Surface ferrimagnetic order in RuO2 film

Jiahua Lu; Huangzhaoxiang Chen; Zhe Zhang; Xinyue Wang; Donghang Xie; Bo Liu; Liang He; Yao Li; Jun Du; Zhi Wang; Junwei Luo; Rong Zhang; Yongbing Xu; Xuezhong Ruan

arXiv · 2604.10659

Surface ferrimagnetic order in RuO2 film

Jiahua Lu·Huangzhaoxiang Chen·Zhe Zhang·Xinyue Wang·Donghang Xie·Bo Liu·Liang He·Yao Li·Jun Du·Zhi Wang·Junwei Luo·Rong Zhang·Yongbing Xu·Xuezhong Ruan

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Abstract

RuO2, widely proposed as a prototypical altermagnet, remains intensely debated with regard to its magnetic nature. Here, we demonstrate that RuO2 is non-magnetic in the bulk, but possesses a spontaneous surface ferrimagnetic order. Using spin- and angle-resolved photoemission spectroscopy, we directly detect a narrow surface state with identical spin polarizations at opposite momenta and at the Brillouin-zone center, incompatible with the spin texture of any altermagnetic order. First-principles calculations identify the non-magnetic bulk state and reveal that the detected magnetism is confined to the fully oxygen-terminated surface, where the charge transfer from Ru to O at surface triggers a ferrimagnetic alignment between adjacent Ru sublattices with antiparallel moments of +0.48 uB and -0.04 uB. Our findings provide a unified explanation reconciling debating reports on the magnetism of RuO2, establishing surface ferrimagnetism as the origin of the observed magnetic signals, and distinguishing it unambiguously from altermagnetism.

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Jiahua Lu, Huangzhaoxiang Chen, Zhe Zhang, Xinyue Wang, Donghang Xie, Bo Liu, Liang He, Yao Li, Jun Du, Zhi Wang, Junwei Luo, Rong Zhang, Yongbing Xu, Xuezhong Ruan. 2026-04-12. Surface ferrimagnetic order in RuO2 film. https://arxiv.org/abs/2604.10659

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