Ferromagnet-superconductor interfaces: The length scales of interactions

Abstract

Heterostructures and superlattices consisting of the half-metal ferromagnet La0.67Ca0.33MnO3 (LCMO) and the superconductor YBa2Cu3O7 (YBCO) stacked along the c-axis of the superconductor were fabricated by pulsed laser deposition techniques. Apart from their structural characterization by x-ray diffractometry and high resolution TEM, the magnetic as well as electronic interaction at the interfaces and between the layers is studied by a variety of techniques ranging from transport measurements to magnetic, neutron diffraction and XMCD analysis. It turns out that these interaction effects occurring at several different length scales. At a short length scale of ∼ 3 nm, charge transfer and/or orbital reconstruction as revealed by resonant x-ray absorption and XMCD measurements are dominant, the length scale of ∼ 10 nm is the regime of self-injection of spin-polarized quasiparticles and at a scale in the 100 nm range and above magnetic interactions are present affecting the flux-line lattice of the superconductor, the domain structure of the magnetic layer as well as the interlayer coupling. The different and controversially discussed ferromagnet/superconducting interactions in YBCO/LCMO hybrids are analyzed and combined to a universal picture. © 2008 IOP Publishing Ltd.