Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R40: Complex Oxide Films and Heterostructures IIIFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Zhigang Chen, San Francisco State Univ Room: BCEC 208 |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R40.00001: Phase transitions and magnetic domain coexistence in Nd0.5Sr0.5MnO3 thin films I-Ting Chiu, Apurva Mehta, Alexander Michael Kane, Rajesh V Chopdekar, Christopher Rouleau, Alpha N'Diaye, Elke Arenholz, Yayoi Takamura We present a study of the physical properties of perovskite oxide Nd0.5Sr0.5MnO3 (NSMO) thin films grown on (110)-oriented SrTiO3 substrates. In bulk form, NSMO displays magnetic and electronic transitions from paramagnetic/insulator to ferromagnetic (FM)/metal and then to antiferromagnetic (AFM)/charge-ordered insulating phase with decreasing temperature. In thin films, AFM ordering only occurs in an anisotropic strain state such as those obtained in (110)-oriented substrates which allows for Jahn-Teller distortions of the MnO6 octahedral and MnO6 bond length distortions [1]. In this work, resonant x-ray reflectivity and magnetometry measurements showed that the NSMO film breaks up into three layers with different density and magnetic properties. X-ray magnetic circular dichroism confirmed the FM-AFM transition occurs between 80 K and 160 K for the main portion of the NSMO film, while x-ray magnetic linear dichroism provided a clear signature of the AFM phase at 80 K. At an intermediate temperature of 110 K, photoemission electron microscopy demonstrated the coexistence of FM and AFM domains. These temperature-dependent transitions have strong potential applications in next generation memory devices. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R40.00002: Growth and Physical properties of full chemically ordered manganites Lina Deng Chemical doping is a widely used method to control materials’ physical properties. The dopants are usually randomly distributed. This unavoidably introduces disordering into the materials, which may affect the physical properties of the materials. This is especially true for electronic phase separation (EPS) phenomena in manganites, which is known to have a close correlation with disordering. In this work, we use superlattice growth to form chemically ordered manganites, and compare with conventional manganites whose chemical dopants are randomly distributed. Specifically, one unit cell LaMnO3 / one unit cell PrMnO3 / one unite cell CaMnO3 tricolor superlattices have been grown on NGO (110) and STO (100) substrates by laser molecular beam epitaxy, forming chemically ordered La1/3Pr1/3Ca1/3MnO3 (O-LPCMO) thin films. In stark contrast to the conventional La1/3Pr1/3Ca1/3MnO3 (R-LPCMO) thin films which are characterized by large scale EPS, the O-LPCMO films show no signs of EPS. This indicates that dopants induced disordering plays a critical role in large scale EPS in manganites. Our experimental results show that the O-LPCMO system is in a charge-ordered insulating state which is consistent with the first principle calculations. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R40.00003: The role of extreme configurational disorder in entropy stabilized single crystal perovskite oxides Thomas Ward, Yogesh Sharma, Alessandro Mazza The ABO3 perovskite and its derivatives are broadly important to a range of fundamental and applied interests. Modification of the A and B sites through substitutional doping allows for a wide variety of distortions and charge states to be tuned. Local distortions arising from cation size variance are balanced by internal changes to Jahn-Teller distortions and octahedral tilts and rotations. In strongly correlated systems, these shifts to local environment are often central to the emergence of important macroscopic functionalities. In this talk, we will describe our recent work using entropy stabilization to synthesize single crystal ABO3 perovskite films possessing 6 or more cations to begin to explore how extreme levels of microscopic disorder might be used to generate unexpected long-range ordering responses. We will discuss how the element specific magnetic and charge states of the cations in La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 films are impacted by the extreme site to site disorder. Experimental results from STEM-EELs, XRD, XMCD, neutron diffraction, and SQUID magnetometry will be presented. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R40.00004: Charge order and phase separation nature of the insulating La0.67Ca0.33MnO3 thin film on NdGaO3 substrate Mingqiang Gu, James M Rondinelli Doped manganite systems have been intensively studied due to their rich phase diagrams at different temperature, strain, pressure, and composition conditions. La0.67Ca0.33MnO3 thin film grown on NdGaO3 substrate has found to exhibit abnormal antiferromagnetic (AFM) insulating ground state, which violates the bulk phase diagram. The puzzle that why the ground state of this d3.67 system becomes insulating is studied with density functional theory (DFT) calculation. Several potential scheme has been examined, including substrate strain, pinning of Jahn-Teller distortion, and charge order (CO), within different magnetic configurations. We find that without charge order, neither substrate strain nor increased Jahn-Teller distortion are sufficient to induce the insulating state. With Mn4+/Mn3+ valence states ordered in a stripe type pattern along the b lattice vector, the AFM insulating state can be observed. However, an unrealistic large uniaxial strain is required to assist this phase to beat the ferromagnetic (FM) phase. Further study suggests mixture of the CO [Mn4+]0.5/[Mn3+]0.5 and pure LaMnO3 micro regions in the sample. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R40.00005: Studying Influence of Normal Metal on Magnetic Properties of Y3Fe5O12 Thin Film Locally Using Scanning Ferromagnetic Resonance Force Microscopy Guanzhong Wu, Shane White, William Ruane, Jack T Brangham, Yang Cheng, Fengyuan Yang, P Chris Hammel We image the boundary separating regions of altered internal magnetic fields in Y3Fe5O12(YIG) thin films arising from patterning metal films on the YIG film surface. High quality YIG thin films have proven to be useful for spintronics research. However, detailed investigations of internal magnetic variations in patterned devices are still lacking. Spatial maps of the internal fields were acquired using ferromagnetic resonance force microscopy(FMRFM); a technique allowing for nano to micro-scale spatial resolution and high sensitivity to magnetic fields within the film. FMRFM scans laterally across the YIG-YIG/M (M = Au, Pt) boundary indicate an internal field step that is tens of Gauss. Micromagnetic simulations assuming the presence of uniaxial anisotropy in both the bare YIG and the YIG/M bilayer qualitatively match experimental measurements. We discuss possible physical causes of this field shift, methods used to image the spatial magnetization profile, and implications for future spintronic devices. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R40.00006: Effects of the apical-oxygen vacancy and magnetism on the ultra-thin LaNiO3 layer studied using DFT+DMFT Xingyu Liao, Hyowon Park While the bulk LaNiO3 remains metallic at all temperatures, the ultrathin films of LaNiO3 shows a metal-insulator transition as the layer thickness reduces to 2 unit cells. Recent experiment shows that the NiO2 surface layer without top LaO layer can have higher resistivity than the same NiO2 layer with apical oxygens. In this talk, I will present the density functional theory plus dynamical mean field theory (DFT+DMFT) calculations for the one-layer LaNiO3 slab including the LaAlO3 substrate and the vacuum. The slab geometry with the capping LaO layer is metallic even with DFT+DMFT although Ni eg orbitals are renormalized compared to DFT bands. We also move the top LaO layer away from the surface layer to simulate the effect of apical oxygens on the electronic structure. As the apical oxygen moves away from the Ni ion, an effective charge transfer occurs toward the dz2 orbital and the Wannier orbital level is shifted below the dx2-y2 orbital. Moreover, the DMFT self energy makes the dz2 orbital more incoherent and it eventually becomes Mott insulating in the absence of apical oxygens. We also simulate the antiferromagnetic calculations with the up-up-down-down spin structure as measured in experiment. The results will be also compared with the above paramagnetic calculations. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R40.00007: Synthesis and Characterization of Ru-doped BaSnO3Thin Films and Heterostructures Emily Lindgren, Urusa S Alaan, Yuri Suzuki Epitaxial doped stannate thin films have been identified recently as high mobility oxide semiconductors that could form the foundation of an all-oxide electronics. Adding magnetic functionality to this class of materials may provide for a spin-based electronics. Toward this end, we have grown epitaxial thin films of Ru doped BaSnO3(BSO) and multilayers of alternating La doped and Ru doped BaSnO3 on (001) SrTiO3substrates using pulsed laser deposition. X-ray photoelectron spectroscopy was used to verify successful incorporation of both La and Ru into the BSO lattice. X-ray diffraction measurements confirm epitaxial growth of the single layer and multi-layered films. Both single layer and multi-layered films are under epitaxial tensile strain according to X-ray diffraction. Omega rocking curves of both types of samples show excellent crystallinity with typical FWHM values of 0.096○ and 0.073○. Both types of films exhibit a paramagnetic response which saturates at approximately 1μB/Ru4+, thus indicating paramagnetism but no ferromagnetic order. Single layer Ru doped BSO films exhibit insulating behavior while layered films have a typical mobility value of 37 cm2/Vs, carrier concentration of 11019cm-3and resistivity of 0.4 mΩcm at 300K. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R40.00008: Structural, Electrical and Magnetic Properties of Solid Solution Films between SrRuO3 and BaSnO3 Pingchun Wu, Ying-Hao Chu A series of SrRuO3/BaSnO3 solid solutions have been fabricated via laser molecular beam epitaxy. With the help of high-energy electron beam reflection, the ratio of SRO/BSO is precisely controlled in the scale of monolayer. The epitaxial relation was analyzed by x-ray diffraction and transmission electron microscopy. The lattice constants of c-axis varied with the change of the ratio between SRO and BSO, which is consistent with the results calculated by Vegard’s law. After successfully fabricate a series of SRO/BSO, temperature-dependent resistances measurement has been carried out. It was found that electrical behavior of SRO/BSO was varied from pure metallic to insulating while the ratio of BSO increased in the solid solutions. A metal-insulating transition can also be found in specific ratio. Further, the increase of BSO will result in an enlarged magnetoresistance in the solid solutions. In the magnetic hysteresis loops, the decrease in saturated magnetic moment, coercivity and the change in anisotropy can also be found. This experiment realizes an accurately control of solid solutions in the scale of monolayer. The structural, electrical and magnetic properties of SRO/BSOs have been systematically analyzed and the origin of these differences has also been discussed. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R40.00009: Magnetic Field Control of the Fermi Surface Topology in EuTiO3 Kaveh Ahadi, Xuezeng Lu, Salva Salmani-Rezaie, Patrick Marshall, James M Rondinelli, Susanne Stemmer Spin-orbit coupling plays a central role in the anomalous Hall effect (AHE) of itinerant ferromagnets and in materials with topologically non-trivial electronic states. Recently, AHE attracted significant attention in antiferromagnetic metals and semiconductors. For example, significant AHEs in non-collinear antiferromagnets have been discovered. The degenerately doped antiferromagnetic semiconductor EuTiO3 is a unique testbed for these ideas for several reasons. Despite a small net magnetization, it exhibits an intrinsic AHE that changes sign as a function of the carrier density. We report on the symmetry of the anisotropic magnetoresistance (AMR) in doped EuTiO3 films as a function of the applied magnetic field. Multiple transitions in the AMR symmetry are observed and are attributed to magnetic field induced changes in the band topology. At high fields a transition from positive to negative magnetoresistance coincides with change from four-fold to two-fold symmetry in the AMR. This indicates a non-trivial phase transition in the electronic structure. We discuss the results in the context of Weyl points that form in the band structure of the EuTiO3. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R40.00010: Electronic wave function spatial extension of the oxygen vacancies on EuO1-x surface. Te-Yu Chien, Aaron Wang, Gaurab Rimal, Robert Nielsen, Yuri Dahnovsky, Jinke Tang EuO1-x thin films deposited by pulsed laser deposition on Si(100) were studied by scanning tunneling microscopy and spectroscopy at room temperature. Oxygen vacancies in EuO1-x are visualized through dI/dV mapping and the apparent sizes of the oxygen vacancies are found to be 1.8 nm ± 0.5 nm. These apparent sizes are considered as the spatial extension of the electron wave function originated from the oxygen vacancies. It is further argued that this observed electronic wave function might be the precursor of the bound magnetic polaron formation occurred at lower temperature. Moreover, some of the oxygen vacancies were found (1) hopping to adjacent site; (2) emerging (vacancy creation); and (3) disappearing (vacancy annihilation), indicating that the oxygen vacancies on the EuO1-x surface at room temperature are not extremely stable. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R40.00011: Magnetic phase transitions in thin films of the near-itinerant spinel CoV2O4 Christie J Thompson, Christianne Beekman Spinel vanadates are frustrated antiferromagnets, of interest due to the orbital physics that can be tuned via structural perturbations. The V-V distance determines proximity of the system to a localized-itinerant crossover, with CoV2O4 the closest known material to this transition. Previously, we have shown that CoV2O4 films are orthorhombic rather than cubic. The films undergo a spin canting/orbital order transition at low temperature, i.e., they show very different magnetic properties compared to bulk [1]. Based on recent magnetization measurements as a function of temperature we find signatures of three distinct magnetic transitions in the films. We investigate temperature, field, and film thickness dependence of these transitions, and we discuss the roles that single-ion anisotropy and shape anisotropy play. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R40.00012: Room-temperature ferromagnetic insulating state in highly cation-ordered Sr2Fe1+xRe1-xO6 films Chang Hee Sohn, Elizabeth Skoropata, Yongseong Choi, Xiang Gao, Ankur Rastogi, Amanda Huon, Michael A McGuire, Lauren Nuckols, Yanwen Zhang, John William Freeland, Daniel Haskel, Ho Nyung Lee Ferromagnetic insulators with high Curie temperatures are critical components for developing quantum electronic/spintronic devices. However, since ferromagnetism generally accompanies metallicity, ferromagnetic insulators have been very limited in nature. Here, we report a highly insulating ferromagnetic state found in 3d-5d double perovskite Sr2Fe1+xRe1-xO6 (-0.2<x<0.2) epitaxial films by modifying the Fe/Re ratio. Beyond the original ferromagnetic metallic ground state in a stoichiometric film, Fe-rich films showed demanding ferromagnetic insulating states with three orders of higher room-temperature resistance than that of the metallic film, a high Curie temperature about 400 K, and a large saturated magnetization about 1.8 uB/f.u. In this presentation, we discuss about the growth, related physical properties, and the origin of the emerging ferromagnetic insulating state based on x-ray and optical spectroscopy. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R40.00013: Observation of Compensation Temperature in Epitaxial Tm3Fe5O12 Thin Films by Polar Magneto-Optic Kerr Effect Yanjun Ma, Cheng Cen Since ferrimagnetic rare-earth iron garnets (RIG) R3Fe5O12 are excellent insulators with Curie temperatures well above room temperature, such materials have been extensively exploited in spintronics, leading to novel discoveries such as anomalous Hall effect in the heterostructure formed by topological insulator and Tm3Fe5O12 (TmIG). While the recent research on TmIG thin films has been focusing on the behavior of their perpendicular magnetic anisotropy (PMA) in high temperature region, the magnetic properties of TmIG thin films at lower temperatures are elusive. In this report, we measured the low temperature magnetic properties of epitaxial TmIG films by polar magneto-optic Kerr effect. The divergence of the out-of-plane coercive filed and the reverse of the sign of out-of-plane magnetization were observed consecutively, indicating the existence of compensation temperature in TmIG. Further investigation showed that the temperature making divergent was dependent on the thickness and strain state of the film. Since the compensation temperature in bulk TmIG has never been established, our findings demonstrate that it is worth investigating low temperature magnetism in low dimensional rare-earth iron garnets to advance the research of RIG-based spintronics. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R40.00014: Exotic Ferroelectric and Multiferroic Properties in Epitaxial YFeO3 Thin Films and YFeO3-CoFe2O4 Nanocomposites Shuai Ning, Caroline Anne Ross Multiferroics have been attracting considerable interest in the past decades, and researchers never stop searching for materials exhibiting multiferroic behavior. For orthoferrites, there should be no ferroelectricity in theory due to their centrosymmetric structure. However, when epitaxially grown, the strain can significantly modify the symmetry and physical properties. Here, we present the exotic ferroelectric properties of epitaxial YFeO3 (YFO) thin films on perovskite substrates prepared by pulsed laser deposition (PLD). A nearly single-domain structure is observed in as-grown 40 nm-thick YFO thin films characterized by Piezoresponse force microscopy (PFM), and it can be fully switched suggested by the ideal ferroelectric hysteresis loop and by domain patterns written by a bias of +/- 8 V. The spontaneous polarization direction is highly dependent on the epitaxial strain, which could be tuned either out-of-plane or in-plane. Via co-deposition by PLD, the nanocomposites consisting of YFO and CoFe2O4 (CFO) have been prepared, in which phase separation is successfully achieved. Both ferroelectricity and ferromagnetism are observed originating from YFO and CFO respectively, indicating a promising magnetoelectric coupling in this 2-phase multiferroic nanocomposite. |
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