{"id":1064,"date":"2017-02-16T17:19:33","date_gmt":"2017-02-16T17:19:33","guid":{"rendered":"http:\/\/www.demo.onlypixels.com\/iisc-phy-anil\/?page_id=1064"},"modified":"2024-04-05T05:59:44","modified_gmt":"2024-04-05T05:59:44","slug":"multifunctional-oxides","status":"publish","type":"page","link":"https:\/\/physics.iisc.ac.in\/~anil\/research\/multifunctional-oxides\/","title":{"rendered":"Multifunctional Oxides"},"content":{"rendered":"\n

Transition metal oxides (TMO) provides an ideal platform for the study of electron correlations, due to their significant electronic and magnetic properties arise from the complex interactions between their charge, orbital, spin, and lattice degrees of freedom. Among TMOs, perovskite oxides and their heterostructures are most popular for their exciting electronic and magnetic properties. Spinels, especially ferrites are another class of oxide material that exhibit interesting properties as well as promising applications. <\/p>\n\n\n\n

 In our lab, we are extensively using Pulsed Laser Deposition (PLD) technique to grow high quality epitaxial oxide thin films by monitoring the atomic layer-by-layer growth using Reflection High Energy Electron Diffraction (RHEED) system. For the bulk sample preparation, we have access to a dedicated chemical lab where we perform the synthesis of oxide materials using either solid state synthesis route or with different aqueous solution techniques (gel routes) such as sol-gel method, pechini method, citrate method and amorphous citrate method.   Bulk samples as well as thin films grown in our lab so far includes Manganites, Iridates, Nickelates, Ferrites etc.  X-Ray diffraction techniques were mainly used for the verification of crystal structure and phase identification of these bulk and thin film samples. Apart from X-ray diffraction techniques, we also use Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), Scanning Transmission Electron Microscopy (STEM) and Transmission Electron Spectroscopy (TEM) to do the structural characterizations of the epitaxial thin films grown using PLD. Moreover, we have access to a well-functioned central lab facility mainly maintained by our lab, for conducting various transport and magnetic property studies. The thermomagnetic and isothermal field dependent magnetization measurements were used to carried out in a commercial SQUID magnetometer, while the zero-field and filed dependent transport measurements were used to performed using a PPMS system. Glimpse of some of the significant outcomes from our lab can be found in the following sections.<\/p>\n\n\n\n

Magnetoresistance effects in Pt\/EuO1\u2212x<\/sub><\/h2>\n\n\n\n

We report on the angular and field dependence of the magnetoresistance (MR) in bilayers of Pt\/EuO1\u2212x thin films, measured in both in-plane and out-of-plane geometries at different temperatures (T). The presence of oxygen vacancies manifested by a metal\u2013insulator transition as well as a high-T ferromagnet-to-paramagnet transition (TP<\/sub>) was observed in the bilayers. The anisotropic magnetoresistance could be extracted in the entire T-range, even above TP<\/sub>, exhibiting two sign crossovers. We attribute its T-evolution to the rotation of the easy axis of the magnetization direction from a high-T out-of-plane to a low-T in-plane orientation. In addition, we provide direct experimental evidence of the spin Hall effect-induced spin Hall magnetoresistance, systematically considering several known MR contributions that can arise from the films’ (111) texture and interface.<\/p>\n\n\n\n

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(a) Schematic of the sample stack, Hall bar, and the measurement configuration. The adopted coordinate systems defined by j, t, and n are labeled. (b) Different configuration adopted in ADMR measurements. (c) M\u2013H hysteresis loops at 10\u2009K with the field applied along j and n highlighting the ip easy axis direction.<\/em><\/p>\n\n\n\n

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(a) R(H) at different T values for H oriented parallel (\u03b3=0\u00b0) and perpendicular (\u03b3=90\u00b0) to n. The magnified figure depicts the expanded view near the origin showing the hysteretic switching of R. (b) confirms the linear relationship between the calculated AMR and the applied AC. (c) T-dependence of the scaled AMR. The 0.25\u2009T data correspond to the ADMR results, whereas data for the other two H values are extracted from FDMR. (d) High temperature sign crossover temperature at different applied H values (0.06\u2009T and 0.20\u2009T correspond to field sweep and 0.25\u2009T to field rotation) obtained from (c)<\/em><\/p>\n\n\n\n

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https:\/\/aip.scitation.org\/doi\/full\/10.1063\/5.0004049<\/a><\/p>\n\n\n\n

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Role of spin mixing conductance in determining thermal spin pumping near the ferromagnetic phase transition in EuO1\u2212x <\/sub>and La2<\/sub>NiMnO6<\/sub><\/h2>\n\n\n\n

We present a comprehensive study of the temperature (T) dependence of the longitudinal spin Seebeck effect (LSSE) in Pt\/EuO1\u2212x and Pt\/La2NiMnO6 (LNMO) hybrid structures across their Curie temperatures (Tc). Both systems host ferromagnetic<\/em> interaction below Tc, and hence present optimal conditions for testing magnon spin current based theories against ferrimagnetic<\/em> yttrium iron garnet. Notably, we observe an anomalous Nernst effect generated voltage in bare EuO1\u2212x, however, we find LSSE predominates the thermal signals in the bilayers with Pt. The T dependence of the LSSE in small T range near Tc could be fitted to a power law of the form (Tc\u2212T)P. The derived critical exponent P was verified for different methods of LSSE representation and sample crystallinity. The results are explained based on the magnon-driven thermal spin pumping mechanism that relates the T dependence of LSSE to the spin mixing conductance (Gmix) at the heavy metal\/ferromagnet interface, which in turn is known to vary in accordance with the square of the spontaneous magnetization (Ms). Additionally, the T dependence of the real part of Gmix derived from spin Hall magnetoresistance measurements at different temperatures for the Pt\/LNMO structure further establishes the interdependence.<\/p>\n\n\n\n

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(a),(c) HR-XRD of the epitaxial LNMO\/STO and polycrystalline Pt\/EuO\/Pt\/Si sample respectively. Inset of (a) shows the presence of clear Laue oscillations on either side of the substrate peak. Panels (b) and (d) represent the final device configuration for LSSE measurements.<\/em><\/p>\n\n\n\n

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(a) Variation of VISHE with in-plane angle \u03b1 at 50 K and subsequent fit to a sine function to determine the amplitude, denoted by an arrow. (b) Hysteretic switching of VISHE as function of in-plane field applied along \u03b1=0 at 175 K. (c),(d) resistivity as a function of temperature for Pt and LNMO layer respectively, (e) LSSE amplitudes represented as SSC (open triangles) and SSR (open circles) at different temperature and power law fitting near Tc. Insets show linear relation between generated voltage, temperature gradient and applied power.<\/em><\/p>\n\n\n\n

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(a) Schematic illustration of the device geometry used for measuring ANE. (b) Variation of stack resistance with temperature for conducting EuO1\u2212x and insulating LNMO. Inset shows the peak in dR\/dT for the conducting EuO1\u2212x at Tc of bulk EuO. (c) Calculated T dependence of resistivity of EuO1\u2212x considering a trilayer resistance model. (d) Measured ANE, ANEred, and ( ANEred + LSSE) voltage in EuO1\u2212x and Pt(5 nm)\/ EuO1\u2212x at 25 K as a function of in-plane field angle for a constant power of 2 mW. The values are scaled as ( VTH\u00d7heater area)\/ L. (e) Field dependence of the thermal voltage in Pt\/EuO1\u2212x for different applied power confirming the ferromagnetic origin of the signal. (f),(g) T dependence of the reduced ANE voltage for EuO1\u2212x (red triangles) and reduced ANE + LSSE for Pt\/EuO1\u2212x (blue circles) in SSC and SSR units respectively. (h) LSSE voltages as SSC and SSR after separation of reduced ANE voltage from the total thermal voltage. Corresponding fits to power law and value of critical exponents are also indicated.<\/em><\/p>\n\n\n\n

https:\/\/journals.aps.org\/prb\/abstract\/10.1103\/PhysRevB.100.224403<\/a><\/p>\n\n\n\n

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Structural and electrical transport properties of two distinct phases of epitaxial SrIrO3<\/sub> thin films<\/h2>\n\n\n\n

Metastable orthorhombic SrIrO3<\/sub> (SIO) is an arch-type spin-orbit coupled material. In this work, we demonstrate a controlled growth of relatively thick (200 nm) SIO films that transform from bulk “6H-type” structure with monoclinic distortion to an orthorhombic lattice by controlling growth temperature. Extensive studies based on high-resolution X-ray diffraction and transmission electron microscopy infer two distinct structural phases of SIO. Electrical transport reveals a weak temperature-dependent semi-metallic character for both phases. However, the temperature-dependent Hall-coefficient for the orthorhombic SIO exhibits a prominent sign change, suggesting a multiband character in the vicinity of EF<\/sub>. These findings thus unravel the subtle structure-property relation in SIO epitaxial thin films. In essence, our study delineates the distinct structural and electrical transport properties of monoclinic vs. orthorhombic SIO thin films which are important to understand the underlying electronic properties and structural stability of SIO thin films for developing the future oxide electronic technology.<\/p>\n\n\n\n

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https:\/\/iopscience.iop.org\/article\/10.1209+\/0295-5075\/122\/28003\/pdf<\/a><\/p>\n\n\n\n

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Magnetic ground state of the multiferroic hexagonal  LuFeO3<\/sub>  <\/h2>\n\n\n\n

In this study, we have successfully stabilized a single phase hexagonal LuFeO3<\/sub> in the bulk form without any doping by sol-gel method and investigated its structural, electric, and magnetic properties. The hexagonal crystal structure with P63<\/sub>cm<\/em> space group has been confirmed by x-ray-diffraction, neutron-diffraction, and Raman spectroscopy study at room temperature. Neutron diffraction confirms the hexagonal phase of LuFeO3<\/sub> persists down to 6 K. Further, the x-ray photoelectron spectroscopy established the 3+ oxidation state of Fe ions. The temperature-dependent magnetic dc susceptibility, specific heat, and neutron-diffraction studies confirm an antiferromagnetic ordering below the N\u00e9el temperature (TN<\/sub>) \u223c130K. Analysis of magnetic neutron-diffraction patterns reveals an in-plane (ab-plane) 120\u2218<\/sup> antiferromagnetic structure, characterized by a propagation vector k=(000) with an ordered moment of 2. 84\u03bcB<\/sub>\/Fe3+<\/sup> at 6 K.<\/p>\n\n\n\n

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The 120\u2218<\/sup> antifferomagnetic ordering is further confirmed by spin-orbit coupling density functional theory calculations. The on-site coulomb interaction (U) and Hund’s parameter (JH<\/sub>) on Fe atoms reproduced the neutron-diffraction \u03931<\/sub> spin pattern among the Fe atoms. P\u2212E<\/em> loop measurements at room temperature confirm an intrinsic ferroelectricity of the sample with remnant polarization Pr<\/sub>\u223c0.18\u03bcC\/cm2<\/sup>. A clear anomaly in the dielectric data is observed at \u223cTN<\/sub> revealing the presence of magnetoelectric coupling. A change in the lattice constants at TN<\/sub> has also been found, indicating the presence of a strong magnetoelastic coupling. Thus, a coupling between lattice, electric, and magnetic degrees of freedom is established in bulk hexagonal LuFeO3<\/sub>. This makes the material a fascinating candidate for fundamental physics and also promising from a practical application point of view.<\/p>\n\n\n\n

https:\/\/journals.aps.org\/prb\/pdf\/10.1103\/PhysRevB.97.184419<\/a><\/p>\n\n\n\n

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Interface-induced exchange bias effects in bilayer LSMO\/ ESMO heterostructures <\/h2>\n\n\n\n

In this project, we fabricated Eu0.45<\/sub>Sr0.55<\/sub>MnO3<\/sub> (ESMO) layers epitaxially conjoined at the interface to La0.7<\/sub>Sr0.3<\/sub>MnO3<\/sub> (LSMO) layers with a bilayer heterostructure form and also their single reference layers on SrTiO3<\/sub> (001) substrate. Interestingly, we observed a zero-field-cooled spontaneous-positive and field-cooled conventional-negative exchange bias effects in epitaxial bilayer composed of LSMO with ferromagnetic (FM) and ESMO with A-type antiferromagnetic (AF) heterostructures respectively. A temperature dependent magnetization study of LSMO\/ESMO bilayers manifest FM ordering (TC<\/sub>) of LSMO at ~320\u2009K, charge\/orbital ordering of ESMO at ~194\u2009K and AF ordering (TN<\/sub>) of ESMO at ~150\u2009K. The random field Ising model has demonstrated an interesting observation of inverse dependence of exchange bias effect on AF layer thickness due to the competition between FM-AF interface coupling and AF domain wall energy. The isothermally field induced unidirectional exchange anisotropy formed at the interface of FM-LSMO layer and the kinetically phase-arrested magnetic phase obtained from the metamagnetic AF-ESMO layer could be responsible for the spontaneous exchange bias effect. Importantly, no magnetic poling is needed, as necessary for the applications.<\/p>\n\n\n\n

\"\"<\/figure><\/div>\n\n\n\n

The FM-AF interface exchange interaction has been ascribed to the AF coupling with \u2211J<\/strong>ex<\/sub>S<\/em><\/strong>FM<\/sub>\u22c5S<\/em><\/strong>AF<\/sub> (J<\/strong>ex<\/sub>\u2248J<\/strong>AF<\/sub>, coupling constant between AF spins) for the spontaneous positive hysteresis loop shift, and the field-cooled conventional exchange bias has been attributed to the ferromagnetically exchanged interface with J<\/strong>ex<\/sub>\u2248J<\/strong>F<\/sub> (coupling constant between FM spins). The conjunction of spontaneous exchange bias effect along with conventional exchange bias effect is a highly desirable attribute as it can reveal an additional degree of freedom that can be harnessed in spintronic device applications. Thus, our observations offer a new perspective to study the EB effect without magnetically annealing the sample.<\/p>\n\n\n\n

https:\/\/www.nature.com\/articles\/s41598-017-07033-x<\/a><\/p>\n\n\n\n

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Inter-layer magneto-electric coupling in BiFeO3<\/sub>\/SrRuO3<\/sub> heterostructure <\/h2>\n\n\n\n

This work discusses about the existence of a strong magnetic interaction and magneto-electric coupling between the BiFeO3<\/sub> (BFO) and SrRuO3<\/sub> (SRO) layers in a heterostructure. Interlayer magneto-electric coupling was investigated by impedance spectroscopy over a temperature range of 80\u2009K\u2013260\u2009K. In-plane impedance measurements were performed using interdigitated gold electrodes fabricated on the BFO layer. The Nyquist plots at different temperatures were fitted with an equivalent circuit model of the heterostructure. A pronounced dip in the temperature coefficient of equivalent-capacitance and a distinct increase in the temperature coefficient of equivalent-resistance of the BFO layer were observed on cooling across ferromagnetic TC<\/sub> of the bottom SRO layer.<\/p>\n\n\n\n

Temperature dependent capacitance (at 0\u2009T magnetic fields) and magneto-capacitance (at 5\u2009T magnetic fields) plots showed anomalies near 160\u2009K. A shift of the hysteresis loop along the magnetization axis in field cooled M-H measurements was also found, which indicates the presence of pinned SRO moments due to the magnetic interaction at the interface. These observations suggest a strong magneto-electric coupling between the BiFeO3<\/sub> and SrRuO3<\/sub> layers of this heterostructure.<\/p>\n\n\n\n

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https:\/\/aip.scitation.org\/doi\/full\/10.1063\/1.5001480<\/a><\/p>\n\n\n\n

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Antiphase boundary (APB) induced anomalous weak ferromagnetism and exchange bias effect in single-phase antiferromagnetic compound LMFO<\/h2>\n\n\n\n

The emergence of exchange bias effect in Fe3<\/sub>O4<\/sub> thin films has been since attributed to the presence of antiphase boundary (APB) growth defects despite lack of direct experimental evidence. This report demonstrates the APB induced anomalous weak ferromagnetism and exchange bias property of single-phase antiferromagnetic (AFM) system LuMn0.5<\/sub>Fe0.5<\/sub>O3<\/sub> (LMFO). 57<\/sup>Fe M\u00f6ssbauer spectroscopy and high-resolution transmission electron microscopy (HRTEM) measurements were used to probe the origin of the observed effect.<\/p>\n\n\n\n

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In addition to the sextet component corresponding to the long-range AFM ordering, the measured M\u00f6ssbauer spectra reveal the presence of a small component (10%\u201312%) near zero velocity with unusually small internal field. This indicates the presence of APB defects. From micro structural investigations using HRTEM, presence of APB type defects and dislocations are confirmed. In addition to the exchange bias effect, upon field cooling, hysteresis loop exhibits large vertical shift due to strong pinning effect of the APB. Finally, we further annealed the optimally sintered sample LMFO and studied the evolution of defects, and their influence on weak ferromagnetism and exchange bias properties. These new experimental findings may pave the way in creating novel functionalities in materials using APB-type growth defects.<\/p>\n\n\n\n

https:\/\/iopscience.iop.org\/article\/10.1088\/1361-648X\/aacc09\/pdf<\/a><\/p>\n\n\n\n

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Present Members:<\/h2>\n\n\n\n
  • Amrit Raj K<\/li>
  • Krishna Jha<\/li>
  • Santosh Kumar Khetan<\/li>
  • Pranjul Garg<\/li>
  • Dr. Aditya Wagh<\/li>
  • Dr. Shwetha Bhat<\/li><\/ul>\n\n\n\n

    Past Members:<\/h2>\n\n\n\n
    • Dr. Debkanta Samal<\/li>
    • Dr. Debangsu Roy<\/li>
    • Dr. Kaustuv Manna<\/li>
    • Dr. Chanchal Sow<\/li>
    • Dr. Anomitra Sil<\/li>
    • Dr. Tanushree Sarkar<\/li>
    • Dr. Kingshuk Mallick<\/li>
    • Dr. P. Monalisha<\/li>
    • Dr. Mithun Ghosh<\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"

      Transition metal oxides (TMO) provides an ideal platform for the study of electron correlations, due to their significant electronic and magnetic properties arise from the complex interactions between their charge, orbital, spin, and lattice degrees of freedom. Among TMOs, perovskite oxides and their heterostructures are most popular for their exciting electronic and magnetic properties. Spinels, […]<\/p>\n","protected":false},"author":3,"featured_media":0,"parent":171,"menu_order":4,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1064","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/pages\/1064"}],"collection":[{"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/comments?post=1064"}],"version-history":[{"count":15,"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/pages\/1064\/revisions"}],"predecessor-version":[{"id":2107,"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/pages\/1064\/revisions\/2107"}],"up":[{"embeddable":true,"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/pages\/171"}],"wp:attachment":[{"href":"https:\/\/physics.iisc.ac.in\/~anil\/wp-json\/wp\/v2\/media?parent=1064"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}