18 research outputs found
Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices; a designed playground for honeycomb physics
We report the fabrication of (111)-oriented superlattice structures with
alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two
layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1
bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological
state may be anticipated. The successful growth of superlattice structures on
an atomic level along the [111] direction was clearly demonstrated by
superlattice reflections in x-ray diffraction patterns and by
atomically-resolved transmission electron microscope images. The ground states
of the superlattice films were found to be magnetic insulators, which may
suggest the importance of electron correlations in Ir perovskites in addition
to the much discussed topological effects.Comment: 14 pages, 4 figure
Spin current generation from an epitaxial tungsten dioxide WO
We report on efficient spin current generation at room temperature in rutile
type WO grown on AlO(0001) substrate. The optimal WO
film has (010)-oriented monoclinically distorted rutile structure with metallic
conductivity due to 5 electrons, as characterized by x-ray
diffraction, electronic transport, and x-ray photoelectron spectroscopy. By
conducting harmonic Hall measurement in NiFe/WO bilayer, we
estimate two symmetries of the spin-orbit torque (SOT), i.e., dampinglike (DL)
and fieldlike ones to find that the former is larger than the latter. By
comparison with the NiFe/W control sample, the observed DL SOT
efficiency of WO (+0.174) is about two thirds of that of W
(-0.281) in magnitude, with a striking difference in their signs. The magnitude
of the of WO exhibits comparable value to those of widely
reported Pt and Ta, and Ir oxide IrO. The positive sign of the
of WO can be explained by the preceding theoretical study
based on the 4 oxides. These results highlight that the epitaxial
WO offers a great opportunity of rutile oxides with spintronic
functionalities, leading to future spin-orbit torque-controlled devices.Comment: 14 pages, 4 figure
Spin-orbit torque generation in bilayers composed of CoFeB and epitaxial SrIrO grown on an orthorhombic DyScO substrate
We report on the highly efficient spin-orbit torque (SOT) generation in
epitaxial SrIrO(SIO), which is grown on an orthorhombic DyScO(110)
substrate. By conducting harmonic Hall measurement in
CoFeB (CoFeB)/SIO bilayers, we characterize two kinds of
the SOTs, i.e., dampinglike (DL) and fieldlike ones to find that the former is
much larger than the latter. By comparison with the Pt control sample with the
same CoFeB thickness, the observed DL SOT efficiency of SIO
(0.32) is three times higher than that of Pt (0.093). The
is nearly constant as a function of the CoFeB thickness,
suggesting that the SIO plays a crucial role in the large SOT generation. These
results on the CoFeB/SIO bilayers highlight that the epitaxial SIO is promising
for low-current and reliable spin-orbit torque-controlled devices.Comment: arXiv admin note: text overlap with arXiv:2305.1788
Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site
Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been
fabricated by the pulsed laser deposition of LixIr2O4 precursor and the
subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a
spinel (AB2O4) without A cations in the tetrahedral site, which is
isostructural to lambda-MnO2. Ir ions form a pyrochlore sublattice, which is
known to give rise to a strong geometrical frustration. This Ir spinel was
found to be a narrow gap insulator, in remarkable contrast to the metallic
ground state of rutile-type IrO2. We argue that an interplay of strong
spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground
state as in a layered perovskite Sr2IrO4.Comment: 9 pages, 3 figure
Strongly correlated oxides for energy harvesting
We review recent advances in strongly correlated oxides as thermoelectric materials in pursuit of energy harvesting. We discuss two topics: one is the enhancement of the ordinary thermoelectric properties by controlling orbital degrees of freedom and orbital fluctuation not only in bulk but also at the interface of correlated oxides. The other topic is the use of new phenomena driven by spin-orbit coupling (SOC) of materials. In 5d electron oxides, we show some SOC-related transport phenomena, which potentially contribute to energy harvesting. We outline the current status and a future perspective of oxides as thermoelectric materials