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

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 )

La1-xAxMnO3 based perovskite materials

Metal-insulator transition

Charge order

Paramagnetic ferromagnetic transition

Colossal

Magnetoresistance

La

O

Mn

A : Divalent atom Hole doping

Ca, Sr, Ba etc.

INTRODUCTION

La0.7Ca0.3MnO3

MECHANISMSA: Divalent atom Mn is in Mn+3 & Mn+4 states

A : Tetravalent atom (Ce4+)

Electron dopingMn is in Mn+3 & Mn+2 states

Double exchange & J-T distortion of MnO6 octahedra are the main factors.

Same mechanisms

Ot2g

eg eg

t2g

Double ExchangeMn3+ Mn4+ t2g

eg

Jahn-Teller Distortion

Crystal field splitting

Mn

Mn3+

G – TypeCaMnO3

A – TypeLaMnO3

The interaction is ferromagnetic for overlap of dz2 orbitals in the plane, and antiferromagnetic along the perpendicular axis

3d orbitals

eg

t2g t2g

eg

3z2-r2

x2-y2

yz, zx

xy

x2-y2

3z2-r2

xy

yz, zx

2

11

2

3d orbitals

eg

t2g t2g

eg

3z2-r2

x2-y2

yz, zx

xy

x2-y2

3z2-r2

xy

yz, zx

2

11

2

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

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.

•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 acharge surplus.

PHYSICAL REVIEW LETTERS 83, 5118 , 1999

150 200 250 300

0.00

0.02

0.04

0.06

0.08

0.10

Temperature (K)

Resis

tivity (

-c

m)

(H=0)

(H)

0

10

20

30

40

La0.7Ca0.3MnO3

(a)

MR

(%)

MR (%)

100 150 200 250 300

0

20

40

60

80

100(b)

M(e

mu/g

)

Temperature (K)

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

Diluted magnetic Semiconductors : ZnO, CuAlO2, TiO2

Manganites (La1-xAxMnO3 )

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 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).

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 sample

Why is it special?

Creating the lightHow 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 99.9986% of the speed of light

How does it work?

And are finally transferred into the storage ring

How does it work?

Bending magnetSweeping searchlightAt each deflection of the electron path a beam of radiation is produced.

UndulatorProduces a very narrow beam of coherent light, amplified by up to 104

Types of light sources

Insertion devices - produce higher intensity

WigglerBeams 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 (10-6m) 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.

Synchrotron light - propertiesProperties?

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) 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

Band structure of Fe and Mn in

20 30 40 50 60 70 80

Inte

nsit

y (a

. u.)

2

LSMO

(206

)

(330

)

(400

), (

224)

(204

)(3

12),

(02

4)

(114

)

(220

)

(202

)

(200

), (

112)

(110

)

LSMFO

X-ray diffraction study ofLa0.7Sr0.3MnO3 (LSMO) & La0.7Sr0.3Mn0.95Fe0.05O3

(LSMFO)

J. Phys. D: Appl. Phys. 42, 185410 (2009)

X-ray diffractograms show single phase formation for both LSMO and LSMFO with orthorhombic structure.

Valence Band Structure of La0.7Sr0.3MnO3 & La0.7Sr0.3Mn0.95Fe0.05O3

0.8 0.4 0.0 -0.4 -0.8

6 4 2 0

C

B

AInte

nsi

ty (

a.u

.)

Binding Energy (eV)

LSMO LSMFO

Ef

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)

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 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).

eg(σ )

t2g(π)

O-2p (π)

J. Phys. D: Applied Physics 42, 185410 (2009)

Resistivity vs Temperature forLa0.7Sr0.3MnO3 & La0.7Sr0.3Mn0.95Fe0.05O3

100 150 200 250 300 350 4000.000

0.004

0.008

0.012

Res

isti

vity

(.c

m)

Temperature(K)

LSMO LSMFO

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.

Magnetization vs Field forLa0.7Sr0.3MnO3 & La0.7Sr0.3Mn0.95Fe0.05O3

-6000 -4000 -2000 0 2000 4000 6000-80

-60

-40

-20

0

20

40

60

80

Mag

net

izat

ion

(em

u/g

)

Field (Gauss)

LSMO LSMFO

LSMO has higher value of magnetization at room temperature as compared to LSMFO.

Department of PhysicsUniversity of Pune

Thank you