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7 May 2013

Volume 113, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 174302 (2013); http://dx.doi.org/10.1063/1.4798262 (4 pages)

Yuichiro Kurokawa, Takehiko Hihara, and Ikuo Ichinose
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back to top Multiferroic Materials

Multiferroicity in spin ice Ho2Ti2O7: An investigation on single crystals

D. Liu, L. Lin, M. F. Liu, Z. B. Yan, S. Dong, and J.-M. Liu

J. Appl. Phys. 113, 17D901 (2013); http://dx.doi.org/10.1063/1.4793704 (3 pages)

Online Publication Date: 4 March 2013

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The single crystals of rare-earth titanate pyrochlore compound Ho2Ti2O7 are grown and their multiferroicity along the [110] and [111] directions is investigated. The ferroelectricity below ∼28 K, with a polarization of ∼2.50 μC/m2 along the ⟨111⟩ direction at 2 K, qualitatively fitting with the theoretical scenario proposed by Khomskii (Nat. Commun. 3, 904 (2012)), is revealed. The magnetoelectric responses along both the [110] and [111] directions are observed, but different underlying mechanisms associated with the specific spin configurations are suggested.
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75.85.+t Magnetoelectric effects, multiferroics
77.80.-e Ferroelectricity and antiferroelectricity

Magnetic orders and electronic structure in LaMnO3/SrTiO3 superlattices

H. M. Liu, C. Y. Ma, P. X. Zhou, S. Dong, and J.-M. Liu

J. Appl. Phys. 113, 17D902 (2013); http://dx.doi.org/10.1063/1.4793705 (3 pages)

Online Publication Date: 4 March 2013

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The magnetic properties and electronic structure of (LaMnO3)n/(SrTiO3)m superlattices are investigated using the full-scale first principles density functional theory calculations in order to reveal the magnetic ground state and transport of the thin LaMnO3 layers sandwiched by relatively thick SrTiO3 layers. The LaMnO3 layer in the superlattices favors the ferromagnetic metallic state rather than the A-type antiferromagnetic insulator. It is revealed that the strain and asymmetric chemical environment may induce tiny magnetic moment to Ti ions of the SrTiO3 layer near the interface. The possible mechanism for these phenomena is discussed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.21.Cd Superlattices
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials

Chemically modulated multiferroicity in Dy-doped Gd2Ti2O7

L. Lin, Z. Y. Zhao, D. Liu, Y. L. Xie, S. Dong, Z. B. Yan, and J.-M. Liu

J. Appl. Phys. 113, 17D903 (2013); http://dx.doi.org/10.1063/1.4794129 (3 pages)

Online Publication Date: 6 March 2013

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The ferroelectricity and magnetoelectric coupling of Gd2Ti2O7 and Gd2−xDyxTi2O7 with Dy3+ substitution of Gd3+ are investigated. For Gd2Ti2O7, a ferroelectric polarization emerges at ∼30 K and is only ∼1.80 μC/m2 at 2 K, while the magnetoelectric response is quite weak. The Dy3+ substitution in Gd2−xDyxTi2O7, however, results in significant enhancement of polarization with remarkable magnetoelectric response up to 35% at 2 K under a magnetic field of 9 T, suggesting the multiferroicity of Gd2−xDyxTi2O7. It is understood that the chemical modulation of the multiferroicity is basically related to the extreme sensitivity of the spin-spin interactions in this highly frustrated system.
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77.80.-e Ferroelectricity and antiferroelectricity
75.85.+t Magnetoelectric effects, multiferroics
76.30.-v Electron paramagnetic resonance and relaxation
77.22.Ej Polarization and depolarization

Anisotropy of crystal growth mechanisms, dielectricity, and magnetism of multiferroic Bi2FeMnO6 thin films

P. Liu, Z. X. Cheng, Y. Du, L. Y. Feng, H. Fang, X. L. Wang, and S. X. Dou

J. Appl. Phys. 113, 17D904 (2013); http://dx.doi.org/10.1063/1.4794724 (3 pages)

Online Publication Date: 11 March 2013

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Epitaxial Bi2FeMnO6 (BFMO) thin films deposited on various Nb:SrTiO3 substrates show that the lattice parameters are very sensitive to epitaxial strains. Compressive and tensile strains are induced to the in-plane lattice constants of the (100) and (111) oriented films, respectively, while that of the (110) oriented thin film stay unstrained. The thin films also exhibit a strongly anisotropic growth habit depending on the substrate. Spiral growth, such as in the (100) BFMO film, is unique in samples prepared by pulsed laser deposition. Extrinsic dielectric constants at low frequencies are attributed to oxygen vacancies via the Maxwell-Wagner effect. All the samples show saturated hysteresis loops with very small coercive fields at 200 K, indicating the presence of weak ferromagnetism.
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81.15.Fg Pulsed laser ablation deposition
61.72.jd Vacancies
68.55.aj Insulators
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
77.22.Ch Permittivity (dielectric function)

Photo-induced electric phenomena in antiferromagnetic BiFeO3 ceramics

C.-M. Hung, M.-D. Jiang, J. Anthoninappen, and C.-S. Tu

J. Appl. Phys. 113, 17D905 (2013); http://dx.doi.org/10.1063/1.4794743 (3 pages)

Online Publication Date: 11 March 2013

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Photovoltage and photocurrent density have been measured in BiFeO3 multiferroic ceramic (with electrodes of indium tin oxide and Au films) before and after a dc E-field poling sequence. The photovoltaic responses under near-ultraviolet illumination (λ = 405 nm) exhibit nonlinear dependence on light intensity. The relation between photovoltaic responses and light intensity can be described using the exponential equations VOC = Vb[1−exp(−I/α)] and JSC = Jb[1 − exp(−I/β)], where VOC, JSC, Vb, and Jb are the open-circuit photovoltage, short-circuit photocurrent density, balanced photovoltage, and balanced photocurrent density, respectively. The maximal power conversion efficiency is about 0.002% at illumination intensity of 2.3 W/m2. The photovoltaic responses can be enhanced after a dc E-field poling.
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72.40.+w Photoconduction and photovoltaic effects
75.50.Ee Antiferromagnetics
75.85.+t Magnetoelectric effects, multiferroics

Effect of Ni substitution on Y-type barium ferrite

Mi Hee Won and Chul Sung Kim

J. Appl. Phys. 113, 17D906 (2013); http://dx.doi.org/10.1063/1.4794879 (3 pages)

Online Publication Date: 13 March 2013

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Here, we have investigated the crystal structure and magnetic properties of Ni-substituted Y-type barium ferrite. The single-phased Ba2Co2−xNixFe12O22 (x = 0.0, 0.5, 1.0) samples were synthesized by solid-state reaction method. The crystal structure of samples was determined to be rhombohedral with R-3 m. The Rietveld refinement showed that the unit cell volume (Vu) of the samples decreased with increasing Ni contents because the ionic radius of the Ni2+ is smaller than that of Co2+. Saturation magnetization (Ms) and coercivity (Hc) of Ba2Co2−xNixFe12O22 were also decreased with Ni concentration. The temperature dependence of the magnetization curve of Ba2CoNiFe12O22 under 100 Oe showed the magnetic structure transitions from helimagnet to ferrimagnet around 204 K and from ferrimagnet to paramagnet around 720 K. While the spin transition temperature (TS) of the samples decreased with Ni substitution, the Curie temperature (TC) increased with increasing Ni contents. The Mössbauer spectra analysis showed the coexistence of Fe ions at six sub-lattices with different occupancy ratio. Also, from temperature dependence of isomer shift value and magnetic hyperfine field (Hhf), we determined that Fe ions were at high spin Fe3+ state. In addition, we have observed an abrupt change in Hhf around 204 K, corresponding to the helimagnet to ferrimagnet phase transition shown in zero-field-cooled curve. Also, the experimentally observed increase in Hhf with Ni contents can be attributed to the change in the super-exchange interaction.
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61.66.Fn Inorganic compounds
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.78.-n Magnetization dynamics

Multiferroic and structural properties of BiFeO3 close to the strain induced phase transition on different substrates

Christian Mix and Gerhard Jakob

J. Appl. Phys. 113, 17D907 (2013); http://dx.doi.org/10.1063/1.4795216 (3 pages)

Online Publication Date: 13 March 2013

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Single phase BiFeO3 (BFO) thin films have been grown strained on different substrates by pulsed laser deposition. The crystal structure and symmetry were investigated by detailed X-ray diffraction and reciprocal space maps as a function of the layer thicknesses of BFO and La0.7Sr0.3MnO3 (LSMO) buffer layers. Corresponding changes in surface morphology and ferroelectric domain structure were observed. The influence of the BFO layer thickness and the use of a LSMO buffer layer proved to be crucial for good ferroelectric and structural properties of BFO. Limits for the stability of bulk-like or strain dominated and ferroelectric domain structures are found for growth under different levels of compressive strain.
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68.55.at Other materials
77.80.B- Phase transitions and Curie point
77.55.Nv Multiferroic/magnetoelectric films
77.80.Dj Domain structure; hysteresis
81.15.Fg Pulsed laser ablation deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)

Dielectric response and origin in antiferromagnetic/ferroelectric (1 − x)BiFeO3-(x)BaTiO3 ceramics

C.-S. Tu, R. R. Chien, T.-H. Wang, J. Anthoninappen, and Y.-T. Peng

J. Appl. Phys. 113, 17D908 (2013); http://dx.doi.org/10.1063/1.4795420 (3 pages)

Online Publication Date: 18 March 2013

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Dielectric permittivity (ε) and conductivity (σ) have been measured in (1 − x)BiFeO3-(x)BaTiO3 (BFO-xBT) multiferroic ceramics for x = 0.0, 0.05, and 0.10 as functions of temperature and frequency. A one-dimensional across-barrier model with intrinsic barriers B every lattice constant a and extrinsic barriers B + Δ every distance d is introduced to describe the dielectric response and conductivity. The across-barrier hopping is responsible for the high-temperature conductivity and dielectric relaxation in the lower temperature region. Good qualitative fits of dielectric permittivity and conductivity are obtained as functions of temperature and frequency. BaTiO3 substitution can enhance the intrinsic barrier and reduce the hopping conductivity.
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77.80.-e Ferroelectricity and antiferroelectricity
75.85.+t Magnetoelectric effects, multiferroics
61.66.Fn Inorganic compounds
75.50.Ee Antiferromagnetics
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Ab initio study on magnetic anisotropy change of SrCoxTixFe12−2xO19

Min Feng, Bin Shao, Jian Wu, and Xu Zuo

J. Appl. Phys. 113, 17D909 (2013); http://dx.doi.org/10.1063/1.4795821 (3 pages)

Online Publication Date: 21 March 2013

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The magnetic anisotropy change of Co-Ti substituted Sr-M hexaferrite has been investigated by using general gradient approximation (GGA) with on-site coulomb repulsion added (GGA + U) and force theorem method. The calculated dependence of magnetic anisotropy energy on angles of SrFe12O19 fits very well with theoretical description, and anisotropy constant K1 agrees well with experimental value. The impact of occupancy of Co2+ and Ti4+ on magnetic anisotropy in SrCo2Ti2Fe8O19 has been studied. The results show that Co2+ in 4f2 site and Ti4+ in 12 k site both contribute to the reduction of uniaxial magnetic anisotropy, and as Co2+ and Ti4+ in their first preference of substitution site, magnetic anisotropy of SrCo2Ti2Fe8O19 is weak, which would facilitate the formation of conical magnetic structure to induce electric polarization. As substitution rate x increases from 0 to 3, the magnetic anisotropy of SrCoxTixFe12−2xO19 is found to change from uniaxial to planar.
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75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Magnetic field induced ferroelectric transition of quasi one-dimensional frustrated quantum spin chain system Rb2Cu2Mo3O12

Yukio Yasui, Yudai Yanagisawa, Ryuji Okazaki, Ichiro Terasaki, Yasuhiro Yamaguchi, and Tsuyoshi Kimura

J. Appl. Phys. 113, 17D910 (2013); http://dx.doi.org/10.1063/1.4795844 (3 pages)

Online Publication Date: 22 March 2013

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Dielectric and magnetic properties have been studied in magnetic fields up to 9 T for a quasi-one-dimensional frustrated spin-1/2 system Rb2Cu2Mo3O12, which does not exhibit a three-dimensional magnetic transition. By applying magnetic fields, a peak structure is found to appear in the dielectric constant—temperature curve at Tc ∼ 8 K. A ferroelectric polarization has been observed below Tc in magnetic fields. However, the temperature dependence of magnetic susceptibility does not show any anomaly at Tc. These results indicate that the ferroelectric transition is found to be induced by applying magnetic fields though no magnetic transition is induced. The observed magnetic field induced ferroelectric transition is considered to be a new type of ferroelectric transition triggered by the magnetism of frustrated quantum spin systems.
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77.80.B- Phase transitions and Curie point
75.30.Cr Saturation moments and magnetic susceptibilities
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Effects of residual and tunable strain in thin films of La0.7Ba0.3MnO3

J. F. Wang, Y. C. Jiang, Z. P. Wu, and J. Gao

J. Appl. Phys. 113, 17D911 (2013); http://dx.doi.org/10.1063/1.4796050 (3 pages)

Online Publication Date: 22 March 2013

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The effects of residual and tunable strain in thin films of La0.7Ba0.3MnO3 (LBMO) were investigated. Different residual strains were achieved by depositing LBMO films with various thicknesses on 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 (PMN-PT) and SrTiO3 (STO). For LBMO on PMN-PT, when the thickness changes the resistance evolves dramatically. All samples on STO have a clear metal-to-insulator transition near room temperature. The tunable strain was modulated through the converse piezoelectric effects of PMN-PT. Clear voltage-controlled resistance modulations (|ΔR|/Rmax ∼ 90%) were observed in LBMO/PMN-PT. The magnitude and nonlinearity of elastoresistance are the largest in the thinnest sample. |ΔR|/R decreases as the thickness increases and is still substantial even the film is as thick as 150 nm. For thicker samples, the nonlinearity becomes weaker and the resistance changes linearly with voltage approximately.
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73.61.Ng Insulators
72.20.Fr Low-field transport and mobility; piezoresistance
77.65.-j Piezoelectricity and electromechanical effects
68.55.-a Thin film structure and morphology

Magnetodielectric response of coexisting phases in half doped manganites

S. Dash, A. Banerjee, and P. Chaddah

J. Appl. Phys. 113, 17D912 (2013); http://dx.doi.org/10.1063/1.4795843 (3 pages)

Online Publication Date: 26 March 2013

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The magnetic field dependence of dielectric permittivity and resistivity has been measured simultaneously in two separate half doped manganites Pr0.75Na0.25MnO3 and Pr0.5Ca0.5Mn0.975Al0.025O3. A gigantic change in dielectric permittivity was detected near the percolation threshold. The hysteresis in dielectric permittivity as well as in resistivity supports the first order nature of the insulator-metal transition while the tunability is due to the coexisting of phases across the transition. A highly resistivity correlated dielectric behaviour has been observed throughout the insulator to metal transition evidencing the dielectric catastrophe phenomenon. The field dependent dielectric data are analyzed in the framework of Maxwell-Garnett theory in association with Mott-Hubbard model.
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77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
72.20.Fr Low-field transport and mobility; piezoresistance

High symmetric SrRuO3 (001) thin films: Perfectly lattice-matched electrodes for multiferroic BiFeO3

Murtaza Bohra, C. P. Wu, H. J. Yeh, and H. Chou

J. Appl. Phys. 113, 17D913 (2013); http://dx.doi.org/10.1063/1.4795864 (3 pages)

Online Publication Date: 27 March 2013

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High symmetric tetragonal (c/a < 1 and c/a > 1) and cubic (c/a = 1) SrRuO3 thin films were developed on SrTiO3 substrate by controlling RF-power and substrate temperature. These SrRuO3 symmetries exhibit larger in-plane lattice parameters (3.936–3.98 Å) compared to bulk orthorhombic SrRuO3 (3.93 Å), and are coincidentally similar to the predicted high temperature tetragonal (>820 K) and cubic (>950 K) SrRuO3 phases. Importantly, the lattice parameters of cubic (c/a = 1) SrRuO3 (3.968 Å) films match very well to the pseudocubic BiFeO3 (3.966 Å), opening new perspectives for BiFeO3/SrRuO3/SrTiO3 heterostructures for spintronics. Due to high crystal symmetry and large unit cell expansion (∇V/V = ∼1.1%-4.2%), a non-Fermi-liquid (R ∝ T3/2) and weak anisotropic magnetic behaviors, and reduced TC's are commonly observed which are different from the orthorhombic SrRuO3.
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75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
61.66.Fn Inorganic compounds
77.80.-e Ferroelectricity and antiferroelectricity
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Ak Magnetic properties of monolayers and thin films

The ferroelectricity of Bi0.9Pb0.1FeO3 films grown on atomic flat SrRuO3/SrTiO3 substrates

H. Chou, K. C. Liu, C. T. Wu, C. P. Wu, M. Bohra, A. Pyatakov, Y. C. Chen, C. C. Yu, and S. J. Sun

J. Appl. Phys. 113, 17D914 (2013); http://dx.doi.org/10.1063/1.4795846 (3 pages)

Online Publication Date: 27 March 2013

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Bi0.9Pb0.1FeO3 (BPFO) films were grown on SrRuO3 (SRO)/SrTiO3 (STO) substrates. The surface morphology of BPFO films is highly dependent on that of the SRO layer. Though the step height of STO (100) substrate is equal to one unit cell of STO crystal, the height and width of steps on the surface of SRO and BPFO are larger, which supports a step bunching growth mode on both the SRO layer and BPFO films. At zero bias voltage, the BPFO film exhibits a natural dipole polarization toward the SRO layer, which is believed to be due to the negative charge accumulation at the BPFO/SRO interface, and manifests of 71° and 109° but 180° domain walls. Doping of Pb distorted the BPFO crystal lattice to near cubic that weakens the electric anisotropy and forms a two-step flipping process. To complete a 180° dipole flipping procedure, the dipole moment first rotates 71° to adjacent states followed by a 109° rotation to the final 180° state.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.Dj Domain structure; hysteresis
68.35.bt Other materials

Investigation of A- and B-site Fe substituted BaTiO3 ceramics

Neelam Maikhuri, Amrish K. Panwar, and A. K. Jha

J. Appl. Phys. 113, 17D915 (2013); http://dx.doi.org/10.1063/1.4796193 (3 pages)

Online Publication Date: 28 March 2013

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In this work, we report the synthesis and investigations of Ba1−xFexTiO3 (BFeT) and BaTi1−x FexO3 (BTFe) ceramics by solid state reaction method. BFeT show relaxor behaviour in the studied frequency range i.e., 10 kHz to 100 kHz with high dielectric constant in a wide temperature range of 75 °C. BTFe shows frequency dispersion at 10 kHz and almost flat dielectric response at 100 kHz and lower dielectric constant value compared to BFeT. Polarization–electric field loops of both BFeT and BTFe shows suppressed ferroelectric behaviour as compared to pristine BaTiO3(BT). Magnetization–magnetic field loops show ferromagnetic behaviour in both BFeT and BTFe at room temperature.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.Jk Relaxor ferroelectrics
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Spontaneous exchange bias in a nanocomposite of BiFeO3-Bi2Fe4O9

Tuhin Maity, Sudipta Goswami, Dipten Bhattacharya, Gopes C. Das, and Saibal Roy

J. Appl. Phys. 113, 17D916 (2013); http://dx.doi.org/10.1063/1.4796149 (3 pages)

Online Publication Date: 29 March 2013

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We have observed a large as well as path-dependent spontaneous exchange bias (HSEB) (∼30–60 mT) in a nanocomposite of BiFeO3-Bi2Fe4O9 across 5–300 K when it is measured in an unmagnetized state following zero-field cooling and appropriate demagnetization. The path dependency yields a variation in the exchange bias depending on the sign of the starting field and the path followed in tracing the hysteresis loop. The asymmetry thus observed—ΔHSEB—is found to be decreasing nonmonotonically across 5–300 K with a peak around 200 K. The ΔHSEB together with large HSEB could have significant ramification in tuning the exchange bias driven effects and consequent applications.
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75.75.-c Magnetic properties of nanostructures
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High quality multiferroic BiFeO3 films prepared by pulsed laser deposition on glass substrates at reduced temperatures

H. W. Chang, F. T. Yuan, S. H. Tien, P. Y. Li, C. R. Wang, C. S. Tu, and S. U. Jen

J. Appl. Phys. 113, 17D917 (2013); http://dx.doi.org/10.1063/1.4796194 (3 pages)

Online Publication Date: 29 March 2013

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Phase structure and ferroelectric properties of BiFeO3 (BFO) films grown on Pt(111) buffered glass substrates at various growth temperatures and oxygen pressures have been studied. The optimization of the 20-nm-thick Pt(111) bottom electrode enables BFO films to form perovskite single phase structure at reduced temperatures between 400–500 °C. Microstructure of fine grains and smooth surface is obtained, which is favorable for applications. Multiferroic properties including 2Pr of 15.1–124 μC/cm2, Ec of 351–680 kV/cm, and Ms of 5–8 emu/cm3 are achieved within the oxygen pressure range of 10–75 mTorr. The optimized ferroelectric properties are comparable to the reported values of BFO samples using Si and MgO single crystal substrates. The results of this study may broaden the possibility of the use of BFO films.
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81.15.Fg Pulsed laser ablation deposition
75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
77.80.-e Ferroelectricity and antiferroelectricity
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ng Insulators

Room-temperature magnetoelectric properties of Fe doped BaZr0.05Ti0.95O3

Mukesh Kumari, Chandra Prakash, and Ratnamala Chatterjee

J. Appl. Phys. 113, 17D918 (2013); http://dx.doi.org/10.1063/1.4795425 (3 pages)

Online Publication Date: 4 April 2013

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To explore the magnetoelectric effect in lead free bulk ceramics, solid solutions of BaZr0.05(FexTi1−3x/4)0.95O3 have been synthesized using conventional solid state reaction route with x = 0.000 to 0.020 in steps of 0.005. A small amount of Fe content shows an immense effect on properties of barium zirconium titanate. Room temperature X-ray diffraction studies substantiate the formation and purity of these polycrystalline samples in an orthorhombic crystal system. Temperature dependent dielectric study revealed a decrease in ferroelectric Curie temperature with a decrease in dielectric constant values as x varied from 0.000 to 0.020. Ferroelectricity is still maintained and well saturated loops are observed with Fe substitution at these levels; although the remnant polarization Pr values decrease substantially with increasing Fe content. The best value of magnetoelectric coupling coefficient (α) at room temperature is found to be 145.30 mV/cm.Oe for x = 0.015 sample. In conclusion, in a non-Pb based simple perovskite system a reasonably large magnetoelectric coupling is demonstrated.
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75.85.+t Magnetoelectric effects, multiferroics
77.80.B- Phase transitions and Curie point
77.84.Cg PZT ceramics and other titanates
61.66.Fn Inorganic compounds
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization

Magnetic and structural properties of BiFeO3 thin films grown epitaxially on SrTiO3/Si substrates

Ryan P. Laughlin, Daniel A. Currie, Rocio Contreras-Guererro, Aruna Dedigama, Weerasinghe Priyantha, Ravindranath Droopad, Nikoleta Theodoropoulou, Peng Gao, and Xiaoqing Pan

J. Appl. Phys. 113, 17D919 (2013); http://dx.doi.org/10.1063/1.4796150 (3 pages)

Online Publication Date: 11 April 2013

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The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO3 (BFO) films grown on 20 nm SrTiO3 (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O2. Careful control of the O2 during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO2 layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O2 plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O2 pressure of 5 × 10−8 mbar. Cross-sectional transmission electron microscopy (TEM) confirms the high crystallinity of the films and shows sharp, atomically flat interfaces. The selected area diffraction pattern (SADP) reveals that BFO grows in a distorted rhombohedral crystal structure. X-ray diffraction does not show formation of second phases and is consistent with the TEM and SADP results. The BFO films show AF behavior with a Neel temperature that exceeds 350 K, as expected (TN = 673 K) and with a residual ferromagnetic behavior that decreases with film thickness and is consistent with the G-type AF due to the canted spins. The saturation magnetization per unit volume for a 40 nm thick film was 180 emu/cm3 at an in-plane magnetic field of 8 kOe. The ferroelectric behavior of the films was verified using piezoresponse force microscopy.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
77.80.-e Ferroelectricity and antiferroelectricity
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of La substitution on structure and magnetic properties of sol-gel prepared BiFeO3

Pittala Suresh and S. Srinath

J. Appl. Phys. 113, 17D920 (2013); http://dx.doi.org/10.1063/1.4801509 (3 pages)

Online Publication Date: 12 April 2013

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Detailed Rietveld analysis of the room temperature (RT) x-ray diffraction data of LaxBi1−xFeO3 (LBFO) ceramics (0 ≤ x ≤ 0.4) prepared by sol-gel route revealed that the system retains distorted rhombohedral R3c structure of parent compound BiFeO3 (BFO) for x ≤ 0.2 but transforms to orthorhombic Pbnm structure for x > 0.2. The fundamental 12 Raman modes of pure BFO (x = 0.0) are reduced to 10 modes for x = 0.2 and further reduced to 7 modes for x = 0.4, which is a clear indication of structural modification and symmetry changes brought about by La doping. The coercive field, HC, increases remarkably with an increase in La doping and x = 0.4 exhibits the highest HC (19.5 kOe at RT) reported so far in any rare earth doped BFO, which will have a great potential for practical application in non-volatile memory devices. Moreover, high-field magnetization and remanence, Mr, increase linearly with La doping content due to the gradual change in spin cycloid structure. M(T) curve shows an anomaly at 50 K, similar to that expected in a spin glass system. The Néel temperature (TN) of the LBFO increases with x, approaching that of the LaFeO3.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.30.Hv Other nonmetallic inorganics

Weak ferromagnetic behavior of BiFeO3 at low temperature

Seungkyu Han and Chul Sung Kim

J. Appl. Phys. 113, 17D921 (2013); http://dx.doi.org/10.1063/1.4801338 (3 pages)

Online Publication Date: 16 April 2013

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Polycrystalline BiFeO3, having a spherical shape with a diameter of about 78 μm, has been synthesized by low-temperature hydrothermal method. The observed Raman and x-ray photo electron spectroscopy (XPS) spectra of the sample show the spectra of typical single-phased BiFeO3, and the x-ray diffractometry (XRD) measurement further confirmed that the synthesized sample is single phase. The value of isomer shift from Mössbauer analysis indicates the Fe3+ ionic state without Fe2+ ionic state as observed from XPS measurement. The experimentally measured M-H curves show antiferromagnetic behavior at 295 K and weak ferromagnetic behavior at 4.2 K. The appearance of two different magnetic behaviors is due to the fact that the antiferromagnetic coupling becomes weak because of the presence of two distorted octahedral sites. Since the effect of the lattice distortion strongly depends on the thermal agitation effect, the weak ferromagnetic behavior can be observed only at 4.2 K. The detailed Mössbauer spectra analysis result confirms the existence of two distortion octahedral sites, which is in an agreement with XRD results.
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81.10.Dn Growth from solutions
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
75.50.Ee Antiferromagnetics
76.80.+y Mössbauer effect; other γ-ray spectroscopy
78.30.Hv Other nonmetallic inorganics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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