Divalent manganese in A -position of perovskite cell: X-ray absorption finite structure study of La 0.6 Sr 0.4 − x Mn Ti x O manganites A N Ulyanov, D S Yang, N Chau, S C Yu, and S I Yoo Citation: Journal of Applied Physics 103, 07F722 (2008); doi: 10.1063/1.2839318 View online: http://dx.doi.org/10.1063/1.2839318 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/103/7?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Rietveld fitting of x-ray diffraction spectra for the double phase composites La 0.7 − x Sr 0.3 Mn − y O − 1.5 ( x + y ) / ( Mn O ) y / J Appl Phys 105, 013905 (2009); 10.1063/1.3054355 Observation of 300 K high energy magnetodielectric contrast in the bilayer manganite ( La 0.4 Pr 0.6 ) 1.2 Sr 1.8 Mn O Appl Phys Lett 91, 021913 (2007); 10.1063/1.2757120 Electronic and magnetic phase diagram of La 0.5 Sr 0.5 Co − x Fe x O ( x 0.6 ) perovskites J Appl Phys 97, 10A508 (2005); 10.1063/1.1855197 Structural, magnetic, and transport properties in La0.7Ca0.3Mn1−xScxO3 J Appl Phys 90, 4609 (2001); 10.1063/1.1405833 Lattice effects on the magnetic and transport properties of La 0.67−x Sm x Sr 0.33 CoO perovskites Appl Phys Lett 75, 1772 (1999); 10.1063/1.124815 [This article is copyrighted as indicated in the article Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to ] IP: 137.99.31.134 On: Thu, 09 Oct 2014 23:28:42 JOURNAL OF APPLIED PHYSICS 103, 07F722 ͑2008͒ Divalent manganese in A-position of perovskite cell: X-ray absorption finite structure study of La0.6Sr0.4−xMnTixO3 manganites A N Ulyanov,1,a͒,b͒ D S Yang,2 N Chau,3 S C Yu,4 and S I Yoo1,a͒,c͒ Department of Materials Science and Engineering, Seoul National University, Seoul 151-744, Republic of Korea Physics Division, School of Science Education, Chungbuk National University, Cheongju 361-763, Republic of Korea Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Vietnam Department of Physics, Chungbuk National University, Cheongju 361-763, Republic of Korea ͑Presented on November 2007; received 12 September 2007; accepted 10 December 2007; published online 28 February 2008͒ Local structure and magnetic properties of Ti doped A-site deficient La0.6Sr0.4−xMnTixO3+␦ ¯ c phase manganites ͑0.15ജ x ജ 0͒ have been studied The compositions belong to rhombohedral R3 Segregation of ͑La0.6Sr0.4−xMny͒͑Mn1−y−zTix͒O3+␦ phase and fallout of ͑z / 3͒Mn3O4 oxide was observed with x increase Some amount ͑y͒ of Mn, being in divalent valence state, occupies the A ͑=La, Sr͒-position of perovskite cell Samples with x = and 0.05 are ferromagnetic with Curie temperature TC = 350 and 172 K, respectively Samples with x = 0.1 and 0.15 are in spin͑cluster͒-glass states at low temperatures © 2008 American Institute of Physics ͓DOI: 10.1063/1.2839318͔ In the last decades, properties of perovskite such as Ln1−⌬1R⌬1Mn1−⌬2M ⌬2O3 lanthanum manganites have attracted a growing attention because of their interesting properties and rich phase diagram, especially the colossal magnetoresistivity effect observed ͑Ln is a trivalent rare earth, Y; R is a divalent alkali earth, Sn and Pb; and M is a transition metal͒.1 The parent LaMnO3 compound is antiferromagnetic insulator Substitution of trivalent Ln3+ ion by divalent R2+ ion gives rise to a coexistence of Mn3+ and Mn4+ ions and, at some hole doping level ͑⌬1͒, manganites become a conductive ferromagnetic materials According to double exchange ͑DE͒ model,2 transfer of itinerant eg electrons between neighboring Mn3+ and Mn4+ ions through O2− ions results in ferromagnetic interaction due to the on site Hund’s coupling Ion size mismatch was introduced to explain the dependence of Curie temperature ͑TC͒ on average ionic radius in A ͑=Ln, R͒-position of ABO3 perovskite cell.3 B ͑=Mn, M͒-site doping by transition metals damages the traveling path of itinerant eg electrons and changes both magnetic B – O – B interaction, and B–O distances and B – O – B angles, thus, affecting the properties of perovskite manganites ͑e.g., see Refs 4–6 and references therein͒ The effect depends on size and electron configuration of dopants Deficiency of La and/or Mn ions ͑or the oxygen excess ␦͒ in LaMnO3 composition also causes the appearance of Mn3+ – Mn4+ mixedvalence state.7–11 Such, the self-doped manganites exhibit both ferromagnetic-paramagnetic and metal-insulator transitions Properties of A- and B-site substituted manganites have been accurately studied and characterized in literature At the same time, the self-doped compositions are less carefully investigated and their description contains some vagueness.10,12,13 The problem is in the complexity of the a͒ Authors to whom correspondence should be addressed Electronic mail: aគnគulyanov@yahoo.com c͒ Electronic mail: siyoo@snu.ac.kr b͒ 0021-8979/2008/103͑7͒/07F722/3/$23.00 self-doped manganites from the crystallochemistry point of view; how the structure accommodates the nonstoichiometry and vacancies An early structural study of LaMnO3+␦ manganites showed no excess oxygen in the interstitial positions of the perovskite cell.14 Instead, there were found appropriate amounts of vacancies in both La and Mn sites, which indicated the cation deficient origin of the entire structure sceleton Recent magnetic and structural study of La1−⌬1MnO3 ͑0.3ജ ⌬1 ജ 0͒ showed a fallout of Mn3O4 oxide and segregation of vacancy-doped La0.9MnO3 phase with ⌬1 increase.7 The phase segregation explains the composition independent magnetic properties of La1−⌬1MnO3 observed in the wide, 0.3ജ ⌬1 ജ 0.1, range According to Refs and 9, the La1−⌬1MnO3 can accommodate vacancies up to ⌬1 = 0.125 and 0.13, respectively Recently, in the crystallochemical characterization of vacancy-doped LaMnO3 samples with different La/ Mn ratios by neutron diffraction, it was suggested that the occurrence of Mn ions at the La site be at La/ MnϽ 1.10 At the same time, authors noted that the samples’ local structure can be quite satisfactory refined in any ͑with and without Mn in La sublattice͒ distribution models and without supporting additional evidence, it is impossible to choose the proper one The Mn2+ ions were detected in strontium deficiency Pr0.7Sr0.3−xMnO3 manganites by nuclear magnetic resonance spectroscopy, but the location of the ions was not determined.12 To explain the properties of Nd-deficient Nd0.9−xCaxMnO3 compositions, it was hypothesized that a part of Nd ions can be substituted by Mn ions.13 To elucidate these peculiarities, we present the careful local structure analysis of La0.6Sr0.4−xMnTixO3+␦ manganites To this end, we employed the x-ray absorption fine structure ͑XAFS͒ analysis, which gives the information for both the neighborhood of XAFS atoms and their valence states Samples were synthesized and characterized as in Ref 15 La0.6Sr0.4−xMnTixO3+␦ manganites ͑x = 0.0, 0.05, 0.1, and 0.15͒ were prepared by conventional solid state reaction 103, 07F722-1 © 2008 American Institute of Physics [This article is copyrighted as indicated in the article Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to ] IP: 137.99.31.134 On: Thu, 09 Oct 2014 23:28:42 07F722-2 Ulyanov et al J Appl Phys 103, 07F722 ͑2008͒ FIG ͑Color online͒ EXAFS spectra for La0.6Sr0.4−xMnTixO3+␦ manganites ͑x = 0.0, 0.05, 0.1, and 0.15͒, and linear combination ͑LinComb, dotted line͒ for 0.9La0.6Sr0.4MnO3 and ͑0.1/ 3͒Mn3O4 The x = and LinComb lines almost coincide FIG ͑Color online͒ ͑a͒ XANES spectra and temperature dependencies of magnetization ͑on the inset͒ for La0.6Sr0.4−xMnTixO3+␦ manganites ͑x = 0.0, 0.05, 0.1, and 0.15, from the right to the left͒ ͑b͒ XANES spectra for La0.6Sr0.4MnO3 ͑x = 0͒ phase ͑solid line͒, and for linear combination ͑LinComb, dotted line͒ for 0.9La0.6Sr0.4MnO3 and ͑0.1/ 3͒Mn3O4 The x = and LinComb lines almost coincide Figure also shows the XANES spectra for La0.6Sr0.3MnTi0.1O3 ͑x = 0.1͒, LaMnO3, and Mn3O4 and MnO oxides method According to powder x-ray Cu K␣ analysis ͓x-ray diffraction ͑XRD͔͒ the samples belong to rhombohedral ¯ c͒ phase and contain ͑at x 0͒ small amount of Mn O ͑R3 impurity oxide On the basis of the XRD data, the oxide amount is estimated to be less than wt % and no anomalies in the magnetization data could be attributed to the impurity phase Magnetization measurements were carried out with the superconducting quantum interference device ͑Quantum Design MPMSXL͒ magnetometer Curie temperature ͑TC͒, determined as an inflection point on temperature dependence of magnetization, decreases dramatically from 350 to 172 K with x increase from to 0.05 ͑see inset of Fig 1͒ It is believed that compounds with higher x content are in spin͑cluster͒-glass-like state at low temperatures and transition to paramagnetic state is observed at 120 and 100 K for the x = 0.1 and 0.15 samples, respectively Spin ͑cluster͒glass-like behavior of La0.6Sr0.4−xMnTixO3+␦ manganites with x = 0.1 was also reported in Ref 16 Topfer and Goodenough17 also pointed out that lanthanum manganites with small content of cation vacancies exhibit spin-glass behavior below the Curie point Detailed discussion of these features lie beyond the scope of present report and will be published elsewhere XAFS experiments were performed at the 3C extended x-ray absorption fine structure ͑EXAFS͒ beam line of Pohang Light Source ͑PLS͒ in Korea PLS operates with electron energy of 2.5 GeV and maximum current of 230 mA X-rays were monochromatized by Si͑111͒ double-crystal monochromator with energy resolution, ⌬E / E = ϫ 10−4 Higher harmonics were removed by a 15% detuning of the crystal XAFS spectra were obtained near the Mn K edge ͑6540 eV͒ in a fluorescence mode at room temperature XAFS represents EXAFS, and x-ray absorption near edge structure ͑XANES͒ analysis EXAFS gives information about the local structure around central atoms Electronic configuration ͑valence͒ of the core Mn cations can be deduced with the XANES spectra, obtained directly by the normalization of absorption spectra.18 XANES ͑Fig 1͒, EXAFS ͑Fig 2͒, and Fourier transform of EXAFS spectra ͑Fig 3͒ show continuous change with x XANES spectra shift to lower energy and essentially broaden with x It is important to emphasize that XANES spectra of La1−xCaxMnO3 compositions19,20 showed almost the same shape with x and only shifted parallel to each other with increasing of Ca contents The shift of the absorption edge from the lower to higher energy with x was caused by the change of average Mn valence from 3+ ͑in LaMnO3͒ to 4+ ͑in CaMnO3͒ The main absorption for the Mn3+ ion ͑in FIG ͑Color online͒ Fourier transform of EXAFS spectra for La0.6Sr0.4−xMnTixO3+␦ compositions ͑x = 0.0, 0.05, 0.1, and 0.15͒, and linear combination ͑LinComb, dotted line͒ for 0.9La0.6Sr0.4MnO3 and ͑0.1/ 3͒Mn3O4 The x = and LinComb lines almost coincide [This article is copyrighted as indicated in the article Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to ] IP: 137.99.31.134 On: Thu, 09 Oct 2014 23:28:42 07F722-3 J Appl Phys 103, 07F722 ͑2008͒ Ulyanov et al LaMnO3͒ was observed at the interval from 6550 to 6556 eV A very different picture has been observed in our study ͑see Fig 1, where XANES spectra for La0.6Sr0.4−xMnTixO3+␦, MnO, and Mn3O4 are presented͒ The spectrum for the La0.6Sr0.4MnO3 ͑x = 0͒ composition shows almost the same shape and position as those in La0.7Ca0.3MnO3 ͑Ref 19͒ and even small amount of Ti ͑x = 0.05͒ causes considerable changes in XANES spectra The spectra become broader because of increase of absorption at low energy ͑E Ͻ 6.55 keV͒—the low energy “tail” appears The tail becomes wider and more intensive with x The changes of XANES spectra probably originate from the occurrence of divalent Mn ions, which is manifested by the appearance of x-ray absorption at energies lower than that for the LaMnO3, where the Mn is only in trivalent state ͓see Fig 1͑a͒ and 1͑b͔͒ Sharp increase of absorption for the x = 0.1 and 0.15 compositions begins at the same energy as that for Mn2+ ion in MnO oxide Essential changes of EXAFS spectra ͑Fig 2͒ and Fourier transform of EXAFS spectra ͑Fig 3͒ are also observed The changes can be attributed to nonuniform distribution of Mn ions—partial occupation of A-position by the Mn ions Really, it is well established18 that the ͑i͒ regularity in appearance of high intensity peaks of Fourier transform of EXAFS spectra, as for the x = samples, evidences for uniform distribution of Mn atoms in lattice, and, vice versa, a complete disappearance of third and forth peaks with x, as for the x ജ 0.10 compositions, is an evidence of nonuniform distribution of Mn ions in perovskite cell and ͑ii͒ smoothing of EXAFS spectra also confirms the nonuniform distribution of XAFS atoms in compositions studied We suppose that the Mn2+ occupy the A-position, and Mn3+,4+ ions, as usually, occupy the B ͑=Mn, Ti͒-site By normalizing the number of atoms in B-site to unit the La0.6Sr0.4−xMnTixO3+␦ compositions can be presented as self-doped A-site deficient compositions of La0.6/͑1+x͒Sr͑0.4−x͒/͑1+x͒Mn1/͑1+x͒Tix/͑1+x͒O3 The A-position is occupied by La3+ and Sr2+ ions with ionic radii 1.216 and 1.31 Å, respectively ͑all ionic radii are taken according to Shannon21͒ The most preferable ions, which can occupy the A-position ͑to accommodate the vacancies͒ among the Mn2+ ͑=0.83 Å͒, Mn3+ ͑=0.645 Å͒, and Mn4+ ͑=0.53 Å͒ are the Mn2+ ion as the largest one We have to note that if the Ti4+ ͑=0.605 Å͒ ions occupy the A-position there will not be strong change in the EXAFS and Fourier spectra There will be the only a weak change in intensity of second peak, which is caused by the backscattering of electrons by the atoms, located in the A-position ͑e.g., see results for La0.7Ca0.3−xBaxMnO3 manganites22͒ Thus, it is finally possible to describe the compositions as ͑La0.6Sr0.4−xMny͒ ϫ͑Mn1−y−zTix͒O3+␦1 + ͑z / 3͒Mn3O4, where y and z depend on x The atoms in first and second brackets occupy the A- and B-positions, respectively Similar La0.9MnO3 + ͑z / 3͒Mn3O4 segregation in the range 0.9ജ La/ Mnജ 0.7 was reported7 when studying the La1−⌬1MnO3 compositions To be sure that the change in XAFS spectra, observed with x, are not caused by the fall out of the parasitic Mn3O4 phase, the simulation of the spectra was done We fitted the XANES, EXAFS and Fourier transform of EXAFS spectra by linear combination ␤ ␮LinComb = ͑1 − ␤͒␮͑La0.6Sr0.4MnO3͒ + ␮͑Mn3O4͒ ͑1͒ of spectra for La0.6Sr0.4MnO3 phase and Mn3O4 ͑similar to fitting presented in Ref 7͒ Only very weak changes of the spectra ͑for ␤ = 0.1͒ were obtained It confirms that the changes observed in XAFS spectra are caused by the internal change of local structure of La0.6Sr0.4−xMnTixO3+␦ with Ti content Change in Curie temperature for the B-site substituted manganites mainly originates from the weakening of the DE interaction due to the breaking of the pathway for itinerant eg electrons caused by the difference in electron configurations between the Mn3+, Mn4+ ions, and transition metal ions ͑E-factor͒ and by the structural S-factor: change of ͗Mn–O͘ bond distances and ͗Mn–O–Mn͘ bond angles because of the difference in Mn and dopant size ionic radii ͑see, e.g., Ref and references therein͒ The stronger TC decrease in La0.6Sr0.4−xMnTixO3+␦ than that in La0.7Ca0.3Mn1−xTixO3 ͑Ref 4͒ and La0.7Sr0.3Mn1−xTixO3 ͑Ref 5͒ is obviously caused by the occurrence of Mn2+ ions in A-position of perovskite cell and deficiency of atoms in above position in addition to the E- and S-factors In conclusion, the segregation of ͑La0.6Sr0.4−xMny͒ ϫ͑Mn1−y−zTix͒O3+␦1 phase and fallout of ͑z / 3͒Mn3O4 oxide with x increase was observed The x increase causes the Mn2+ ions appearance and deficiency of atoms in A-position, which together with the substitution of Ti for Mn in B-site causes the strong decrease in Curie temperature and changes the character of low temperature magnetic state of samples with high x value The research was supported by BK21 Materials Education and Research Division B Salamon and M Jaine, Rev Mod Phys 73, 583 ͑2001͒ C Zener, Phys Rev 82, 403 ͑1951͒ H Y Hwang et al., Phys Rev Lett 75, 914 ͑1995͒ X Liu, X Xu, and Y Zhang, Phys Rev B 62, 15112 ͑2000͒ N Kallel et al., J Magn Magn Mater 261, 56 ͑2003͒ A N Ulyanov and S C Yu, J Appl Phys 97, 10H702 ͑2005͒ G Dezanneau et al., Phys Rev B 69, 014412 ͑2004͒ P A Joy et al., J Phys.: Condens Matter 14, L663 ͑2002͒ V Markovich et al., J Phys.: Condens Matter 15, 3985 ͑2003͒ 10 M Wołcyrz et al., J Alloys Compd 353, 170 ͑2003͒ 11 V Markovich et al., Phys Rev B 63, 054423 ͑2001͒ 12 D Abou-Ras et al., J Magn Magn Mater 233, 147 ͑2001͒ 13 I O Troyanchuk et al., J Magn Magn Mater 303, 111 ͑2006͒ 14 B C Tofield and W R Scott, J Solid State Chem 10, 183 ͑1974͒ 15 A N Ulyanov et al., J Magn Magn Mater 300, e175 ͑2006͒ 16 M Phan et al., Abstracts of 49th Annual Conference on Magnetism and Magnetic Material, Jacksonville, Florida, USA, November, 2004 ͑unpublished͒ 17 J Topfer and J B Goodenough, Chem Mater 9, 1467 ͑1997͒ 18 X-ray absorption: Principles, Applications, Techniques of EXAFS, and XANES, edited by D C Koningsberger and R Prins ͑Wiley Interscience, New York, 1988͒ 19 C H Booth et al., Phys Rev B 57, 10440 ͑1998͒ 20 G Subías et al., Phys Rev B 56, 8183 ͑1997͒ 21 R D Shannon, Acta Crystallogr., Sect A: Cryst Phys., Diffr., Theor Gen Crystallogr 32, 751 ͑1976͒ 22 A N Ulyanov et al., J Phys Soc Jpn 72, 1204 ͑2003͒ [This article is copyrighted as indicated in the article Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to ] IP: 137.99.31.134 On: Thu, 09 Oct 2014 23:28:42 ...JOURNAL OF APPLIED PHYSICS 103, 07F722 ͑2008͒ Divalent manganese in A-position of perovskite cell: X-ray absorption finite structure study of La0.6Sr0.4−xMnTixO3 manganites A N Ulyanov,1,a͒,b͒... oxygen in the interstitial positions of the perovskite cell.14 Instead, there were found appropriate amounts of vacancies in both La and Mn sites, which indicated the cation deficient origin of the... Ti content Change in Curie temperature for the B-site substituted manganites mainly originates from the weakening of the DE interaction due to the breaking of the pathway for itinerant eg electrons