Some features ofSingle Layered Manganites

La1-xSr1+xMnO4

G. Allodi, C. Baumann, B. Büchner, D. Cattani, R. De Renzi, P. Reutler

Layered Structure

SE1-xA1+xMnO4

TetragonalI4/mmmb

ca

Ionic description of Mn-ionsin a crystal field

3z2-r2

x2-y2

xz

yz

xy

Orbital states of Jahn-Teller active ions are discribed as linear superpositions !!!

Layered Structure

SE1-xA1+xMnO4

0,0 0,1 0,2 0,3 0,4 0,5 0,6

3,78

3,79

3,80

3,81

3,82

3,83

3,84

3,85

3,86

3,87

a,b

(Å)

doping x

12,3

12,4

12,5

12,6

12,7

12,8

12,9

13,0

13,1

13,2

13,3

13,4

c (

Å)

TetragonalI4/mmmb

ca

:Mn3+a b

c :Mn3+

:Mn

4+

a bc

Moritomo, PRB Moritomo, PRB 5151, 3297 , 3297 (95)(95)

Bao, SSC Bao, SSC 9898, 55 (96), 55 (96)

P. Reutler, unpublished data, LLB ParisP. Reutler, unpublished data, LLB Paris

0.0 0.1 0.2 0.3 0.4 0.5 0.6

2.00

2.05

2.10

2.15

2.20

2.25

2.30

0.0 0.1 0.2 0.3 0.4 0.5 0.61.88

1.90

1.92

1.94Raumtemperatur Einkristalldiffraktion Pulverdiffraktion

Tiefe Temperaturen Einkristalldiffraktion Pulverdiffraktion

d Mn-

O(2

) (Å)

Dotierung x

Dotierung x

d

Mn-O

(1) (Å)

(La,Sr)

Mn

(La,Sr)

Mn

0.0 0.1 0.2 0.3 0.4 0.5 0.6

1.02

1.04

1.06

1.08

1.10

1.12

1.14

1.16

1.18

1.20

1.22

0.0 0.1 0.2 0.3 0.4 0.5 0.63.77

3.78

3.79

3.80

3.81

3.82

3.83

3.84

3.85

3.86

3.87

D =

d Mn-

O(1

)

Raumtemperatur Einkristalldiffraktion Pulverdiffraktion Literatur

Tiefe Temperaturen Einkristalldiffraktion Pulverdiffraktion

d Mn-

O(2

)

Dotierung x

12.4

12.5

12.6

12.7

12.8

12.9

13.0

13.1

13.2GitterkonstantenRaumtemperatur

c (Å)

a (Å

)

Dotierung x

Crystallographic aspects

Distortion

Strongly elongatedoctahedra

D>1 for all x

For comparison LaMnO3(PRB57, 3189 (1998))

Mn-O(1) (Å) 1.968, 1907Mn-O(2) (Å) 2.178

Flop from out of planeto inplane orbitals at 1/8<x<1/4

d3z2-r2

unoccupied

dxy,xz,yz

Between two empty statesno electron hopping possible localizedlocalized

d3z2-r2

unoccupied

dxy,xz,yz

non-vanishing transfer integralElectron hopping possible delocalizeddelocalized

+dx2-y2

or others

Electronic origin for the transfer

into orbitals lying in the ab-plane

0.0 0.1 0.2 0.3 0.4 0.5 0.6

1.02

1.04

1.06

1.08

1.10

1.12

1.14

1.16

1.18

1.20

1.22

0.0 0.1 0.2 0.3 0.4 0.5 0.63.77

3.78

3.79

3.80

3.81

3.82

3.83

3.84

3.85

3.86

3.87

D =

d Mn-

O(1

)

Raumtemperatur Einkristalldiffraktion Pulverdiffraktion Literatur

Tiefe Temperaturen Einkristalldiffraktion Pulverdiffraktion

d Mn-

O(2

)

Dotierung x

12.4

12.5

12.6

12.7

12.8

12.9

13.0

13.1

13.2GitterkonstantenRaumtemperatur

c (Å)

a (Å

)

Dotierung x

Neither d3z²-r² nor

dx²-y² states are true

eigenstates

Electronic Properties

Overall insulating behaviourNo very CMR

FM exchangebetween

Mn3+ and Mn4+

ondelocalization

La1Sr1MnO4 (x=0)

Under holedoping

AFM exchange between two occupiedt2g orbitals

AFM?FM?

Goodenough-Anderson-Kanamori Rules:

AFM exchangebetween

Mn3+ and Mn4+

onlocalized

holes

unoccupied t2goccupied t2g

AFM !!Hopping possibile?

Magnetism of La1-xSr1+xMnO4

AFM of La1Sr1MnO4 and La7/8Sr9/8MnO4

0 50 100 150 200

0

1x105

50 1000.00

0.25

0.50

0.75

1.00

x = 0

Temperature (K)

In

ten

sity (

a.u

.)

TN=127 K

TN~ 65 K

x = 1/8

Inte

nsity (

a.u

.)

Temperature (K)

(0.5 0.5 0)+x(1 1 0)

* 150 magnetic reflections taken at 5C.2, LLB, France** high resolution powder neutron diffraction at 3T.2, LLB, France

P. Reutler, unpublished

Neutron diffraction

A

B

C-type AFM

In a body cell no magnetic couplings to next planes FRUSTRATION

La1Sr1MnO4 TN=127 K; 3.20* µB /MnLa7/8Sr9/8MnO4 TN~65 K; 2.4** µB /Mn

AFM of La1Sr1MnO4 and La7/8Sr9/8MnO4

0 50 100 150 200 250 3000.005

0.010

0.015

0.020

0.025

La1Sr

1MnO

4

TStat

= 36 K

TN = 127 KBc

B||c

ZFC

FC

FC & ZFC

B = 1 T

M/ B

( B

/ Mn

T)

Temperatur (K)

Bc : nearly free spins at low temperaturesB||c :only much smaller features at higher temperatures

free free xyxy- spins - spins ~0.2 µB /Mn

La1Sr1MnO4

La7/8Sr9/8MnO4

La7/8Sr9/8MnO4

+ =

C-Typ AFM longrange Order

xy-Momente (0.2 µB /Mn)

● Delocaliztion, but no metallicity● Long range antiferromagnetism and simultaniously● Quasi free spins perpedincular perpedincular to ordered moments

Canting of AFM ordered spinmomentsCanting of AFM ordered spinmoments

μSR of La7/8Sr9/8MnO4

Three contributions:

- Slowly decaying Backround- Precession Ordered moments- NON DETECTED PARTdue to very fast depolarizing signalquasi-static disordered moments

~60% missing initial polarisation

4.2K

TN

The magnetism of The magnetism of

LaLa7/87/8SrSr

9/89/8MnOMnO4 4 is is

intrinsicallyintrinsicallyinhomogeneousinhomogeneous

firstdatum

The rest of of La1+xSr1-xMnO4

Shortrange static magnstism in La0.6Sr1.4MnO4 by Muons

Depolarization Curves described by Kubo-Tojabe-Function for T<18K

Zero field 55Mn-NMR

Shortrange static magnstism in La3/4Sr5/4MnO4 by Muons

Austauschwechselwirkung

FM Austauschzwischen

Mn3+ und Mn4+

beiDeloklisierung

La1Sr1MnO4 (x=0)

Lochdotierung

AFM Austausch zwischen zwei besetzent2g Orbitalen

AFM?FM?

Goodenough-Anderson-Kanamori Regeln:

AFM Austauschzwischen

Mn3+ und Mn4+

beilokalisierten

Löchern

unbesetzes t2gbesetzes t2g

AFM !!Hopping möglich?

Collective order of correlated orbitals

Orbital form is parameterized by on two sublattices A,B

Orderof

orthogonal Orbitals

on two sublattices A,B

collective order dynamic orderis fixed by further

mechanism(on site anisotropy)

Energy degeneracy

for allSee also QF and orbital order:See also QF and orbital order:van den Brink, PRB van den Brink, PRB 5959, 6795 (99); Feiner, PRL , 6795 (99); Feiner, PRL 7878, 2799 , 2799 (97)(97)