Strain-mediated parallel to antiparallel 

magnetization reorientation in Co/Cu multilayers

Prepared for CORE Summer 2023

by Eugene Jeong

Carnegie Mellon University

Advised by Dr. Shane Lindemann

NIST Center for Neutron Research, Neutron-Condensed Science Group

1

‘The Center for High Resolution Neutron Scattering (CHRNS) is a national user facility jointly funded by the NIST Center for 

Neutron Research (NCNR) and the National Science Foundation (NSF) under Agreement No. DMR-2010792.’
Strain-Mediated Magnetoelectric Coupling

Strain

Magnetization 

direction

Magnetostrictive

effect: Co changes 

magnetization 

direction under strain

Favored rotation 

direction exists due to 

magnetic anisotropy

2

PMN-PT

Ti/Pt

Co 1

Oblique view Top view

Ferroelectric 

PMN-PT produces 

strain under 

applied electric 

field

90°
Parallel-Antiparallel Magnetization Reorientation

Cu

Co 2

Strain

3

PMN-PT

Ti/Pt

Co 1

Cu

Co 2

Co 1

Cu

Co 2

Co 1

Cross-section view

Cross-section view

Top

view
Achieve a large change in electrical resistance 

using an applied magnetic field

Giant Magnetoresistance (GMR)

Figure from: Tsymbal & Pettifor, 

“Perspectives of Giant 

Magnetoresistance” (2001). [1] 4

Cu

Co 2

Co 1

Cu

Co 2

Co 1

Cu

Co 2

Co 1
Magnetic Memory

• Strain-mediated magnetic memory (SME-RAM)

• No write current needed

• Potential for much lower write energy

Table values transcribed from: Hu et al., Nat Commun 2, 553 (2011). [2]

5

Flash-NAND MRAM STT-RAM SME-RAM

Storage capacity >1 Gb 16 Mb 1 Gb >>1 Gb

Write time 1 ms 20 ns 3-10 ns <10 ns

Read time 50 ns 10 ns 10 ns 10 ns

Write energy (pJ per bit) >0.01 70 0.1 1.6×10-4
Project Overview

PMN-PT

Ti/Pt

Co

Cu

Co

Ferroelectric

Electrode

Ferromagnetic

Nonmagnetic

Ferromagnetic Strain causes 

magnetization switch 

(parallel to antiparallel)

Applying voltage 

(writing a bit) 

causes strain

1

2

3

Electrical resistance 

changes

(the bit is stored)

Achieve a large change in electrical resistance 

using an applied electric field

6
Outline

PMN-PT

Ti/Pt

Co

Cu

Co

• Film growth

• Depositing the electrode

and multilayer

7
Outline

PMN-PT

Ti/Pt

Co

Cu

Co

8

• Film growth

• Depositing the electrode

and multilayer

• Strain hysteresis

• Measuring the bulk PMN-PT substrate
Outline

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• Film growth

• Depositing the electrode

and multilayer

• Strain hysteresis

• Measuring the bulk PMN-PT substrate

• Magnetic hysteresis

• Characterizing the magnetic properties 

under different growth conditions

PMN-PT

Ti/Pt

Co

Cu

Co ?

?
Outline • Film growth • Depositing the electrode

and multilayer

• Strain hysteresis • Measuring the bulk PMN

-PT substrate

• Magnetic hysteresis • Characterizing the magnetic properties 

under different growth conditions

•X-ray diffraction & reflectivity • Verifying the structure of the materials

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PMN-PT

Ti/Pt

Co

Cu

Co
Film Growth

PMN-PT

Ti/Pt

Co

Cu

Co

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Film growth

• Objectives

• Grow electrodes, Co & Cu thin films

• Control magnetic anisotropy of Co by placing 

magnets in sputter chamber

Image: NanoFab Tool: Denton 

Vacuum Discovery 550 Sputtering 

System B104 Right | NIST

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Strain hysteresis PMN-PT

Ti/Pt

Co

Cu

Co

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Measurement Setup

• Objective: demonstrate that we can 

place PMN-PT in two distinct strain 

states at zero voltage PMN-PT

Ti/Pt

Strain gauge

High voltage supply

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Source Measure Unit

Strain gauge used

Image from: omega.com
Magnetic 

Hysteresis PMN

-PT

Ti/Pt

Co

Cu

Co

??

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Magnetic hysteresis measurement

• Objective: show that placing 

magnets in sputter growth 

chamber controls magnetic 

anisotropy direction

16

3 5 7 9

2 4 6 8 10

5 7 9

2 4 8 10

Grown without 

magnets

Grown with 

magnets

Hard axis directions
X-Ray 

Measurements

PMN-PT

Ti/Pt

Co

Cu

Co

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X-ray Diffraction & Reflectivity

Image: NanoFab Tool: Rigaku SmartLab XRay Diffraction | NIST

• Objectives

• Estimate film thicknesses to determine 

sputter growth rates

• Determine PMN-PT substrate orientations

• Identify possible texturing in Co films

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Conclusions

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Summary

• Grew electrodes, Co, Cu films by sputter deposition

• Began x-ray diffraction and reflectivity measurements for these films

• Demonstrated that two PMN-PT strain states can be achieved

• Showed effects of magnets during growth on magnetic anisotropy of 

sputtered Co films

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Further Work

• Continue x-ray characterization

• Identify structure changes in Co when magnets used during growth

• Take more strain hysteresis measurements of PMN-PT 

• Measure both directions with a new sample

• Take magnetic hysteresis measurements of Co films from all angles

• Understand magnetic anisotropy characteristics

• Grow Co/Cu multilayers for magnetic measurement

• Verify parallel to antiparallel reorientation

• Grow Co/Cu on PMN-PT to complete the device

• Verify giant magnetoresistance-like effect

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Acknowledgments

Thank you to:

• CORE and SURF directors

• Drs. Susana Teixeira, Julie Borchers, Leland Harriger

• NCNR staff

• Dr. Shane Lindemann

• CNST staff

• And everybody else who supported me this summer!

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References

1. E. Y. Tsymbal and D. G. Pettifor, "Perspectives of Giant Magnetoresistance,“ in 

Solid State Physics, H. Ehrenreich and F. Spaepen, Ed., Academic Press, 2001, 

vol. 56, pp. 113-237.

2. J.-M. Hu, Z. Li, L.-Q. Chen, and C.-W. Nan, “High-density magnetoresistive

random access memory operating at ultralow voltage at room 

temperature,” Nat. Commun., vol. 2, no. 553, Nov. 2011, 

doi:10.1038/ncomms1564

3. J.-J. Wang, T.-N. Yang, B. Wang, M. S. Rzchowski, C.-B. Eom, and L.-Q. Chen, 

“Strain-Induced Interlayer Parallel-to-Antiparallel Magnetic Transitions of 

Twisted Bilayers,” Adv. Theory Simul., vol. 4, no. 2000215, Mar. 2021, 

doi:10.1002/adts.202000215

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Extra Slides

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25

Figure from: Wang et al., Adv Theory Simul 4, 3 (2021). [3]
Wheatstone Bridge Setup

VG

IL IR

IS

PMN-PT

Ti/Pt

Strain gauge (Rx)

High voltage supply

26