Two-dimensional electron gases (2DEGs) at perovskite oxide interfaces, such as strontium titanate (STO), have garnered significant attention due to their induced ferromagnetic (FM), spin–orbit coupling, and superconducting properties. The 2DEG, formed at the interface between STO and either insulating oxides or reactive metals, exhibits efficient charge-to-spin interconversion in STO/NM(non-magnetic) /FM structures. The insulating oxide layer at the STO interface attenuates the spin currents injected into the ferromagnet. In contrast, the metallic layers facilitate efficient spin current injection but suffer from spin current diffusion. Here, we present an approach to overcome these challenges by directly creating a 2DEG at the STO surface through Ar+ ion bombardment. This method enables efficient spin-to-charge conversion without an intermediate NM layer. Our experimental and simulation results demonstrate the generation of unconventional spin currents at the STO(Ar+)/NiFe(Permalloy) interface. Our findings may enable applications of complex oxide and ferromagnet interfaces for efficient charge-to-spin conversion, paving the way for low-power, room-temperature oxide-based spintronic devices.

1.
W.
Han
,
Y.
Otani
, and
S.
Maekawa
, “
Quantum materials for spin and charge conversion
,”
NPJ Quantum Mater.
3
(
1
),
27
(
2018
).
2.
Y.-L.
Han
,
S.-C.
Shen
,
J.
You
,
H.-O.
Li
,
Z.-Z.
Luo
,
C.-J.
Li
,
G.-L.
Qu
,
C.-M.
Xiong
,
R.-F.
Dou
,
L.
He
,
D.
Naugle
,
G.-P.
Guo
, and
J.-C.
Nie
, “
Two-dimensional superconductivity at (110) LaAlO3/SrTiO3 interfaces
,”
Appl. Phys. Lett.
105
(
19
),
192603
(
2014
).
3.
N.
Reyren
,
S.
Gariglio
,
A. D.
Caviglia
,
D.
Jaccard
,
T.
Schneider
, and
J.-M.
Triscone
, “
Anisotropy of the superconducting transport properties of the LaAlO3/SrTiO3 interface
,”
Appl. Phys. Lett.
94
(
11
),
112506
(
2009
).
4.
K.
Han
,
K.
Hu
,
X.
Li
,
K.
Huang
,
Z.
Huang
,
S.
Zeng
,
D.
Qi
,
C.
Ye
,
J.
Yang
,
H.
Xu
,
A.
Ariando
,
J.
Yi
,
W.
,
S.
Yan
, and
X. R.
Wang
, “
Erasable and recreatable two-dimensional electron gas at the heterointerface of SrTiO3 and a water-dissolvable overlayer
,”
Sci. Adv.
5
(
8
),
eaaw7286
(
2019
).
5.
H. Y.
Hwang
,
Y.
Iwasa
,
M.
Kawasaki
,
B.
Keimer
,
N.
Nagaosa
, and
Y.
Tokura
, “
Emergent phenomena at oxide interfaces
,”
Nat. Mater.
11
(
2
),
103
113
(
2012
).
6.
D. A.
Dikin
,
M.
Mehta
,
C. W.
Bark
,
C. M.
Folkman
,
C. B.
Eom
, and
V.
Chandrasekhar
, “
Coexistence of superconductivity and ferromagnetism in two dimensions
,”
Phys. Rev. Lett.
107
(
5
),
56802
(
2011
).
7.
L.
Li
,
C.
Richter
,
J.
Mannhart
, and
R. C.
Ashoori
, “
Coexistence of magnetic order and two-dimensional superconductivity at LaAlO3/SrTiO3 interfaces
,”
Nat. Phys.
7
(
10
),
762
766
(
2011
).
8.
U.
Shashank
,
A.
Deka
,
C.
Ye
,
S.
Gupta
,
R.
Medwal
,
R. S.
Rawat
,
H.
Asada
,
X.
Renshaw Wang
, and
Y.
Fukuma
, “
Room-temperature charge-to-spin conversion from quasi-2D electron gas at SrTiO3-based interfaces
,”
Phys. Status Solidi RRL
17
(
6
),
2200377
(
2023
).
9.
G.
Herranz
,
F.
Sánchez
,
N.
Dix
,
M.
Scigaj
, and
J.
Fontcuberta
, “
High mobility conduction at (110) and (111) LaAlO3/SrTiO3 interfaces
,”
Sci. Rep.
2
(
1
),
758
(
2012
).
10.
A. S.
Everhardt
,
M.
Mahendra
,
X.
Huang
,
S.
Sayed
,
T. A.
Gosavi
,
Y.
Tang
,
C.-C.
Lin
,
S.
Manipatruni
,
I. A.
Young
,
S.
Datta
,
J.-P.
Wang
, and
R.
Ramesh
, “
Tunable charge to spin conversion in strontium iridate thin films
,”
Phys. Rev. Mater.
3
(
5
),
51201
(
2019
).
11.
E.
Lesne
,
Y.
Fu
,
S.
Oyarzun
,
J. C.
Rojas-Sánchez
,
D. C.
Vaz
,
H.
Naganuma
,
G.
Sicoli
,
J.-P.
Attané
,
M.
Jamet
,
E.
Jacquet
,
J.-M.
George
,
A.
Barthélémy
,
H.
Jaffrès
,
A.
Fert
,
M.
Bibes
, and
L.
Vila
, “
Highly efficient and tunable spin-to-charge conversion through Rashba coupling at oxide interfaces
,”
Nat. Mater.
15
(
12
),
1261
1266
(
2016
).
12.
H.
Yang
,
B.
Zhang
,
X.
Zhang
,
X.
Yan
,
W.
Cai
,
Y.
Zhao
,
J.
Sun
,
K. L.
Wang
,
D.
Zhu
, and
W.
Zhao
, “
Giant charge-to-spin conversion efficiency in SrTiO3-based electron gas interface
,”
Phys. Rev. Appl.
12
(
3
),
034004
(
2019
).
13.
J.
Zhang
,
J.
Zhang
,
X.
Chi
,
R.
Hao
,
W.
Chen
,
H.
Yang
,
D.
Zhu
,
Q.
Zhang
,
W.
Zhao
,
H.
Zhang
, and
J.
Sun
, “
Giant efficiency for charge-to-spin conversion via the electron gas at the LaTiO3+δ\SrTiO3 interface
,”
Phys. Rev. B
105
(
19
),
195110
(
2022
).
14.
L. M.
Vicente-Arche
,
S.
Mallik
,
M.
Cosset-Cheneau
,
P.
Noël
,
D. C.
Vaz
,
F.
Trier
,
T. A.
Gosavi
,
C.-C.
Lin
,
D. E.
Nikonov
,
I. A.
Young
,
A.
Sander
,
A.
Barthélémy
,
J.-P.
Attané
,
L.
Vila
, and
M.
Bibes
, “
Metal/SrTiO3 two-dimensional electron gases for spin-to-charge conversion
,”
Phys. Rev. Mater.
5
(
6
),
064005
(
2021
).
15.
Y.
Wang
,
R.
Ramaswamy
,
M.
Motapothula
,
K.
Narayanapillai
,
D.
Zhu
,
J.
Yu
,
T.
Venkatesan
, and
H.
Yang
, “
Room-temperature giant charge-to-spin conversion at the SrTiO3–LaAlO3 oxide interface
,”
Nano Lett.
17
(
12
),
7659
7664
(
2017
).
16.
A.
Ohtomo
and
H. Y.
Hwang
, “
A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface
,”
Nature
427
(
6973
),
423
426
(
2004
).
17.
K.
Gopinadhan
,
A.
Annadi
,
Y.
Kim
,
A.
Srivastava
,
B.
Kumar
,
J.
Chen
,
J. M. D.
Coey
,
Ariando
, and
T.
Venkatesan
, “
Gate tunable in- and out-of-plane spin–orbit coupling and spin-splitting anisotropy at LaAlO3/SrTiO3 (110) interface
,”
Adv. Electron. Mater.
1
(
8
),
1500114
(
2015
).
18.
J. C. R.
Sánchez
,
L.
Vila
,
G.
Desfonds
,
S.
Gambarelli
,
J. P.
Attané
,
J. M.
De Teresa
,
C.
Magén
, and
A.
Fert
, “
Spin-to-charge conversion using Rashba coupling at the interface between non-magnetic materials
,”
Nat. Commun.
4
,
2944
(
2013
).
19.
F.
Hellman
,
A.
Hoffmann
,
Y.
Tserkovnyak
,
G. S. D.
Beach
,
E. E.
Fullerton
,
C.
Leighton
,
A. H.
MacDonald
,
D. C.
Ralph
,
D. A.
Arena
,
H. A.
Dürr
,
P.
Fischer
,
J.
Grollier
,
J. P.
Heremans
,
T.
Jungwirth
,
A. V.
Kimel
,
B.
Koopmans
,
I. N.
Krivorotov
,
S. J.
May
,
A. K.
Petford-Long
,
J. M.
Rondinelli
,
N.
Samarth
,
I. K.
Schuller
,
A. N.
Slavin
,
M. D.
Stiles
,
O.
Tchernyshyov
,
A.
Thiaville
, and
B. L.
Zink
, “
Interface-induced phenomena in magnetism
,”
Rev. Mod. Phys.
89
(
2
),
025006
(
2017
).
20.
J.
Chen
,
K.
Wu
,
W.
Hu
, and
J.
Yang
, “
Spin-orbit coupling in 2D semiconductors: A theoretical perspective
,”
J. Phys. Chem. Lett.
12
(
51
),
12256
12268
(
2021
).
21.
A.
Manchon
,
H. C.
Koo
,
J.
Nitta
,
S. M.
Frolov
, and
R. A.
Duine
, “
New perspectives for Rashba spin-orbit coupling
,”
Nat. Mater.
14
(
9
),
871
882
(
2015
).
22.
S.
Shi
,
A.
Wang
,
Y.
Wang
,
R.
Ramaswamy
,
L.
Shen
,
J.
Moon
,
D.
Zhu
,
J.
Yu
,
S.
Oh
,
Y.
Feng
, and
H.
Yang
, “
Efficient charge-spin conversion and magnetization switching through the Rashba effect at topological-insulator/Ag interfaces
,”
Phys. Rev. B
97
(
4
),
041115
(
2018
).
23.
J.
Nitta
,
T.
Akazaki
,
H.
Takayanagi
, and
T.
Enoki
, “
Gate control of spin-orbit interaction in an inverted In0.53Ga0.47As/In0.52Al0.48As heterostructure
,”
Phys. Rev. Lett.
78
,
1335
1338
(
1997
).
24.
R.
Ohshima
,
Y.
Ando
,
K.
Matsuzaki
,
T.
Susaki
,
M.
Weiler
,
S.
Klingler
,
H.
Huebl
,
E.
Shikoh
,
T.
Shinjo
,
S. T. B.
Goennenwein
, and
M.
Shiraishi
, “
Strong evidence for d-electron spin transport at room temperature at a LaAlO3/SrTiO3 interface
,”
Nat. Mater.
16
(
6
),
609
614
(
2017
).
25.
V. M.
Edelstein
, “
Spin polarization of conduction electrons induced by electric current in two-dimensional asymmetric electron systems
,”
Solid State Commun.
73
(
3
),
233
235
(
1990
).
26.
Q.
Song
,
H.
Zhang
,
T.
Su
,
W.
Yuan
,
Y.
Chen
,
W.
Xing
,
J.
Shi
,
J.
Sun
, and
W.
Han
, “
Observation of inverse Edelstein effect in Rashba-split 2DEG between SrTiO3 and LaAlO3 at room temperature
,”
Sci. Adv.
3
(
3
),
e1602312
(
2017
).
27.
C. H.
Du
,
H. L.
Wang
,
Y.
Pu
,
T. L.
Meyer
,
P. M.
Woodward
,
F. Y.
Yang
, and
P. C.
Hammel
, “
Probing the spin pumping mechanism: Exchange coupling with exponential decay in Y3Fe5O12/barrier/Pt heterostructures
,”
Phys. Rev. Lett.
111
(
24
),
247202
(
2013
).
28.
S.
Zhang
and
A.
Fert
, “
Conversion between spin and charge currents with topological insulators
,”
Phys. Rev. B
94
(
18
),
184423
(
2016
).
29.
H.
He
,
L.
Tai
,
H.
Wu
,
D.
Wu
,
A.
Razavi
,
T. A.
Gosavi
,
E. S.
Walker
,
K.
Oguz
,
C.-C.
Lin
,
K.
Wong
,
Y.
Liu
,
B.
Dai
, and
K. L.
Wang
, “
Conversion between spin and charge currents in topological-insulator/nonmagnetic-metal systems
,”
Phys. Rev. B
104
(
22
),
L220407
(
2021
).
30.
J.-W.
Chang
,
J. S.
Lee
,
T. H.
Lee
,
J.
Kim
, and
Y.-J.
Doh
, “
Controlled formation of high-mobility shallow electron gases in SrTiO3 single crystal
,”
Appl. Phys. Express
8
(
5
),
055701
(
2015
).
31.
L.
Iglesias
,
A.
Sarantopoulos
,
C.
Magén
, and
F.
Rivadulla
, “
Oxygen vacancies in strained SrTiO3 thin films: Formation enthalpy and manipulation
,”
Phys. Rev. B
95
(
16
),
165138
(
2017
).
32.
Y.
Li
,
S. N.
Phattalung
,
S.
Limpijumnong
,
J.
Kim
, and
J.
Yu
, “
Formation of oxygen vacancies and charge carriers induced in the n-type interface of a LaAlO3 overlayer on SrTiO3(001)
,”
Phys. Rev. B
84
(
24
),
245307
(
2011
).
33.
N. D.
Browning
,
J. P.
Buban
,
H. O.
Moltaji
,
S. J.
Pennycook
,
G.
Duscher
,
K. D.
Johnson
,
R. P.
Rodrigues
, and
V. P.
Dravid
, “
The influence of atomic structure on the formation of electrical barriers at grain boundaries in SrTiO3
,”
Appl. Phys. Lett.
74
(
18
),
2638
2640
(
1999
).
34.
Q.
Wang
,
W.
Zhang
,
W.
Zhang
, and
H.
Zeng
, “
In-situ monitor of insulator to metal transition in SrTiO3 by Ar+ irradiation
,”
Appl. Surf. Sci.
365
,
84
87
(
2016
).
35.
C.
Cantoni
,
J.
Gazquez
,
F.
Miletto Granozio
,
M. P.
Oxley
,
M.
Varela
,
A. R.
Lupini
,
S. J.
Pennycook
,
C.
Aruta
,
U. S.
di Uccio
,
P.
Perna
, and
D.
Maccariello
, “
Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: Direct measurements with atomic-column spatial resolution
,”
Adv. Mater.
24
(
29
),
3952
3957
(
2012
).
36.
H.
Tan
,
J.
Verbeeck
,
A.
Abakumov
, and
G.
Van Tendeloo
, “
Oxidation state and chemical shift investigation in transition metal oxides by EELS
,”
Ultramicroscopy
116
,
24
33
(
2012
).
37.
L.
Liu
,
T.
Moriyama
,
D. C.
Ralph
, and
R. A.
Buhrman
, “
Spin-torque ferromagnetic resonance induced by the spin Hall effect
,”
Phys. Rev. Lett.
106
(
3
),
036601
(
2011
).
38.
L.
Liu
,
C.-F.
Pai
,
Y.
Li
,
H. W.
Tseng
,
D. C.
Ralph
, and
R. A.
Buhrman
, “
Spin-torque switching with the giant spin Hall effect of Tantalum
,”
Science
336
(
6081
),
555
558
(
2012
).
39.
M.
Harder
,
Y.
Gui
, and
C.-M.
Hu
, “
Electrical detection of magnetization dynamics via spin rectification effects
,”
Phys. Rep.
661
,
1
59
(
2016
).
40.
D.
MacNeill
,
G. M.
Stiehl
,
M. H. D.
Guimaraes
,
R. A.
Buhrman
,
J.
Park
, and
D. C.
Ralph
, “
Control of spin–orbit torques through crystal symmetry in WTe2/ferromagnet bilayers
,”
Nat. Phys.
13
(
3
),
300
305
(
2017
).
41.
S.
Gupta
,
R.
Medwal
,
D.
Kodama
,
K.
Kondou
,
Y.
Otani
, and
Y.
Fukuma
, “
Important role of magnetization precession angle measurement in inverse spin Hall effect induced by spin pumping
,”
Appl. Phys. Lett.
110
(
2
),
022404
(
2017
).
42.
G. M.
Stiehl
,
D.
MacNeill
,
N.
Sivadas
,
I.
El Baggari
,
M. H. D.
Guimarães
,
N. D.
Reynolds
,
L. F.
Kourkoutis
,
C. J.
Fennie
,
R. A.
Buhrman
, and
D. C.
Ralph
, “
Current-induced torques with Dresselhaus symmetry due to resistance anisotropy in 2D materials
,”
ACS Nano
13
(
2
),
2599
2605
(
2019
).
43.
S.
Karimeddiny
and
D. C.
Ralph
, “
Resolving discrepancies in spin-torque ferromagnetic resonance measurements: Lineshape versus linewidth analyses
,”
Phys. Rev. Appl.
15
(
6
),
064017
(
2021
).
44.
C.
Kittel
,
Introduction to Solid State Physics
(
John Wiley & Sons, Inc
,
2005
).
45.
U.
Shashank
,
R.
Medwal
,
T.
Shibata
,
R.
Nongjai
,
J. V.
Vas
,
M.
Duchamp
,
K.
Asokan
,
R. S.
Rawat
,
H.
Asada
,
S.
Gupta
, and
Y.
Fukuma
, “
Enhanced spin Hall effect in S-implanted Pt
,”
Adv. Quantum Technol.
4
(
1
),
2000112
(
2021
).
46.
U.
Shashank
,
R.
Medwal
,
Y.
Nakamura
,
J. R.
Mohan
,
R.
Nongjai
,
A.
Kandasami
,
R. S.
Rawat
,
H.
Asada
,
S.
Gupta
, and
Y.
Fukuma
, “
Highly dose dependent damping-like spin–orbit torque efficiency in O-implanted Pt
,”
Appl. Phys. Lett.
118
(
25
),
252406
(
2021
).
47.
U.
Shashank
,
Y.
Nakamura
,
Y.
Kusaba
,
T.
Tomoda
,
R.
Nongjai
,
A.
Kandasami
,
R.
Medwal
,
R. S.
Rawat
,
H.
Asada
,
S.
Gupta
, and
Y.
Fukuma
, “
Disentanglement of intrinsic and extrinsic side-jump scattering induced spin Hall effect in N-implanted Pt
,”
Phys. Rev. B
107
(
6
),
064402
(
2023
).
48.
Y.
Zhao
,
Q.
Song
,
S.-H.
Yang
,
T.
Su
,
W.
Yuan
,
S. S. P.
Parkin
,
J.
Shi
, and
W.
Han
, “
Experimental investigation of temperature-dependent Gilbert damping in permalloy thin films
,”
Sci. Rep.
6
(
1
),
22890
(
2016
).
49.
K.
Garello
,
I. M.
Miron
,
C. O.
Avci
,
F.
Freimuth
,
Y.
Mokrousov
,
S.
Blügel
,
S.
Auffret
,
O.
Boulle
,
G.
Gaudin
, and
P.
Gambardella
, “
Symmetry and magnitude of spin–orbit torques in ferromagnetic heterostructures
,”
Nat. Nanotechnol.
8
(
8
),
587
593
(
2013
).
50.
M.
Aoki
,
E.
Shigematsu
,
R.
Ohshima
,
T.
Shinjo
,
M.
Shiraishi
, and
Y.
Ando
, “
Coexistence of low-frequency spin-torque ferromagnetic resonance and unidirectional spin Hall magnetoresistance
,”
Phys. Rev. B
104
(
9
),
094401
(
2021
).
51.
J.
Zhou
,
X.
Shu
,
Y.
Liu
,
X.
Wang
,
W.
Lin
,
S.
Chen
,
L.
Liu
,
Q.
Xie
,
T.
Hong
,
P.
Yang
,
B.
Yan
,
X.
Han
, and
J.
Chen
, “
Magnetic asymmetry induced anomalous spin-orbit torque in IrMn
,”
Phys. Rev. B
101
(
18
),
184403
(
2020
).
52.
T.
Nan
,
C. X.
Quintela
,
J.
Irwin
,
G.
Gurung
,
D. F.
Shao
,
J.
Gibbons
,
N.
Campbell
,
K.
Song
,
S.-Y.
Choi
,
L.
Guo
,
R. D.
Johnson
,
P.
Manuel
,
R. V.
Chopdekar
,
I.
Hallsteinsen
,
T.
Tybell
,
P. J.
Ryan
,
J.-W.
Kim
,
Y.
Choi
,
P. G.
Radaelli
,
D. C.
Ralph
,
E. Y.
Tsymbal
,
M. S.
Rzchowski
, and
C. B.
Eom
, “
Controlling spin current polarization through non-collinear antiferromagnetism
,”
Nat. Commun.
11
(
1
),
4671
(
2020
).
53.
J. E.
Hirsch
, “
Spin Hall effect
,”
Phys. Rev. Lett.
83
(
9
),
1834
1837
(
1999
).
54.
A.
Bose
,
N. J.
Schreiber
,
R.
Jain
,
D.-F.
Shao
,
H. P.
Nair
,
J.
Sun
,
X. S.
Zhang
,
D. A.
Muller
,
E. Y.
Tsymbal
,
D. G.
Schlom
, and
D. C.
Ralph
, “
Tilted spin current generated by the collinear antiferromagnet ruthenium dioxide
,”
Nat. Electron.
5
(
5
),
267
274
(
2022
).
55.
T. M.
Cham
,
S.
Karimeddiny
,
V.
Gupta
,
J. A.
Mittelstaedt
, and
D. C.
Ralph
, “
Separation of artifacts from spin-torque ferromagnetic resonance measurements of spin-orbit torque for the low-symmetry van der Waals semi-metal ZrTe3
,”
Adv. Quantum Technol.
5
(
2
),
2100111
(
2022
).
56.
A.
Vansteenkiste
,
J.
Leliaert
,
M.
Dvornik
,
M.
Helsen
,
F.
Garcia-Sanchez
, and
B.
Van Waeyenberge
, “
The design and verification of MuMax3
,”
AIP Adv.
4
(
10
),
107133
(
2014
).
57.
J. C.
Slonczewski
, “
Current-driven excitation of magnetic multilayers
,”
J. Magn. Magn. Mater.
159
(
1–2
),
L1
L7
(
1996
).
58.
J.
Park
,
G. E.
Rowlands
,
O. J.
Lee
,
D. C.
Ralph
, and
R. A.
Buhrman
, “
Macrospin modeling of sub-ns pulse switching of perpendicularly magnetized free layer via spin-orbit torques for cryogenic memory applications
,”
Appl. Phys. Lett.
105
(
10
),
102404
(
2014
).
59.
M. R.
Karim
,
S.
Manna
,
A. K.
Gupta
,
J. R.
Mohan
,
S. K.
Maharana
,
J. V.
Vas
,
A.
Bose
,
S.
Gupta
,
R. S.
Rawat
,
H.
Asada
,
Y.
Fukuma
, and
R.
Medwal
, “
Observation of out-of-plane spin-orbit torque in a polycrystalline Py/IrMn3 heterostructure
,”
Phys. Rev. B
110
,
245423
(
2024
).
60.
J.-W.
Xu
and
A. D.
Kent
, “
Charge-to-spin conversion efficiency in ferromagnetic nanowires by spin torque ferromagnetic resonance: Reconciling lineshape and linewidth analysis methods
,”
Phys. Rev. Appl.
14
(
1
),
014012
(
2020
).
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