Superconductivity-driven ferromagnetism and spin manipulation using vortices in the magnetic superconductor...

Magnetic superconductors are specific materials exhibiting two antagonistic phenomena, superconductivity and magnetism, whose mutual interaction induces various emergent 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. In this study, we report the experimental observation of the ferromagnetic order induced by superconducting vortices in the high-critical-temperature (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 show a ferromagnetic hysteresis of the Eu²⁺ spin alignment. We demonstrate that the direction of the Eu²⁺ moments is dominated by the distribution of pinned vortices based on the critical state model. Moreover, we demonstrate the manipulation of spin texture by controlling the direction of superconducting vortices, which can help realize spin manipulation devices using magnetic superconductors.