Nanocrystalline multiferroic BiFeO3 thin films made by room temperature sputtering and thermal annealing, and formation of an iron oxide-induced exchange bias

doi:10.1016/j.jallcom.2016.11.344

Journal of Alloys and Compounds

Volume 695, 25 February 2017, Pages 3061-3068

https://doi.org/10.1016/j.jallcom.2016.11.344 Get rights and content

Highlights

•
Multiferroic nanocrystalline BiFeO₃ films successfully made.
•
The films also contain magnetite, maghemite, hematite, and FeO.
•
The magnetic properties are primarily due to magnetite and maghemite nanoparticles.
•
An iron oxide-induced exchange bias is observed.

Abstract

Multiferroic nanocrystalline BiFeO₃ films have been successfully made by room temperature sputtering and thermal annealing in oxygen at 500 °C. Nanocrystalline Bi was seen before annealing as well as β-Bi₂O₃ and the iron oxide phases, magnetite, maghemite, and FeO. Superparamagnetism was observed that can be attributed to magnetite and maghemite nanoparticles. The thermally annealed film contained BiFeO₃ nanoparticles and magnetite, maghemite, and hematite as well as unidentified BiFe_xO_y phases. Superparamagnetism was also seen after annealing and the magnetic properties are predominately due to magnetite and maghemite nanoparticles rather than from multiferroic BiFeO₃. The saturation magnetic moment was 60% lower after annealing, which was due to some of the Fe in the iron oxide nanoparticles being incorporated into the BiFeO₃ nanoparticles. An exchange bias was observed before and after annealing that cannot be attributed to a structure that includes BiFeO₃. It is likely to arise from magnetite and maghemite cores with spin-disordered shells.

Introduction

Substantial research effort is being focused on multiferroic materials that simultaneously display more than one ferroic order ((anti-)ferromagnetic, ferroelectric, and ferroelastic) because this can result in a coupling between the electric and magnetic fields, and hence an intrinsic magneto-electric effect [1], [2]. The appearance of magneto-electric coupling can lead to new devices such as magneto-electric RAM [3], [4], zero power magnetic sensors [2], [5], [6], and electrostatically tunable inductors [7], [8]. Considerable attention has focused on BiFeO₃ because it was one of the first compounds to be shown to be multiferroic at room temperature [2]. The magnetic and electric dipole ordering temperatures are also far above room temperature where the Néel temperature is 643 K and the ferroelectric ordering temperature is 1103 K [2]. It displays G-type antiferromagnetic order and there is canting of the magnetic moments and a spin cycloid structure with a period of 62 nm [9]. The bulk compound has a small net magnetic moment when averaged over the spin cycloid period [10]. The measured magnetic moment in bulk BiFeO₃ can be significantly enhanced by partial substitution of different ions for Bi or Fe [11] that may be due to suppression of the spin cycloid. An exchange bias, B_ex, has been reported in thin film multilayers that use BiFeO₃ as a pinning layer next to a ferromagnetic layer [2], [12], [13] where it can be electrically switched [2], [11], which is particularly useful for magneto-electric RAM. B_ex can occur when an antiferromagnetic phase is adjacent to a ferromagnetic phase and the sample is cooled through the Néel temperature in the presence of an applied magnetic field [14], [15], [16].

A number of studies on BiFeO₃ nanoparticles and nanoceramics have reported that the saturation moment per Fe, m_s,Fe, is enhanced when the nanoparticle size is reduced [10], [17], [18], [19], [20] and it can reach 0.41 μ_B/Fe [17], where μ_B is the Bohr magneton. This is far greater than the bulk value of 0.02 μ_B/Fe [10]. It has been suggested that this occurs because the nanoparticles are smaller than the spin cycloid period, there is a suppression or modification of the spin cycloid structure, and there are uncompensated surface spins that lead to a ferromagnetic shell [10], [17], [18], [19], [21]. The small nanoparticle size can also lead to enhanced magneto-electric [19] and multiferroic properties [22]. An exchange bias has also been reported that is absent in bulk BiFeO₃ [10], [17], [19] where it is either increases [17], [19] or decreases as the nanoparticle size is reduced [10]. It is believed to arise in BiFeO₃ from a ferromagnetic shell induced in part by uncompensated surface spins [10], [17], [19]. Interestingly, there have been a few studies that do not report a significant enhancement of the saturation moment per Fe or the appearance of B_ex [23], [24] although a small amount of Eu doping leads to a large enhancement of the saturation moment [24]. This suggests that the appearance of an enhanced moment and exchange bias depends on the nanoparticle preparation method. This is consistent with previous reports on other nanoparticle ferrites and related magnetic systems where the preparation method affects the morphology and magnetic properties [25], [26]. It would be interesting to see if small BiFeO₃ nanoparticles can be made in thin films that might be more practical than nanoparticle powders for application purposes.

In the report we present the results from structural, vibrational and magnetic measurements on thin films that were made by ion beam sputtering of a BiFeO₃ target at room temperature followed by annealing in an oxygen atmosphere. We show that annealing leads to the formation of BiFeO₃ nanoparticles. There is a large saturation magnetic moment and an exchange bias that is predominantly due to magnetic iron oxides.

Section snippets

Methods

An Ar⁺ ion beam sputtering system [27] was used to deposit thin films at room temperature using a bulk BiFeO₃ rotatable target in a high vacuum (∼2 × 10⁻⁵ Pa) and with an anode voltage of 20 kV. The films were deposited onto a 100 nm thick SiO₂ film on a crystalline Si (100) substrate. They were annealed in a 100% oxygen atmosphere for 15 min at 500 °C. Cross-sectional transmission electron microscope (TEM) images were taken using a Tecnai TF20 with an acceleration voltage of 200 kV. The

Results and discussion

Fig. 1 shows the RBS spectra from an as-made film and a 500 °C annealed film. In both cases the peaks from Bi and Fe can clearly be seen as well as the Si edges and lower energy peaks from oxygen in the sputtered film and the SiO₂ film. Two Si edges are evident in the RBS data where the higher energy edge is due to Si in the SiO₂ layer and the lower energy edge is from Si in the substrate. The only significant difference in the RBS spectra before and after annealing is that the Bi peak

Conclusions

In conclusion, nanocrystalline BiFeO₃ films have been made by room temperature sputtering and thermal annealing at 500 °C in an oxygen atmosphere. XRD measurements before annealing show the presence of nanocrystalline Bi, and other unidentified BiFe_xO_y phases. SAED shows that there is also some magnetite or maghemite as well as some FeO. The Raman data are consistent with the presence of Bi and β-Bi₂O₃ as well as magnetite, maghemite, and hematite. Annealing in an oxygen atmosphere at 500 °C

Acknowledgments

We acknowledge funding support from the New Zealand Ministry of Business, Innovation and Employment (C0X01206, C05X1404) and the MacDiarmid Institute for Advanced Materials and Nanotechnology.

References (56)

Z. Li et al.
A novel multiferroic/full-heusler BiFeO₃/Co₂FeAl_0.5Si_0.5 heterostructure: structural, ferroelectric and magnetic properties
J. Alloy. Compd.
(2016)
J. Nogués et al.
Exchange bias
J. Magn. Magn. Mater.
(1999)
G. Dhir et al.
Sol–gel synthesized BiFeO₃ nanoparticles: enhanced magnetoelectric coupling with reduced particle size
J. Magn. Magn. Mater.
(2015)
B. Dhanalakshmi et al.
Effect of Mn doping on structural, dielectric and multiferroics properties of BiFeO₃ nanoceramics
J. Alloy. Compd.
(2016)
S.V. Vijayasundaram et al.
Substitution-driven enhanced magnetic and ferroelectric properties of BiFeO₃ nanoparticles
J. Alloy. Compd.
(2016)
A. Mukherjee et al.
Enhancement of multiferroic properties of nanocrystalline BiFeO₃ powder by Gd-doping
J. Alloy. Compd.
(2014)
A. Diallo et al.
Magnetic behavior of biosynthesized Co₃O₄ nanoparticles
J. Magn. Magn. Mater.
(2017)
J. Kennedy et al.
Controlling preferred orientation and electrical conductivity of zinc oxide thin films by post growth annealing treatment
Appl. Surf. Sci.
(2016)
L.R. Doolittle
Algorithms for the rapid simulation of Rutherford backscattering spectral
Nucl. Instrum. Methods Phys. B
(1985)
K. Liu et al.
Structural, electronic and optical properties of BiFeO₃ studied by first-principles
J. Alloy. Compd.
(2011)

Z. Irshad et al.

First principles study of structural, electronic and magnetic properties of ferromagnetic Bi₂Fe₄O₉

J. Alloy. Compd.

(2015)

K. Nadeem et al.

Effect of dipolar and exchange interactions on magnetic blocking of maghemite nanoparticles

J. Magn. Magn. Mater.

(2011)

W. Erenstein et al.

Multiferroic and magnetoelectric materials

Nature

(2006)

K.F. Wang et al.

Multiferroicity: the coupling between magnetic and polarization orders

Adv. Phys.

(2009)

J.L. Ortiz-Quiñonez et al.

Easy synthesis of high-purity BiFeO₃ nanoparticles: new insights derived from the structural, optical, and magnetic characterization

Inorg. Chem.

(2013)

K. Maruyama et al.

New Ferroelectric material for embedded FRAM LSIs

Fujitsu Sci. Tech. J.

(2007)

R.V. Petrov et al.

Magnetoelectric current sensor

D.T. Huong Giang et al.

Magnetoelectric sensor for microtesla magnetic-fields based on (Fe₈₀Co₂₀)₇₈S_i12B₁₀/PZT laminates

Sens. Actuators A

(2009)

R.V. Petrov et al.

Magneto-electric transducers

J. Lou et al.

Electrostatically tunable magnetoelectric inductors with large inductance tunability

Appl. Phys. Lett.

(2009)

I. Sosnowska et al.

Spiral magnetic ordering in bismuth ferrite

J. Phys. C Solid State Phys.

(1982)

T.J. Park et al.

Size-dependent magnetic properties of single-crystal multiferroics BiFeO₃ nanoparticles

Nano Lett.

(2007)

X. Li et al.

Effect of Ba and Mn doping on microstructure and multiferroic properties of BiFeO₃ ceramics

J. Alloy. Compd.

(2016)

S.M. Wu et al.

Reversible electric control of exchange bias in a multiferroic field-effect device

Nat. Mater.

(2010)

W.H. Meiklejohn et al.

New magnetic anisotropy

Phys. Rev.

(1957)

A.P. Malozemoff

Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces

Phys. Rev. B

(1987)

R. Mazumder et al.

Ferromagnetism in nanoscale BiFeO₃

Appl. Phys. Lett.

(2007)

V.A. Reddy et al.

Particle size dependent magnetic properties and phase transitions in multiferroic BiFeO₃ nano-particles

J. Alloy. Compd.

(2012)

Cited by (31)

Efficient synthesis of recyclable porous BiFeO<inf>3</inf>/rGO thin film via sol-gel method as an enhanced photocatalyst
2024, Colloids and Surfaces A: Physicochemical and Engineering Aspects
This paper outlines the creation of BiFeO₃-reduced graphene oxide (BrGO) thin films through a straightforward in-situ sol-gel method, followed by dip-coating and subsequent heat treatment. The resulting thin films exhibit high efficiency and reusability. Modifying the content of reduced graphene oxide (rGO) resulted in an exceptional porous morphology featuring a perovskite structure in a single phase. Due to in-situ synthesis, BiFeO₃ (BFO) nanoparticles were grafted on rGO nanosheets and formed an intimate interface. Incorporating 5 wt% of rGO into the BFO composite led to a reduction in nanoparticle size range from 400 to 160 nm, an increase in film thickness from 220 to 375 nm, and an improvement in specific surface area from 4.13 to 34.69 m².g⁻¹. These alterations render the composite a viable choice for photocatalytic applications owing to its elevated active surface area. Also, adding rGO reduced the band gap energy from 2.4 to 2.2 eV, inhibiting the recombination of electron-hole pairs in comparison to BFO. Furthermore, the BrGO thin film exhibited increased photocurrent density, a consistent photocurrent response, and a reduced arc in the Nyquist plot. These observations validate an enhanced capability to generate, separate, and transfer photogenerated charges. The BrGO thin film exhibited exceptional photocatalytic efficacy, achieving nearly complete decomposition (96%) of organic dyes within 180 min under visible light. A comprehensive investigation into the photodegradation mechanism, considering energy band alignment and scavenger tests, revealed that holes and hydroxyl radicals are the most potent reactive species. The facile synthesis, elevated photocatalytic performance, and recyclability of the BrGO thin film position it as an optimal choice for widespread use in large-scale water purification applications.
Thin film processing of multiferroic BiFeO3: From sophistication to simplicity. A review
2022, Boletin de la Sociedad Espanola de Ceramica y Vidrio
Citation Excerpt :
The PVD methodology encompasses different techniques that differ from each other in the mechanism they use to sublimate the material to be deposited on the substrate. Many of these techniques have been widely used to obtain BiFeO3 thin films during the past decade [68–90]. One of the most used would be the sputtering technique deposition.
The obtaining of BiFeO₃ in the form of a thin film represents a critical issue for its application in electronic devices since this is the required geometry for the integration of this material in microelectronic circuits. There are several techniques for this purpose, from those that use a gas or plasma phase to transport the precursors to the substrate, which would be included within the PVD or CVD techniques (for its acronym Physical Vapor Deposition and Chemical Vapor Deposition) to those that use a phase liquid for this transport, which would be included under the CSD (Chemical Vapor Deposition) techniques. However, among the large number of published papers, there is much controversy about which of them would be most suitable. It has been clearly demonstrated that all of them have the sufficient capacity to produce uniform and homogeneous thin films in thickness throughout the entire substrate, and although in many articles pure BiFeO₃ films have been obtained with an exploitable functional response, others have reported the typical drawbacks that usually entails the obtaining this material: appearance of secondary phases, high leakages or a poor functional response. Nevertheless, there is a common aspect in the specialized literature that seems to be in agreement: the first group of techniques require very sophisticated equipment that involves high energy consumption in terms of temperature and pressure (vaccum), while the techniques that are based on solutions are characterized by their higher simplicity. In this context, the purpose of the present review is to summarize the main aspects of each technique in the obtaining of BiFeO₃ thin films, from those that are more sophisticated to the simplest and environmentally benevolent ones, in order to provide an easier understanding of them.
La obtención de BiFeO₃ en forma de lámina delgada representa una cuestión crítica para su aplicación en dispositivos electrónicos ya que es la geometría requerida para la integración de este material en circuitos microelectrónicos. Existen varias técnicas para este fin, desde las que utilizan una fase gaseosa o plasmática para transportar los precursores al sustrato, que se englobarían dentro de las técnicas PVD o CVD (por sus siglas en inglés de Physical Vapor Deposition y Chemical Vapor Deposition) hasta las que utilizan una fase líquida para este transporte, que se englobarían dentro de las técnicas CSD (Chemical Vapor Deposition). Sin embargo, entre el gran número de trabajos publicados, hay mucha controversia sobre cuál de ellas sería la más adecuada. Se ha demostrado claramente que todas ellas tienen la capacidad suficiente para producir películas delgadas uniformes y homogéneas en espesor a lo largo de todo el sustrato, y aunque en muchos artículos se han obtenido películas puras de BiFeO₃ con una respuesta funcional aprovechable, otros han reportado los típicos inconvenientes que suele conllevar la obtención de este material: aparición de fases secundarias, corrientes de fuga altas o una pobre respuesta funcional. Sin embargo, hay un aspecto común en la literatura especializada que parece coincidir: el primer grupo de técnicas requiere de equipos muy sofisticados que implican un consumo energético alto en términos de temperatura y presión (vacío), mientras que las técnicas que se basan en disoluciones se caracterizan por su mayor simplicidad. En este contexto, el propósito de la presente revisión es resumir los principales aspectos de cada técnica en la obtención de películas delgadas de BiFeO₃, desde las más sofisticadas hasta las más sencillas y respetuosas con el medio ambiente, con el fin de facilitar su comprensión.
Preparation, photocatalytic and antibacterial studies on novel doped ferrite nanoparticles: Characterization and mechanism evaluation
2022, Colloids and Surfaces A: Physicochemical and Engineering Aspects
This work is presented to evaluate the influence of titanium dopant on the various properties of barium ferrite nanoparticles (BaFe₂O₄). Ba_1−xTi_xFe₂O_4+δ with x varying from 0.0 to 1.0 were prepared by chemical technique. The titanium doping results in creation of cationic vacancies with the increased surface area. The crystalline size was decreased with the enhanced Ti⁴⁺ doping process. The saturation magnetization was decreased with the increased Ti⁴⁺ content. Photocatalytic properties of un-doped and doped BaFe₂O₄ was investigated for alizarin yellow (AY) dye. The Ba_0.3Ti_0.7Fe₂O_4.7 nanoparticles act as the best photocatalyst with the degradation potential (100.0 %). The enhanced photocatalytic amount was obtained due to the narrowing of band gap of Ba_0.3Ti_0.7Fe₂O_4.7 (2.07 eV). The stability and reusability test shows that the amount of degradation was negligibly decreased after 5th cycles. Thus, the Ti⁴⁺ doped barium ferrite proved to be great method in modifying the photocatalytic response in the degradation process. Antibacterial analysis depicts that the high content of Ti⁴⁺ doped barium ferrite showed higher antibacterial properties against Staphylococcus aureus and Helicobacter pylori.
Saturation magnetization as a function of temperature in Zn doped YIG nanoparticles
2022, Physica E: Low-Dimensional Systems and Nanostructures
The behavior of saturation magnetization as a function of temperature ( $M_{S} (T)$ ), in Zinc doped YIG nanoparticles was investigated. The samples, with crystallite size between 40 nm and 78 nm were synthesized by the sol–gel method. With the data obtained through the vibrating sample magnetometry, an adjustment with the Approach law to obtain the saturation magnetization at temperatures between 50 K and 300 K was performed. With the data it was possible to get the $M_{S} \times T$ experimental plots. Curves were fitted with the most recent proposal by Cojocaru et al., where an expression for $M (T)$ is derived using a three-dimensional generalization of Heisenberg’s Hamiltonian, that take into account geometry, size and boundary conditions of magnetic nanoparticles. A good correspondence was obtained between the experimental data and the adjustment through the proposal. Analyzing the parameters obtained through the fitting, it was possible to visualize a weakening in the ferrimagnetic coupling with increased doping of Zn. It was also possible to see a good adjustment of the proposal with the change in the nanoparticles shape. The proposal proved to be very useful for the study of the nanoparticles.
Dimensionality induced enhancement of ferromagnetic spin order and ferroelectric polarization in Ga doped α-Fe<inf>2</inf>O<inf>3</inf> thin films
2022, Applied Surface Science
The thin films of Ga doped hematite (α-Fe₂O₃) were grown on p-Si 〈1 1 1〉 substrate using Pulsed Laser Deposition technique. The as-grown films indicated crystalline peaks of rhombohedral structure. The films exhibited enhancement of ferromagnetic properties. The reduction of dimensionality of the materials in thin films (2D) has shown unusual magnetic spin order and exchange bias effect at temperatures < 70 K. The ferromagnetic parameters (magnetization, coercivity) showed dependence on composition, deposition conditions and heat treatment of the films. The as-grown films showed a good signature of ferroelectric polarization. The as-grown films of Fe_1.8Ga_0.2O₃, having relatively large surface roughness, exhibited smaller magnetic moment in comparison to as-grown films of Fe_1.6Ga_0.4O₃ with small surface roughness. The X-ray photoelectron spectroscopy measurements confirmed a chemically homogeneous state of high spin Fe³⁺ ions in as-grown films of Fe_1.6Ga_0.4O₃ composition, whereas chemical state of Fe ions is consisting of the mixture of high spin Fe³⁺ and Fe²⁺ states in as-grown films of Fe_1.₈Ga_0.₂O₃.
Iron oxide nanoparticles in biological systems: Antibacterial and toxicology perspective
2021, JCIS Open
Citation Excerpt :
The different synthesis routes via “top-down” and “bottom-up” are employed by different researchers to define the particle size, morphology, and magnetic properties of iron oxide. Top-down major methods are pulsed laser ablation [33], laser ablation [34], Aerosol spray pyrolysis [35] sputtering [36] and gas-phase deposition [37]. These synthesis routes are often difficult due to the setup mechanism and not easily scale up.
There has been an increasing number of studies in magnetic nanoparticles with auspicious applications in medicine. Among the oxides of magnetic nanoparticles, iron oxide has emerged as an indispensable tool in nanotechnology, particularly bio-nanotechnology. This is attributed to its exceptional properties such as size, shape, magnetism, and biocompatibility. In this review, iron oxide nanoparticles were exploited in different model organisms ranging from prokaryotes to eukaryotes, elucidating their cellular functions relative to their antibacterial activity, drug delivery, and toxicity.

View all citing articles on Scopus

View full text

Nanocrystalline multiferroic BiFeO3 thin films made by room temperature sputtering and thermal annealing, and formation of an iron oxide-induced exchange bias

Highlights

Abstract

Introduction

Section snippets

Methods

Results and discussion

Conclusions

Acknowledgments

J. Alloy. Compd.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

J. Alloy. Compd.

J. Alloy. Compd.

J. Alloy. Compd.

J. Magn. Magn. Mater.

Appl. Surf. Sci.

Nucl. Instrum. Methods Phys. B

J. Alloy. Compd.

J. Alloy. Compd.

J. Magn. Magn. Mater.

Multiferroic and magnetoelectric materials

Nature

Multiferroicity: the coupling between magnetic and polarization orders

Adv. Phys.

Easy synthesis of high-purity BiFeO3 nanoparticles: new insights derived from the structural, optical, and magnetic characterization

Inorg. Chem.

New Ferroelectric material for embedded FRAM LSIs

Fujitsu Sci. Tech. J.

Magnetoelectric current sensor

Magnetoelectric sensor for microtesla magnetic-fields based on (Fe80Co20)78Si12B10/PZT laminates

Sens. Actuators A

Magneto-electric transducers

Electrostatically tunable magnetoelectric inductors with large inductance tunability

Appl. Phys. Lett.

Spiral magnetic ordering in bismuth ferrite

J. Phys. C Solid State Phys.

Size-dependent magnetic properties of single-crystal multiferroics BiFeO3 nanoparticles

Nano Lett.

Effect of Ba and Mn doping on microstructure and multiferroic properties of BiFeO3 ceramics

J. Alloy. Compd.

Reversible electric control of exchange bias in a multiferroic field-effect device

Nat. Mater.

New magnetic anisotropy

Phys. Rev.

Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interfaces

Phys. Rev. B

Ferromagnetism in nanoscale BiFeO3

Appl. Phys. Lett.

Particle size dependent magnetic properties and phase transitions in multiferroic BiFeO3 nano-particles

J. Alloy. Compd.

Nanocrystalline multiferroic BiFeO₃ thin films made by room temperature sputtering and thermal annealing, and formation of an iron oxide-induced exchange bias

Easy synthesis of high-purity BiFeO₃ nanoparticles: new insights derived from the structural, optical, and magnetic characterization

Magnetoelectric sensor for microtesla magnetic-fields based on (Fe₈₀Co₂₀)₇₈S_i12B₁₀/PZT laminates

Size-dependent magnetic properties of single-crystal multiferroics BiFeO₃ nanoparticles

Effect of Ba and Mn doping on microstructure and multiferroic properties of BiFeO₃ ceramics

Ferromagnetism in nanoscale BiFeO₃

Particle size dependent magnetic properties and phase transitions in multiferroic BiFeO₃ nano-particles