Bulletin of the American Physical Society
2023 Annual Meeting of the APS Mid-Atlantic Section
Friday–Sunday, November 3–5, 2023; University of Delaware, Newark, Delaware
Session B02: Magnetism and Spintronics
5:00 PM–6:36 PM,
Friday, November 3, 2023
University of Delaware
Room: Gore 104
Chair: Hang CHEN, CUHK
Abstract: B02.00004 : Observation of orbital liquid in ultrathin magnetic films*
6:00 PM–6:36 PM
Presenter:
Sergei Urazhdin
(Emory University)
Authors:
Sergei Urazhdin
(Emory University)
Sergei V Ivanov
(Emory University)
Joshua Peacock
(Emory University)
Guanxiong Chen
(Emory University)
Vladislav E Demidov
(Muenster, Germany)
Sergej O Demokritov
(Muenster University)
John W Freeland
(Argonne National Laboratory)
Bjorn Wehinger
(ESRF)
Nicholas B Brookes
(European Sync Rad Fac (ESRF))
Magnetoelectronic measurements of heterostructures based on ultrathin transition metal ferromagnets reveal two separate magnetic order parameters: one associated with spin ordering at the Curie point TC1, and another “anomalous” order parameter with a critical point Tc2 about 50K above the Curie temperature. Remarkably, magneto-optical measurements are not sensitive to the anomalous contribution, suggesting that the origin of the latter is qualitatively different from spin magnetism. X-ray magnetic circular dichroism (XMCD) measurements reveal that the “anomalous” order parameter is associated with incipient orbital ferromagnetism whose signatures vanish below Tc2 without the onset of ferromagnetic orbital ordering. Electric current applied to micropatterned structures in this regime reveals that orbital magnetism is “hidden” but does not disappear below Tc2.
I will show that these anomalous behaviors are captured by a simple Hubbard model of orbital correlations among nearest neighbor sites in an ultrathin ferromagnetic layer, leading to the conclusion that orbital moments form an orbital liquid – a long-range correlated orbital state that lacks ordering due to the geometric orbital frustration, analogous to quantum spin liquids formed by frustrated spins [2]. In the studied orbital liquid, orbital moments are ferromagnetically coupled, which would be impossible for spin liquid due to spin conservation. I will discuss the implications of these results for our understanding of magnetism and for the emerging field of orbitronics.
[1] D. Go, et al. “Orbitronics: Orbital currents in solids”, EPL 135, 37001 (2021).
[2] S. Ivanov, J. Peacock, S. Urazhdin “Orbital correlations in ultrathin films of late transition metals”, Phys. Rev. Mater. 7, 01440 (2023)
*This work was supported by the NSF Award ECCS-2005786. Nanofabrication and magnetoelectronic measurements by G. Chen were supported by the DOE BES award DE-SC0018976.
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