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

The effective resistance is greater in the antiparallel configuration than in the parallel configuration, no mailer what the sign of β is. 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.

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

La 1-x A x MnO 3 based perovskite materials Metal- insulator transition Charge order Paramagnetic ferromagnetic transition Colossal Magnetoresist ance La O Mn A : Divalent atom Hole doping Ca, Sr, Ba etc. INTRODUCTION

La 0.7 Ca 0.3 MnO 3

MECHANISMS A: Divalent atom Mn is in Mn +3 & Mn +4 states A : Tetravalent atom (Ce 4+ ) Electron doping Mn is in Mn +3 & Mn +2 states Double exchange & J-T distortion of MnO 6 octahedra are the main factors. Same mechanisms O t 2g egeg egeg Double Exchange Mn 3+ Mn 4+ t 2g egeg Jahn-Teller Distortion Crystal field splitting Mn Mn 3+

G – Type CaMnO 3 A – Type LaMnO 3 The interaction is ferromagnetic for overlap of dz 2 orbitals in the plane, and antiferromagnetic along the perpendicular axis

A schematic view of Jahn-Teller distortion of an Mn +3 ion. Distortion of MnO 6 octahedra due to Jahn-Teller distortion

Illustration of the orbital overlap in a plane of the perovskite structure. The d xy orbital (a t 2g orbital) has little overlap with the 2p orbitals of the oxygen neighbours, whereas the dx 2 and dy 2 orbitals (e g orbitals) overlap strongly with the oxygen p x or p y orbitals to form a σ* band. Displacements of the oxygen atoms in the plane are indicated by arrows.

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

Schiffer et al. PRL (1995)

Diluted magnetic Semiconductors : ZnO, CuAlO 2, TiO 2 Manganites (La 1-x A x MnO 3 ) Doping of magnetic and non-magnetic Element at different site Synthesis (Polycrystalline samples by Solid State Reaction Route and Thin Films by Pulsed Laser Deposition Ion Implantation and Heavy Ion Irradiation Charge Ordering and Phase Separation

Proposed phase diagram of La 1-x Sr x MnO 3 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).

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

Why is it special?

Creating the light How does it work?

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

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

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

Bending magnet Sweeping searchlight At each deflection of the electron path a beam of radiation is produced. Undulator Produces a very narrow beam of coherent light, amplified by up to 10 4 Types of light sources Insertion devices - produce higher intensity Wiggler Beams emitted at each pole reinforce each other and appear as a broad beam of incoherent light. How does it work?

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 -6 m) 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. Synchrotron light - properties Properties?

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

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

b) La 1-x Ca x Mn 1-y Fe y O 3, where the Fe e g↑ band is completely filled and (1-x-y)/2(1-y) of the Mn e g↑ band is filled. a) La 1-x Ca x Fe 1-x Mn x O 3, where the bottom of the Mn e g↑ band lies slightly below the top of the Fe e g↑ band Band structure of Fe and Mn in

X-ray diffraction study of La 0.7 Sr 0.3 MnO 3 (LSMO) & La 0.7 Sr 0.3 Mn 0.95 Fe 0.05 O 3 (LSMFO) J. Phys. D: Appl. Phys. 42, (2009) X-ray diffractograms show single phase formation for both LSMO and LSMFO with orthorhombic structure.

Valence Band Structure of La 0.7 Sr 0.3 MnO 3 & La 0.7 Sr 0.3 Mn 0.95 Fe 0.05 O 3 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 e g (  ) and t 2g (  ) levels. The peak A and B are attributed to the e g (  ) and t 2g (  ) 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 (E F ) 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 E F. J. Phys. D: Applied Physics 42, (2009)

Deconvoluted VBS spectra 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 e g (σ ) and t 2g (π) levels, respectively Peak C is due to the O-2p (π) character e g states are pushed towards E F on Fe doping, thereby increasing the DOSs at E F and the overlap between the O-2p and e g states decreases on Fe doping (encircled region). e g (σ ) t 2g (π) O-2p (π) J. Phys. D: Applied Physics 42, (2009)

Resistivity vs Temperature for La 0.7 Sr 0.3 MnO 3 & La 0.7 Sr 0.3 Mn 0.95 Fe 0.05 O 3 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 E F and hence should be more metallic than that of LSMO.

Magnetization vs Field for La 0.7 Sr 0.3 MnO 3 & La 0.7 Sr 0.3 Mn 0.95 Fe 0.05 O 3 LSMO has higher value of magnetization at room temperature as compared to LSMFO.

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