S. Dussan

Structural and optical properties of nanocrystalline Zn1−xMnxO

The multi phonon Raman scattering in Mn doped (1%–10%) ZnO was observed at room temperature using 514.5nm Ar+ laser. The additional optical modes at 327, 332, 482, 532, and 680cm−1 in Zn1−xMnxO targets were identified as the second order Raman modes in the disordered lattice and the precipitation of the secondary phase ZnMn2O4. The crystalline grain sizes of 1%, 3%, 5%, and 10% Mn doped ZnO samples were calculated by phonon confinement model as 31.8, 18.3, 15.9, and 14.1nm, respectively. The optical band gap was found to be increased (3.27–3.41eV) due to the Mn doping.

Magnetic effects on dielectric and polarization behavior of multiferroic heterostructures

PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3(PZT/LSMO) bilayer with surface roughness ∼1.8 nm thin films have been grown by pulsed laser deposition on LaAlO3(LAO) substrates. High remnant polarization (30–54 μC/cm2), dielectric constant (400–1700), and well saturated magnetization were observed depending upon the deposition temperature of the ferromagnetic layer and applied frequencies. Giant frequency-dependent change in dielectric constant and loss were observed above the ferromagnetic-paramagnetic temperature. The frequency dependent dielectric anomalies are attributed to the change in metallic and magnetic nature of LSMO and also the interfacial effect across the bilayer; an enhanced magnetoelectric interaction may be due to the Parish–Littlewood mechanism of inhomogeneity near the metal-dielectric interface.

Room temperature multiferroic effects in superlattice nanocapacitors

A composite nanocapacitor was fabricated based on ferroelectric PbZr0.52Ti0.48O3(PZT) and half-metallic oxide La0.67Sr0.33MnO3(LSMO) with 5 nm/1 nm periodicity, respectively. X-ray θ-2θ scan and Φ-scan revealed epitaxial growth of nanocapacitors. At room temperature, a microscopic polarization of 11 μC/cm2 and magnetization of 50 emu/cm3 were measured for superlattice nanocapacitors. Local piezo force microscopy measurements revealed switching of polarization under external bias field confirming ferroelectric behavior. Zero field cooling measurements showed the existence of cusp in magnetization at low temperatures indicating spin-glass-like behavior contrary to Pb(ZrxTi1−x)O3/LaxSr1−xMnO3 bilayer structure. Frequency dependent dielectric anomaly was observed near room temperature suggesting dynamic magneto (resistance)-dielectric coupling.

Effect of electrode resistance on dielectric and transport properties of multiferroic superlattice: A Impedance spectroscopy study

Fundamental microscopic processes that take place throughout of ferroelectric PbZr1−xTixO3 (x = 0.48) (PZT) and ferromagnetic La1−xSrxMnO3 (x = 0.33) (LSMO) superlattices (SLs) architecture including the influences of electrode on functional properties are analyzed using impedance spectroscopy technique (IS). Temperature and frequency dependence impedance and ac conductivity are investigated in the ranges of 100–600 K and 102–106 Hz suggesting a strong dependence between temperature and electrode contribution in the electrical properties. The results are interpreted using the alternative Z′ as a function of Z″/F representation, more commonly this representation applied in the cases when the complex impedance curves show overlapped arcs due to the relative small differences in relaxations frequencies. Activation energy is obtained from the Arrhenius plot of relaxation time and ac conductivity in order to identify the conduction mechanism present in the superlattices.

Raman scattering measurements of phonon anharmonicity in CuAlO2 thin films

CuAlO2 thin films were grown on single crystalline sapphire substrates with c-axis orientation by rf sputtering method. The x-ray diffraction data indicate the formation of delafossite structure and tend to be oriented along (001). Temperature dependent Raman spectra of CuAlO2 thin films were measured from 80 to 1273 K, and we observed two optical modes at Eg (∼418 cm−1) and A1g(∼767 cm−1) showing anomalous frequency and linewidth shifts with temperature, which were interpreted as an experimental evidence of combined effect of lattice expansion and anharmonic phonon-phonon interaction in CuAlO2. At high temperature, polaronic state and change in effective mass due to lattice expansion also affect the frequency shift and the linewidth of the observed Raman modes.

Magnetic control of ferroelectric interfaces

We report the strong magnetic field dependence of ferroelectric PbZr(0.52)Ti(0.48)O(3) (PZT) films on half-metallic oxide La(0.67)Sr(0.33)MnO(3) (LSMO) electrodes. As the field H is increased, the hysteresis loop first broadens (becomes lossy) and then disappears at approximately H = 0.34 T and ambient temperatures. The data are compared with the theories of Pirč et al (2009 Phys. Rev. B 79 214114), Parish and Littlewood (2008 Phys. Rev. Lett. 101 166602) and Catalan (2006 Appl. Phys. Lett. 88 102902). The results are interpreted as due not to magnetocapacitance but to the sharp negative magnetoresistance in LSMO at low magnetic fields (Hwang et al 1996 Phys. Rev. Lett. 77 2041), which causes a dramatic increase in leakage current through the PZT.

Synthesis, Structural and Magnetic Properties of Ni-Doped In2O3 Nanoparticles

Pure and Ni-doped In2-xNixO3 (x = 0.0, 0.01, 0.05, 0.1) nanocrystalline powders were synthesized using sol-gel process. The XRD patterns revealed the formation of nanocrystalline particles with cubic bixbyte crystal structure. The average crystal size was calculated from XRD patterns using Debye-Scherers Equation for (222) peak and it was found to be 8 nm. This observation agrees well with the particle size estimated from the transmission electron microscope (TEM). The observed Raman peaks in the doped materials were negligibly shifted towards the lower frequency. This clearly indicates that Ni ions are incorporate into the host In2O3 structure, in agreement with the XPS measurements. The Raman spectra show that the nanoparticles are free of secondary crystalline phase. The temperature dependent magnetization showed no evidence of ferromagnetism at room temperature.

Anomalous Enhancement in Magnetization of BiFeO3 – CoFe2O4 Heterostructure Multilayer Thin Films Deposited on SrTiO3 with Different Orientation

The magnetic properties of BiFeO3(BFO) – CoFe2O4(CFO) heterostructure thin films, grown on (100), (110) and (111) SrTiO3 (STO) substrates by employing pulsed laser deposition (PLD) method, have been studied. The XRD patterns of BFO-CFO multilayer thin films compared with the pure CFO and BFO thin films grown using under identical conditions evidenced that all peaks present correspond to CFO and BFO structure in two separate phases. Micro-Raman spectra analysis also reveals the presence of BFO and CFO in two separate phases in the heterostructures thin films. The anomalous enhancement in magnetization has been observed for BFO−CFO multilayer thin films, relative to pure BFO thin films in all three different orientations. The saturation magnetization for (100), (111) and (110) oriented BFO-CFO thin films are 44, 62 and 80 emu/cc suggesting that (110) is most preferable direction to achieve the magneto electric (ME) coupling effect.

Fabrication and Characterization of Artificially Designed PZT/LSMO Multiferroics Heterostructure

Highly oriented and epitaxial bilayers of PbZr 0.52 Ti 0.48 O 3 /La 0.67 Sr 0.33 MnO 3 (PZT/LSMO) thin films have been grown by pulsed laser deposition on two different substrates (100) - MgO and -LaAlO 3 (LAO) respectively. The structural analysis using X-ray diffraction (XRD) evidenced that layered structure was formed without any secondary phase. Atomic force microscopy (AFM) images shown change in the grain size and surface roughness with change of the substrate. Room temperature magnetization-field (M-H) exhibited well-shaped magnetization hysteresis loops, good saturation and low coercivity. The electrical properties of hetrostructure exhibited high remnant polarization (30-54 μC/cm 2 ) and dielectric constant (400-1700) depending upon the different substrate and temperature deposition of FM layer. Frequency dependent change in dielectric constant and loss were observed above metallic ferromagnet to insulator paramagnet transition temperature. It is important to note that the frequency dependent dielectric anomalies are attributed to the change in metallic nature of LSMO bottom electrode and also the bilayer.

Multiferroics properties in BiFeO3/CoFe2O4 heterostructures thin films deposited on (111) SrTiO3

The multiferroic properties of BiFeO3-CoFe2O4 (BFO-CFO) heterostructures thin film grown on (111) SrTiO3 (STO) substrates by employing pulsed laser deposition (PLD) method, have been studied.X ray diffraction analysis reveals the presence of BFO and CFO in two separate phases. The heterostructures BFO/CFO/STO(111) thin films show well – shaped hysteresis loop with saturated magnetization and coercive field, which are much larger than pure BFO/STO thin film. The frequency dependent dielectric anomalies in BFO-CFO multilayer are attributed to the interfacial effect across the presence of CFO as a separate phase embedded in BFO matrix.