Abstract Body

The coexistence of superconductivity and magnetism has been a long-standing issue in the field of superconductivity due to the antagonistic nature of these two ordered states. The interplay between superconductivity and magnetism creates numerous exotic physical phenomena, such as the reentrant superconducting transition associated with the suppression of superconductivity around the magnetic transition temperature (T_m), highlighting the impact of magnetism on superconductivity. The recently discovered iron-based magnetic superconductor EuRbFe₄As₄ shows high-critical-temperature (high-T_c) superconductivity and helimagnetic order at the ground state [1]. Here we show the experimental observation of the ferromagnetic order induced by superconducting vortices in the high-T_c magnetic superconductor EuRbFe₄As₄. Although the ground state of the Eu²⁺ moments in EuRbFe₄As₄ is helimagnetism below T_m, neutron diffraction and magnetization experiments revealed a ferromagnetic hysteresis of the Eu²⁺ spin alignment, highlighting a unique interplay between magnetism and superconductivity. Moreover, we show that the direction of the Eu²⁺ moments is dominated by the distribution of pinned vortices based on the Bean’s critical state model, demonstrating the capability of manipulating the spin texture by controlling the direction of superconducting vortices. Such a spin manipulation would pave the way to novel devices using magnetic superconductors [2].

Figure 1: (a) Crystal structure of EuRbFe₄As₄. Blue arrows indicate the direction of the Eu²⁺ moments. (b) The schematic diagram of the helical magnetic structure under the zero-field-cooled condition. (c) Ferromagnetic alignment of the Eu²⁺ moments induced by vortices under magnetic field.

References

[1] K. Iida et al., Phys. Rev. B 100, 014506 (2019).
[2] S. Ishida et al., Proc. Natl. Acad. Sci. USA 118, e2101101118 (2021).

Acknowledgment

This work was supported by the Austria-Japan Bilateral Joint Research Project hosted by the Japan Society for the Promotion of Science (JSPS) and by the Austrian Science Fund (FWF): I2814-N36 and a Grant-in-Aid for Scientific Research (JSPS Grant No. 19K15034, 19H05823, and JP16H06439).