Cobalt-induced structural modulation in multiferroic Aurivillius-phase oxides

DOI: 10.1039/D0TC01443E

Authors: Vladimir Koval (Institute of Materials Research, Slovak Academy of Sciences) , Yu Shi (Lanzhou University) , Ivan Škorvánek (Institute of Experimental Physics, Slovak Academy of Sciences) , Giuseppe Viola (Queen Mary University of London) , Radovan Bures (Institute of Materials Research, Slovak Academy of Sciences) , Karel Saksl (Institute of Materials Research, Slovak Academy of Sciences) , Pavla Roupcova (Institute of Physics of Materials ASCR; CEITEC Brno University of Technology) , Man Zhang (Queen Mary University of London) , Chenlong Jia (Lanzhou University) , Haixue Yan (Queen Mary University of London)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Materials Chemistry C

State: Published (Approved)
Published: May 2020
Diamond Proposal Number(s): 18273

Abstract: Attaining robust magnetic long-range order in ferroelectric Aurivillius-phase oxides at room temperature has recently attracted considerable attention of material scientists and engineers for the development of magnetoelectric-active materials in microelectronics and spintronics. Here, we report the structural evolution and its relation to the macroscopic magnetization of the series samples of Aurivillius (Bi4.3Gd0.7)(Fe1-xCox)1+yTi3-2yNbyO15 (x=0, 0.3, 0.5 and y=0, 0.3) compounds prepared by solid state reaction, aiming at shedding light on the Co substitution-induced ferromagnetism at room temperature and above. The Co-free composition showed a single-phase four-layered Aurivillius structure (a space group A21am), while the Co substitution was found to give rise to a mixed-layer structure composed of four- and three-layered phases. Rietveld analysis of the synchrotron X-ray diffraction data showed that the reduction in the number of layers across the Aurivillius morphotropic transition boundary is accompanied by a structural phase transformation from A21am to B2cb. The disordered intergrowth of these phases was evidenced by high-resolution transmission electron microscopy and found to originate from a nanoscale structural modulation occurring at the interface between the two phases. A sextet suggesting a long-range magnetic ordering in the doped samples was deduced from Mössbauer spectra. Magnetic-property measurements, indeed, confirmed a ferromagnetic state of these samples at elevated temperatures. The highest values of the remanent and saturation magnetization at room temperature were obtained for the compositions with x=0.3, in which the occurrence and enhancement of the magnetization can be attributed to the ferromagnetic clustering of the FeO6 and CoO6 octahedra and, partly, also to the spin canting effects and/or a double-exchange magnetic interaction between the mixed valence cobalt through oxygen. The cooperative freezing of randomly distributed Fe-O-Co clusters is suggested to be responsible for the spin glass-like behaviour observed at low temperatures.

Diamond Keywords: Ferroelectricity; Ferromagnetism

Subject Areas: Materials, Chemistry


Instruments: I15-Extreme Conditions

Other Facilities: Beamline P65 at PETRA III

Added On: 28/05/2020 14:20

Discipline Tags:

Quantum Materials Multiferroics Physics Magnetism Materials Science Perovskites Metallurgy

Technical Tags:

Diffraction X-ray Powder Diffraction