Ionic and redox control of magnetism can produce large changes to a variety of magnetic properties using a relatively small voltage. A model structure that continues to be of interest is Pt/Co/GdOxHy/Au, where the Co magnetic layer oxidation state and perpendicular magnetic anisotropy can be toggled using voltage control of proton transport through the GdOxHy electrolyte layer. The hydration of the oxide layer to form a hydroxide phase is the key to improve the speed of these magneto-ionic devices, but there is insufficient understanding of protonic defect incorporation and transport during hydration and electrical gating. In this work, we use polarized neutron reflectometry (PNR) to observe the effects of hydration and electrical gating by scanning in an as-grown state, a hydrated state, and in operando during electrical gating. We directly measure the depth profile of hydrogen and confirm the transformation from oxide (Gd2O3) to hydroxide [Gd(OH)3]. We observe the accumulation of H in the Co magnetic layer and the effects of gating on the structure and hydrogen content of the other layers in the device stack. Using PNR and secondary ion mass spectrometry, we find evidence for much more complex chemistry at the Co/GdOxHy interface than was previously assumed, including evidence for persistent CoO phases and CoOxHy phases. We offer insight on using PNR to observe relatively fast proton dynamics in the system and fitting a rather complex set of parameters to achieve a physical result for the fit spectrum and scattering length density profiles.

1.
U.
Bauer
,
S.
Emori
, and
G. S.
Beach
, “
Voltage-controlled domain wall traps in ferromagnetic nanowires
,”
Nat. Nanotechnol.
8
,
411
416
(
2013
).
2.
U.
Bauer
,
L.
Yao
,
A. J.
Tan
,
P.
Agrawal
,
S.
Emori
,
H. L.
Tuller
,
S. V.
Dijken
, and
G. S. D.
Beach
, “
Magneto-ionic control of interfacial magnetism
,”
Nat. Mater.
14
,
174
(
2015
).
3.
M.
Nichterwitz
,
S.
Honnali
,
M.
Kutuzau
,
S.
Guo
,
J.
Zehner
,
K.
Nielsch
, and
K.
Leistner
, “
Advances in magneto-ionic materials and perspectives for their application
,”
APL Mater.
9
,
030903
(
2021
).
4.
D. A.
Gilbert
,
J.
Olamit
,
R. K.
Dumas
,
B. J.
Kirby
,
A. J.
Grutter
,
B. B.
Maranville
,
E.
Arenholz
,
J. A.
Borchers
, and
K.
Liu
, “
Controllable positive exchange bias via redoxdriven oxygen migration
,”
Nat. Commun.
7
,
1
8
(
2016
).
5.
N.
Lu
,
P.
Zhang
,
Q.
Zhang
,
R.
Qiao
,
Q.
He
,
H. B.
Li
,
Y.
Wang
,
J.
Guo
,
D.
Zhang
,
Z.
Duan
,
Z.
Li
,
M.
Wang
,
S.
Yang
,
M.
Yan
,
E.
Arenholz
,
S.
Zhou
,
W.
Yang
,
L.
Gu
,
C. W.
Nan
,
J.
Wu
,
Y.
Tokura
, and
P.
Yu
, “
Electric-field control of tri-state phase transformation with a selective dual-ion switch
,”
Nature
546
,
124
128
(
2017
).
6.
S.
Dasgupta
,
B.
Das
,
Q.
Li
,
D.
Wang
,
T. T.
Baby
,
S.
Indris
,
M.
Knapp
,
H.
Ehrenberg
,
K.
Fink
,
R.
Kruk
, and
H.
Hahn
, “
Toward on-and-off magnetism: reversible electro-chemistry to control magnetic phase transitions in spinel ferrites
,”
Adv. Funct. Mater.
26
,
7507
7515
(
2016
).
7.
A. J.
Tan
,
M.
Huang
,
C. O.
Avci
,
F.
Büttner
,
M.
Mann
,
W.
Hu
,
C.
Mazzoli
,
S.
Wilkins
,
H. L.
Tuller
, and
G. S.
Beach
, “
Magneto-ionic control of magnetism using a solid-state proton pump
,”
Nat. Mater.
18
,
35
41
(
2019
).
8.
A. J.
Tan
,
M.
Huang
,
S.
Sheffels
,
F.
Büttner
,
S.
Kim
,
A. H.
Hunt
,
I.
Waluyo
,
H. L.
Tuller
, and
G. S.
Beach
, “
Hydration of gadolinium oxide (Gd Ox) and its effect on voltage-induced Co oxidation in a Pt/Co/Gd Ox/Au heterostructure
,”
Phys. Rev. Mater.
3
,
064408
(
2019
).
9.
K. Y.
Lee
,
S.
Jo
,
A. J.
Tan
,
M.
Huang
,
D.
Choi
,
J. H.
Park
,
H. I.
Ji
,
J. W.
Son
,
J.
Chang
,
G. S.
Beach
, and
S.
Woo
, “
Fast magneto-ionic switching of interface anisotropy using yttria-stabilized zirconia gate oxide
,”
Nano Lett.
20
,
3435
3441
(
2020
).
10.
J.
de Rojas
,
A.
Quintana
,
A.
Lopeandía
,
J.
Salguero
,
B.
Muñiz
,
F.
Ibrahim
,
M.
Chshiev
,
A.
Nicolenco
,
M. O.
Liedke
,
M.
Butterling
,
A.
Wagner
,
V.
Sireus
,
L.
Abad
,
C. J.
Jensen
,
K.
Liu
,
J.
Nogués
,
J. L.
Costa-Krämer
,
E.
Menéndez
, and
J.
Sort
, “
Voltage-driven motion of nitrogen ions: A new paradigm for magneto-ionics
,”
Nat. Commun.
11
,
5871
(
2020
).
11.
C.
Bi
,
Y.
Liu
,
T.
Newhouse-Illige
,
M.
Xu
,
M.
Rosales
,
J. W.
Freeland
,
O.
Mryasov
,
S.
Zhang
,
S. G.
Te Velthuis
, and
W. G.
Wang
, “
Reversible control of Co magnetism by voltage-induced oxidation
,”
Phys. Rev. Lett.
113
,
267202
(
2014
).
12.
G.
Hao
,
N.
Noviasky
,
S.
Cao
,
I.
Sabirianov
,
Y.
Yin
,
C. C.
Ilie
,
E.
Kirianov
,
N.
Sharma
,
A.
Sokolov
,
A.
Marshall
,
X.
Xu
, and
P. A.
Dowben
, “
Some device implications of voltage controlled magnetic anisotropy in Co/Gd2O3 thin films through REDOX chemistry
,”
J. Magn. Magn. Mater.
451
,
487
492
(
2018
).
13.
M.
Sakamaki
and
K.
Amemiya
, “
Observation of an electric field-induced interface redox reaction and magnetic modification in GdOx/Co thin film by means of depth-resolved x-ray absorption spectroscopy
,”
Phys. Chem. Chem. Phys.
20
,
20004
20009
(
2018
).
14.
J.
Zehner
,
D.
Wolf
,
M. U.
Hasan
,
M.
Huang
,
D.
Bono
,
K.
Nielsch
,
K.
Leistner
, and
G. S.
Beach
, “
Magnetoionic control of perpendicular exchange bias
,”
Phys. Rev. Mater.
5
,
L061401
(
2021
).
15.
S.
Emori
,
U.
Bauer
,
S.
Woo
, and
G. S.
Beach
, “
Large voltage-induced modification of spin-orbit torques in Pt/Co/GdOx
,”
Appl. Phys. Lett.
105
,
222401
222406
(
2014
).
16.
R.
Mishra
,
F.
Mahfouzi
,
D.
Kumar
,
K.
Cai
,
M.
Chen
,
X.
Qiu
,
N.
Kioussis
, and
H.
Yang
, “
Electric-field control of spin accumulation direction for spin-orbit torques
,”
Nat. Commun.
10
,
248
(
2019
).
17.
M.
Huang
,
M. U.
Hasan
,
K.
Klyukin
,
D.
Zhang
,
D.
Lyu
,
P.
Gargiani
,
M.
Valvidares
,
S.
Sheffels
,
A.
Churikova
,
F.
Büttner
,
J.
Zehner
,
L.
Caretta
,
K. Y.
Lee
,
J.
Chang
,
J. P.
Wang
,
K.
Leistner
,
B.
Yildiz
, and
G. S.
Beach
, “
Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures
,”
Nat. Nanotechnol.
16
,
981
988
(
2021
).
18.
Y.
Chen
,
A.
Nicolenco
,
P.
Molet
,
A.
Mihi
,
E.
Pellicer
,
J.
Sort
,
Y.
Chen
,
A.
Mihi
, and
E.
Pellicer
, “
Magneto-ionic suppression of magnetic vortices
,”
Sci. Technol. Adv. Mater.
22
,
972
984
(
2021
).
19.
A.
Manchon
,
C.
Ducruet
,
L.
Lombard
,
S.
Auffret
,
B.
Rodmacq
,
B.
Dieny
,
S.
Pizzini
,
J.
Vogel
,
V.
Uhlir
,
M.
Hochstrasser
,
A.
Manchon
,
C.
Ducruet
,
L.
Lombard
,
S.
Auffret
, and
B.
Rodmacq
, “
Analysis of anisotropy crossover due to oxygen in Pt/Co/MOx trilayer
,”
J Appl. Phys.
104
,
043914
(
2008
).
20.
T.
Tsuruoka
,
I.
Valov
,
C.
Mannequin
,
T.
Hasegawa
,
R.
Waser
, and
M.
Aono
, “
Humidity effects on the redox reactions and ionic transport in a Cu/Ta2 O5/Pt atomic switch structure
,”
Jpn. J. Appl. Phys.
55
,
06GJ09
(
2016
).
21.
F.
Messerschmitt
,
M.
Kubicek
, and
J. L.
Rupp
, “
How does moisture affect the physical property of memristance for anionic-electronic resistive switching memories?
,”
Adv. Funct. Mater.
25
,
5117
5125
(
2015
).
22.
F.
Messerschmitt
,
M.
Jansen
, and
J. L.
Rupp
, “
When memristance crosses the path with humidity sensing—About the importance of protons and its opportunities in valence change memristors
,”
Adv. Electron. Mater.
4
,
1800282
(
2018
).
23.
T.
Tsuruoka
,
K.
Terabe
,
T.
Hasegawa
,
I.
Valov
,
R.
Waser
, and
M.
Aono
, “
Effects of moisture on the switching characteristics of oxide-based, gapless-type atomic switches
,”
Adv. Funct. Mater.
22
,
70
77
(
2012
).
24.
M.
Lübben
,
S.
Wiefels
,
R.
Waser
, and
I.
Valov
, “
Processes and effects of oxygen and moisture in resistively switching TaOx and HfOx
,”
Adv. Electron. Mater.
4
,
1700458
(
2018
).
25.
T.
Norby
,
M.
Widerøe
,
R.
Glöckner
, and
Y.
Larring
, “
Hydrogen in oxides
,”
Dalton Trans.
2004
,
3012
3018
.
26.
K. D.
Kreuer
, “
Proton-conducting oxides
,”
Annu. Rev. Mater. Res.
33
,
333
359
(
2003
).
27.
H. L.
Tuller
and
S. R.
Bishop
, “
Point defects in oxides: Tailoring materials through defect engineering
,”
Annu. Rev. Mater. Res.
41
,
369
398
(
2011
).
28.
T.
Moeller
and
H. E.
Kremers
, “
The basicity characteristics of scandium, yttrium, and the rare earth elements
,”
Chem. Rev.
37
,
97
159
(
1945
).
29.
S.
Jeon
and
H.
Hwang
, “
Effect of hygroscopic nature on the electrical characteristics of lanthanide oxides (Pr2O3, Sm2O3, Gd2O3, and Dy2O3)
,”
J. Appl. Phys.
93
,
6393
6395
(
2003
).
30.
Y.
Larring
and
T.
Norby
, “
Protons in rare earth oxides
,”
Solid State Ionics
77
,
147
151
(
1995
).
31.
L.
Mazzei
,
M.
Wolff
,
D.
Pergolesi
,
J. A.
Dura
,
L.
Börjesson
,
P.
Gutfreund
,
M.
Bettinelli
,
T.
Lippert
, and
M.
Karlsson
, “
Structure and conductivity of epitaxial thin films of in-doped BaZrO3-based proton conductors
,”
J. Phys. Chem. C
120
,
28415
28422
(
2016
).
32.
K.
Ogura
,
S.
Haruyama
, and
K.
Nagasaki
, “
The electrochemical oxidation and reduction of gold
,”
J. Electrochem. Soc.
118
,
531
(
1971
).
33.
T.
Miyazaki
,
R.
Hasegawa
,
H.
Yamaguchi
,
H.
Oh-Oka
,
H.
Nagato
,
I.
Amemiya
, and
S.
Uchikoga
, “
Electrical control of plasmon resonance of gold nanoparticles using electrochemical oxidation
,”
J. Phys. Chem. C
113
,
8484
8490
(
2009
).
34.
M.
Wang
,
J.
Binns
,
M. E.
Donnelly
,
M.
Peña-Alvarez
,
P.
Dalladay-Simpson
, and
R. T.
Howie
, “
High pressure synthesis and stability of cobalt hydrides
,”
J. Chem. Phys.
148
,
144310
(
2018
).
35.
B. J.
Sarkar
,
A.
Bandyopadhyay
,
J.
Mandal
,
A. K.
Deb
, and
P. K.
Chakrabarti
, “
Paramagnetic to ferromagnetic phase transition of Co doped Gd2O3 prepared by chemical route
,”
J. Alloys Compd.
656
,
339
346
(
2016
).
36.
F.
Letellier
,
V.
Baltz
,
L.
Lechevallier
,
R.
Lardé
,
J. F.
Jacquot
,
B.
Rodmacq
,
J. M.
Le Breton
, and
B.
Dieny
, “
Effects of sputter-deposition-induced and post-deposition thermally activated intermixing on the exchange bias properties of [Pt/Co] ×3/(Pt)/IrMn films
,”
J. Phys. D: Appl. Phys.
45
,
275001
(
2012
).
37.
C. C.
Huang
,
T. Y.
Liu
,
C. H.
Su
,
Y. W.
Lo
,
J. H.
Chen
, and
C. S.
Yeh
, “
Superparamagnetic hollow and paramagnetic porous Gd2O3 particles
,”
Chem. Mater.
20
,
3840
3848
(
2008
).

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