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Register a new userMagneto-elastic Effects in $text{Tb}_{3}text{Ga}_{5}text{O}_{12}$
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We report new results for the elastic constants studied in Faraday and Cotton-Mouton geometry in Tb$_3$Ga$_5$O$_{12}$ (TGG), a frustrated magnetic substance with strong spin-phonon interaction and remarkable crystal-electric-field (CEF) effects. We analyze the data in the framework of CEF theory taking into account the individual surroundings of the six inequivalent Tb$^{3+}$-ion positions. This theory describes both, elastic constants in the magnetic field and as a function of temperature. Moreover we present sound-attenuation data for the acoustic Cotton-Mouton effect in TGG.
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Reversible hydrogen incorporation was recently attested [N. Lu, $textit{et al.}$, Nature $textbf{546}$, 124 (2017)] in ${text{SrCo}text{O}_{2.5}}$, the brownmillerite phase (BM) of strontium cobalt oxide (SCO), opening new avenues in catalysis and energy applications. However, existing theoretical studies of BM-SCO are insufficient, and that of ${text{HSrCo}text{O}_{2.5}}$, the newly-reported hydrogenated SCO (H-SCO), is especially scarce. In this work, we demonstrate how the electron-counting model (ECM) can be used in understanding the phases, particularly in explaining the stability of the oxygen-vacancy channels (OVCs), and in examining the Co valance problem. Using density-functional theoretical (DFT) methods, we analyze the crystalline, electronic, and magnetic structures of BM- and H-SCO. Based on our structure search, we discovered stable phases with large bandgaps (> 1 eV) for both BM-SCO and H-SCO, agreeing better with experiments on the electronic structures. Our calculations also indicate limited charge transfer from H to O that may explain the special stability of the H-SCO phase and the reversibility of H incorporation observed in experiments. In contrary to the initial study, our calculation also suggests intrinsic antiferromagnetism (AFM) of H-SCO, showing how the measured ferromagnetism (FM) has possible roots in hole doping.
The magnetic state of heavy metal Pt thin films in proximity to the ferrimagnetic insulator Y$_{3}$Fe$_{5}$O$_{12}$ has been investigated systematically by means of x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity measurements combined with angle-dependent magnetotransport studies. To reveal intermixing effects as the possible cause for induced magnetic moments in Pt, we compare thin film heterostructures with different order of the layer stacking and different interface properties. For standard Pt layers on Y$_{3}$Fe$_{5}$O$_{12}$ thin films, we do not detect any static magnetic polarization in Pt. These samples show an angle-dependent magnetoresistance behavior, which is consistent with the established spin Hall magnetoresistance. In contrast, for the inverted layer sequence, Y$_{3}$Fe$_{5}$O$_{12}$ thin films grown on Pt layers, Pt displays a finite induced magnetic moment comparable to that of all-metallic Pt/Fe bilayers. This magnetic moment is found to originate from finite intermixing at the Y$_{3}$Fe$_{5}$O$_{12}$/Pt interface. As a consequence, we found a complex angle-dependent magnetoresistance indicating a superposition of the spin Hall and the anisotropic magnetoresistance in these type of samples. Both effects can be disentangled from each other due to their different angle dependence and their characteristic temperature evolution.
Temperature-dependent London penetration depth, $lambda(T)$, of a high quality optimally-doped $text{YBa}_{2}text{Cu}_{3}text{O}_{7-delta}$ single crystal was measured using tunnel-diode-resonator technique. Controlled artificial disorder was induced by low-temperature (20~K) irradiation by 2.5 MeV electrons at two large doses of $3.8times10^{19}$and $5.3times10^{19}$ electrons per $textrm{cm}^{2}$. The irradiation caused significant suppression of the superconductors critical temperature, $T_{c}$, from 94.6 K to 90.0 K, and to 78.7 K, respectively. The low-temperature behavior of $lambdaleft(Tright)$ evolves from a $T-$ linear in pristine state to a $T^{2}-$ behavior after irradiation, expected for a line-nodal $d-$wave superconductor. However, the original theory that explained such behavior assumed a unitary limit of the scattering potential, whereas usually in normal metals and semiconductors, Born scattering is sufficient to describe the experiment. To estimate the scattering potential strength, we calculated the superfluid density, $rho_{s}=lambda^{2}left(0right)/lambda^{2}left(Tright)$, varying the amount and strength of non-magnetic scattering using a self-consistent $t-$matrix theory. Comparing experimental and theoretical coefficients $A$ and $B$ of the low-temperature power series, $rho_{s}approx1-At-Bt^{2}$, we determine the amplitude of the scattering phase shift to be around 65$^{o}$. Knowing this value is important for further theoretical analysis of the microscopic mechanisms of superconductivity in $text{YBa}_{2}text{Cu}_{3}text{O}_{7-delta}$ high$-T_{c}$ superconductor.
$text{BiFeO}_text{3}$ has drawn a great attention over last several decades due to its promising multiferroic character. In the ground state the bulk $text{BiFeO}_text{3}$ is found to be in the rhombohedral phase. However, it has been possible to stabilize $text{BiFeO}_text{3}$ with tetragonal structure. The importance of tetragonal phase is due to its much larger value of the electric polarization and the possible stabilization of ferromagnetism as in the rhombohedral phase. Furthermore, the tetragonal structure of $text{BiFeO}_text{3}$ has been reported with different $c/a$ ratio, opening up the possibility of a much richer set of electronic phases. In this work, we have used density functional theory based first-principle method to study the ferromagnetic phase of the tetragonal $text{BiFeO}_text{3}$ structure as a function of the $c/a$ ratio. We have found that as the $c/a$ ratio decreases from $1.264$ to $1.016$, the tetragonal $text{BiFeO}_text{3}$ evolve from a ferromagnetic semiconductor to a ferromagnetic metal, while passing through a emph{half-metallic} phase. This evolution of the electronic properties becomes even more interesting when viewed with respect to the volume of each structure. The most stable half-metallic phase initially counter-intuitively evolve to the magnetic-semiconducting phase with a reduction in the volume, and after further reduction in the volume it finally becomes a metal. So far, this type of metal to insulator transition on compression was known to exist only in alkali metals, especially in Lithium, in heavy alkaline earth metals, and in some binary compound.
Epitaxial perovskite oxide interfaces with different symmetry of the epitaxial layers have attracted considerable attention due to the emergence of novel behaviors and phenomena. In this paper, we show by aberration corrected transmission electron microscopy that orthorhombic $text{LaInO}_text{3}$ films grow in form of three different types of domains on the cubic $text{BaSnO}_text{3}$ pseudosubstrate. Quantitative evaluation of our TEM data shows that $c_{pc}$-oriented and $a_{pc}/b_{pc}$-oriented domains are present with similar probability. While continuum elasticity theory suggests that $c_{pc}$-oriented domains should exhibit a significantly higher strain energy density than $a_{pc}/b_{pc}$-oriented domains, density functional calculations confirm that $c_{pc}$- and $a_{pc}$-oriented domains on $text{BaSnO}_text{3}$ have similar energies.
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