Magnetic and ferroelectric properties of oxygen octahedron/tetrahedron mixed ultrathin multiferroic layer by oxygen desorption

BiFeO3 epitaxial films (t(BFO)=1-10nm) were grown on a LaSrMnO3 (t(LSMO)=70nm) buffer layer and capped with a Ru or Ru/Al layer. The BiFeO3 ultrathin film (t(BFO)=3nm) was confirmed to be continuous and flat over a wide area. Piezoelectric response and switching of spontaneous polarization were observed in the ultrathin films by switching-spectroscopy piezoelectric force microscopy measurements. Using the lock-in method with a modulation frequency of 10Hz in x-ray absorption spectroscopy (XAS), a difference was observed between the left- and right-circularly polarized XAS signals of Fe L-3 and L-2 owing to x-ray magnetic circular dichroism (XMCD). The number of Fe L-3 and L-2 XMCD peaks indicated that a mixture of oxygen octahedron and tetrahedron (divalent and trivalent) structures might be formed. The t(BFO) dependence of XMCD revealed that approximately 1nm thick ferro-like magnetic properties emerged on the BiFeO3 side of the BiFeO3/Ru interface. Ru may partially extract oxygen from BiFeO3, forming an oxygen tetrahedron structure. The BiFeO3/Ru bilayer exhibits both a piezoelectric response and ferro-like magnetism, which is promising as the basic structure of multiferroic tunnel junctions.

Automated summary

The study revealed that the BiFeO3/Ru bilayer structure exhibits both piezoelectric response and ferro-like magnetism, making it a promising candidate for the basic structure of multiferroic tunnel junctions.