some features of single layered manganites la 1-x sr 1+x mno 4 g. allodi, c. baumann, b. büchner,...
Post on 30-Jan-2016
215 views
TRANSCRIPT
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P. Reutler, unpublished data, LLB ParisP. Reutler, unpublished data, LLB Paris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)