Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Z6: Focus Session: Magnetic Oxide Thin Films and Heterostructures: Manganite Thin Films |
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Sponsoring Units: DMP GMAG Chair: H. Jeffrey Gardner, University of Nebraska-Lincoln Room: 108 |
Friday, March 7, 2014 11:15AM - 11:27AM |
Z6.00001: Emergent Phenomena in La5/8Ca3/8MnO3 /Pr5/8Ca3/8MnO3 Superlattices Zhu Yinyan, Du Kai, Zhang Kai, Yin Lifeng, Shen Jian In this work, we study the magnetic and transport properties of La5/8Ca3/8MnO3 (LCMO)/Pr5/8Ca3/8MnO3(PCMO) superlattices. For comparison, La1$-$x$-$yPryCaxMnO3 (LPCMO) thin films with the same nominal doping concentration have also been grown and characterized. The spatial rearrangement of the doped cations and the presence of interfaces appear to have dramatic effect on the physical properties of the superlattices. Specifically, the transport and magnetic properties of the [LCMO2n/PCMOn]t show strong dependence on n, which differ greatly from those of the La10/24Pr5/24Ca3/8MnO3 thin films. It is especially striking that the n$=$1 superlattice has a metal-insulator transition temperature that nearly 100 K higher than that of the La10/24Pr5/24Ca3/8MnO3 thin film. These emergent phenomena are caused by the interplay between interfacial effect and artificial chemical phase separation between two contrasting ground states along the film stacking direction. [Preview Abstract] |
Friday, March 7, 2014 11:27AM - 11:39AM |
Z6.00002: Anisotropic magnetoresistance in colossal magnetoresistive oxide La$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$MnO$_{3}$ thin films Le Zhang, Vijay Singh, Anil Rajapitamahuni, Xia Hong We present our studies of the anisotropic magnetoresitance (AMR) in colossal magnetoresistive oxide La$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$MnO$_{3}$ (LSMO, x $=$ 0.3, 0.5) thin films as a function of temperature, magnetic field and film thickness. LSMO thin films with thickness below 10 nm are grown on SrTiO$_{3}$ (001) and NdGaO$_{3}$(110) substrates via off-axis magnetron sputtering. X-ray diffraction and atomic force microscopy studies reveal high crystallinity and atomically smooth surfaces of these films. As the thickness of the films decreases, the metal insulator transition temperature (T$_{\mathrm{MI}})$ shifts to below the bulk value. Films thinner than 3 nm become totally insulating. We extract the AMR from the resistance change as a function of the orientation between current and magnetic field. AMR reaches the maximum value in the vicinity of T$_{\mathrm{MI}}$. At low magnetic field ($\sim$ 100 Oe), the angular dependence of AMR deviates from a sinusoidal shape, which is attributed to the effect of magnetocrystalline anisotropy. We discuss the effects of the carrier density, film thickness, and substrate strain on the AMR. [Preview Abstract] |
Friday, March 7, 2014 11:39AM - 11:51AM |
Z6.00003: Ferromagnetic Metallic Edge State in Manganites Stripes Kai Du, Kai Zhang, Shuai Dong, Jian Shao, Jiebin Niu, Jinjie Chen, Yinyan Zhu, Lifeng Yin, Jian Shen Recently, spin-orbital interaction induced edge states in systems such as topological insulators and graphene ribbon have attracted great attention. However, whether edge states may exist in strongly correlated oxides is not yet known. In this work, using perovskite manganites as prototype systems, we experimentally demonstrate that edge states do exist in strongly correlated oxides. Our observation is made by employing magnetic force microscope (MFM) and transport measurement techniques to study manganites stripes as a function of temperature and magnetic field. Distinct appearance of ferromagnetic metallic phase was observed along the edge of manganites stripes. The edge states have strong influence on the transport properties of the stripes, leading to an increase of metal-insulator transition (MIT) temperature with decreasing width of the stripes. Model calculations show that the edge states are associated with the broken symmetry effect of the antiferromagnetic charge-ordered states in manganites. [Preview Abstract] |
Friday, March 7, 2014 11:51AM - 12:03PM |
Z6.00004: Telegraph Noise in LSMO Nanowires John J. Damasco, Nicholas T. Bronn, Xiaoqian M. Chen, Anoop R. Damodaran, Karthik Jambunathan, Lane W. Martin, Peter Abbamonte, Nadya Mason Lanthanum strontium manganites (La$_{1-x}$Sr$_{x}$MnO$_{3}$) are oxide materials that exhibit colossal magnetoresistance and have potential in spintronics applications. Their resistivity is affected by the competition between a double exchange mechanism and a Jahn-Teller distortion. We present magnetic-field dependent transport measurements on PLD-grown La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ nanowires. First, we show signatures of bimodal random telegraph noise that occur at temperatures below 100 K. We also discuss the temperature dependence of the resistance, which is consistent with a meta-stability in the nanowire. Both behaviors can be explained by a competition between ferromagnetic metallic and charge-ordered insulating domains, caused by double exchange and the Jahn-Teller distortion, respectively. [Preview Abstract] |
Friday, March 7, 2014 12:03PM - 12:15PM |
Z6.00005: Low Temperature Magnetic Force Microscopy of La$_{\mathrm{2-2x}}$Sr$_{\mathrm{1+2x}}$Mn$_{2}$O$_{7}$ Neliza Leon Brito, J.-S. Zhou, J.B. Goodenough, Alex de Lozanne, Jeehoon Kim, Roman Movshovich We present micromagnetic studies of La$_{\mathrm{2-2x}}$Sr$_{\mathrm{1+2x}}$Mn$_{2}$O$_{7}$ (x $=$ 0.32, 0.36, 0.40) taken with a magnetic force microscope at 4 K in magnetic fields up to 5 T. The x $=$ 0.32 sample shows branching domains with magnetization in/out of the surface that evolve into stripes and bubbles as a function of increasing field until saturation is reached at $\sim$ 0.29 T. The rms average of the magnetic images show an unexpected non-monotonic dependence on field that is not observed in SQUID data of a sister sample. We speculate that this difference is caused by the micro vs. macro nature of the two measurements. The magnetic microstructure for the doping level of x $=$ 0.36 agrees with the expected in-plane magnetization. The sample reaches saturation by magnetic domain reorientation at \textbar H\textbar \textgreater 0.18 T. The x $=$ 0.40 sample also shows in-plane magnetization, but the increasing magnetic field does not appear to change noticeably the magnetic domain structure and only seems to change the magnitude of the contrast. From the drastic change in contrast, it would appear the sample reaches saturation around 0.4 T. Since this is the only sample that required polishing, it may be that this caused strong pinning of the domains at the surface. [Preview Abstract] |
Friday, March 7, 2014 12:15PM - 12:27PM |
Z6.00006: Nanostructure engineering of epitaxial colossal magnetoresistive oxide thin films Anil Rajapitamahuni, Vijay Raj Singh, Le Zhang, Xia Hong We have fabricated nanostructured colossal magnetoresistive (CMR) oxide thin films to study the effect of phase separation. Using off-axis radio frequency magnetron sputtering, we have grown epitaxial single crystalline 4-6 nm La0.5Sr0.5MnO3 (LSMO) and La0.7Ca0.3MnO3 (LCMO) films on (110) NdGaO3 and (001) SrTiO3 substrates, respectively. X-ray diffraction and atomic force microscopy characterizations show the films have high crystalinity and RMS roughness of 2-3 {\AA}. Films close to the electrical dead layer thickness (3-5 nm) are patterned into periodic depth modulation by e-beam lithography and fluorine based reactive ion etching. We fabricated nanostructures with periodic thickness variations of 1-2 nm and 100-200 nm periodicities. The etched patterns retain the atomic smoothness of the as grown films. We have the control of the etching depth with sub-nanometer precision on both LSMO and LCMO films. We discuss the effect of the periodicity and depth modulation of the nanostructures on the I-V characteristics and magnetotransport properties of these CMR thin films within the phase separation model. [Preview Abstract] |
Friday, March 7, 2014 12:27PM - 12:39PM |
Z6.00007: Probing magnetic inhomogeneity in La0. 67Ca0.33MnO3 by optical spin wave resonances Yuhang Ren, Haibin Zhao, Yu Gong, David Scienzo, Yonatan Abranyos, Gunter Luepke, Qi Li We report on our recent study of spin wave resonances in ferromagnetic La0.67Ca0.33MnO3 (LCMO) thin films by ultrafast Kerr-rotation experiments. Coherent magnetization precessions were generated and detected by subpicosecond laser pulses. Confined higher order spin wave modes are identified in addition to fundamental modes at 10 K. We determine spin stiffness, magnetic and surface anisotropy parameters for both 60-nm and 100-nm LCMO samples. Significant changes in anisotropy parameters are explained by the formation and extension of magnetic inhomogeneity in the 100-nm LCMO film. Our results show the new picosecond time-resolved magneto-optical method is a powerful tool for detecting magnetic inhomogeneity. [Preview Abstract] |
Friday, March 7, 2014 12:39PM - 12:51PM |
Z6.00008: Intrinsic Insulating Ferromagnetism in Manganese Oxide Thin Films Yusheng Hou, Hongjun Xiang, Xingao Gong Recently, LaMnO$_{\mathrm{3}}$ thin films attract considerable attentions not only because LaMnO$_{\mathrm{3}}$ is the most common magnetic component in all fabricated oxide superlattices/interfaces, but also because experiment observed exotic insulating ferromagnetism in LaMnO$_{\mathrm{3}}$ thin film grown on SrTiO$_{\mathrm{3}}$. However, there is no any model or theory/calculation to explain such striking insulating ferromagnetism. In this work, by means of genetic algorithm optimization, first-principles calculations and the orbital-degenerate double-exchange model studies, we successfully find the insulating ferromagnetic phase of the epitaxially strained LaMnO$_{\mathrm{3}}$ film grown on the cubic SrTiO$_{\mathrm{3}}$ substrate. The unexpected insulating ferromagnetism, which was observed experimentally but not fully understood, originates from the G-type orbital order $d_{{3z}^{2}-r^{2}} \mathord{\left/ {\vphantom {d_{{3z}^{2}-r^{2}} d_{x^{2}-y}}} \right. \kern-\nulldelimiterspace} d_{x^{2}-y}$ and the insulating gap opens as a result of both the orbital ordering and the strong electron-phonon coupling. Our work provides new insight into how a prototypical antiferromagnetic Mott insulator transforms into the ferromagnetic insulator. [Preview Abstract] |
Friday, March 7, 2014 12:51PM - 1:03PM |
Z6.00009: Signatures of electronic phase separation in the Hall effect of anisotropically-strained La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ films with a magnetically driven percolative phase transition Liuqi Yu, Xiaohang Zhang, S. von Moln\'ar, P. Xiong, Lingfei Wang, W.B. Wu Hall measurements have been performed on La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) films with varying degrees of anisotropic strain. The strain is induced by epitaxial growth on NdGaO$_{3}$ substrate and controlled via post annealing. An antiferromagnetic insulating (AFI) state emerges upon annealing at low temperatures.\footnote{Z. Huang et al., JAP 105, 113919(2009)} The Hall effect (HE) data exhibit many unusual features that are indicative of a magnetically driven percolation. In the paramagnetic phase, it is found the Hall resistivity shows a distinct slope change at a constant critical magnetization over the temperature range, which is interpreted as a critical point of a magnetic field driven percolative phase transition. At lower temperatures near the metal-insulator transition, a negative Hall resistivity peak emerges. This Hall resistivity dip correlates with the emergence and strengthening of the AFI state, and is suppressed with the melting of the AFI state by an in-plane field. The Hall resistivity dips in LCMO resemble the giant HE in granular metal films near the composition-driven percolation,\footnote{X. X. Zhang et al., PRL 86, 5562 (2001)} which is interpreted as a result of the enhancement of Hall coefficient beyond the percolation point. The observations reveal an important manifestation of the magnetic field driven percolative phase transition in the HE of LCMO with an insulating background. Work supported in part by NSF DMR-0908625 and DMR-1308613. [Preview Abstract] |
Friday, March 7, 2014 1:03PM - 1:15PM |
Z6.00010: Transport and magnetic properties of CMR manganites with antidot arrays Kai Zhang, Kai Du, Jiebin Niu, Wengang Wei, Jinjie Chen, Lifeng Yin, Jian Shen We fabricated and characterized a series of manganites thin film samples with different densities of antidots. With increasing antidot density, the samples show higher MIT temperature and lower resistivity under zero and low magnetic fields. These differences become smaller and finally vanished when the magnetic field is large enough to melt the charge ordered phase in the system, which is expected in our theoretical explanations. We believe that emerging edge states at the ring of antidotes play a significant role for observed metal-insulator transition and electrical transport properties, which are of great importance of real storage and sensor device design. Magnetic property measurements and theoretical simulation also support the conclusion. These results open up new ways to control and tune the strongly correlated oxides without introduce any new material or field. [Preview Abstract] |
Friday, March 7, 2014 1:15PM - 1:27PM |
Z6.00011: Effects of preparation conditions on the physical properties of nickel ferrite thin films Hillary Belliveau, Manuel Bonilla, Patrick McArdle, Casey Miller The effects of the deposition temperature, pressure, and oxygen partial pressure were investigated on the structural, electrical, and magnetic properties of nickel ferrite (NiFe$_{\mathrm{2}}$O$_{\mathrm{4}})$ thin films grown by magnetron sputtering. The samples were grown on Si (100), Si (100) with 500nm of amorphous SiO$_{\mathrm{2}}$, and on MgO (100) substrates. Increasing the deposition temperature allowed the NiFe$_{\mathrm{2}}$O$_{\mathrm{4}}$ (004) XRD peak to appear at higher oxygen partial pressures. Between films of the same oxygen pressure, increasing the deposition temperature reduced the FWHM and increased the intensity of the NiFe$_{\mathrm{2}}$O$_{\mathrm{4}}$ (004) XRD peak. The films were 800 to 1000nm thick as measured by profilometry. Increasing the oxygen partial pressure reduces the intensity of the (004) NiFe$_{\mathrm{2}}$O$_{\mathrm{4}}$ XRD peak, and allows us to tune the material from a conducting material (rho $=$ 114 microOhm*cm at T$=$220K) to an insulating one (rho$=$ 2475 Ohm*cm at T$=$220K). The resistivity at 220K decreased as the deposition temperature was increased for films grown at the same oxygen partial pressure. The magnetic properties were investigated with magneto-optical Kerr effect and vibrating sample magnetometry. [Preview Abstract] |
Friday, March 7, 2014 1:27PM - 1:39PM |
Z6.00012: Magnetic properties of epitaxial hexagonal HoFeO$_{3}$ thin films Xiao Wang, Zhuyun Xiao, Xiaoshan Xu, Wenbin Wang, David Keavney, Yaohua Liu, X.M. Cheng Multiferroic materials exhibit multiple ferroic orders simultaneously and thus have great potential applications in information technology, sensing and actuation. Epitaxial hexagonal HoFeO$_{3}$ (h-HFO) films are very promising candidates as multiferroic materials with room temperature ferromagnetism, because magnetic Ho$^{3+}$ ions are expected to have stronger exchange interactions with Fe$^{3+}$ ions than the well-studied h-LuFeO$_{3}$ films. We report study of magnetic properties of epitaxial h-HFO thin films deposited using laser molecular beam epitaxy on Yttria-stabilized zirconia (YSZ) substrates. X-ray diffraction measurements confirmed the epitaxial registry and six-fold symmetry of the film. Temperature dependence of magnetization of the film measured by a Quantum Design SQUID magnetometer shows dominating paramagnetic characteristic. Element specific x-ray magnetic circular dichroism measurements performed at beamline 4-ID-C of the Advanced Photon Source show a ferromagnetic ordering of Fe and an exchange coupling between Ho$^{3+}$ and Fe$^{3+}$ ions. [Preview Abstract] |
Friday, March 7, 2014 1:39PM - 1:51PM |
Z6.00013: Nonvolatile Three-Step Ferroelectric Switching in Tensile Strained BiFeO$_{3}$ Thin Films Jin Hong Lee, Kanghyun Chu, Kwang-Eun Kim, Chan-Ho Yang Misfit strain has been one of key control parameters to improve the magnetoelectric coupling between ferroelectricity and magnetism in multiferroic epitaxial thin films. Lately, it was discovered that a bulk-like phase of multiferroic bismuth ferrite (BiFeO$_{3})$, through compressive or tensile misfit strain, can be transformed into a highly-elongated tetragonal-like phase [1-3] or an orthorhombic phase [4], respectively, thereby offering new chances into magnetoelectric applications. Although the heteroepitaxial misfit strains via (001) interfaces have been intensively studied, strain effects arising from the other directional interfaces such as (110) have not been studied much. In this talk, we present the uniaxial-tensile-strain effects on the (110) oriented BiFeO$_{3}$ thin films. Our detailed piezoresponse force microscopy analysis, X-ray reciprocal space mapping, and Landau free energy modeling give strong evidences of electrically switchable, non-volatile, three out-of-plane polarization states. These findings provide useful implications for a new type of magnetoelectric devices based on phase competition.\\[4pt] [1] H. Bea \textit{et al}., Phys. Rev. Lett. \textbf{102}, 217603 (2009).\\[0pt] [2] R. J. Zeches \textit{et al}., Science \textbf{326}, 977 (2009).\\[0pt] [3] K. T. Ko \textit{et al}., Nat. Commun. \textbf{2}, 567 (2011).\\[0pt] [4] J. C. Yang \textit{et al}., Phys. Rev. Lett. \textbf{109}, 247606 (2012). [Preview Abstract] |
Friday, March 7, 2014 1:51PM - 2:03PM |
Z6.00014: Photo-induced dynamics of charge ordering in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ probed by ultrafast hard x-ray diffraction Yi Zhu, Jason Hoffman, Clare Rowland, Donald Walko, John Freeland, Philip Ryan, Richard Schaller, Anand Bhattacharya, Haidan Wen La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ thin films exhibit strong charge ordering due to charge disproportionation of Fe$^{3+}$/Fe$^{5+}$ ions along the [111] direction below T$_{c}$ $\sim$ 200K. In this study, a La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ thin film was excited by ultrafast 355nm laser pulses, and the response of the charge ordering and the lattice was directly observed via ultrafast hard x-ray diffraction. We identified the threshold of the excitation laser fluence to melt the charge ordering diffraction peak. We also found charge ordering recovers in a few nanoseconds, faster than the lattice recovery. These findings indicate the non-thermal nature of the photo-induced dynamics of charge disordering in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$. [Preview Abstract] |
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