Structural, Electrical and Multiferroic Properties of Nb-doped Bi7Fe3Ti3O21 Thin Films

라그하반,김진원,김상수 한국물리학회 2015 새물리 Vol.65 No.6

The effects of donor Nb5+-ion doping on the structural, electrical, and multiferroic properties of an Aurivillius Bi7Fe3Ti3O21 thin film were investigated. Incorporation of Nb5+-ions into the Ti4+-sites of the Bi7Fe3Ti3O21 thin film resulted in a substantial improvement of its electrical and multiferroic properties. From the study of the electrical properties, the Bi7Fe3Ti2.94Nb0.06O21+δ thin film exhibited a low leakage current density of 5.11×10−6 A/cm2 at 100 kV/cm, which was about one order of magnitude lower than that of the untreated Bi7Fe3Ti3O21 thin film. The ferroelectric P −E hysteresis loops of the Bi7Fe3Ti2.94Nb0.06O21+ thin film showed a large remnant polarization (2Pr) of 20.6 μC/cm2 at 630 kV/cm whereas the 2Pr value measured for the untreated Bi7Fe3Ti3O21 thin film was 3.5 μC/cm2 at 318 kV/cm. Furthermore, a well-saturated magnetic hysteresis loop with an enhanced magnetization was observed for the Bi7Fe3Ti2.94Nb0.06O21+δ thin film at room temperature.

Effects of Nd-doping on the Structural, Electrical, and Multiferroic Properties of Bi7Fe3Ti3O21 Thin Films

라그하반,김진원,최지야,김상수 한국물리학회 2015 새물리 Vol.65 No.4

Aurivillius-phase six-layered Bi7Fe3Ti3O21 (BFTO21) and Nd-doped Bi6.4Nd0.6Fe3Ti3O21 (BNdFTO21) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method in order to investigate their structural, electrical, and multiferroic properties. Doping the Bi sites of the BFTO21 with Nd3+-ions led to remarkable improvements in the electrical and the multiferroic properties. The electrical study of the BNdFTO21 thin film showed a low leakage current density of 4.38 × 10−6 A/cm2 at an applied electric field of 100 kV/cm, which was about one order of magnitude lower than that of the BFTO21 thin film. The ferroelectric P − E hysteresis loop of the BNdFTO21 thin film exhibited a large remnant polarization (2Pr) of 24 μC/cm2 and a low coercive electric field (2Ec) of 154 kV/cm at an applied electric field of 239 kV/cm. Furthermore, the magnetization and the coercive magnetic field that were observed for the BNdFTO21 thin film at room temperature were drastically enhanced compared to those observed for the BFTO21 thin film.

Coupled Lattice Polarization and Ferromagnetism in Multiferroic NiTiO₃ Thin Films

Varga, Tamas,Droubay, Timothy C.,Kovarik, Libor,Nandasiri, Manjula I.,Shutthanandan, Vaithiyalingam,Hu, Dehong,Kim, Bumsoo,Jeon, Seokwoo,Hong, Seungbum,Li, Yulan,Chambers, Scott A. American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.26

<P>Polarization-induced weak ferromagnetism (WFM) was demonstrated a few years back in LiNbO3-type compounds, MTiO3 (M = Fe, Mn, Ni). Although the coexistence of ferroelectric polarization and ferromagnetism has been demonstrated in this rare multiferroic family before, first in bulk FeTiO3, then in thin-film NiTiO3, the coupling of the two order parameters has not been confirmed Here, we report the stabilization of polar, ferromagnetic NiTiO3 by oxide epitaxy on a LiNbO3 substrate utilizing tensile strain and demonstrate the theoretically predicted coupling between its polarization and ferromagnetism by X-ray magnetic circular dichroism under applied fields. The experimentally observed direction of ferroic ordering in the film is supported by simulations using the phase-field approach. Our work validates symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and WFM in MTiO3 transition metal titanates crystallizing in the LiNbO3 structure. It also demonstrates the applicability of epitaxial strain as a viable alternative to high-pressure crystal growth to stabilize metastable materials and a valuable tuning parameter to simultaneously control two ferroic order parameters to create a multiferroic. Multiferroic NiTiO3 has potential applications in spintronics where ferroic switching is used, such as new four-stage memories and electromagnetic switches.</P>

Multiferroic and energy-storage characteristics of polycrystalline Ca-doped BiFeO3 thin films on Si substrates

안윤호,손종역 한국세라믹학회 2023 한국세라믹학회지 Vol.60 No.2

Significant progress has been made in the enhancement of multiferroic properties with possibilities for energy harvesting and storage applications. In this study, BiFeO3 (BFO) thin films were doped with Ca, and the multiferroic, piezoelectric, and energy-storage properties of Bi1−xCaxFeO3−δ (x = 0.3, BCFO) thin films were compared with those of BFO to investigate the effects of the doping. The BCFO thin films were deposited on Pt/TiO2/SiO2/Si substrates using pulsed laser deposition. The BCFO thin films having a polycrystalline structure, exhibited improved crystallinity and larger grains, compared with the BFO thin films. The high crystallinity further resulted in the BCFO thin films exhibiting improved leakage current, ferroelectric, and ferromagnetic characteristics, compared with the BFO thin films. The morphotropic phase boundary formed in the mixed crystal phase, which was driven by the Ca doping, and it improved the piezoelectric coefficients of the BCFO thin films. Additionally, we found that the BCFO thin films have superior energy-storage characteristics, compared with the BFO thin films, owing to the improved ferroelectric properties. Our findings suggest that the Ca doping of the BFO thin films improves their multiferroic properties, piezoelectric response, and energy-storage characteristics.

First-principles calculations on ferroelectricity and lattice dynamics of Type-II multiferroic SmMn2O5

Dai Jian-Qing,Yuan Jin 한국물리학회 2021 Current Applied Physics Vol.29 No.-

In this work, we report on the structural, electronic, and ferroelectric properties of SmMn2O5 by using firstprinciples density functional theory plus on-site Coulomb interaction (DFT + U) calculations. A thorough analysis was preformed to reveal the competing characteristics of different high-temperature (T) phases and the polarization mechanism in the low-T multiferroic phase. We show that the structural characteristics of the high-T phases have a strong influence on the low-T multiferroicity. In addition to the spin-induced lattice distortion that reduces substantially the purely electronic ferroelectricity, the dominant polarization mechanism in low-T SmMn2O5 still originates from the electronic polarization. By performing mode decomposition of the Hellmann– Feynman forces and the lattice distortion induced by the q = (0.5, 0, 0) magnetic order, we find that the Raman-active Ag mode characterized by the Mn4+O6 octahedron distortion and synergistic displacement of Mn3+ and Sm ions is of primary importance, while the infrared (IR)-active B2u mode plays a secondary role. These findings provide a theoretical foundation for future studies concerning the enhanced magnetoelectric effects of SmMn2O5 due to its pure exchange–striction mechanism.

Investigation of crystal structure and magnetic properties in Zn doped Bi0.84La0.16FeO3 ceramics at morphotropic phase boundary

Tho, P.T.,Dang, N.V.,Nghia, N.X.,Khiem, L.H.,Xuan, C.T.A.,Kim, H.S.,Lee, B.W. Elsevier 2018 The Journal of physics and chemistry of solids Vol.121 No.-

<P><B>Abstract</B></P> <P>In this investigation, we have studied the crystal structure and magnetic properties of Zn doped Bi0.84La0.16FeO3 (<I>x</I> = 0.02–0.1) ceramics at the morphotropic phase boundary of rhombohedral and orthorhombic phases. Rietveld refinement of the obtained XRD patterns and Raman spectroscopy confirm the presence of multiphases crystal structure of <I>R3c</I> rhombohedral and <I>Pbam</I> orthorhombic. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization and coercivity with dominating of orthorhombic phase. The isothermal structural transition from <I>R3c</I> to <I>Pbam</I> is caused for the decrease in magnetization and the increase in coercivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The crystal structure of Bi<SUB>0.84</SUB>La<SUB>0.16</SUB>Fe<SUB>1-x</SUB>Zn<SUB>x</SUB>O<SUB>3</SUB> at the morphotropic phase boundary. </LI> <LI> The microstructure reveals the coexistence crystal phase and their phase boundary. </LI> <LI> The isothermal structural transition induces the change in magnetic properties. </LI> <LI> The vertical shift (exchange bias) is observed in compounds. </LI> </UL> </P>

Structure and Magnetic Properties of Multiferroic DyMnO3 Epitaxial Thin Films Grown on Different Substrates

W. T. Wang 한국자기학회 2020 Journal of Magnetics Vol.25 No.2

Fabrication of thin films is crucial in the study of fundamental properties of matter and designs of devices. In this work, multiferroic dysprosium manganites DyMnO3 thin films were grown epitaxially on SrTiO3 (001) and yttrium stabilized zirconia (111) [YSZ (111)] substrates by pulsed laser deposition technique. The fabricated films showed perfectly orthorhombic crystallization on SrTiO3 (001) and hexagonal crystallization on YSZ (111) substrates. At low temperatures, the magnetic measurements revealed three magnetic transitions at 10 K, 21 K and 43 K for orthorhombic DyMnO3 film, 7 K, 38 K and 58 K for hexagonal DyMnO3 film, respectively. The results are consistent with those observed in bulk materials, corresponding to magnetic ordering of the Dy3+ ion spins, antiferromagnetic transitions and spin reorientation respectively. This work provides a convenient method to manipulate the film structure by choosing suitable substrates, and it can be used in the study of magnetic properties of multiferroic manganites and related device fabrication.

Effect of Ba and Ho co-doping on crystal structure, phase transformation, magnetic properties and dielectric properties of BiFeO3

Jogender Singh, Ashish Agarwal,Ashish Agarwal,Sujata Sanghi,Tanvi Bhasin,Manisha Yadav,Umesh Bhakar,Ompal Singh 한국물리학회 2019 Current Applied Physics Vol.19 No.3

Multiferroics having composition Bi0.80-xBa0.20HoxFeO3 (BBFO, BBHFO5, BBHFO10, BBHFO15 and BBHFO20 for x=0.0, 0.05, 0.10, 0.15 and 0.20 respectively) were synthesized by method of solid state reaction. The crystal structure has been studied using X-ray diffraction technique. The X-ray patterns show enormous transform in crystal structure at concentration x=0.20. The Rietveld refinement of XRD patterns indicates that at concentration x=0.0 sample have rhombohedral structure with R3c space group while for the concentration x=0.05, 0.10, 0.15 and 0.20, the mixed phase including rhombohedral R3c and triclinic P1 space groups were obtained with best fitting. This phase transformation in crystal structure is observed due to mismatching of ionic radii of doped ions and parent ions. Magnetic properties of all samples were carried out by using vibrating sample magnetometry. M-H hysteresis loops shows that with doping of Ba and Ho antiferromagnetic BiFeO3 (BFO) transforms into ferromagnetic. The dielectric and ferroelectric measurements were carried out which shows that dielectric constant, dielectric loss and ferroelectric properties are enhanced with co-doping of Ho in comparison of the pristine BFO due to structure deformation and decrease in oxygen vacancies with higher concentration of Ho. Significant improvement has been observed in dielectric constant and remnant magnetization values with increasing content of Ho and decrease in the dielectric loss.

Multiferroic properties and ferroelectric domain structures of Yb-doped BiFeO₃ thin films on glass substrates

Ahn, Yoonho,Son, Jong Yeog Elsevier 2019 PHYSICA B-CONDENSED MATTER - Vol.558 No.-

<P><B>Abstract</B></P> <P>We investigated the growth characteristics and multiferroic properties of BiFeO<SUB>3</SUB> (BFO) and Yb-doped BiFeO<SUB>3</SUB> (Bi<SUB>0.85</SUB>Yb<SUB>0.15</SUB>FeO<SUB>3</SUB>, YBFO) thin films grown on Pt/Ta/glass substrates. X-ray diffraction experiments showed that both BFO and YBFO thin films had preferentially (111)-oriented polycrystalline structures. Yb doping of BFO thin films led to enhanced multiferroic properties in terms of the ferroelectricity (remanent polarization of about 41.5 μC/cm<SUP>2</SUP>) and ferromagnetism (remanent magnetization of about 1.91 emu/cm<SUP>3</SUP>). According to piezoresponse force microscopy experiments, the YBFO thin films possessed larger ferroelectric domain structures than the BFO thin films due to the higher domain wall energy of the YBFO thin films.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Yb-doped BiFeO3 (Bi0.85Yb0.15FeO3, YBFO) thin films are deposited on Pt/Ta/glass substrates. </LI> <LI> Yb doping enhances the multiferroic properties substantially. </LI> <LI> The YBFO thin films possess larger ferroelectric domain structures than the BFO thin films. </LI> </UL> </P>

Structural, Electrical, and Multiferroic Properties of Aurivillius (Bi7−xLax)Fe3Ti3O21 Thin Films

C. M. Raghavan,J. W. Kim,J. Y. Choi,S. S. Kim,J-W. Kim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.1

The effects of La3+- ion doping on the structural, electrical, and multiferroic properties of the six-layered Aurivillius-phase Bi7Fe3Ti3O21 thin film were investigated. A chemical solution deposition method was used to deposit the (Bi7−xLax)Fe3Ti3O21 (x = 0 and 0.6) thin films on Pt(111)/Ti/SiO2/Si(100) substrates. The formation of Aurivillius orthorhombic structures was confirmed by using X-ray diffraction and Raman spectroscopy studies. The (Bi6.4La0.6)Fe3Ti3O21 thin film exhibited a low leakage current density (1.84 × 10−6 A/cm2 at an applied electric field of 100 kV/cm) and a large remnant polarization (20.20 μC/cm2 at an applied electric field of 318 kV/cm) as compared to the Bi7Fe3Ti3O21 thin film. The enhanced electrical and multiferroic properties are ascribed to a reduced oxygen concentration and a structural distortion. Both thin films were weakly ferromagnetic at room temperature.