Spin dynamics and a nearly continuous magnetic phase transition in an entropy-stabilized oxide antiferromagnet
Benjamin A. Frandsen, K. Alec Petersen, Nicolas A. Ducharme, Alexander G. Shaw, Ethan J. Gibson, Barry Winn, Jiaqiang Yan, Junjie Zhang, Michael E. Manley, Raphaël P. Hermann
The magnetic order and the spin dynamics in the antiferromagnetic entropy-stabilized oxide (Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)O (MgO-ESO) have been studied using muon spin relaxation ($μ$SR) and inelastic neutron scattering. We find that antiferromagnetic order develops gradually in the sample volume as it is cooled below 140 K, becoming fully ordered around 100 K. The spin dynamics show a critical slowing down in the vicinity of the transition, and the magnetic order parameter grows continuously in the ordered state. These results indicate that the antiferromagnetic transition is continuous but proceeds with a Gaussian distribution of ordering temperatures. The magnetic contribution to the specific heat determined from inelastic neutron scattering likewise shows a broad feature centered around 120 K. High-resolution inelastic neutron scattering further reveals an initially gapped spectrum at low temperature which sees an increase in a quasielastic contribution upon heating until the ordering temperature.
Layered oxides have been intensively studied due to their high designability for various electronic functions. Here we synthesize a new oxide as epitaxial thin film form by pulsed laser deposition. Film characterizations including cross-section and plan-view transmission electron microscopy confirm that the film is composed of twisted stack of triangular-lattice Rh and Bi layers. We foresee that the concept of twisted oxide layers will open up a new route to design further functional layered oxides.
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 …
Magnetization plateaus, visible as anomalies in magnetic susceptibility at low temperatures, are one of the hallmarks of frustrated magnetism. We show how an extremely robust half-magnetization plateau can arise from coupling between spin and lattice degrees of freedom in a pyrochlore antiferromagnet, and develop a detailed symmetry of analysis of the simplest possible scenario for such a plateau state. The application of this theory to the spinel oxides CdCr2O4 and HgCr2O4, where a robust half magnetization plateau has been observed, is discussed.
In this paper, we study the elastic properties of the entropy-stabilized oxide (Mg, Co, Ni, Cu, Zn)O, using experimental and first principles techniques. Our measurements of the indentation modulus on grains with a wide range of crystallographic orientations of the entropy-stabilized oxide revealed a high degree of elastic isotropy at ambient conditions. First principles calculations predict mild elastic anisotropy for the paramagnetic structure, which decreases when the system is considered to be non-magnetic. When the antiferromagnetic state of CoO, CuO and NiO is accounted for in the calcul…
Neutron diffraction measurements on multiferroic LuFe2O4 show changes in the antiferromagnetic (AFM) structure characterized by wavevector q = (1/3 1/3 1/2) as a function of electric field cooling procedures. The increase of intensity from all magnetic domains and the decrease in the 2D magnetic order observed below the Neel temperature are indicative of increased ferroelectric charge order. The AFM order changes the dynamics of the CO state, and stabilizes it. It is determined that the increase in electric polarization observed at the magnetic ordering temperature is due to a transition from …
Signatures of symmetry-stabilized Dirac fermions in correlated oxide CaNbO3 thin films
Oak Ridge National Laboratory（橡树岭国家实验室）；Kyung Hee University（庆熙大学）；Pusan National University（釜山国立大学）；Florida State University（佛罗里达州立大学）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Argonne National Laboratory（阿贡国家实验室）；Gachon University（嘉泉大学）
Nanocrystalline materials are well known for their beneficial mechanical and physical properties. However, it is of utmost importance to stabilize the microstructure at elevated temperatures to broaden the window of application e.g. by pinning grain boundaries through impurities or oxides. CuCo alloys, severe plastically deformed using high-pressure torsion, were used to investigate the evolution of oxides upon annealing. These investigations were performed using electron microscopy, synchrotron high-energy X-ray scattering and atom probe tomography. Monitoring the evolution of oxides by in-si…
Low-temperature transport and magnetization measurements for the antiferromagnets SrMnO(3) and CaMnO(3) identify an impurity band of mobile states separated by energy E from electrons bound in Coulombic potentials. Very weak electric fields are sufficient to excite bound electrons to the impurity band, increasing the mobile carrier concentration by more than three orders of magnitude. The data argue against the formation of self-trapped magnetic polarons (MPs) predicted by theory, and rather imply that bound MPs become stable only for kT<<E.
Additive manufacturing represents a revolution due to its unique capabilities for freeform fabrication of near net shapes with strong reduction of waste material and capital cost. These unfair advantages are especially relevant for expensive and energy-demanding manufacturing processes of advanced ceramics such as Yttria-stabilized Zirconia, the state-of-the-art electrolyte in Solid Oxide Fuel Cell applications. In this study, self-supported electrolytes of yttria-stabilized zirconia have been printed by using a stereolithography three-dimensional printer. Printed electrolytes and complete cel…
The application of weak electric fields (<~ 100 V/cm) is found to dramatically enhance the lattice thermal conductivity of the antiferromagnetic (AF) insulator CaMnO(3) over a broad range of temperature about the Neel ordering point (125 K). The effect is coincident with field-induced de-trapping of bound electrons, suggesting that phonon scattering associated with short- and long-ranged AF order is suppressed in the presence of the mobilized charge. This interplay between bound charge and spin-phonon coupling might allow for the reversible control of spin fluctuations using weak external fiel…
Entropy stabilization has garnered significant attention as a new approach to designing novel materials. Much of the work in this area has focused on bulk ceramic processing, leaving entropy-stabilized thin films relatively underexplored. Following an extensive multi-variable investigation of polycrystalline (Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)O thin films deposited via pulsed laser deposition (PLD), it is shown here that substrate temperature and deposition pressure have strong and repeatable effects on film texture and lattice parameter. Further analysis shows that films depo…
A direct correlation is seen between the coercive field (HC) and the magnetic-field-dependent resistivity (MR) in SrMnO3/SrRuO3 superlattices of perpendicular magnetic anisotropy. The magnetoresistance shows a sharp jump at Hc for in-plane current and the out-of-plane magnetic field. Both HC and high-field MR also oscillate with the thickness of the SrMnO3 spacer layers separating the metallic ruthenate. Since the spacer in these superlattices has no mobile carriers to facilitate an oscillatory coupling, we attribute the observed behavior to the spin-polarized quantum tunneling of electrons be…
Antiferromagnetic transition metal oxides are an established and widely studied materials system in the context of spin-based electronics, commonly used as passive elements in exchange bias-based memory devices. Currently, major interest has resurged due to the recent observation of long-distance spin transport, current-induced switching, and THz emission. As a result, insulating transition metal oxides are now considered to be attractive candidates for active elements in novel spintronic devices. Here, we discuss some of the most promising materials systems and highlight recent advances in re…
Hydrostatic pressure effects on the temperature- and magnetic field dependencies of the in-plane and out-of-plane magnetization of the bi-layered perovskite Sr3Ru2O7 have been studied by SQUID magnetometer measurements under a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature value of the paramagnetic susceptibility has been found to systematically decrease with increasing pressure. The effect is accompanied by an increase of the temperature Tmax of a pronounced peak of susceptibility. Thus, magnetization measurements under hydrostatic pressure reveal that the lattice c…
Probing Elastic Isotropy in Entropy Stabilized Transition Metal Oxides: Experimental Estimation of Single Crystal Elastic Constants from Polycrystalline Materials
Interdiffusion between the yttria stabilized zirconia (YSZ) electrolyte and the gadolinia doped ceria (CGO) barrier layer is one of the major causes to the degradation of solid oxide fuel cells (SOFCs). We present in this work experimental investigations on CGO-YSZ bi-layer electrolyte sintered at 1250 C or 1315 C and element transport as a function of sintering temperature and dwelling time. In order to quantitatively simulate the experimental observations, the CALPHAD-type thermodynamic assessment of the CGO-YSZ system is performed by simplifying the system to a CeO2-ZrO2 quasi-binary system…
We investigate the frustrated magnetic interactions in cubic transition metal oxides with orbital degeneracy. The $e_g$ orbitals order easier and their ordering explains the $A$-type antiferromagnetic phase in KCuF$_3$ and LaMnO$_3$. In $t_{2g}$ systems the magnetic order changes at a transition from an orbital liquid to orbital ordered states. The fluctuations of $t_{2g}$ orbitals play a prominent role in LaVO$_3$ and YVO$_3$, where they compete with the Jahn-Teller effect and trigger the C-type antiferromagnetic order.
Voltage control of interfacial magnetism has been greatly highlighted in spintronics research for many years, as it might enable ultra-low power technologies. Among few suggested approaches, magneto-ionic control of magnetism has demonstrated large modulation of magnetic anisotropy. Moreover, the recent demonstration of magneto-ionic devices using hydrogen ions presented relatively fast magnetization toggle switching, tsw ~ 100 ms, at room temperature. However, the operation speed may need to be significantly improved to be used for modern electronic devices. Here, we demonstrate that the spee…
We report an alternative mechanism for the physical origin of the temperature-dependent ferromagnetic relaxation of Permalloy (NiFe) thin films. Through spin-pumping experiments, we demonstrate that the peak in the temperature-dependence of NiFe damping can be understood in terms of enhanced spin angular momentum absorption at the magnetic phase transition in antiferromagnetic surface-oxidized layers. These results suggest new avenues for the investigation of an incompletely-understood phenomenon in physics.
Data-Driven Prediction of NaCl-Type Entropy-Stabilized Oxide Compositions from First-Principles and Supervised Learning
Univ Paris Est Creteil, CNRS, ICMPE（巴黎东克雷泰伊大学，法国国家科学研究中心，分子化学与材料研究所）；Université Paris-Saclay, CNRS, Institut de chimie moléculaire et des matériaux d’Orsay（巴黎萨克雷大学，法国国家科学研究中心，奥赛分子化学与材料研究所）
We report neutron scattering measurements of the spinel oxide LiGaCr$_{4}$O$_{8}$, in which magnetic ions Cr$^{3+}$ form a breathing pyrochlore lattice. Our experiments reveal the coexistence of a nearly dispersionless resonance mode and dispersive spin wave excitations in the magnetically ordered state, which can be quantitatively described by a quantum spin model of hexagonal loops and linear spin wave theory with the same set of exchange parameters, respectively. Comparison to other Cr spinel oxides reveals a linear relationship between the resonance energy and lattice constant across all t…
Specific heat and magnetization measurements have been carried out under a range of magnetic fields on single crystals of Ca3Co2O6. This compound is composed of Ising magnetic chains that are arranged on a triangular lattice. The intrachain and interchain couplings are ferromagnetic and antiferromagnetic, respectively. This situation gives rise to geometrical frustration, that bears some similarity to the classical problem of a two-dimensional Ising triangular antiferromagnet. This paper reports on the ordering process at low-T and the possibility of one-dimensional features at high-T.
Perovskite oxides exhibit a rich variety of structural phases hosting different physical phenomena that generate multiple technological applications. We find that topological phonons, i.e., nodal rings, nodal lines, and Weyl points, are ubiquitous in oxide perovskites in terms of structures (tetragonal, orthorhombic, and rhombohedral), compounds (BaTiO3, PbTiO3, and SrTiO3), and external conditions (photoexcitation, strain, and temperature). In particular, in the tetragonal phase of these compounds, all types of topological phonons can simultaneously emerge when stabilized by photoexcitation, …
The (001) surface of NiO, an antiferromagnet at room temperature, was investigated under ultra-high vacuum conditions with frequency modulation atomic force microscopy (FM-AFM). The antiferromagnetic coupling between ions leads to a spin superstructure on (001) surfaces. Exchange interaction between the probe of a force microscope and the NiO (001) surface should allow to image spin superstructures in real space. The surface was imaged with three different probing tips: nonmagnetic W tips, ferromagnetic Co tips and antiferromagnetic NiO tips - and atomic resolution was achieved with all three …
Specific heat measurements were carried out on the closely related spin-chain oxides Ca3Co2O6 and Ca3CoRhO6. Both compounds consist of Ising magnetic chains that are arranged on a triangular lattice. The spin coupling along and between the chains are ferromagnetic and antiferromagnetic, respectively. Geometrical frustration is expected from the combination of these magnetic features. The present study reports that the specific heat data of these compounds exhibit similarities in the spin-freezing process at low T, whereas striking differences exist in the antiferromagnetic interchain ordering …
Stabilizing high-valent redox couples and exotic electronic states necessitate an understanding of the stabilization mechanism. In oxides, whether they are being considered for energy storage or computing, highly oxidized oxide-anion species rehybridize to form short covalent bonds and are related to significant local structural distortions. In intercalation oxide electrodes for batteries, while such reorganization partially stabilizes oxygen redox, it also gives rise to substantial hysteresis. In this work, we investigate oxygen redox in layered Na2-XMn3O7, a positive electrode material with …
Oxidative stress, which is one of the main harmful mechanisms of pathologies including is-chemic stroke, contributes to both neurons and endothelial cell damages, leading to vascular lesions. Although many antioxidants have been tested in preclinical studies, no treatment is currently available for stroke patients. Since cerium oxide nanoparticles (CNPs) exhibit remarkable antioxidant capacities, our objective is to develop an innovative coating to enhance CNPs biocompatibility without disrupting their antioxidant capacities or enhance their toxicity. This study reports the synthesis and chara…
Several challenges in designing an operational Skyrmion racetrack memory are well-known. Among those challenges, a few contradictions can be identified if researchers were to rely only on metallic materials. Hence, expanding the exploration on Skyrmion Physics into oxide materials is essential to bridge the contradicting gap. In this topical review, we first briefly revise the theories and criteria involved in stabilizing and manipulating Skymions, followed by studying the behaviors of dipolar-stabilized magnetic bubbles. Next, we explore the properties of multiferroic Skyrmions with magnetoel…
We report for the first time the magnetic structure of the high entropy oxide $(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})O$ using neutron powder diffraction. This material exhibits a sluggish magnetic transition but possesses a long-range ordered antiferromagnetic ground state, as revealed by DC and AC magnetic susceptibility, elastic and inelastic neutron scattering measurements. The magnetic propagation wavevector is k=(1/2, 1/2, 1/2) based on the cubic structure Fm-3m, and the magnetic structure consists of ferromagnetic sheets in the (111) planes with spins antiparallel between two neighbo…
The exchange bias effect is an essential component of magnetic memory and spintronic devices. Whereas recent research has shown that anisotropies perpendicular to the device plane provide superior stability against thermal noise, it has proven remarkably difficult to realize perpendicular exchange bias in thin-film structures. Here we demonstrate a strong perpendicular exchange bias effect in heterostructures of the quasi-two-dimensional canted antiferromagnet La$_2$CuO$_4$ and ferromagnetic (La,Sr)MnO$_3$ synthesized by ozone-assisted molecular beam epitaxy. The magnitude of this effect can b…
Li5OsO6 and Li5ReO6 polycrystalline samples were synthesized by conventional solid state methods. Employing powder neutron diffraction data, the crystal structure of Li5OsO6 was re-investigated. Li5OsO6 crystallizes in C2/m space group in an ordered NaCl structure type where a = 5.0472(1) A, b = 8.7827(2) A, c = 5.0079(1) A, Beta = 109.777(2) degree and V = 208.90(1).A^3 Magnetic susceptibility and heat capacity data indicate an AFM long range order below 40K although there is evidence for low dimensional short range order above 80K. As well, the frustration index, f = |theta|/TN ~1, in contra…
A major impediment towards realizing technologies based on the emerging principles of antiferromagnetic spintronics is the shortage of suitable materials. In this paper, we propose a design of polar|nonpolar heterostructures of perovskite oxides, where a single unit cell of SrIrO3 is sandwiched between a thin film of LaAlO3 and a substrate of SrTiO3. Our calculations within the framework of density-functional theory + Hubbard U + spin-orbit coupling reveal a two-dimensional conducting layer with electron and hole pockets at the interface, exhibiting a strong anisotropic Rashba-Dresselhaus effe…
Magnetic skyrmions are topological solitons with a nanoscale winding spin texture that hold promise for spintronics applications. Until now, skyrmions have been observed in a variety of magnets that exhibit nearly parallel alignment for the neighbouring spins, but theoretically, skyrmions with anti-parallel neighbouring spins are also possible. The latter, antiferromagnetic skyrmions, may allow more flexible control compared to the conventional ferromagnetic skyrmions. Here, by combining neutron scattering and Monte Carlo simulations, we show that a fractional antiferromagnetic skyrmion lattic…
Atomically sharp oxide heterostructures often exhibit unusual physical properties that are absent in the constituent bulk materials. The interplay between electrostatic boundary conditions, strain and dimensionality in ultrathin epitaxial films can result in monolayer-scale transitions in electronic or magnetic properties. Here we report an atomically sharp antiferromagnetic-to-ferromagnetic phase transition when atomically growing polar antiferromagnetic LaMnO3 (001) films on SrTiO3 substrates. For a thickness of five unit cells or less, the films are antiferromagnetic, but for six unit cells…
Measurements of the static magnetic susceptibility and of the nuclear magnetic resonance of multiwalled vanadium-oxide nanotubes are reported. In this nanoscale magnet the structural low-dimensionality and mixed valency of vanadium ions yield a complex temperature dependence of the static magnetization and the nuclear relaxation rates. Analysis of the different contributions to the magnetism allows to identify individual interlayer magnetic sites as well as strongly antiferromagnetically coupled vanadium spins (S = 1/2) in the double layers of the nanotube's wall. In particular, the data give …
Antiferromagnetic thin films typically exhibit a multi-domain state, and control of the antiferromagnetic Néel vector is challenging as antiferromagnetic materials are robust to magnetic perturbations. By relying on anisotropic in-plane strain engineering of epitaxial thin films of the prototypical antiferromagnetic material LaFeO3, uniaxial Néel vector control is demonstrated. Orthorhombic (011)- and (101)-oriented DyScO3, GdScO3 and NdGaO3 substrates are used to engineer different anisotropic in-plane strain states. The anisotropic in-plane strain stabilises structurally monodomain monoclini…
Magnetic interfaces and the phenomena arising from them drive both the design of modern spintronics and fundamental research. Recently, it was revealed that through designing magnetic frustration in configurationally complex entropy stabilized oxides, exchange bias can occur in structurally single crystal films. This eliminates the need for complex heterostructures and nanocomposites in the design and control of magnetic response phenomena. In this work, we demonstrate through hole doping of a high entropy perovskite oxide that tuning of magnetic responses can be achieved. With detailed magnet…
Non-collinear antiferromagnetic materials have received dramatically increasing attention in the field of spintronics as their exotic topological features such as the Berry-curvature-induced anomalous Hall effect and possible magnetic Weyl states could be utilized in future topological antiferromagnetic spintronic devices. In this work, we report the successful integration of the antiferromagnetic metal Mn3Sn thin films onto ferroelectric oxide PMN-PT. By optimizing growth, we realized the large anomalous Hall effect with small switching magnetic fields of several tens mT fully comparable to t…
Heterostructures of Co-doped ZnO and Permalloy were investigated for their static and dynamic magnetic interaction. The highly Co-doped ZnO is paramagentic at room temperature and becomes an uncompensated antiferromagnet at low temperatures, showing a narrowly opened hysteresis and a vertical exchange bias shift even in the absence of any ferromagnetic layer. At low temperatures in combination with Permalloy an exchange bias is found causing a horizontal as well as vertical shift of the hysteresis of the heterostructure together with an increase in coercive field. Furthermore, an increase in t…
Several M3 TeO6 (M = Mn, Co, Ni, Cu) oxides order antiferromagnetically at low temperatures (near or below 60 K), while displaying interesting dielectric properties at high temperatures (ferroelectricity below 1000 K in M = Ni case). We have investigated and analyzed the structural and magnetic properties of Mn-doped Co3 TeO6 and Ni3 TeO6, which order antiferromagnetically at temperatures higher than their undoped counterparts.
A comprehensive theoretical and experimental study is presented of the magnetic susceptibility versus temperature χ(T) of spin S = 1/2 two- and three-leg Heisenberg ladders and ladder oxide compounds. Extensive quantum Monte Carlo simulations of χ(T) were carried out for both isolated and coupled two-leg ladders with spatially anisotropic intraladder exchange. Accurate fits to these and related literature QMC data were obtained. We have also calculated the one- and two-magnon dispersion relations and the dynamical spin structure factor for anisotropic isolated 2 x 12 ladders. The exchange cons…
Unlike widely explored complex oxide heterostructures grown along [001], the study of [111]-oriented heterointerfaces are very limited thus far. One of the main challenges is to overcome the polar discontinuity that hinders the epitaxy of atomically sharp interfaces. Here, by taking the LaCoO3/SrTiO3(111) as a prototype, we show that the reconstruction, which effectively compensates the surface polarity, can stabilize the epitaxy of the heterostructure with polar discontinuity. Reconstructed substrate surface is prepared, while the growth is controlled to form reconstruction on the film surfac…
The prospects of half-metallic ferromagnetism being induced by the incorporation of C atoms into alkaline-earth-metal-oxides are investigated by the first principle calculation. The origin of the ferromagnetism is discussed through the calculation of the electronic structure and exchange coupling constant by using the pseudo-potential-like self-interaction-corrected local spin density method. The Curie temperature ($T_c$) is also predicted by employing the Monte Carlo simulation. It is shown that by taking the electron self-interaction into account, the half-metallic ferromagnetism induced by …
The possible importance of oxide formation for the catalytic activity of transition metals in heterogenous oxidation catalysis has evoked a lively discussion over the recent years. On the more noble transition metals (like Pd, Pt or Ag) the low stability of the common bulk oxides suggests primarily sub-nanometer thin oxide films, so-called surface oxides, as potential candidates that may be stabilized under gas phase conditions representative of technological oxidation catalysis. We address this issue for the Pd(100) model catalyst surface with first-principles kinetic Monte Carlo (kMC) simula…
This paper reviews the present understanding of the origin of ferromagnetic response of diluted magnetic semiconductors and diluted magnetic oxides as well as in some nominally magnetically undoped materials. It is argued that these systems can be grouped into four classes. To the first belong composite materials in which precipitations of a known ferromagnetic, ferrimagnetic or antiferromagnetic compound account for magnetic characteristics at high temperatures. The second class forms alloys showing chemical nano-scale phase separation into the regions with small and large concentrations of t…
From the first-principles calculations, we have studied the electronic and magnetic structures of compound Na$_2$Ti$_2$Pn$_2$O (Pn = As or Sb). We find that in the ground state Na$_2$Ti$_2$As$_2$O is a blocked checkerboard antiferromagnetic semiconductor with a small band gap of about 0.15 eV, in contrast, Na$_2$Ti$_2$Sb$_2$O is a bi-collinear antiferromagnetic semimetal, both with a small moment of about 0.5$μ_B$ around each Ti atom. We show that there is a strong Fermi surface nesting in Na$_2$Ti$_2$Pn$_2$O. And we verify that the blocked checkerboard and bi-collinear antiferromagnetic state…
Dielectric and magnetic phenomena in spin and charge frustrated system RFe2O4 (R is a rare-earth metal ion) are studied. An electronic model for charge, spin and orbital degrees in a pair of triangular-lattice planes is derived. We analyze this model by utilizing the mean-field approximation and the Monte-Carlo simulation in a finite size cluster. A three fold-type charge ordered structure with charge imbalance between the planes is stabilized in finite temperatures. This polar charge order is reinforced by spin ordering of Fe ions. This novel magneto-dielectric phenomenon is caused by spin fr…
Atomically sharp oxide heterostructures exhibit a range of novel physical phenomena that do not occur in the parent bulk compounds. The most prominent example is the appearance of highly conducting and superconducting states at the interface between the band insulators LaAlO3 and SrTiO3. Here we report a new emergent phenomenon at the LaMnO3/SrTiO3 interface in which an antiferromagnetic insulator abruptly transforms into a magnetic state that exhibits unexpected nanoscale superparamagnetic dynamics. Upon increasing the thickness of LaMnO3 above five unit cells, our scanning nanoSQUID-on-tip m…
We report variational and fixed-node diffusion quantum Monte Carlo (QMC) calculations of anti-ferromagnetic iron oxide (FeO) in the ground state B1 crystal structure. The goal of this study was a systematic investigation of the sensitivity of several ground state properties to a variety of QMC wave function generation techniques including advanced wave functions such as multi-determinant expansions and backflow transformations. We found that the predicted lattice distortion was largely controlled by the choice of single particle orbitals used to construct the wave function, rather than by subs…
