167 research outputs found
Emergence of ferroelectricity at the morphotropic phase boundary of ultrathin BiFeO
We demonstrate the robustness of polarization in ultrathin compressive
strained BiFeO single layers and heterostructures during epitaxial
thin-film growth. Using in-situ optical second harmonic generation (ISHG), we
explore the emergence of ferroelectric phases at the strain-driven morphotropic
phase boundary in the ultrathin regime. We find that the epitaxial films grow
in the ferroelectric tetragonal (T-) phase without exhibition of a critical
thickness. The robustness of this high-temperature T-phase against
depolarizing-field effects is further demonstrated during the growth of
capacitor-like (metal|ferroelectric|metal) heterostructures. Using
temperature-dependent ISHG post-deposition, we identify the thickness-dependent
onset of the monoclinic distortion in the T-matrix and trace the signature of
the subsequent emergence of the strain-relaxed rhombohedral-like monoclinic
phase. Our results show that strain-driven T-phase stabilization in BiFeO
yields a prominent candidate material for realizing ultrathin ferroelectric
devices.Comment: 5 pages, 3 figure
Current-induced switching of YIG/Pt bilayers with in-plane magnetization due to Oersted fields
We report on the switching of the in-plane magnetization of thin yttrium iron
garnet (YIG)/Pt bilayers induced by an electrical current. The switching is
either field-induced and assisted by a dc current, or current-induced and
assisted by a static magnetic field. The reversal of the magnetization occurs
at a current density as low as ~A/cm and magnetic fields of ~T, two orders of magnitude smaller than in ferromagnetic metals,
consistently with the weak uniaxial anisotropy of the YIG layers. We use the
transverse component of the spin Hall magnetoresistance to sense the magnetic
orientation of YIG while sweeping the current. Our measurements and simulations
reveal that the current-induced effective field responsible for switching is
due to the Oersted field generated by the current flowing in the Pt layer
rather than by spin-orbit torques, and that the switching efficiency is
influenced by pinning of the magnetic domains
BiFeO3/La0.7Sr0.3MnO3 heterostructures deposited on Spark Plasma Sintered LaAlO3 Substrates
Multiferroic BiFeO3 (BFO) / La0.7Sr0.3MnO3 heterostructured thin films were
grown by pulsed laser deposition on polished spark plasma sintered LaAlO3 (LAO)
polycrystalline substrates. Both polycrystalline LAO substrates and BFO films
were locally characterized using electron backscattering diffraction (EBSD),
which confirmed the high-quality local epitaxial growth on each substrate
grain. Piezoforce microscopy was used to image and switch the piezo-domains,
and the results are consistent with the relative orientation of the
ferroelectric variants with the surface normal. This high-throughput synthesis
process opens the routes towards wide survey of electronic properties as a
function of crystalline orientation in complex oxide thin film synthesis.Comment: 10 pages, 4 figures, Submitted to Applied Physics Letter
Training the polarization in integrated La0.15Bi0.85FeO3-based devices
The functionalities of BiFeO3-based magnetoelectric multiferroic heterostructures rely on the controlled manipulation of their ferroelectric domains and of the corresponding net in-plane polarization, as this aspect guides the voltage-controlled magnetic switching. Chemical substitution has emerged as a key to push the energy dissipation of the BiFeO3 into the attojoule range but appears to result in a disordered domain configuration. Using non-invasive optical second-harmonic generation on heavily La-substituted BiFeO3 films, it is shown that a weak net in-plane polarization remains imprinted in the pristine films despite the apparent domain disorder. It is found that this ingrained net in-plane polarization can be trained with out-of-plane electric fields compatible with applications. Operando studies on capacitor heterostructures treated in this way show the full restoration of the domain configuration of pristine BiFeO3 along with a giant net in-plane polarization enhancement. Thus, the experiments reveal a surprising robustness of the net in-plane polarization of BiFeO3 against chemical modification, an important criterion in ongoing attempts to integrate magnetoelectric materials into energy-efficient device
Composition Dependence of Structural Parameters and Properties of Gallium Ferrite
We show the effect of composition on structural and magnetic characteristics
of pure phase polycrystalline GaFeO (GFO) for compositions between
0.8 <= x <= 1.3. X-ray analysis reveals that lattice parameters of GFO exhibit
a linear dependence on Fe content in single phase region indicating
manifestation of Vegard's law. Increasing Fe content of the samples also leads
to stretching of bonds as indicated by the Raman peak shifts. Further, low
temperature magnetic measurements show that the coercivity of the samples is
maximum for Ga:Fe ratio of 1:1 driven by a competition between decreasing
crystallite size and increasing magnetic anisotropy.Comment: 15 pages with 4 figure
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