C. A. F. Vaz

Magnetoelectric Coupling Effects in Multiferroic Complex Oxide Composite Structures

The study of magnetoelectric materials has recently received renewed interest, in large part stimulated by breakthroughs in the controlled growth of complex materials and by the search for novel materials with functionalities suitable for next generation electronic devices. In this Progress Report, we present an overview of recent developments in the field, with emphasis on magnetoelectric coupling effects in complex oxide multiferroic composite materials.

Origin of the magnetoelectric coupling effect in Pb(Zr0.2Ti0.8)O{3}/La{0.8}Sr{0.2}MnO{3} Multiferroic heterostructures.

The electronic valence state of Mn in Pb(Zr0.2Ti0.8)O{3}/La{0.8}Sr{0.2}MnO{3} multiferroic heterostructures is probed by near edge x-ray absorption spectroscopy as a function of the ferroelectric polarization. We observe a temperature independent shift in the absorption edge of Mn associated with a change in valency induced by charge carrier modulation in the La0.8Sr0.2MnO3, demonstrating the electronic origin of the magnetoelectric effect. Spectroscopic, magnetic, and electric characterization shows that the large magnetoelectric response originates from a modified interfacial spin configuration, opening a new pathway to the electronic control of spin in complex oxide materials.

Magnetic anisotropy modulation of magnetite in Fe3O4/BaTiO3(100) epitaxial structures

Temperature dependent magnetometry and transport measurements on epitaxial Fe3O4 films grown on BaTiO3(100) single crystals by molecular beam epitaxy show a series of discontinuities, due to changes in the magnetic anisotropy induced by strain from the different crystal phases of BaTiO3. The magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO3 at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with the magnetoelastic anisotropies. These results demonstrate the possibility of using the piezoelectric response of BaTiO3 to modulate the magnetic anisotropy of magnetite films.

Temperature dependence of the magnetoelectric effect in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 multiferroic heterostructures

The magnetoelectric response of Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 (PZT/LSMO) artificial multiferroic heterostructures as a function of temperature, electric, and magnetic field, shows that the largest magnetoelectric coupling is attained at temperatures near the magnetic critical point of LSMO, at ∼180 K (−13.5 Oe cm kV−1). The magnetoelectric coupling displays a strong temperature dependence, changing sign at 150 K and saturating to positive values below ∼100 K (+6 Oe cm kV−1). The magnetoelectric curve switches hysteretically between two states in response to the ferroelectric switching. The peak in the magnetoelectric response coincides with the observation of on/off switching of magnetism in LSMO near the critical region, where the sensitivity to electric field is largest, making it a promising approach for device applications.

Experimental study of the interfacial cobalt oxide in Co 3 O 4 / α − Al 2 O 3 ( 0001 ) epitaxial films

A detailed spectroscopic and structural characterization of ultrathin cobalt oxide films grown by O-assisted molecular-beam epitaxy on

Origin of 90° domain wall pinning in Pb(Zr0.2Ti0.8)O3 heteroepitaxial thin films

\ensuremath{\alpha}\ensuremath{-}{\text{Al}}_{2}{\text{O}}_{3}(0001)

Interface and electronic characterization of thin epitaxial Co3O4 films

single crystals is reported. The experimental results show that the cobalt oxide films become progressively more disordered with increasing thickness, starting from the early stages of deposition. Low-energy electron-diffraction patterns suggest that the unit cell remains similar to that of

Control of magnetism in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 multiferroic heterostructures (invited)

\ensuremath{\alpha}{\text{-Al}}_{2}{\text{O}}_{3}(0001)

Dynamic Evanescent Phonon Coupling Across the La 1 − x Sr x MnO 3 / SrTiO 3 Interface

up to a thickness of

Intrinsic interfacial phenomena in manganite heterostructures

17\text{ }\text{\AA{}}