Magnetic Exchange Fields and Domain Wall Superconductivity at an All-Oxide Superconductor-Ferromagnet Insulator Interface

At a superconductor-ferromagnet ($S/F$) interface, the $F$ layer can introduce a magnetic exchange field within the $S$ layer, which acts to locally spin split the superconducting density of states. The effect of magnetic exchange fields on superconductivity has been thoroughly explored at $S$-ferromagnet insulator ($S/\mathrm{FI}$) interfaces for isotropic $s$-wave $S$ and a thickness that is smaller than the superconducting coherence length. Here we report a magnetic exchange field effect at an all-oxide $S/\mathrm{FI}$ interface involving the anisotropic $d$-wave high temperature superconductor praseodymium cerium copper oxide (PCCO) and the FI praseodymium calcium manganese oxide (PCMO). The magnetic exchange field in PCCO, detected via magnetotransport measurements through the superconducting transition, is localized to the $\mathrm{PCCO}/\mathrm{PCMO}$ interface with an average magnitude that depends on the presence or absence of magnetic domain walls in PCMO. The results are promising for the development of all-oxide superconducting spintronic devices involving unconventional pairing and high temperature superconductors.

Figure 1

(a) High angle x-ray diffraction from $\mathrm{PCCO}(26\mathrm{nm})/\mathrm{PCMO}(106\mathrm{nm})/\mathrm{STO}$ and corresponding (b)–(d) Rocking curves on the PCMO ${(001)}_c$, PCCO (110), and PCCO (006) peaks showing FWHM values of 0.14°, 1.20°, and 1.32°, respectively.

Figure 2

$R(H)$ (left axis) in the superconducting transition and $m(H)$ (right axis) for (a) $\mathrm{PCCO}(26\mathrm{nm})/\mathrm{PCMO}(106\mathrm{nm})/\mathrm{STO}$, (b) $\mathrm{PCMO}(53\mathrm{nm})/\mathrm{PCCO}(94\mathrm{nm})/\mathrm{PCMO}(106\mathrm{nm})/\mathrm{STO}$, and (c) $\mathrm{PCMO}(53\mathrm{nm})/\mathrm{PCO}(3\mathrm{nm})/\mathrm{PCCO}(94\mathrm{nm})/\mathrm{PCO}(3\mathrm{nm})/\mathrm{PCMO}(106\mathrm{nm})/\mathrm{STO}$. (a)–(c) (bottom right insets) $R(T)$ with the corresponding temperature for the data in the main panel indicated (round datum point). (b) (bottom right inset) Includes the normalized resistance switching width vs temperature. (Top left inset) Illustrate the corresponding sample structures in (a)–(c).

Figure 3

(a) $H_{c2}$ vs $T$ for $\mathrm{PCMO}(53\mathrm{nm})/\mathrm{PCCO}(94\mathrm{nm})/\mathrm{PCMO}(106\mathrm{nm})$. (Inset) $R(T)$ for $H$ approximately parallel to the $ab$ ($H//ab$) and $c$ plane ($H//c$) of PCCO. (b) A schematic illustration of a superconducting film of PCCO on a layer of demagnetized PCMO. (c) The effective $\mathrm{\Delta }{T}_c^{\prime }$ vs $d_{\mathrm{PCCO}}$ for $\mathrm{PCMO}/\mathrm{PCCO}/\mathrm{STO}$ (squares), $\mathrm{PCMO}/\mathrm{PCCO}/\mathrm{PCMO}/\mathrm{STO}$ (circles), and $\mathrm{PCMO}/\mathrm{PCO}/\mathrm{PCCO}/\mathrm{STO}$ (triangles) samples. Dashed lines are a guide to the eye.