28 research outputs found
Absence of long-range chemical ordering in equimolar FeCoCrNi
Equimolar FeCoCrNi alloys have been the topic of recent research as "high-entropy alloys," where the name is derived from the high configurational entropy of mixing for a random solid solution. Despite their name, no systematic study of ordering in this alloy system has been performed to
date. Here, we present results from anomalous x-ray scattering and neutron scattering on quenched and annealed samples. An alloy of FeNi_3 was prepared in the same manner to act as a control. Evidence of long-range chemical ordering is clearly observed in the annealed FeNi_3 sample from both experimental techniques. The FeCoCrNi sample given the same heat treatment lacks long-range chemical order
Control of octahedral rotations in (LaNiO)/(SrMnO) superlattices
Oxygen octahedral rotations have been measured in short-period
(LaNiO)/(SrMnO) superlattices using synchrotron diffraction.
The in-plane and out-of-plane bond angles and lengths are found to
systematically vary with superlattice composition. Rotations are suppressed in
structures with , producing a nearly cubic form of LaNiO. Large
rotations are present in structures with , leading to reduced bond angles
in SrMnO. The metal-oxygen-metal bond lengths decrease as rotations are
reduced, in contrast to behavior previously observed in strained, single layer
films. This result demonstrates that superlattice structures can be used to
stabilize non-equilibrium octahedral behavior in a manner distinct from
epitaxial strain, providing a novel means to engineer the electronic and
ferroic properties of oxide heterostructures.Comment: 4 pages, 4 figures, submitted to PR
Decoupling carrier concentration and electron-phonon coupling in oxide heterostructures observed with resonant inelastic x-ray scattering
We report the observation of multiple phonon satellite features in ultra thin
superlattices of form SrIrO/SrTiO using resonant inelastic x-ray
scattering. As the values of and vary the energy loss spectra show a
systematic evolution in the relative intensity of the phonon satellites. Using
a closed-form solution for the cross section, we extract the variation in the
electron-phonon coupling strength as a function of and . Combined with
the negligible carrier doping into the SrTiO layers, these results indicate
that tuning of the electron-phonon coupling can be effectively decoupled from
doping. This work showcases both a feasible method to extract the
electron-phonon coupling in superlattices and unveils a potential route for
tuning this coupling which is often associated with superconductivity in
SrTiO-based systems.Comment: 4 pages, 5 figure
Charge transport and magnetization profile at the interface between a correlated metal and an antiferromagnetic insulator
A combination of spectroscopic probes was used to develop a detailed
experimental description of the transport and magnetic properties of
superlattices composed of the paramagnetic metal CaRuO and the
antiferromagnetic insulator CaMnO. The charge carrier density and Ru
valence state in the superlattices are not significantly different from those
of bulk CaRuO. The small charge transfer across the interface implied by
these observations confirms predictions derived from density functional
calculations. However, a ferromagnetic polarization due to canted Mn spins
penetrates 3-4 unit cells into CaMnO, far exceeding the corresponding
predictions. The discrepancy may indicate the formation of magnetic polarons at
the interface.Comment: 4 pages, 3 figure
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Enhanced interfacial ferromagnetism and exchange bias in (111)-oriented LaNiO3/CaMnO3 superlattices
Emergent properties of complex oxide interfaces are based on interface reconstruction that is driven by mismatch of electronic bands, valence states, interaction lengths, and even crystal symmetry of the interface. In particular, emergent ferromagnetism at the interface of two materials that do not exhibit ferro- or ferrimagnetism in the bulk has been stabilized as a result of competing exchange interactions. When LaNiO3 and CaMnO3, which are a paramagnetic metal and antiferromagnetic insulator in the bulk, respectively, are brought together, ferromagnetism emerges at the interface. Here we show that in (111)-oriented LaNiO3/CaMnO3 (LNO/CMO) superlattices, Ni2+-Mn4+ superexchange interactions due to polar mismatch at the LNO/CMO interfaces are responsible for the emergent ferromagnetism. Compared to (001)-oriented LNO/CMO superlattices, (111)-oriented LNO/CMO superlattices exhibit enhanced interfacial ferromagnetism with a TC>200 K, greater than the bulk antiferromagnetic transition temperature of CaMnO3 and a saturated magnetic moment enhanced by up to a factor of 3. Furthermore, we observe exchange bias in (111)-oriented superlattices. The strong exchange interactions along the (111) interface, manifest in the enhanced Tc and exchange bias, make this class of CMO-based materials with (111)-oriented interfaces good candidates for low-dimensional spin-polarized materials in spintronic applications