title: Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1-x Fex)nO(3n+1)-δ Ruddlesden-Popper superstructures.
abstract: Bulk crystals and thin films of PbTi(1-x)FexO3(-δ) (PTFO) are multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pbn+1(Ti(1-x)Fex)nO3(n+1)-δ forms spontaneously during pulsed laser deposition of PTFO on LaAlO3 substrates. High-resolution transmission electron microscopy, x-ray diffraction and x-ray photoemission spectroscopy were utilised to perform a structural and compositional analysis, demonstrating that n ≃ 8 and x ≃ 0.5. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes and the observation of second harmonic generation establishes a non-centrosymmetric point group for Pbn+1(Ti0.5Fe0.5)nO3(n+1)-δ, a prerequisite for (but not proof of) ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.
authors.affiliation: University of Oxford, Department of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.
authors.forename: K I
authors.initials: KI
authors.lastname: Doig
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: J J P
authors.initials: JJ
authors.lastname: Peters
authors.affiliation: Indian Institute of Technology Bombay, Mumbai 400076, India.
authors.forename: S
authors.initials: S
authors.lastname: Nawaz
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Walker
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Walker
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: M R
authors.initials: MR
authors.lastname: Lees
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Beanland
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: A M
authors.initials: AM
authors.lastname: Sanchez
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: C F
authors.initials: CF
authors.lastname: McConville
authors.affiliation: Indian Institute of Technology Bombay, Mumbai 400076, India.
authors.forename: V R
authors.initials: VR
authors.lastname: Palkar
authors.affiliation: University of Warwick, Department of Physics, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
authors.forename: J
authors.initials: J
authors.lastname: Lloyd-Hughes