Search results for "engineering"
showing 10 items of 44231 documents
Spin Hall magnetoresistance in antiferromagnetic insulators
2020
Antiferromagnetic materials promise improved performance for spintronic applications, as they are robust against external magnetic field perturbations and allow for faster magnetization dynamics compared to ferromagnets. The direct observation of the antiferromagnetic state, however, is challenging due to the absence of a macroscopic magnetization. Here, we show that the spin Hall magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic spin structure via simple electrical transport experiments by investigating the easy-plane antiferromagnetic insulators $\alpha$-Fe2O3 (hematite) and NiO in bilayer heterostructures with a Pt heavy metal top electrode. While rotating an ext…
An insulating doped antiferromagnet with low magnetic symmetry as a room temperature spin conduit
2020
We report room temperature long-distance spin transport of magnons in antiferromagnetic thin film hematite doped with Zn. The additional dopants significantly alter the magnetic anisotropies, resulting in a complex equilibrium spin structure that is capable of efficiently transporting spin angular momentum at room temperature without the need for a well-defined, pure easy-axis or easy-plane anisotropy. We find intrinsic magnon spin-diffusion lengths of up to 1.5 {\mu}m, and magnetic domain governed decay lengths of 175 nm for the low frequency magnons, through electrical transport measurements demonstrating that the introduction of non-magnetic dopants does not strongly reduce the transport…
Tailoring the anomalous Hall effect of SrRuO$_3$ thin films by strain: a first principles study
2021
Motivated by the recently observed unconventional Hall effect in ultra-thin films of ferromagnetic SrRuO$_3$ (SRO) we investigate the effect of strain-induced oxygen octahedral distortion in the electronic structure and anomalous Hall response of the SRO ultra-thin films by virtue of density functional theory calculations. Our findings reveal that the ferromagnetic SRO films grown on SrTiO$_3$ (in-plane strain of $-$0.47$\%$) have an orthorhombic (both tilting and rotation) distorted structure and with an increasing amount of substrate-induced compressive strain the octahedral tilting angle is found to be suppressed gradually, with SRO films grown on NdGaO$_3$ (in-plane strain of $-$1.7$\%$…
Large Zero-Field Cooled Exchange-Bias in BulkMn2PtGa
2013
We report a large exchange-bias (EB) effect after zero-field cooling the new tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The first-principle calculation and the magnetic measurements reveal that Mn2PtGa orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that ferrimagnetic (FI) ordering is essential to isothermally induce the exchange anisotropy needed for the zero-field cooled (ZFC) EB during the virgin magnetization process. The complex magnetic behavior at low temperatures is characterized by the coexistence of a field induced irreversible magnetic behavior and a spin-glass-like phase. The field induced irreversibility originates from an unusual…
Phase segregation in Mg$_{x}$Zn$_{1-x}$O probed by optical absorption and photoluminescence at high pressure
2017
The appearance of segregated wurtzite Mg$_x$Zn$_{1-x}$O with low Mg content in thin films with $x>0.3$ affected by phase separation, cannot be reliably probed with crystallographic techniques owing to its embedded nanocrystalline configuration. Here we show a high-pressure approach which exploits the distinctive behaviors under pressure of wurtzite Mg$_x$Zn$_{1-x}$O thin films with different Mg contents to unveil phase segregation for $x>0.3$. By using ambient conditions photoluminescence (PL), and with optical absorption and PL under high pressure for $x=0.3$ we show that the appearance of a segregated wurtzite phase with a magnesium content of x $\sim$ 0.1 is inherent to the wurtzit…
Effective strain manipulation of the antiferromagnetic state of polycrystalline NiO
2021
As a candidate material for applications such as magnetic memory, polycrystalline antiferromagnets offer the same robustness to external magnetic fields, THz spin dynamics, and lack of stray field as their single crystalline counterparts, but without the limitation of epitaxial growth and lattice matched substrates. Here, we first report the detection of the average Neel vector orientiation in polycrystalline NiO via spin Hall magnetoresistance (SMR). Secondly, by applying strain through a piezo-electric substrate, we reduce the critical magnetic field required to reach a saturation of the SMR signal, indicating a change of the anisotropy. Our results are consistent with polycrystalline NiO…
Amorphous ultra-wide bandgap ZnOx thin films deposited at cryogenic temperatures
2020
Crystalline wurtzite zinc oxide (w-ZnO) can be used as a wide band gap semiconductor for light emitting devices and for transparent or high temperature electronics. The use of amorphous zinc oxide (a-ZnO) can be an advantage in these applications. In this paper we report on X-ray amorphous a-ZnOx thin films (~500 nm) deposited at cryogenic temperatures by reactive magnetron sputtering. The substrates were cooled by a nitrogen flow through the copper substrate holder during the deposition. The films were characterized by X-ray diffraction (XRD), Raman, infrared, UV-Vis-NIR spectroscopies, and ellipsometry. The a-ZnOx films on glass and Ti substrates were obtained at the substrate holder temp…
Dielectric response of BaTiO3 electronic states under AC fields via microsecond time-resolved X-ray absorption spectroscopy
2021
Abstract For the first time, the dielectric response of a BaTiO 3 thin film under an AC electric field is investigated using microsecond time-resolved X-ray absorption spectroscopy at the Ti K-edge in order to clarify correlated contributions of each constituent atom on the electronic states. Intensities of the pre-edge e g peak and shoulder structure just below the main edge increase with an increase in the amplitude of the applied electric field, whereas that of the main peak decreases in an opposite manner. Based on the multiple scattering theory, the increase and decrease of the e g and main peaks are simulated for different Ti off-center displacements. Our results indicate that these s…
Optical properties of GaSe, characterization and simulation
2021
Abstract The study focuses on structural and optical characterizations and properties of the GaSe lamellar material in one hand and on a numerical simulation of the photovoltaic properties of the ITO/GaSe heterojunction in a second hand. A few layers of GaSe were exfoliated from bulk GaSe on PET substrate. The optical transmission was recorded at room temperature. It shows that GaSe exhibits both indirect and direct band gaps of about 1.92 and 2.2 eV respectively. A value, as high as 104 cm−1, of the absorption coefficient was obtained. The corresponding refractive index has been determined numerically according to the Sellmeier and Cauchy models. The interesting value of absorption shows o…
A half-metallic half-Heusler alloy having the largest atomic-like magnetic moment at optimized lattice constant
2016
For half-Heusler alloys, the general formula is XYZ, where X can be a transition or alkali metal element, Y is another transition metal element, typically Mn or Cr, and Z is a group IV element or a pnicitide. The atomic arrangements within a unit-cell show three configurations. Before this study, most of the predictions of half-metallic properties of half-Heusler alloys at the lattice constants differing from their optimized lattice constant. Based on the electropositivity of X and electronegativity of Z for half-Heusler alloys, we found that one of the configurations of LiCrS exhibits half-metallic properties at its optimized lattice constant of 5.803Å, and has the maximum atomic-like magn…