Field re-entrant superconductivity in Eu-doped infinite-layer nickelates

Intertwined superconducting and magnetic orders may give rise to exotic quantum phases^1-7, including field-induced and re-entrant superconductivity^8-10. However, this magnetism-enhanced superconductivity has remained unknown in superconductors with higher transition temperatures^1-3. Although infinite-layer nickelates represent a new class of unconventional superconductors^11-20, the impact of rare-earth magnetism on superconducting properties remains largely unexplored. Here we show that Eu-doped infinite-layer nickelate Sm_0.95-xCa_0.05Eu_xNiO₂ exhibits a magnetic-field-induced re-entrant superconducting phase in the Eu-rich overdoped regime. Zero-resistance transport and high-field diamagnetic screening confirm the superconducting nature of this phase, which emerges after the initial suppression of low-field superconductivity and remains robust across a broad range of temperatures, fields and field orientations. In the same doping range, we observe nonlinear Hall transport and hysteretic magnetoresistance, indicating the unconventional nature of the re-entrant behaviour. Although partially consistent with a compensation mechanism between the Eu-derived exchange field and the applied field, our data show pronounced deviations from this model at the highest doping levels. Our findings establish infinite-layer nickelates as a fertile platform for exploring magnetically driven high-field superconductivity in strongly correlated oxides.