Abstract: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 Xray 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 heterostru… Show more
“…The calculated in-plane lattice parameter of the SCO layer is 3.868 Å, the same as that of the LSAT substrate, which further confirms the strained nature of the SCO layer in both the single-layer film and the heterostructure. On the other hand, the lattice parameter of LSMO in the cubic notation is 3.875 Å, 11 slightly greater than that of the LSAT substrate, and therefore, is buried under the reflections of the latter. Besides, the thickness of the LSMO layers is only 9 uc, which is close to 3.5 nm, and therefore it would be hard to detect from the labbased diffractometer.…”
A strained SrCoO2.5 thin
film possesses negative charge
transfer energy (Δ) and charge disproportionation. In the La0.7Sr0.3MnO3/SrCoO2.5 heterostructure,
it is observed that the interfacial strong covalent bonding increases
the value of negative Δ of the SrCoO2.5 layer, while
charge transfer from the La0.7Sr0.3MnO3 layer melts the charge disproportionation in the SrCoO2.5 layer. Strain-stabilized c-axis orbital polarization
is observed in the interfacial Mn/Co ions of the heterostructure.
The Co 3d orbital reconstruction is found in the heterostructure due
to the strong covalent bond created between the Co 3d and Mn 3d orbitals
at the interface. The antiferromagnetic coupling between the Mn and
Co ions is observed at the interface of ferromagnetic La0.7Sr0.3MnO3 and SrCoO2.5 layers, which
is envisaged from the interfacial Mn/Co orbital polarization and molecular
orbital picture. Importantly, such antiferromagnetic coupling observed
at room temperature will be very helpful in energy-efficient spintronic
applications. The antiferromagnetic interaction at the interfacial
region between the ferromagnetic layers produces the exchange-bias
effect in the heterostructure. Our result demonstrates valuable insight
into the correlation between the electronic states and the magnetic
interactions in the artificially intricated heterostructure containing
charge-disproportionated insulator and metal to investigate novel
interfacial phenomena in other such heterostructures and superlattices.
“…The calculated in-plane lattice parameter of the SCO layer is 3.868 Å, the same as that of the LSAT substrate, which further confirms the strained nature of the SCO layer in both the single-layer film and the heterostructure. On the other hand, the lattice parameter of LSMO in the cubic notation is 3.875 Å, 11 slightly greater than that of the LSAT substrate, and therefore, is buried under the reflections of the latter. Besides, the thickness of the LSMO layers is only 9 uc, which is close to 3.5 nm, and therefore it would be hard to detect from the labbased diffractometer.…”
A strained SrCoO2.5 thin
film possesses negative charge
transfer energy (Δ) and charge disproportionation. In the La0.7Sr0.3MnO3/SrCoO2.5 heterostructure,
it is observed that the interfacial strong covalent bonding increases
the value of negative Δ of the SrCoO2.5 layer, while
charge transfer from the La0.7Sr0.3MnO3 layer melts the charge disproportionation in the SrCoO2.5 layer. Strain-stabilized c-axis orbital polarization
is observed in the interfacial Mn/Co ions of the heterostructure.
The Co 3d orbital reconstruction is found in the heterostructure due
to the strong covalent bond created between the Co 3d and Mn 3d orbitals
at the interface. The antiferromagnetic coupling between the Mn and
Co ions is observed at the interface of ferromagnetic La0.7Sr0.3MnO3 and SrCoO2.5 layers, which
is envisaged from the interfacial Mn/Co orbital polarization and molecular
orbital picture. Importantly, such antiferromagnetic coupling observed
at room temperature will be very helpful in energy-efficient spintronic
applications. The antiferromagnetic interaction at the interfacial
region between the ferromagnetic layers produces the exchange-bias
effect in the heterostructure. Our result demonstrates valuable insight
into the correlation between the electronic states and the magnetic
interactions in the artificially intricated heterostructure containing
charge-disproportionated insulator and metal to investigate novel
interfacial phenomena in other such heterostructures and superlattices.
“…This would then decrease the hopping transport probability and consequently decrease the mobile hole density responsible for p-type electrical (semi)conductivity by small polaron hopping. Additionally, a Jahn–Teller-like distortion may occur as observed in CrO 2 or other perovskite oxides such as La 2/3 Sr 1/3 MnO 3 , , LaCoO 3 , and SrVO 3 , where in-plane tensile strain would lower and favor the occupied in-plane Cr 3d t 2g ( xy ) orbital ground state (Figure ). On the contrary, the biaxial in-plane compressive strain (smaller Cr–O bond length, ⟨Cr–O–Cr⟩ bond angle than 162°, and unit-cell volume) would increase the Cr 3d–O 2p orbital hybridization (bandwidth) and/or lower the occupied out-of-plane Cr 3d t 2g ( xz and yz ) orbitals that would tend to be more delocalized and increase the hopping transport probability (Figure ).…”
Section: Results
and Discussionmentioning
confidence: 99%
“…This would then decrease the hopping transport probability and consequently decrease the mobile hole density responsible for p-type electrical (semi)conductivity by small polaron hopping. Additionally, a Jahn-Teller like distortion may occur as observed in CrO2 67 or other perovskite oxides such as La2/3Sr1/3MnO3 39,68 , LaCoO3 41 and SrVO3 19 where in-plane tensile strain would lower and favor the occupied in-plane Cr 3d t2g (xy) orbital ground state (Figure 6).…”
The impact of epitaxial strain on the structural, electronic, and thermoelectric properties of p-type transparent Sr-doped LaCrO3 thin films has been investigated. For this purpose, high-quality fully-strained La0.75Sr0.25CrO3 (LSCO) epitaxial thin films were grown by molecular beam epitaxy on three different (pseudo)cubic ( 001)-oriented perovskite-oxide substrates: LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and DyScO3. The lattice mismatch between the LSCO films and the substrates induces in-plane strain ranging from -2.06% (compressive) to +1.75% (tensile). The electric conductivity can be controlled over two orders of magnitude, σ ranging from ~0.5 S cm -1 (tensile strain) to 35 S cm -1 (compressive strain). Consistently, the Seebeck coefficient S can be finely tuned by a factor of almost two from ~127 µV K -1 (compressive strain) to 208 µV K -1 (tensile strain). Interestingly, we show that the thermoelectric power factor (PF = S 2 σ) can consequently be tuned by almost two orders of magnitude. The compressive strain yields a remarkable enhancement by a factor of three for 2% compressive strain with respect to almost relaxed films. These results demonstrate that epitaxial strain is a powerful lever to control the electric properties of LSCO and enhance its thermoelectric properties, which is of high interest for various devices and key applications such as thermal energy harvesters, coolers, transparent conductors, photo-catalyzers and spintronic memories.
“…Transition metal compounds exhibit electronic properties of high scientific and technological interest, including ferroelectricity [1][2][3][4], quantum magnetism [5][6][7][8][9][10], metal-insulator transitions [11][12][13][14][15][16][17][18][19][20][21] , and high transitiontemperature superconductivity [22][23][24][25][26]. Transition metal oxides derived from the AMO 3 perovskite structure have been a focus of particular attention because any 3d or 4d transition metal can occupy the M site with (typically) partially filled d shells, while variation of the A-site ion can tune the relative valence of the M site ion and the electronic bandwidth.…”
We study the consequences of the approximately trigonal (D 3d ) point symmetry of the transition metal (M) site in two-dimensional van der Waals MX2 dihalides and MX3 trihalides. The trigonal symmetry leads to a 2-2-1 orbital splitting of the transition metal d shell, which may be tuned by the interlayer distance, and changes in the ligand-ligand bond lengths. Orbital order coupled to various lower symmetry lattice modes may lift the remaining orbital degeneracies, and we explain how these may support unique electronic states using ZrI2 and CuCl2 as examples, and offer a brief overview of possible electronic configurations in this class of materials. By building and analysing Wannier models adapted to the appropriate symmetry we examine how the interplay among trigonal symmetry, electronic correlation effects, and p-d orbital charge transfer leads to insulating, orbitally polarized magnetic and/or orbital-selective Mott states. Our work establishes a rigorous framework to understand, control, and tune the electronic states in low-dimensional correlated halides. Our analysis shows that trigonal symmetry and its breaking is a key feature of the 2D halides that needs to be accounted for in search of novel electronic states in materials ranging from CrI3 to α-RuCl3.
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