Spin injection in non-metallic ferromagnet and high-T_C superconductor heterojunction

You-Sheng Chen^1*, Danru Qu^1,2, J. G. Lin^1,2

¹Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
²Center for Atomic Initiatives for New Materials, National Taiwan University, Taipei, Taiwan

* Presenter:You-Sheng Chen, email:youshengchen@ntu.edu.tw

The spin injection experiment provides rich information of the spin accumulation on superconducting gap, which conventionally utilizes a spin polarized current from a ferromagnetic metal inject into a superconductor through a tunneling barrier. In this work, we investigate spin injection on a heterojunction in consist of a disordered non-metallic ferromagnetic manganite, Pr_0.5Sr_0.5MnO₃ (PMSO), and high-T_c superconductor, YBa₂Cu₃O_7-δ (YBCO). PSMO is a phase transition type colossal magnetoresistive material, which shows insulator behavior at zero field and transforms into metal at high field (> 70 kOe). In between, a disordered ferromagnetic state established, which allows a spin current injecting from a semiconductor to a meta to avoid the tunneling barrier. Epitaxial PSMO single layer and PSMO/YBCO heterostructure were prepared by the method of pulse laser deposition (PLD). Data of anisotropic magnetoresistance (AMR) of PSMO and PSMO/YBCO are directly compared by a six-point measurement. The results showed that the interface of PSMO/YBCO exhibits a four-fold symmetric AMR below superconducting T_c. This four-fold symmetric AMR was suppressed by higher field, at which PSMO is a metallic phase. The high field AMR behavior is similar to that of La_0.7Sr_0.3MnO₃ (LSMO)/YBCO. The four-fold symmetry of AMR at interface was attributed to the anisotropy of superconducting gap in d-wave superconducting YBCO, consistent with the previous report in heat transport experiments. Our result suggests the high interfacial transparency on non-metallic ferromagnet/superconductor interface.

Keywords: Spin injection, High TC Superconductor, Anisotropic magnetoresistance, heterojunction