Long-range magnetic coupling across a polar insulating layer

• Published in: Nature communications Vol. 7; no. 1; p. 11015
• Main Authors: Lü, W. M., Saha, Surajit, Wang, X. Renshaw, Liu, Z. Q., Gopinadhan, K., Annadi, A., Zeng, S. W., Huang, Z., Bao, B. C., Cong, C. X., Venkatesan, M., Yu, T., Coey, J. M. D., Ariando, Venkatesan, T.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 16-03-2016; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/119/995; 639/301/119/997; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms11015

Magnetic interactions in solids are normally mediated by short-range exchange or weak dipole fields. Here we report a magnetic interaction that can propagate over long distances (∼10 nm) across a polar insulating oxide spacer. Evidence includes oscillations of magnetization, coercivity and field-cooled loop shift with the thickness of LaAlO
3
in La
0.67
Sr
0.33
MnO
3
/LaAlO
3
/SrTiO
3
heterostructures. Similar modifications of the hysteresis loop appear when two coupled films of La
0.67
Sr
0.33
MnO
3
are separated by LaAlO
3
, or another polar insulator, but they are absent when the oxide spacer layer is nonpolar. The loop shift is attributed to strong spin–orbit coupling and Dzyaloshinskii–Moriya interaction at the interfaces. There is evidence from inelastic light scattering that the polar spacer mediates long-range transmission of orbital magnetization. This coupling mechanism is expected to apply for any conducting ferromagnetic oxide with mixed valence; in view of electron hopping frequency involved, it raises the prospect of terahertz tunability of magnetic coupling.
Magnetic interactions in solids are usually short-range or else they involve itinerant electrons. Here, the authors evidence a long-range magnetic coupling mediated by orbital moments in a polar spacer layer of nonmagnetic insulating oxide, with a sign which oscillates with spacer thickness.