Using density-functional theory (DFT) and its extension to $\mathrm{DFT}+U$, we propose a possible scenario for a strain-induced metal-insulator transition which was reported recently in thin films of $\mathrm{Sr}\mathrm{Cr}{\mathrm{O}}_3$. The metal-insulator transition involves the emergence of a Jahn-Teller (JT) distortion similar to the case of the related rare-earth vanadates, which also exhibit a nominal $d^2$ occupation of the transition metal cation. Our calculations indicate that, for realistic values of the Hubbard $U$ parameter, the unstrained system exhibits a C-type antiferromagnetically ordered ground state that is already rather close to a JT instability. However, the emergence of the JT distortion is disfavored by the large energetic overlap of the $d_{xz}/d_{yz}$ band with the lower-lying $d_{xy}$ band. Tensile epitaxial strain lowers the energy of the $d_{xy}$ band relative to $d_{xz}/d_{yz}$ and thus brings the system closer to the nominal filling of $d_{xy}^1{\left(d_{xz}{d}_{yz}\right)}^1$. The JT distortion then lifts the degeneracy between the $d_{xz}$ and $d_{yz}$ orbitals and thus allows the material to open up a gap in the electronic band structure.

Orthoferrites are a class of magnetic materials with a magnetic ordering temperature above 600 K, predominant $G$-type antiferromagnetic ordering of the Fe-spin system and, depending on the rare-earth ion, a spin reorientation of the Fe spin taking place at lower temperatures. ${\mathrm{DyFeO}}_3$ is of particular interest since the spin reorientation is classified as a Morin transition with the transition temperature depending strongly on the Dy-Fe interaction. Here, we report a detailed study of the magnetic and structural properties of microcrystalline ${\mathrm{DyFeO}}_3$ powder and bulk single crystal using neutron diffraction and magnetometry between 1.5 and 450 K. We find that, while the magnetic properties of the single crystal are largely as expected, the powder shows strongly modified magnetic properties, including a modified spin reorientation and a smaller Dy-Fe interaction energy of the order of 10 μeV. Subtle structural differences between powder and single crystal show that they belong to distinct magnetic space groups. In addition, the Dy ordering at 2 K in the powder is incommensurate, with a modulation vector of 0.0173(5) $c^{*}$, corresponding to a periodicity of ∼58 unit cells.

In this paper we study ${\mathrm{LaAlO}}_3/{\mathrm{Eu}}_{1-x}{\mathrm{La}}_x{\mathrm{TiO}}_3/{\mathrm{SrTiO}}_3$ structures with nominally $x=0,0.1$ and different thicknesses of the ${\mathrm{Eu}}_{1-x}{\mathrm{La}}_x{\mathrm{TiO}}_3$ layer. We observe that both systems have many properties similar to previously studied ${\mathrm{LaAlO}}_3/{\mathrm{EuTiO}}_3/{\mathrm{SrTiO}}_3$ and other oxide interfaces, such as the formation of a two-dimensional electron liquid for two unit cells of ${\mathrm{Eu}}_{1-x}{\mathrm{La}}_x{\mathrm{TiO}}_3$; a metal-insulator transition driven by the increase in thickness of the ${\mathrm{Eu}}_{1-x}{\mathrm{La}}_x{\mathrm{TiO}}_3$ layer; the presence of an anomalous Hall effect when driving the systems above the Lifshitz point with a back-gate voltage; and a minimum in the temperature dependence of the sheet resistance below the Lifshitz point in the one-band regime, which becomes more pronounced with increasing negative gate voltage. However, and notwithstanding the likely presence of magnetism in the system, we do not attribute that minimum to the Kondo effect, but rather to the properties of the ${\mathrm{SrTiO}}_3$ crystal and the inevitable effects of charge trapping when using back gates.

Understanding the phase behavior and microscopic diffusion mechanism of cationic vesicles is crucial for controlled-release kinetics in gene/DNA transfection. Here, we report our findings on the structure, phase behavior, and microscopic dynamics of a vesicle based on a cationic double-chained surfactant, dihexadecyldimethylammonium bromide (DHDAB), which is a promising candidate for a nonviral gene/DNA carrier. Small-angle neutron-scattering measurements reveal that DHDAB aggregates are in the form of unilamellar vesicles. Calorimetric studies show a strong thermal hysteresis in the heating and cooling cycles following different pathways. Two first-order transitions are observed at 303 and 318 K in the heating cycle. Fourier transform infrared spectroscopy reveals that the first transition (at 303 K) is associated with a polymorphic (solid-solid) transition from coagel to an intermediate crystalline (IC) phase, and subsequently the second transition (at 318 K) is an order-disorder transition from IC to the fluid phase. Interestingly, it is found that in the cooling cycle, the fluid phase directly transforms back into the coagel phase without passing through the IC phase. This is also confirmed by an elastic fixed window scan (EFWS) using incoherent neutron scattering. The phase behavior of DHDAB is in strong contrast to that of its longer-chain counterpart, dioctadecyldimethylammonium bromide (DODAB), where the intermediate gel phase was observed during the cooling cycle. Moreover, no polymorphic transition was observed in the heating cycle of DODAB, in which the coagel phase directly converts to the fluid phase. These sharply contrasting phase behaviors for DHDAB and DODAB suggest the strong dependence of membrane phase behavior to the alkyl chain length. EFWS measurements reveal that the phase transitions observed in the DHDAB membrane are associated with strong changes in the DHDAB dynamics. The changes in conformational entropy of DHDAB molecules estimated from EFWS confirm that the coagel-fluid and IC-fluid phase transitions are accompanied by strong changes in the conformations of the alkyl chains. The microscopic dynamics of DHDAB molecules in each of these phases is investigated by employing quasielastic neutron-scattering (QENS). In the ordered phases (coagel and IC), only localized internal dynamics of the DHDAB is observed in the QENS spectra. However, in the fluid phase, the presence of a long-range lateral diffusion is detected in addition to the localized internal dynamics of the alkyl chain. The lateral motion is found to follow Fickian diffusion. The internal dynamics of DHDAB depends on the phase state of the bilayer. In the ordered phase, the internal dynamics is described by a fractional uniaxial rotational diffusion model. However, in the fluid phase, where alkyl tails are disordered with significant gauche defects, the internal dynamics is described using localized translation within confined spheres. This study highlights the rich phase behavior of the DHDAB membrane and the surfactant dynamics across these phases.

We perform first-principles calculations to determine the electronic, magnetic, and transport properties of rare-earth dichalcogenides, taking a monolayer of $H$-phase ${\mathrm{EuS}}_2$ as a representative. We predict that the $H$ phase of the ${\mathrm{EuS}}_2$ monolayer exhibits a half-metallic behavior upon doping with a very high magnetic moment. We find that the electronic structure of ${\mathrm{EuS}}_2$ is very sensitive to the value of Coulomb repulsion $U$, which effectively controls the degree of hybridization between Eu $f$ and S $p$ states. We further predict that the nontrivial electronic structure of ${\mathrm{EuS}}_2$ directly results in a pronounced anomalous Hall effect with nontrivial band topology. Moreover, while we find that the spin Hall effect closely follows the anomalous Hall effect in the system, the orbital complexity of the system results in a very large orbital Hall effect, whose properties depend very sensitively on the strength of correlations. Our findings thus promote rare-earth-based dichalcogenides as a promising platform for topological spintronics and orbitronics.

Neutron diffraction on the centrosymmetric square-net magnet ${\mathrm{EuGa}}_2{\mathrm{Al}}_2$ reveals multiple incommensurate magnetic states (AFM1, 2, 3) in zero field. In applied field, a new magnetic phase (A) is identified from magnetization and transport measurements, bounded by two of the ${\mu }_{0}H=0$ incommensurate magnetic phases (AFM1, helical, and AFM3, cycloidal) with different moment orientations. Moreover, magnetotransport measurements indicate the presence of a topological Hall effect, with maximum values centered in the A phase. Together, these results render ${\mathrm{EuGa}}_2{\mathrm{Al}}_2$ a material with noncoplanar or topological spin texture in applied field. X-ray diffraction reveals an out-of-plane (OOP) charge density wave (CDW) below $T_{\mathrm{CDW}}\sim 50$ K while the magnetic propagation vector lies in plane below $T_N=19.5$ K. Together these data point to a new route to realizing in-plane noncollinear spin textures through an OOP CDW. In turn, these noncollinear spin textures may be unstable against the formation of topological spin textures in an applied field.

We use angle-resolved photoemission to map the Fermi surface and quasiparticle dispersion of bulklike thin films of ${\mathrm{SrMoO}}_3$ grown by pulsed laser deposition. The electronic self-energy deduced from our data reveals weak to moderate correlations in ${\mathrm{SrMoO}}_3$, consistent with our observation of well-defined electronic states over the entire occupied bandwidth. We further introduce spectral function calculations that combine dynamical mean-field theory with an unfolding procedure of density functional calculations and demonstrate good agreement of this approach with our experiments.

The Mo $4d$ shell in the ground state of ${\mathrm{MoO}}_3$ is widely believed to be unoccupied. However, this assumption lacks clear experimental and theoretical corroboration. Using x-ray absorption and emission spectroscopy along with resonant inelastic x-ray scattering, we provide experimental evidence of two-dimensional ${\mathrm{MoO}}_3$ exhibiting enhanced many-body effects due to its reduced dimensionality. The observed phenomena include many-body effects such as $dd$ and spin-flip excitations, valence-hole and excited electron, and core-hole and excited electron bound excitonic states. Moreover, density functional theory and ligand field-based calculations were performed to investigate and interpret the experimental spectra. Considering that these many-body effects can only be observed by the interaction of x-ray photons with ${\mathrm{MoO}}_3$ if the $4d$ state is partially occupied, our experimental and theoretical approach clearly demonstrates a partial occupation of the Mo $4d$ state, refuting the assumption that the ground state is a $4d^0$ state. The Mo d occupancy is $4d^{3.36}$ and $4d^{3.53}$ determined with two different theoretical approaches (density functional theory and multiplet, respectively) and the computed spectra agree very well with our measurements further supporting this finding. Both the two- and three-dimensional samples exhibit strong core-hole effects that reduce the absorption onset at both the Mo $M_{2,3}$ and O $K$ edge. The band gap of the three-dimensional sample is experimentally found to be 3.1 ± 0.2 eV; however, for the two-dimensional material, strong many-body effects, even at the O $K$ edge, prevent an accurate determination of this value. The presence of these quasiparticles influences the band dispersions near the Fermi level, and thus has a key role in the performance of possible ${\mathrm{MoO}}_3$-based devices.

Silicon carbide nanoparticles with diameters around 8 nm and narrow size distribution have been finely mixed with doped silicon nanopowders and sintered into bulk samples to investigate the influence of nanoinclusions on electrical and thermal transport properties. We have compared the thermoelectric properties of samples ranging from 0%–5% volume fraction of silicon carbide. The silicon carbide nanoinclusions lead to a significant improvement in the thermoelectric figure of merit ZT largely due to an enhancement of the Seebeck coefficient. A semiclassical Boltzmann transport equation is used to model the electrical transport properties of the Seebeck coefficient and electrical conductivity. The theoretical analysis confirms that the enhancements in the thermoelectric properties are consistent with the energy selective scattering of electrons induced by the offset between the silicon Fermi level and the carbide conduction band edge. This study proves that careful engineering of the energy-dependent electron scattering rate can provide a route towards relaxing long-standing constraints in the design of thermoelectric materials.

The growth and microstructural properties of ternary monolayers of two-dimensional hexagonal materials are examined, including both individual two-dimensional crystalline grains and in-plane heterostructures, multijunctions, or superlattices. The study is conducted through the development of a ternary phase field crystal model incorporating sublattice ordering and the coupling among the three atomic components. The results demonstrate that a transition of compositional pattern or modulation in this type of two-dimensional ternary crystals, from phase separation to geometrically frustrated lattice atomic ordering, can be controlled via the varying degree of energetic preference of heteroelemental neighboring over the homoelemental ones. Effects of growth and system conditions are quantitatively identified through numerical calculations and analyses of interspecies spatial correlations and the degree of alloy intermixing or disordering. These findings are applied to simulating the growth of monolayer lateral heterostructures with atomically sharp heterointerface, and via the sequential process of edge epitaxy, the formation of the corresponding superlattices or structures with multiple heterojunctions, with outcomes consistent with recent experiments of in-plane multiheterostructures of transition-metal dichalcogenides. Also explored is a distinct type of alloy-based lateral heterostructures and multijunctions, which integrate ternary ordered alloy domains with the adjoining blocks of binary compounds, providing a more extensive variety of two-dimensional heterostructural materials.

Antimonene is a promising two-dimensional material predicted to host intriguing properties. Recent works have claimed the successful preparation of β-antimonene on noble metal surfaces, including Ag(111) and Cu(111). However, as scanning tunneling microscopy gives only the topographic information, the possibility of surface alloying for the claimed β-antimonene remains elusive. In this work, by scanning tunneling spectroscopy and in situ Raman spectroscopy measurements, we provide compelling evidence that the “β-antimonenes” on Ag(111) and Cu(111) reported in previous studies are both surface alloys, namely, ${\mathrm{Ag}}_2\mathrm{Sb}$ and ${\mathrm{Cu}}_2\mathrm{Sb}$. Thus, β-antimonene does not exist on these substrates. Instead, we find that α-antimonene can be grown on both alloy surfaces, with different substrate-induced strain modulation effects. Our work not only clarifies the growth dynamics of Sb on Ag(111) and Cu(111) but also provides two model systems to realize α-antimonene with tunable strains.

We propose a fast method for high-throughput screening of potential superconducting materials. The method is based on calculating metallic screening of zone-center phonon modes, which provides an accurate estimate for the electron-phonon coupling strength. This method is complementary to the recently proposed rigid muffin tin (RMT) method, which amounts to integrating the electron-phonon coupling over the entire Brillouin zone (as opposed to the zone center), but in a relatively inferior approximation. We illustrate the use of this method by applying it to ${\mathrm{MgB}}_{\text{2}}$, where the high-temperature superconductivity is known to be driven largely by the zone-center modes, and compare it to a sister compound ${\mathrm{AlB}}_{\text{2}}$. We further illustrate the usage of this descriptor by screening a large number of binary hydrides, for which accurate first-principle calculations of electron-phonon coupling have been recently published. Together with the RMT descriptor, this method opens a way to perform initial high-throughput screening in search of conventional superconductors via machine learning or data mining.

The glass-forming ability (GFA) of alloys, colloidal dispersions, and other particulate materials, as measured by the critical cooling rate $R_c$, can span more than ten orders of magnitude. Even after numerous previous studies, the physical features that control the GFA are still not well understood. For example, it is well known that mixtures are better glass formers than monodisperse systems and that particle size and cohesive energy differences among constituents improve the GFA, but it is not currently known how particle size differences couple to cohesive energy differences to determine the GFA. We perform molecular dynamics simulations to determine the GFA of equimolar, binary Lennard-Jones (LJ) mixtures versus the normalized cohesive energy difference ${\epsilon }_{\_}$ and mixing energy ${\overline{\epsilon }}_{AB}$ between particles A and B. We find several important results. First, the ${log}_{10}{R}_c$ contours in the ${\overline{\epsilon }}_{AB}\text{−}{\epsilon }_{\_}$ plane are ellipsoidal for all diameter ratios, and thus $R_c$ is determined by the Mahalanobis distance $d_M$ from a given point in the ${\overline{\epsilon }}_{AB}\text{−}{\epsilon }_{\_}$ plane to the center of the ellipsoidal contours. Second, LJ systems for which the larger particles have larger cohesive energy are generally better glass formers than those for which the larger particles have smaller cohesive energy. Third, $d_M({\epsilon }_{\_},{\overline{\epsilon }}_{AB})$ is determined by the relative Voronoi volume difference between particles and local chemical order $S_{AB}$, which gives the average fraction of nearest-neighbor B particles surrounding an A particle and vice versa. In particular, the shifted Mahalanobis distance $d_M-d_M^0$ versus the shifted chemical order $S_{AB}-S_{AB}^0$ collapses onto a hyperbolic master curve for all diameter ratios. These results identify design guidelines for improving the GFA of binary mixtures containing particles with different sizes, cohesive, and mixing energies.

The actual mechanisms occurring at interfaces underlying the Dzyaloshinskii-Moriya interaction (DMI) remain a question in nanomagnetism. In this study, we investigate the origin of the interfacial DMI, aiming at estimating how independent the DMI contributions of the two interfaces of a FM layer are and what their relative weight in the effective DMI amplitude is. To this aim, we explore the correlation between the effective interfacial DMI and the metal properties, namely, atomic number, electronegativity, and the work function of the metal $M$. A clear linear relationship is found between the interfacial DMI and the work function difference at the $\mathrm{Co}/M$ interface. This result is strong evidence of the independent DMI contributions of the two interfaces for the chosen Co thickness(1 nm). It also suggests that the $\mathrm{Co}/\mathrm{Cu}$ interface bears no interfacial DMI. These findings can guide the optimization of the magnetic properties of future devices.

Doped perovskite cobaltites (e.g., ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CoO}}_3$) have been extensively studied for their spin-state physics, electronic inhomogeneity, and insulator-metal transitions. Ferromagnetically interacting spin-state polarons emerge at low $x$ in the phase diagram of these compounds, eventually yielding long-range ferromagnetism. The onset of long-range ferromagnetism ($x\approx 0.18$) is substantially delayed relative to polaron percolation ($x\approx 0.05$), however, generating a troubling inconsistency. Here, Monte Carlo simulations of a disordered classical spin model are used to establish that previously ignored magnetic frustration is responsible for this effect, enabling faithful reproduction of the magnetic phase diagram.

High-quality single crystals of ${\mathrm{KCo}}_2{\mathrm{As}}_2$ with the body-centered tetragonal ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure were grown using KAs self flux. Structural, magnetic, thermal, and electrical transport properties were investigated. No clear evidence for any phase transitions was found in the temperature range 2–300 K. The in-plane electrical resistivity $\rho$ versus temperature $T$ is highly unusual, showing a $T^4$ behavior below 30 K and an anomalous positive curvature up to 300 K, which is different from the linear behavior expected from the Bloch-Grüneisen theory for electron scattering by acoustic phonons. This positive curvature has been previously observed in the in-plane resistivity of high-conductivity layered delafossites such as ${\mathrm{PdCoO}}_2$ and ${\mathrm{PtCoO}}_2$. The in-plane $\rho (T\to 0)=0.36\mu \mathrm{\Omega }$ cm of ${\mathrm{KCo}}_2{\mathrm{As}}_2$ is exceptionally small for this class of compounds. The material also exhibits a magnetoresistance at low $T$ which attains a value of about 40% at $T=2$ K and magnetic field $H=80$ kOe. The magnetic susceptibility $\chi$ of ${\mathrm{KCo}}_2{\mathrm{As}}_2$ is isotropic and about an order of magnitude smaller than the values for the related compounds ${\mathrm{SrCo}}_2{\mathrm{As}}_2$ and ${\mathrm{BaCo}}_2{\mathrm{As}}_2$. The $\chi$ increases above 100 K, which is found from our first-principles calculations to arise from a sharp peak in the electronic density of states just above the Fermi energy $E_{\mathrm{F}}$. Heat capacity $C_{\mathrm{p}}\left(T\right)$ data at low $T$ yield an electronic density of states $N\left(E_{\mathrm{F}}\right)$ that is about 36% larger than predicted by the first-principles theory. The $C_{\mathrm{p}}\left(T\right)$ data near room temperature suggest the presence of excited optic vibration modes, which may also be the source of the positive curvature in $\rho \left(T\right)$. Angle-resolved photoemission spectroscopy measurements are compared with the theoretical predictions of the band structure and Fermi surfaces. Our results show that ${\mathrm{KCo}}_2{\mathrm{As}}_2$ provides a new avenue for investigating the physics of high-purity metals.

It has been a puzzle for over two decades that the enhancement of oxygen diffusion in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$, with respect to the amount of Mg doping, is several orders of magnitude less than expected. The standard model, which envisages that transport is mediated by oxygen vacancies induced to compensate the charge of ${\mathrm{Mg}}^{2+}$ ions substituting ${\mathrm{Al}}^{3+}$ ions, has not been able to explain this anomaly. Here, we report a detailed study of populations of point defects and defect clusters in Mg-doped $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$. By taking into account calculated defect formation energies from the literature, the condition of charge neutrality, and the environmental parameters (chemical potentials) under which the anomalous trend in oxygen diffusivities were previously observed, we are able to arrive at an explanation. A nonlinear relationship between Mg concentration in the system and key native point defects, which serve as mediators of self-diffusion in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$, is predicted: The concentrations of such defects increase much more slowly in the supersaturation regime than in the presaturation regime, matching the anomalous result previously observed in $\alpha \text{−}{\mathrm{Al}}_2{\mathrm{O}}_3$. We identify the reason for this as buffering by positively charged Mg interstitials and Mg–oxygen vacancy clusters, which compensate the negative charges of Mg substitutional defects (${\mathrm{Mg}}_{\text{Al}}^{1-}$). This study answers part of the long-standing question about self-diffusion in alumina, referred to by Heuer and Lagerlöf in 1999 as the corundum conundrum.

Two-dimensional Ruddlesden-Popper (2DRP) halide perovskites have emerged as promising solar absorbers due to their much-enhanced stability compared with their three-dimensional counterparts, but the light conversion efficiency is limited by their intrinsic optoelectronic properties such as increased exciton binding energy and poor cross-layer carrier transport properties. We herein demonstrate, through first-principles calculations, that the efficiency of 2DRP halide perovskites can be enhanced by adopting the short-chain interlayer spacers among perovskite layers. We adopted short-chain alkylmethylammonium (MA) and formamidinium (FA) organic cations to exchange the regular long-chain butylammonium (BA) and phenethylammonium (PEA) cations in 2DRP halide perovskites with the formula $A_{2}B{\mathrm{Pb}}_2{\mathrm{I}}_7$ ($A=\mathrm{BA}$, PEA, MA, and FA; $B=\mathrm{MA}$ and FA). We find that varying the interlayer spacers results in changed distortion of ${\mathrm{PbI}}_6$ octahedra of the perovskite framework, which in turn influences the stability and electronic structure of 2DRP perovskites. Compared with the long-chain BA/PEA intercalated 2DRP perovskites, the short-chain MA/FA intercalated ones have slightly reduced thermodynamic stability, but their calculated bandgaps are closer to the ideal value for solar cells (1.3–1.6 eV), accompanied with comparable carrier effective masses and optical absorption. More importantly, they demonstrate lower exciton binding energies and two orders of magnitude increased out-of-plane carrier tunneling probability. These factors are expected to further enhance the power conversion efficiency of 2DRP-based solar cells.

Using density-functional-theory calculations we assess the effects of the isovalent ${\mathrm{Ca}}^{2+}\to {\mathrm{Mg}}^{2+}$ substitutions on the mineral structure of tobermorite, a major analog of the main hydrated cement phase, calcium-silicate-hydrate (CSH). From the structural point of view, due to its smaller ionic radius, Mg substitution leads to an overall decrease of the lattice parameters for the 9 Å (dry) and 11 Å (hydrated) tobermorite structures used in the study. Furthermore, Mg doping at intralayer sites leads to a considerable distortion of the unit cell due to a changing oxygen coordination number. With the increasing amount of Mg doping, chemical bond analysis shows an overall increase in the bond strength with the crystal cohesion enhancement. In addition, Mg sites in the dry and hydrated tobermorite are characterized by an enhanced reactivity, which may be useful in capturing $\mathrm{C}{\mathrm{O}}_2$. With regard to the elastic properties, Mg doping leads to an overall stiffening of the elastic moduli. However, depending on the particular site, Mg doping may give rise to an increased elastic anisotropy. Overall, the present results indicate that Mg-based tobermorite structures may be useful prospects in the search for alternative components toward the development of high-performance, environmentally friendly cementitious materials.

We have developed a phase mapping method based on machine learning analysis of reflection high-energy electron diffraction (RHEED) images. RHEED produces diffraction patterns containing a wealth of static and dynamic information and is commonly used to determine the growth rate, the growth mode, and the surface morphology of epitaxial thin films. However, the ability to extract quantitative structural information from the RHEED patterns that appear during film growth is limited by the lack of versatile and automated analysis techniques. We have created a deep learning-based analysis method for automating the identification of different RHEED pattern types that occur during the growth of a material. Our approach combines several supervised and unsupervised machine learning techniques and permits the extraction of quantitative phase composition information. We applied this method to the mapping of the structural phase diagram of ${\mathrm{Fe}}_{\mathrm{x}}{\mathrm{O}}_{\mathrm{y}}$ thin films grown by pulsed laser deposition as a function of growth temperature and oxygen pressure close to the hematite-magnetite phase boundary. The in situ RHEED-based mapping method produces results that are qualitatively similar to postsynthesis x-ray diffraction analysis.