Coupling-dependent antiferromagnetic-ferromagnetic ordering in a pinwheel artificial spin ice

Journal Article · 23 December 2024 · Physical Review B (Online)

DOI: https://doi.org/10.1103/PhysRevB.110.214437 · OSTI ID:2483699

Strømberg, Anders  ^[1]; Digernes, Einar  ^[1]; Chopdekar, Rajesh Vilas  ^[2]; Grepstad, Jostein ^[1]; Folven, Erik  ^[1]

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1. Norwegian University of Science and Technology, Trondheim (Norway)
2. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Nanopatterned magnetic thin films offer a platform for exploration of tailored magnetic properties such as emergent long-range order. A prominent example is artificial spin ice (ASI), where an arrangement of nanoscale magnetic elements, acting as macrospins, interact via their dipolar fields. In this study, we discuss the transition from antiferromagnetic (AFM) to ferromagnetic (FM) long-range order in a square lattice ASI as the magnetic elements are gradually rotated through 45⁢° to a “pinwheel” configuration. The AFM-FM transition is observed experimentally using synchrotron radiation x-ray spectromicroscopy and occurs for a certain rotation angle of the nanomagnets, dependent on the dipolar coupling strength determined by the separation of the magnets in the lattice. Large-scale magnetic dipole simulations show that the point-dipole approximation fails to capture the correct AFM-FM transition angle. However, excellent agreement with experimental data is obtained using a dumbbell-dipole model, which better reflects the actual dipolar fields of the magnets. This model also explains the coupling dependence of the transition angle, another feature not captured by the point-dipole model. Our findings resolve a discrepancy between measurement and theory in previous work on “pinwheel” ASIs and establish the coupling dependence of the AFM-FM transition. The revised dipole model, with a more accurate representation of the stray field, offers more precise control of magnetic order in artificial spin systems.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
• Sponsoring Organization: Research Council of Norway; USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 2483699
• Journal Information: Physical Review B (Online), Journal Name: Physical Review B (Online) Journal Issue: 21 Vol. 110; ISSN 2469-9950; ISSN 2469-9969
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English