 and SrTiO 3 , provides opportunities for a new generation of all-oxide electronic devices. Key challenges remain for achieving interfacial electron mobilities much beyond the current value of approximately 1,000 cm 2  V -1  s -1 (at low temperatures). Here we create a new type of two-dimensional electron gas at the heterointerface between SrTiO 3 and a spinel γ-Al 2 O 3 epitaxial film with compatible oxygen ions sublattices. Electron mobilities more than one order of magnitude higher than those of hitherto-investigated perovskite-type interfaces are obtained. The spinel/perovskite two-dimensional electron gas, where the two-dimensional conduction character is revealed by quantum magnetoresistance oscillations, is found to result from interface-stabilized oxygen vacancies confined within a layer of 0.9 nm in proximity to the interface. Our findings pave the way for studies of mesoscopic physics with complex oxides and design of high-mobility all-oxide electronic devices. Highly mobile electrons at the interface of two perovskite oxides are of considerable interest for electronic applications. In this work, the discovery of such an electron gas at the interface of a spinel and a perovskite oxide represents a new approach to look for oxide systems with enhanced properties.

Considering the growing interest in magnetic materials for unconventional computing, data storage, and sensor applications, there is active research not only on material synthesis but also characterisation of their properties. In addition to structural and integral magnetic characterisations, imaging of magnetisation patterns, current distributions and magnetic fields at nano- and microscale is of major importance to understand the material responses and qualify them for specific applications. In this roadmap, we aim to cover a broad portfolio of techniques to perform nano- and microscale magnetic imaging using superconducting quantum interference devices, spin centre and Hall effect magnetometries, scanning probe microscopies, x-ray- and electron-based methods as well as magnetooptics and nanoscale magnetic resonance imaging. The roadmap is aimed as a single access point of information for experts in the field as well as the young generation of students outlining prospects of the development of magnetic imaging technologies for the upcoming decade with a focus on physics, materials science, and chemistry of planar, three-dimensional and geometrically curved objects of different material classes including two-dimensional materials, complex oxides, semi-metals, multiferroics, skyrmions, antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic conductors, superconductors, spintronic and spinorbitronic materials.

Interfaces between complex oxides host a plethora of functional properties including enhanced ionic conductivity, gate-tunable superconductivity and exotic magnetic states. The enhanced electronic, ionic and magnetic properties along the oxide interfaces are generally exploited in functional devices by spatial confinement of ions and electrons. Different patterning methods have been used to spatially control the conductivity at the interface, but a key limitation is the multiple steps needed to fabricate functional devices. In this investigation, inkjet printing of thermally stable oxides is introduced as an alternative pathway for spatially controlling the interface conductivity. We inkjet print yttrium-stabilized zirconia and TiO2 with various shapes and use these as physical masks to confine the electronic conductivity in SrTiO3-based heterostructures. By performing in-situ transport measurements of the electrical conductivity as LaAlO3 and γ-Al2O3 are deposited on SrTiO3, we witness the birth of the interface conductivity and find a consistent transient behavior as conductivity emerges in patterned and non-patterned heterostructures. We find that conductivity appears after the first laser pulse in the pulsed laser deposition corresponding to the film covering only a few percent of the substrate. We attribute the emergence of conductivity to oxygen vacancies formed by a combination of plasma bombardment and oxygen transfer across the interface during growth. In this vein, inkjet patterned hard masks protects the SrTiO3 substrate, effectively confining the conductivity. The study paves a scalable way for realizing energy devices with spatially controlled electronic and ionic interface conductivity.

Interfaces between complex oxides host a plethora of functional properties including enhanced ionic conductivity, gate-tunable superconductivity and exotic magnetic states. The enhanced electronic, ionic and magnetic properties along the oxide interfaces are generally exploited in functional devices by spatial confinement of ions and electrons. Different patterning methods have been used to spatially control the conductivity at the interface, but a key limitation is the multiple steps needed to fabricate functional devices. In this investigation, inkjet printing of thermally stable oxides is introduced as an alternative pathway for spatially controlling the interface conductivity. We inkjet print yttrium-stabilized zirconia and TiO 2 with various shapes and use these as physical masks to confine the electronic conductivity in SrTiO 3 -based heterostructures. By performing in-situ transport measurements of the electrical conductivity as LaAlO 3 and γ -Al 2 O 3 are deposited on SrTiO 3 , we witness the birth of the interface conductivity and find a consistent transient behavior as conductivity emerges in patterned and non-patterned heterostructures. We find that conductivity appears after the first laser pulse in the pulsed laser deposition corresponding to the film covering only a few percent of the substrate. We attribute the emergence of conductivity to oxygen vacancies formed by a combination of plasma bombardment and oxygen transfer across the interface during growth. In this vein, inkjet patterned hard masks protects the SrTiO 3 substrate, effectively confining the conductivity. The study paves a scalable way for realizing energy devices with spatially controlled electronic and ionic interface conductivity.

The magnetic and electronic nature of the gamma-Al2O3/SrTiO3 spinel/perovskite interface is explored by means of x-ray absorption spectroscopy. Polarized x-ray techniques combined with atomic multiplet calculations reveal localized magnetic moments assigned to Ti3+ at the interface with equivalent size for in- and out-of-plane magnetic field directions. Although magnetic fingerprints are revealed, the Ti3+ magnetism can be explained by a paramagnetic response at low temperature under applied magnetic fields. Modeling the x-ray linear dichroism results in a delta0 = 1.9 eV splitting between the t2g and eg states for the Ti4+ 3d0 orbitals. In addition these results indicate that the lowest energy states have the out-of-plane dxz/dyz symmetry. The isotropic magnetic moment behavior and the lowest energy dxz/dyz states are in contrast to the observations for the two-dimensional electron gas at the perovskite/perovskite interface of LaAlO3/SrTiO3, that exhibits an anisotropic magnetic dxy ground state.

Modulation-doped oxide two-dimensional electron gas (2DEG) formed at the LaMnO3 (LMO) buffered disorderd-LaAlO3/SrTiO3 (d-LAO/LMO/STO) heterointerface, provides new opportunities for electronics as well as quantum physics. Herein, we studied the dependence of Sr-doping of La1-xSrxMnO3 (LSMO, x=0, 1/8, 1/3, 1/2, and 1) thus the filling of the Mn eg subbands as well as the LSMO polarity on the transport properties of d-LAO/LSMO/STO. Upon increasing the LSMO film thickness from 1 unit cell (uc) to 2 uc, a sharp metal to insulator transition of interface conduction was observed, independent of x. The resultant electron mobility is often higher than 1900 cm2V-1s-1 at 2 K, which increases upon decreasing x. The sheet carrier density, on the other hand, is in the range of 6.9E1012~1.8E1013 cm-2 (0.01~0.03 e/uc) and is largely independent on x for all the metallic d-LAO/LSMO (1 uc)/STO interfaces. These results are consistent with the charge transfer induced modulation doping scheme and clarify that the polarity of the buffer layer plays a trivial role on the modulation doping. The negligible tunability of the carrier density could result from the reduction of LSMO during the deposition of disordered LAO or that the energy levels of Mn 3d electrons at the interface of LSMO/STO are hardly varied even when changing the LSMO composition from LMO to SrMnO3.

A 3D thermoelectric numerical model is used to investigate different internal heat loss mechanisms for a thermoelectric generator with bismuth telluride p- and n-legs. The model considers all thermoelectric effects, temperature dependent material parameters and simultaneous convective, conductive and radiative heat losses, including surface to surface radiation. For radiative heat losses it is shown that for the temperatures considered here, surface to ambient radiation is a good approximation of the heat loss. For conductive heat transfer the module efficiency is shown to be comparable to the case of radiative losses. Finally, heat losses due to internal natural convection in the module is shown to be negligible for the millimetre sized modules considered here. The combined case of radiative and conductive heat transfer resulted in the lowest efficiency. The optimized load resistance is found to decrease for increased heat loss. The leg dimensions are varied for all heat losses cases and it is shown that the ideal way to construct a TEG module with minimal heat losses and maximum efficiency is to either use a good insulating material between the legs or evacuate the module completely, and use small and wide legs closely spaced.