Altermagnetism revealed in G-type antiferromagnetic multiferroic BiFeO<sub>3</sub>
ORAL · Invited
Abstract
Altermagnets, a family of collinear antiferromagnets (AFMs) showing spin-split bands even in absence of spin-orbit coupling, have attracted substantial attention in recent years. Despite their vanishing net magnetization, altermagnets show a non-vanishing spin splitting that is non-relativistic in nature and can be sizable. These unique features have made altermagnets potentially relevant for spintronics applications.
A necessary condition for altermagnetism is the absence of PT symmetry, where P and T are space- and time-inversion, respectively. This makes ferroelectric AFMs an ideal platform to explore altermagnetism. Here, we report on the altermagnetic spin splitting in G-type BiFeO3 (BFO), a prototypical multiferroic. Due to its relatively high symmetry, the bands of BFO are spin degenerate along the high-symmetry lines in reciprocal space, making its altermagnetic character difficult to identify.
In this work, to make the altermagnetic character of BFO evident, we introduce a new type of generalized path in reciprocal space to highlight the behavior of the bands both along high-symmetry lines and at general k points and to capture the sign alternation of spin splitting typical of altermagnets. We investigate altermagnetism in BFO by defining a spin-splitting function on the Brillouin zone and examining its structure on selected planar cuts. This analysis reveals nodal surfaces of the spin-splitting function and shows how these features capture the g-wave character of altermagnetism in BFO. Finally, we investigate the interplay of altermagnetism and ferroelectricity in BFO. In particular, we show that the spin splitting in BFO is controlled by the pattern of oxygen octahedron rotations which, in conjunction with a polar distortion, relates the paraelectric parent cubic phase of BFO to its low-symmetry ferroelectric rhombohedral phase.
A necessary condition for altermagnetism is the absence of PT symmetry, where P and T are space- and time-inversion, respectively. This makes ferroelectric AFMs an ideal platform to explore altermagnetism. Here, we report on the altermagnetic spin splitting in G-type BiFeO3 (BFO), a prototypical multiferroic. Due to its relatively high symmetry, the bands of BFO are spin degenerate along the high-symmetry lines in reciprocal space, making its altermagnetic character difficult to identify.
In this work, to make the altermagnetic character of BFO evident, we introduce a new type of generalized path in reciprocal space to highlight the behavior of the bands both along high-symmetry lines and at general k points and to capture the sign alternation of spin splitting typical of altermagnets. We investigate altermagnetism in BFO by defining a spin-splitting function on the Brillouin zone and examining its structure on selected planar cuts. This analysis reveals nodal surfaces of the spin-splitting function and shows how these features capture the g-wave character of altermagnetism in BFO. Finally, we investigate the interplay of altermagnetism and ferroelectricity in BFO. In particular, we show that the spin splitting in BFO is controlled by the pattern of oxygen octahedron rotations which, in conjunction with a polar distortion, relates the paraelectric parent cubic phase of BFO to its low-symmetry ferroelectric rhombohedral phase.
*The authors acknowledge support from Office of Naval Research N00014-21-1-2107 (DS, KMR, AU), the Abrahams Fellowship of the Center for Materials Theory at Rutgers University (AU), the Wisconsin Materials Research Science and Engineering Center (NSF DMR-2309000) (YT), the National Research Foundation of Korea (NRF) grant RS-2024-00358551 (SYP), and ANID Fondecyt grant number 1220986 (SERL).
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Publication: G-type antiferromagnetic BiFeO3 is a multiferroic g-wave altermagnet, Phys. Rev. B 112, 104411 (2025).
Presenters
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Andrea Urru
- Rutgers University