We report the observation of strong magnetic proximity coupling in the heterostructure superconductor ${\mathrm{Sr}}_2{\mathrm{VO}}_{3-\delta }\mathrm{FeAs}$, determined by upper critical field $H_{c2}\left(T\right)$ measurements up to 65 T. Using the resistivity and the radio-frequency measurements for both $H\parallel ab$ and $H\parallel c$, we found a strong upward curvature of $H_{c2}^c\left(T\right)$, together with a steep increase in $H_{c2}^{ab}\left(T\right)$ near $T_c$, yielding an anisotropic factor ${\gamma }_H=H_{c2}^{ab}/H_{c2}^c$ up to $\sim 20$, much higher than those of other iron-based superconductors. These are attributed to the Jaccarino-Peter effect, rather than to the multiband effect, due to strong exchange interaction between itinerant Fe spins of the FeAs layers and localized V spins of Mott-insulating ${\mathrm{SrVO}}_{3-\delta }$ layers. These findings provide evidence for strong antiferromagnetic proximity coupling that is comparable to the intralayer superexchange interaction of the ${\mathrm{SrVO}}_{3-\delta }$ layer and sufficient to induce magnetic frustration in ${\mathrm{Sr}}_2{\mathrm{VO}}_{3-\delta }\mathrm{FeAs}$.

• Received 3 October 2020
• Revised 26 February 2022
• Accepted 20 April 2022

DOI:https://doi.org/10.1103/PhysRevB.105.214505