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Effect of iron doping on electrical, electronic and magnetic properties of La 0.7 Sr 0.3 MnO 3

Effect of iron doping on electrical, electronic and magnetic properties of La 0.7 Sr 0.3 MnO 3. S. I. Patil Department of Physics, University of Pune. March. 15, 2012.

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Effect of iron doping on electrical, electronic and magnetic properties of La 0.7 Sr 0.3 MnO 3

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  1. Effect of iron doping on electrical, electronic and magnetic properties of La0.7Sr0.3MnO3 S. I. Patil Department of Physics, University of Pune March. 15, 2012

  2. The effective resistance is greater in the antiparallel configuration than in the parallel configuration, no mailer what the sign of βis. This model is directl inferred from the two-current model, where the current of both spin orientations are assumed separate. This is a reasonable model because a scattering event where the electron flips its spin while keeping its velocity is very rare.

  3. T = 4.2K T = 4.2K Magnetoresistance of a Fe/Cr superlattice. This effect is now obtained at room temperature and fields of about hundred Gauss. ( Baibich and Fert 1988 )

  4. INTRODUCTION Colossal Magnetoresistance La1-xAxMnO3 based perovskite materials Paramagnetic ferromagnetic transition Metal-insulator transition Charge order Mn O A : Divalent atom Hole doping Ca, Sr, Ba etc. La

  5. La0.7Ca0.3MnO3

  6. eg eg t2g t2g O MECHANISMS A: Divalent atom Mn is in Mn+3 & Mn+4 states eg Double exchange & J-T distortion of MnO6 octahedra are the main factors. t2g Mn3+ Mn4+ Double Exchange Mn3+ Crystal field splitting Jahn-Teller Distortion Mn A : Tetravalent atom (Ce4+) Electron doping Same mechanisms Mn is in Mn+3 & Mn+2 states

  7. G – Type CaMnO3 A – Type LaMnO3 The interaction is ferromagnetic for overlap of dz2 orbitals in the plane, and antiferromagnetic along the perpendicular axis

  8. A schematic view of Jahn-Teller distortion of an Mn+3 ion. Distortion of MnO6 octahedra due to Jahn-Teller distortion

  9. Illustration of the orbital overlap in a plane of the perovskite structure. The dxy orbital (a t2g orbital) has little overlap with the 2p orbitals of the oxygen neighbours, whereas the dx2 and dy2 orbitals (eg orbitals) overlap strongly with the oxygen px or py orbitals to form a σ* band. Displacements of the oxygen atoms in the plane are indicated by arrows.

  10. FIG. 1. View of the CE phase in the x-y plane. We choose our basis orbitals such that the gray lobes of the shown orbitals have a negative sign. The dots at the bridge sites represent a • charge surplus. PHYSICAL REVIEW LETTERS 83, 5118 , 1999

  11. Schiffer et al. PRL 75 3336-3339 (1995)

  12. Manganites (La1-xAxMnO3 ) Synthesis (Polycrystalline samples by Solid State Reaction Route and Thin Films by Pulsed Laser Deposition Doping of magnetic and non-magnetic Element at different site Charge Ordering and Phase Separation Ion Implantation and Heavy Ion Irradiation Diluted magnetic Semiconductors : ZnO, CuAlO2, TiO2

  13. Proposed phase diagram of La1-xSrxMnO3 showing coexistence of FM, AFM, and CO phases. I stands for insulator and M for metal. (The capital letters indicate the predominant phase while the lowercase letters are for the minority phase). Patil S I et.al. Phys. Rev. B, 62, 9548–9554 (2000).

  14. Why is it special? Why is wavelength important? sample sample Visible light X-rays To penetrate a sample, you need a wavelength of similar, or smaller magnitude.

  15. Why is it special?

  16. How does it work? Creating the light

  17. Electrons are generated here And initially accelerated in the LINAC How does it work?

  18. How does it work? Then they pass into the booster ring where they are accelerated to 99.9986% of the speed of light

  19. How does it work? And are finally transferred into the storage ring

  20. How does it work? Types of light sources Bending magnet Sweeping searchlight At each deflection of the electron path a beam of radiation is produced. Insertion devices - produce higher intensity Wiggler Beams emitted at each pole reinforce each other and appear as a broad beam of incoherent light. Undulator Produces a very narrow beam of coherent light, amplified by up to 104

  21. Properties? Synchrotron light - properties Brilliant - many orders of magnitude brighter than conventional sources, enabling quick experiments on small samples. Collimated- beam can be focussed down to less than a micron (10-6m) across, enabling chemical speciation to be mapped. Polarised- linear polarisation, minimises background scattering, improves sensitivity Pulsed- electron bunches produce light pulses, enabling process kinetics to be followed. Continuous spectrum- from infrared to hard x-rays, optical devices select and scan the light’s energy.

  22. Properties? Properties of synchrotron light 1. Brilliant - many orders of magnitude brighter than conventional sources, enabling quick experiments on small samples.

  23. Properties? 2. Continuous spectrum- from infrared to hard x-rays

  24. Band structure of Fe and Mn in b) La1-xCaxMn1-yFeyO3 , where the Fe eg↑ band is completely filled and (1-x-y)/2(1-y) of the Mn eg↑ band is filled. a) La1-xCaxFe1-xMnxO3 , where the bottom of the Mn eg↑ band lies slightly below the top of the Fe eg↑ band

  25. X-ray diffraction study of La0.7Sr0.3MnO3 (LSMO) & La0.7Sr0.3Mn0.95Fe0.05O3 (LSMFO) X-ray diffractograms show single phase formation for both LSMO and LSMFO with orthorhombic structure. J. Phys. D: Appl. Phys. 42, 185410 (2009)

  26. Valence Band Structure of La0.7Sr0.3MnO3 & La0.7Sr0.3Mn0.95Fe0.05O3 In perovskite manganites, the Mn ion is surrounded by six oxygen anions (O-2) in octahedral cage, giving rise to the splitting of degenerate 3d orbitals of Mn+3 in to eg() and t2g() levels. The peak A and B are attributed to the eg() and t2g() levels. The peak C is assigned to the O-2p () character. There is huge change (~80%) in the density of state (DOS) near fermi level (EF) for 5% doping of Fe at Mn site in pure LSMO. Thus it appears that the chemical substitutions plays crucial role in manganites and drastically modify the electronic structure near EF. J. Phys. D: Applied Physics 42, 185410 (2009)

  27. Deconvoluted VBS spectra O-2p (π) The spectra were deconvoluted using three Gaussian peaks of fixed FWHM (2 eV). The intensity features at A and B are due to the Mn-3d character . Peaks A and B are attributed to the eg(σ ) and t2g(π) levels, respectively Peak C is due to the O-2p (π) character eg states are pushed towards EF on Fe doping, thereby increasing the DOSs at EF and the overlap between the O-2p and eg states decreases on Fe doping (encircled region). t2g(π) eg(σ ) J. Phys. D: Applied Physics 42, 185410 (2009)

  28. Resistivity vs Temperature for La0.7Sr0.3MnO3 & La0.7Sr0.3Mn0.95Fe0.05O3 LSMFO shows insulator to metal transition (IMT) around 330 K. Insulator to metal transition (IMT) could not be observed for pure LSMO. Both the samples are in metallic state at room temperature, which is also evident from the VBS measurements. LSMFO shows higher value of resistivity as compared to that of LSMO. This result is in contrast with that of valence band measurements, which suggests that LSMFO have higher DOS at EF and hence should be more metallic than that of LSMO.

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