Investigating Magnetic Dead Layers 

in Rhombohedral Perovskites

Jeremy Ashe

Mentored by: Ryan Need 
Purpose

Technological Applications – better data storage & energy efficient 

Electronics (magnitude) Spintronics (magnitude & direction)

+1/2 -1/2

N S

S N
Perovskite Oxides and Their Structures

Cubic perovskite

e.g. SrTiO3 

Rhombohedral perovskite

e.g. La0.7Sr0.3MnO3, LaCoO3 

Perovskites – chemical formula ABO3

un tilted octahedra, magnetic tilted octahedra, nonmagnetic
LCO/LSMO/STO Film & Magnetic Dead Layers (MDLs)

Different curves caused by MDLs

MDLs are regions of depleted ferromagnetism

SrTiO3, LaCoO3, La0.7Sr0.3MnO3 Film

STO

LCO

LSMO

LCO

LSMO

LCO

LSMO

STO LSMO MDL LSMO
STO

LCO

LSMO

LCO

LSMO

LCO

LSMO

STO

LSMO

LCO

LSMO

LCO

LSMO

LCO

STO

LSMO

LCO

LSMO

LCO

LSMO

LCO

STO

LSMO

LCO

LSMO

LCO

LSMO

LCO

LCO/LSMO Superlattice LCO/STO/LSMO 

Superlattice

LCO/LSMO/STO 

Superlattice

LCO/STO/LSMO/STO 

Superlattice

Sample Structures
Polarized Neutron Reflectometry (PNR)

• Neutrons have unique properties

• Electrically neutral

• Magnetic

• Behave like waves

• PNR data shows film’s magnetic and nuclear depth 

• PNR data was collected for the modeling of the thin films

Flips magnetic polarization
Modeling Methods

• Used python scripts in refl1d software to find 

models of the films

• Models fit inputted PNR data

• Python scripts have different film 

parameters

• Lower the χχ2 /Chisq value (statistical 

value), the better the fit

• MDL parameter includes:

• Dead layer presence

• Dead layer length

• Dead layer roughness

• The MDL parameters were systematically 

changed in order to find how χχ2 changed 

with different MDL values Refl1d finding best fit for LCO/LSMO repeated film LSMO LSMO LSMO LSMO LSMO STO LCO LCO LCO LCO LCO
LCO/STO/LSMO/STO Superlattice

• LSMO has MDLs around 4Å at STO interface

• Magnetism in LSMO and LCO is nonuniform

• Magnetic dead layers occur at some 

rhombohedral-to-cubic material interfaces

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12

Chisq 

Dead Layer Length (Å)

ChiSq vs Dead Layer Length

Non-Symmetric Interfaces with

Uniform Magnetism

Symmetric Interfaces with

Uniform Magnetism

Non-uniform Magnetism in

LSMO

Poly. (Non-Symmetric Interfaces

with Uniform Magnetism)

Poly. (Symmetric Interfaces with

Uniform Magnetism)

Poly. (Non-uniform Magnetism

in LSMO)

STO

LSMO

LCO

LSMO

LCO

LSMO

LCO
0

5

10

15

20

25

0 2 4 6 8 10 12 14 16

Chisq

Dead Layer Length (Å)

Chisq vs Dead Layer Length

Non-Symmetric Interface with

Uniform Magnetism in LSMO

Symmetric Interface with Uniform

Magnetism in LSMO

Non-uniform Magnetism in LSMO

Poly. (Non-Symmetric Interface

with Uniform Magnetism in LSMO)

Poly. (Symmetric Interface with

Uniform Magnetism in LSMO)

Poly. (Non-uniform Magnetism in

LSMO)

• LSMO has no MDLs at LCO interface

• Magnetism in LSMO and LCO is non-uniform

• Magnetic dead layers do not occur at some 

rhombohedral-to-rhombohedral material 

STO interfaces

LCO

LSMO

LCO

LSMO

LCO

LSMO

LCO/LSMO Superlattice
0

0.5

1

1.5

2

2.5

3

3.5

4

0 2 4 6 8 10 12

Chisq

Dead Layer Length(Å)

Chisq vs Dead Layer Length

Chisq vs Dead Layers Above with

Dead Layers Below fitting

Chisq vs Dead Layers Below with

Dead Layer Above fitting

Poly. (Chisq vs Dead Layers Above

with Dead Layers Below fitting)

Poly. (Chisq vs Dead Layers Below

with Dead Layer Above fitting)

STO

LSMO

LCO

LSMO

LCO

LSMO

LCO

LCO/LSMO/STO Superlattice

• Reinforces 4Å MDLs in LSMO at STO interface 

• Reinforces no MDLs in LSMO at LCO interface

• Reinforces that the magnetism in LSMO and LCO is 

non-uniform

• Proves findings in LCO/STO/LSMO/STO superlattice 

sample and LCO/LSMO superlattice sample
STO

LSMO

LCO

LSMO

LCO

LSMO

LCO

LCO/STO/LSMO Superlattice

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12

Chisq

Dead Layer Length(Å)

Chisq vs Dead Layer Length with Non-Uniform Magnetism

Chisq vs Dead Layer Above value with

Other Dead Layers Fitting

Chisq vs Dead Layer Below with other

Dead Layers Fitting

Poly. (Chisq vs Dead Layer Above value

with Other Dead Layers Fitting)

Poly. (Chisq vs Dead Layer Below with

other Dead Layers Fitting)

0

5

10

15

20

25

30

35

0 2 4 6 8 10 12 14 16

Chisq

Dead Layer Length (Å)

Chisq vs Dead Layer Length with Non-Uniform Magnetism

Non-Symmetric Interface Roughness

Symmetric Interface Roughness

Poly. (Non-Symmetric Interface

Roughness)

Poly. (Symmetric Interface Roughness)

This sample had very bad fits

Non-conclusive information could be 

determined
Conclusions

STO MDL LSMO

• MDLs occur in LSMO at interface with STO

• MDLs occur at some rhombohedral-to-cubic 

material interfaces

• Sharp change in crystalline structure 

• MDLs do not occur in LSMO at interface with LCO

• MDLs do not occur at some rhombohedral-torhombohedral material interfaces

• Lacks sharp change in crystalline structure 

LCO LSMO
Acknowledgements

Special Thanks:

• Ryan Need, mentor

• SHIP Directors: Julie Borchers, Joe Dura, and Yamali Hernandez 

• SHIP Mentors: Heather Chen-Mayer, Jacob LaManna, Markus Bleuel, Wei Zhou & William 

Ratcliff , Brian Maranville

• Er-jia Guo, Alexander Grutter

• NIST, NIST Center for Neutron Research, Center for High Resolution Neutron Scattering