Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO2/Fe Bilayer Heterostructures

Fields, Shelby S.; Prestigiacomo, Joseph C.; Cress, Cory D.; Combs, Nicholas G.; van ’t Erve, Olaf; Callahan, Patrick G.; Knipling, Keith E.; Jamer, Michelle E.; Abel, Frank M.; Ye, Feng; Minelli, Arianna; Morgan, Zachary J.; Ambaye, Haile; Matsuda, Masaaki; Maity, Avishek; Lauter, Valeria; Bennett, Steven P.

doi:10.1021/acsami.5c20863

Title: Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO₂/Fe Bilayer Heterostructures

Journal Article · Mon Jan 12 00:00:00 UTC 2026 · ACS Applied Materials and Interfaces

DOI: https://doi.org/10.1021/acsami.5c20863 · OSTI ID:3030277

^[1]; Prestigiacomo, Joseph C. ^[1];

^[1]; Combs, Nicholas G. ^[1]; van ’t Erve, Olaf ^[1]; Callahan, Patrick G. ^[1]; Knipling, Keith E. ^[1]; Jamer, Michelle E. ^[2];

^[2];

^[3];

^[3]; Bennett, Steven P. ^[1]

Naval Research Laboratory (NRL), Washington, DC (United States)
US Naval Academy, Annapolis, MD (United States)
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Initially identified as a promising altermagnetic (AM) candidate, rutile RuO₂ has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk nonmagnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patterned RuO₂ Hall bars and film heterostructures display magnetotransport signatures of magnetic ordering. Among the characteristics routinely cited as evidence for AM is the observation of exchange bias (EB) in an intimately contacted Fe-based ferromagnetic (FM) layer, which can arise due to interfacial coupling with a compensated antiferromagnet. Here, within this work, the origins of this EB coupling in Ru-capped RuO₂/Fe bilayers are investigated using polarized neutron diffraction, polarized neutron reflectometry, cross-sectional transmission electron microscopy, and super conducting quantum interference device measurements. These experiments reveal that the EB behavior is driven by the formation of an iron oxide interlayer containing Fe₃O₄ that undergoes a magnetic transition and pins interfacial moments within Fe at low temperature. These findings are confirmed by comparable measurements of Ni-based heterostructures, which do not display EB coupling, as well as magnetometry of additional Fe/Ru bilayers that display oxide-driven EB coupling despite the absence of the epitaxial RuO₂ layer. While these results do not directly refute the possibility of AM ordering in RuO₂ thin films, they reveal that EB, and related magnetotransport phenomena, cannot alone be considered evidence of this characteristic in the rutile structure due to interfacial chemical disorder.

View Accepted Manuscript (DOE)

Cite

Export

Save

Research Organization:: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Organization:: US Department of the Navy, Office of Naval Research (ONR); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)

Grant/Contract Number:: AC05-00OR22725

OSTI ID:: 3030277

Journal Information:: ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Journal Issue: 3 Vol. 18; ISSN 1944-8244; ISSN 1944-8252

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

References (68)

Inverse Altermagnetic Spin Splitting Effect‐Induced Terahertz Emission in RuO₂ Liu, Yu; Bai, Hua; Song, Yuna Advanced Optical Materials, Vol. 11, Issue 16 https://doi.org/10.1002/adom.202300177	journal	May 2023
Confined Magnetization at the Sublattice‐Matched Ruthenium Oxide Heterointerface Fan, Yiyan; Zhang, Qinghua; Lin, Ting Small, Vol. 21, Issue 3 https://doi.org/10.1002/smll.202408247	journal	November 2024
Characterisation and magnetic properties of natural ferric gel Coey, J. M. D.; Readman, P. W. Earth and Planetary Science Letters, Vol. 21, Issue 1 https://doi.org/10.1016/0012-821X(73)90224-0	journal	December 1973
Ultra-high areal capacitance and high rate capability RuO2 thin film electrodes for 3D micro-supercapacitors Asbani, Bouchra; Buvat, Gaetan; Freixas, Jeremy Energy Storage Materials, Vol. 42 https://doi.org/10.1016/j.ensm.2021.07.038	journal	November 2021
Highlights from the magnetism reflectometer at the SNS Lauter, Valeria; Ambaye, Hailemariam; Goyette, Richard Physica B: Condensed Matter, Vol. 404, Issue 17, p. 2543-2546 https://doi.org/10.1016/j.physb.2009.06.021	journal	September 2009
Oxidation state and chemical shift investigation in transition metal oxides by EELS Tan, Haiyan; Verbeeck, Jo; Abakumov, Artem Ultramicroscopy, Vol. 116 https://doi.org/10.1016/j.ultramic.2012.03.002	journal	May 2012
Orientation Control and Mosaicity in Heteroepitaxial RuO₂ Thin Films Grown through Reactive Direct Current Sputtering Fields, Shelby S.; Callahan, Patrick G.; Combs, Nicholas G. Crystal Growth & Design, Vol. 24, Issue 11, p. 4604-4612 https://doi.org/10.1021/acs.cgd.4c00271	journal	May 2024
Size Dependence of Metal–Insulator Transition in Stoichiometric Fe ₃ O ₄ Nanocrystals Lee, Jisoo; Kwon, Soon Gu; Park, Je-Geun Nano Letters, Vol. 15, Issue 7 https://doi.org/10.1021/acs.nanolett.5b00331	journal	June 2015
3D Visualization of the Iron Oxidation State in FeO/Fe ₃ O ₄ Core–Shell Nanocubes from Electron Energy Loss Tomography Torruella, Pau; Arenal, Raúl; de la Peña, Francisco Nano Letters, Vol. 16, Issue 8 https://doi.org/10.1021/acs.nanolett.6b01922	journal	July 2016
Orientation-Dependent Oxygen Evolution on RuO ₂ without Lattice Exchange Stoerzinger, Kelsey A.; Diaz-Morales, Oscar; Kolb, Manuel ACS Energy Letters, Vol. 2, Issue 4 https://doi.org/10.1021/acsenergylett.7b00135	journal	March 2017
Role of Frozen Spins in the Exchange Anisotropy of Core−Shell Fe@Fe ₃ O ₄ Nanoparticles Ong, Quy Khac; Lin, Xiao-Min; Wei, Alexander The Journal of Physical Chemistry C, Vol. 115, Issue 6 https://doi.org/10.1021/jp110716g	journal	January 2011
Role of Magnetism in Catalysis: RuO ₂ (110) Surface Torun, E.; Fang, C. M.; de Wijs, G. A. The Journal of Physical Chemistry C, Vol. 117, Issue 12 https://doi.org/10.1021/jp4020367	journal	March 2013
Verwey Transition in Ultrasmall-Sized Octahedral Fe ₃ O ₄ Nanoparticles Mitra, Arijit; Mohapatra, J.; Meena, S. S. The Journal of Physical Chemistry C, Vol. 118, Issue 33 https://doi.org/10.1021/jp501652e	journal	August 2014
Effects of Oxidation on the Magnetization of Nanoparticulate Magnetite Rebodos, Robert L.; Vikesland, Peter J. Langmuir, Vol. 26, Issue 22 https://doi.org/10.1021/la102461z	journal	November 2010
Synthesis and Structural and Magnetic Characterization of Ni(Core)/NiO(Shell) Nanoparticles Johnston-Peck, Aaron C.; Wang, Junwei; Tracy, Joseph B. ACS Nano, Vol. 3, Issue 5 https://doi.org/10.1021/nn900019x	journal	April 2009
Electronic Conduction of Magnetite (Fe3O4) and its Transition Point at Low Temperatures Verwey, E. J. W. Nature, Vol. 144, Issue 3642 https://doi.org/10.1038/144327b0	journal	August 1939
New Spin Structure in an Amorphous Ferric Gel Coey, J. M. D.; Readman, P. W. Nature, Vol. 246, Issue 5434 https://doi.org/10.1038/246476a0	journal	December 1973
Exchange bias using a spin glass Ali, Mannan; Adie, Patrick; Marrows, Christopher H. Nature Materials, Vol. 6, Issue 1 https://doi.org/10.1038/nmat1809	journal	December 2006
Exchange bias of the interface spin system at the Fe/MgO interface Fan, Y.; Smith, K. J.; Lüpke, G. Nature Nanotechnology, Vol. 8, Issue 6 https://doi.org/10.1038/nnano.2013.94	journal	June 2013
Emergent zero-field anomalous Hall effect in a reconstructed rutile antiferromagnetic metal Wang, Meng; Tanaka, Katsuhiro; Sakai, Shiro Nature Communications, Vol. 14, Issue 1 https://doi.org/10.1038/s41467-023-43962-0	journal	December 2023
Direct observation of altermagnetic band splitting in CrSb thin films Reimers, Sonka; Odenbreit, Lukas; Šmejkal, Libor Nature Communications, Vol. 15, Issue 1 https://doi.org/10.1038/s41467-024-46476-5	journal	March 2024
Electrical manipulation of spin splitting torque in altermagnetic RuO2 Zhang, Yichi; Bai, Hua; Dai, Jiankun Nature Communications, Vol. 16, Issue 1 https://doi.org/10.1038/s41467-025-60891-2	journal	July 2025
Altermagnetic lifting of Kramers spin degeneracy Krempaský, J.; Šmejkal, L.; D’Souza, S. W. Nature, Vol. 626, Issue 7999 https://doi.org/10.1038/s41586-023-06907-7	journal	February 2024
Revealing exchange bias in spin compensated systems for spintronics applications Pal, Koustav; Dey, Suman; Alam, Aftab Scientific Reports, Vol. 14, Issue 1 https://doi.org/10.1038/s41598-024-76130-5	journal	December 2024
Opportunities and challenges for spintronics in the microelectronics industry Dieny, B.; Prejbeanu, I. L.; Garello, K. Nature Electronics, Vol. 3, Issue 8 https://doi.org/10.1038/s41928-020-0461-5	journal	August 2020
An anomalous Hall effect in altermagnetic ruthenium dioxide Feng, Zexin; Zhou, Xiaorong; Šmejkal, Libor Nature Electronics, Vol. 5, Issue 11 https://doi.org/10.1038/s41928-022-00866-z	journal	November 2022
Universal scaling behavior of transport properties in non-magnetic RuO2 Peng, Xin; Liu, Zhihao; Zhang, Shengnan Communications Materials, Vol. 6, Issue 1 https://doi.org/10.1038/s43246-025-00905-0	journal	August 2025
Atom probe tomography Gault, Baptiste; Chiaramonti, Ann; Cojocaru-Mirédin, Oana Nature Reviews Methods Primers, Vol. 1, Issue 1 https://doi.org/10.1038/s43586-021-00047-w	journal	July 2021
Absence of magnetic order in RuO2: insights from μSR spectroscopy and neutron diffraction Keßler, Philipp; Garcia-Gassull, Laura; Suter, Andreas npj Spintronics, Vol. 2, Issue 1 https://doi.org/10.1038/s44306-024-00055-y	journal	October 2024
Domain state exchange bias in a single layer FeRh thin film formed via low energy ion implantation Cress, Cory D.; Erve, Olaf van ’t; Prestigiacomo, Joseph Journal of Materials Chemistry C, Vol. 11, Issue 3 https://doi.org/10.1039/D2TC04014J	journal	January 2023
Techniques de diffusion des neutrons en incidence rasante pour les nanosciences Lauter-Pasyuk, V. École thématique de la Société Française de la Neutronique, Vol. 12 https://doi.org/10.1051/sfn:2007024	journal	January 2007
Néel “orange-peel” coupling in magnetic tunneling junction devices Schrag, B. D.; Anguelouch, A.; Ingvarsson, S. Applied Physics Letters, Vol. 77, Issue 15 https://doi.org/10.1063/1.1315633	journal	October 2000
Effect of surface roughness on magnetic domain wall thickness, domain size, and coercivity Zhao, Y. -P.; Gamache, R. M.; Wang, G. -C. Journal of Applied Physics, Vol. 89, Issue 2 https://doi.org/10.1063/1.1331065	journal	January 2001
Static and dynamic magnetic properties of spherical magnetite nanoparticles Goya, G. F.; Berquó, T. S.; Fonseca, F. C. Journal of Applied Physics, Vol. 94, Issue 5 https://doi.org/10.1063/1.1599959	journal	September 2003
Electrically controlled exchange bias for spintronic applications Binek, Ch.; Hochstrat, A.; Chen, X. Journal of Applied Physics, Vol. 97, Issue 10 https://doi.org/10.1063/1.1853836	journal	May 2005
Atom probe tomography Kelly, Thomas F.; Miller, Michael K. Review of Scientific Instruments, Vol. 78, Issue 3 https://doi.org/10.1063/1.2709758	journal	March 2007
In situ polarized ³ He system for the Magnetism Reflectometer at the Spallation Neutron Source Tong, X.; Jiang, C. Y.; Lauter, V. Review of Scientific Instruments, Vol. 83, Issue 7 https://doi.org/10.1063/1.4731261	journal	July 2012
Compensation of orange-peel coupling effect in magnetic tunnel junction free layer via shape engineering for nanomagnet logic applications Shah, Faisal A.; Sankar, Vijay K.; Li, Peng Journal of Applied Physics, Vol. 115, Issue 17 https://doi.org/10.1063/1.4863935	journal	February 2014
Wake-up and fatigue mechanisms in ferroelectric Hf _0.5 Zr _0.5 O ₂ films with symmetric RuO ₂ electrodes Fields, Shelby S.; Smith, Sean W.; Jaszewski, Samantha T. Journal of Applied Physics, Vol. 130, Issue 13 https://doi.org/10.1063/5.0064145	journal	October 2021
Saturation of the anomalous Hall effect at high magnetic fields in altermagnetic RuO2 Tschirner, Teresa; Keßler, Philipp; Gonzalez Betancourt, Ruben Dario APL Materials, Vol. 11, Issue 10 https://doi.org/10.1063/5.0160335	journal	October 2023
Ellingham diagrams of binary oxides Shang, Shun-Li; Lin, Shuang; Gao, Michael C. APL Materials, Vol. 12, Issue 8 https://doi.org/10.1063/5.0216426	journal	August 2024
Field-free spin–orbit switching of canted magnetization in Pt/Co/Ru/RuO2(101) multilayers Wu, Yunzhuo; Wu, Tong; Chen, Haoran Applied Physics Letters, Vol. 126, Issue 1 https://doi.org/10.1063/5.0246672	journal	January 2025
A new type of wide-angle supermirror analyzer of neutron polarization Syromyatnikov, V. G.; Ulyanov, V. A.; Lauter, V. Journal of Physics: Conference Series, Vol. 528 https://doi.org/10.1088/1742-6596/528/1/012021	journal	July 2014
Enhanced spin accumulation in Fe₃O₄based spin injection devices below the Verwey transition Bhat, Shwetha G.; Kumar, P. S. Anil Materials Research Express, Vol. 3, Issue 12 https://doi.org/10.1088/2053-1591/3/12/125905	journal	December 2016
New Magnetic Anisotropy Meiklejohn, W. H.; Bean, C. P. Physical Review, Vol. 105, Issue 3 https://doi.org/10.1103/PhysRev.105.904	journal	February 1957
Fragility of the magnetic order in the prototypical altermagnet RuO2 Smolyanyuk, Andriy; Mazin, Igor I.; Garcia-Gassull, Laura Physical Review B, Vol. 109, Issue 13 https://doi.org/10.1103/PhysRevB.109.134424	journal	April 2024
Origin of the anomalous Hall effect in Cr-doped RuO 2 Smolyanyuk, Andriy; Šmejkal, Libor; Mazin, Igor I. Physical Review B, Vol. 111, Issue 6 https://doi.org/10.1103/PhysRevB.111.064406	journal	February 2025
Influence of nonstoichiometry on the Verwey transition Aragón, Ricardo; Buttrey, Douglas J.; Shepherd, John P. Physical Review B, Vol. 31, Issue 1 https://doi.org/10.1103/PhysRevB.31.430	journal	January 1985
Electron states, magnetism, and the Verwey transition in magnetite Zhang, Ze; Satpathy, Sashi Physical Review B, Vol. 44, Issue 24 https://doi.org/10.1103/PhysRevB.44.13319	journal	December 1991
Spin-orientation dependence in neutron reflection from a single magnetic film Blundell, S. J.; Gester, M.; Bland, J. A. C. Physical Review B, Vol. 51, Issue 14 https://doi.org/10.1103/PhysRevB.51.9395	journal	April 1995
Impurity effects upon the Verwey transition in magnetite Brabers, V. A. M.; Walz, F.; Kronmüller, H. Physical Review B, Vol. 58, Issue 21 https://doi.org/10.1103/PhysRevB.58.14163	journal	December 1998
Pinned magnetization in the antiferromagnet and ferromagnet of an exchange bias system Fitzsimmons, M. R.; Kirby, B. J.; Roy, S. Physical Review B, Vol. 75, Issue 21 https://doi.org/10.1103/PhysRevB.75.214412	journal	June 2007
Exchange bias in Fe / Fe 3 O 4 core-shell magnetic nanoparticles mediated by frozen interfacial spins Ong, Quy Khac; Wei, Alexander; Lin, Xiao-Min Physical Review B, Vol. 80, Issue 13 https://doi.org/10.1103/PhysRevB.80.134418	journal	October 2009
Exchange bias induced by the Fe3O4Verwey transition de la Venta, J.; Erekhinsky, M.; Wang, Siming Physical Review B, Vol. 85, Issue 13 https://doi.org/10.1103/PhysRevB.85.134447	journal	April 2012
Mechanisms of Exchange Bias with Multiferroic BiFeO 3 Epitaxial Thin Films Béa, H.; Bibes, M.; Ott, F. Physical Review Letters, Vol. 100, Issue 1 https://doi.org/10.1103/PhysRevLett.100.017204	journal	January 2008
Itinerant Antiferromagnetism in RuO 2 Berlijn, T.; Snijders, P. C.; Delaire, O. Physical Review Letters, Vol. 118, Issue 7 https://doi.org/10.1103/PhysRevLett.118.077201	journal	February 2017
Observation of Spin Splitting Torque in a Collinear Antiferromagnet RuO2 Bai, H.; Han, L.; Feng, X. Y. Physical Review Letters, Vol. 128, Issue 19 https://doi.org/10.1103/PhysRevLett.128.197202	journal	May 2022
Chiral Magnons in Altermagnetic RuO2 Šmejkal, Libor; Marmodoro, Alberto; Ahn, Kyo-Hoon Physical Review Letters, Vol. 131, Issue 25 https://doi.org/10.1103/PhysRevLett.131.256703	journal	December 2023
Incommensurate Spin Density Wave in Antiferromagnetic RuO2 Evinced by Abnormal Spin Splitting Torque Feng, Xiaoyu; Bai, Hua; Fan, Xinxin Physical Review Letters, Vol. 132, Issue 8 https://doi.org/10.1103/PhysRevLett.132.086701	journal	February 2024
Absence of Altermagnetic Spin Splitting Character in Rutile Oxide RuO2 Liu, Jiayu; Zhan, Jie; Li, Tongrui Physical Review Letters, Vol. 133, Issue 17 https://doi.org/10.1103/PhysRevLett.133.176401	journal	October 2024
Correlation between Exchange Bias and Pinned Interfacial Spins Ohldag, H.; Scholl, A.; Nolting, F. Physical Review Letters, Vol. 91, Issue 1 https://doi.org/10.1103/PhysRevLett.91.017203	journal	July 2003
Emerging Research Landscape of Altermagnetism Šmejkal, Libor; Sinova, Jairo; Jungwirth, Tomas Physical Review X, Vol. 12, Issue 4 https://doi.org/10.1103/PhysRevX.12.040501	journal	December 2022
Tunneling Magnetoresistance in Altermagnetic RuO2 -Based Magnetic Tunnel Junctions Noh, Seunghyeon; Kim, Gye-Hyeon; Lee, Jiyeon Physical Review Letters, Vol. 134, Issue 24 https://doi.org/10.1103/nrk5-5zrj	journal	June 2025
Anisotropic spin-polarized conductivity in collinear altermagnets Dou, Mingbo; Wang, Xianjie; Tao, L. L. Physical Review B, Vol. 111, Issue 22 https://doi.org/10.1103/w52v-blqm	journal	June 2025
Electrodes for PbZr x Ti1 − x O 3 Ferroelectric Thin Films Vijay, D. P.; Desu, S. B. Journal of The Electrochemical Society, Vol. 140, Issue 9 https://doi.org/10.1149/1.2220877	journal	September 1993
Thermodynamic Properties of the Oxides of Fe, Ni, Pb, Cu, and Mn, by EMF Measurements Charette, G. G.; Flengas, S. N. Journal of The Electrochemical Society, Vol. 115, Issue 8 https://doi.org/10.1149/1.2411434	journal	January 1968
Symmetry-breaking induced surface magnetization in non-magnetic RuO$_2$ Ho, Dai Q.; To, D. Quang; Hu, Ruiqi arXiv https://doi.org/10.48550/arXiv.2502.03751	preprint	January 2025
Effects of altermagnetic order, strain and doping in RuO$_2$ Wickramaratne, Darshana; Currie, Marc; Fields, Shelby S. arXiv https://doi.org/10.48550/arXiv.2502.08872	preprint	January 2025

Similar Records

Engineering exchange bias at the interface of self-polarized ultrathin ferroelectric Ba⁢Ti⁢O₃ and ferromagnetic La_0.67⁢Sr_0.33⁢Mn⁢O₃

Journal Article · Wed Nov 13 00:00:00 UTC 2024 · Physical Review Applied · OSTI ID:2584641

Maity, Tuhin; Bansal, Manisha; Strkalj, Nives; +11 more

Strain-stabilized interfacial polarization tunes work function over 1 eV in RuO₂/TiO₂ heterostructures

Journal Article · Mon Feb 09 00:00:00 UTC 2026 · Nature Communications · OSTI ID:3022077

Jeong, Seung Gyo; Lin, Bonnie Y. X.; Jin, Mengru; +14 more

Strained-Induced Morphological Reconstruction of RuO₂(110) Thin-Film Electrocatalysts

Journal Article · Sun Oct 05 00:00:00 UTC 2025 · Journal of the American Chemical Society · OSTI ID:3009965

Som, Jacob; Reese, Austin J.; Mitrovic, Luka; +8 more

Related Subjects

RuO2
altermagnetism
exchange bias
interfaces
neutron diffraction
spintronics

Title: Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO2/Fe Bilayer Heterostructures

Citation Formats

References (68)

Similar Records

Related Subjects

Title: Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO₂/Fe Bilayer Heterostructures