Ferrimagnetic Oxides Research Articles

High coercivity induced by mechanical milling in cobalt ferrite powders

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe2O4 treated by mechanical milling with different grinding balls. The cobalt ferrite nanoparticles were prepared using a simple hydrothermal method and annealed at 500°C. The non-milled sample presented coercivity of about 1.9kOe, saturation magnetization of 69.5emu/g, and a remanence ratio of 0.42. After milling, two samples attained coercivity of 4.2 and 4.1kOe, and saturation magnetization of 67.0 and 71.4emu/g respectively. The remanence ratio MR/MS for these samples increase to 0.49 and 0.51, respectively. To investigate the influence of the microstructure on the magnetic behavior of these samples, we used X-ray powder diffraction (XPD), transmission electron microscopy, and vibrating sample magnetometry. The XPD analysis by the Williamson–Hall plot was used to estimate the average crystallite size and strain induced by mechanical milling in the samples.

Sensing of Biologically Important Cations Such as Na+, K+, Ca2+, Cu2+, and Fe3+ Using Magnetic Nanoemulsions

We report a simple approach to the ultrasensitive detection of biologically important metal ions using a magnetic nanoemulsion. The nanoemulsion used in our study was an oil-in-water emulsion droplet of average size ∼190 nm containing ferrimagnetic iron oxide nanoparticles of average size ∼10 nm. In a static magnetic field, the emulsion droplets self-assemble into a nanoarray with distinct interdroplet spacing. In the presence of cations in the solution, the nanofluid array shows a large blue shift in the diffracted Bragg peak and a visually perceivable color change due to changes in the electrical double layer upon the diffusion of cations. The colloidal force-distance measurements in the presence of cations show large variations at the onset of repulsion in the presence of cations. The sensor shows good selectivity to Na(+), K(+), Ca(2+), Cu(2+), and Fe(3+) ions and offers a rapid response compared to conventional techniques. This approach can be useful for the recognition of biologically important cations.

Promising ferrimagnetic double perovskite oxides towards high spin polarization at high temperature

We predict through our first-principles calculations that four double perovskite oxides of Bi2ABO6 (AB = FeMo, MnMo, MnOs, CrOs) are half-metallic ferrimagnets. Our calculated results shows that the four optimized structures have negative formation energy, from -0.42 to -0.26 eV per formula unit, which implies that they could probably be realized. In the case of Bi2FeMoO6, the half-metallic gap and Curie temperature are predicted to reach to 0.71 eV and 650 K, respectively, which indicates that high spin polarization could be kept at high temperatures far beyond room temperature. It is believed that some of them could be synthesized soon and would prove useful for spintronic applications.

Nanoparticle magnetization measurements by a high sensitive nano-superconducting quantum interference device

A high sensitive nano superconducting quantum interference device (nanoSQUID) operating as a magnetic flux to critical current transducer with a suitable feedback circuit is employed to measure the magnetization of ferrimagnetic iron oxide nanoparticles. An improved SQUID responsivity has been obtained by using a loop inductance asymmetry. Iron oxide nanoparticles having a mean diameter of 8 nm have been excited by applying a polarizing field in the plane of the nanoSQUID loop. The field dependence of the nanoparticle magnetization at T = 4.2 K shows magnetic hysteresis. Magnetic relaxation measurements are reported and compared with those obtained by using a commercial measurement system.

Chitosan Oligosaccharide-Stabilized Ferrimagnetic Iron Oxide Nanocubes for Magnetically Modulated Cancer Hyperthermia

Magnetic nanoparticles have gained significant attention as a therapeutic agent for cancer treatment. Herein, we developed chitosan oligosaccharide-stabilized ferrimagnetic iron oxide nanocubes (Chito-FIONs) as an effective heat nanomediator for cancer hyperthermia. Dynamic light scattering and transmission electron microscopic analyses revealed that Chito-FIONs were composed of multiple 30-nm-sized FIONs encapsulated by a chitosan polymer shell. Multiple FIONs in an interior increased the total magnetic moments, which leads to localized accumulation under an applied magnetic field. Chito-FIONs also exhibited superior magnetic heating ability with a high specific loss power value (2614 W/g) compared with commercial superparamagnetic Feridex nanoparticles (83 W/g). The magnetically guided Chito-FIONs successfully eradicated target cancer cells through caspase-mediated apoptosis. Furthermore, Chito-FIONs showed excellent antitumor efficacy on an animal tumor model without any severe toxicity.

Water-Dispersible Ferrimagnetic Iron Oxide Nanocubes with Extremely High r2 Relaxivity for Highly Sensitive in Vivo MRI of Tumors

The theoretically predicted maximum r(2) relaxivity of iron oxide nanoparticles was achieved by optimizing the overall size of ferrimagnetic iron oxide nanocubes. Uniform-sized iron oxide nanocubes with an edge length of 22 nm, encapsulated with PEG-phospholipids (WFION), exhibited high colloidal stability in aqueous media. In addition, WFIONs are biocompatible and did not affect cell viability at concentrations up to 0.75 mg Fe/ml. Owing to the enhanced colloidal stability and the high r(2) relaxivity (761 mM(-1) s(-1)), it was possible to successfully perform in vivo MR imaging of tumors by intravenous injection of 22-nm-sized WFIONs, using a clinical 3-T MR scanner.

Exchange coupling behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2 nanocomposite. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupled. Two steps were followed to synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposite: (i) first, preparation of CoFe2O4 nanoparticles using a simple hydrothermal method, and (ii) second, reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe2O4 nanoparticles were investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0kOe at room temperature and 50K. The mean diameter of CoFe2O4 particles is about 16nm. Mossbauer spectra revealed two sites for Fe3+. One site is related to Fe in an octahedral coordination and the other one to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe2O4. TEM measurements of nanocomposite showed the formation of a thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles increase to about 100nm. The magnetization of the nanocomposite showed a hysteresis loop that is characteristic of exchange coupled systems. A maximum energy product (BH)max of 1.22MGOe was achieved at room temperature for CoFe2O4/CoFe2 nanocomposites, which is about 115% higher than the value obtained for CoFe2O4 precursor. The exchange coupling interaction and the enhancement of product (BH)max in nanocomposite CoFe2O4/CoFe2 are discussed.

Novel Applications of Ferrites

The applications of ferrimagnetic oxides, or ferrites, in the last 10 years are reviewed, including thin films and nanoparticles. The general features of the three basic crystal systems and their magnetic structures are briefly discussed, followed by the most interesting applications in electronic circuits as inductors, in high-frequency systems, in power delivering devices, in electromagnetic interference suppression, and in biotechnology. As the field is considerably large, an effort has been made to include the original references discussing each particular application on a more detailed manner.

Multifunctional ferritin cage nanostructures for fluorescence and MR imaging of tumor cells

Bionanoparticles and nanostructures have attracted increasing interest as versatile and promising tools in many applications including biosensing and bioimaging. In this study, to image and detect tumor cells, ferritin cage-based multifunctional hybrid nanostructures were constructed that: (i) displayed both the green fluorescent protein and an Arg-Gly-Asp peptide on the exterior surface of the ferritin cages; and (ii) incorporated ferrimagnetic iron oxide nanoparticles into the ferritin interior cavity. The overall architecture of ferritin cages did not change after being integrated with fusion proteins and ferrimagnetic iron oxide nanoparticles. These multifunctional nanostructures were successfully used as a fluorescent imaging probe and an MRI contrast agent for specifically probing and imaging α(v)β(3) integrin upregulated tumor cells. The work provides a promising strategy for tumor cell detection by simultaneous fluorescence and MR imaging.

Elucidating the morphological and structural evolution of iron oxide nanoparticles formed by sodium carbonate in aqueous medium

Ferrimagnetic iron oxides are the common choice for many current technologies, especially those with application in biology and medicine. Despite the comprehensive knowledge accumulated about their chemistry in the bulk state, the sequence of changes taking place during the precipitation of iron oxide nanoparticles in aqueous media is much less extensive. We show that using sodium carbonate as a co-precipitating agent for the synthesis of uncoated iron oxide nanoparticles, the reaction proceeds sufficiently slowly to enable a detailed study of both the reaction pathway and products. The effect of pH, temperature and reaction time on particle size, morphology, crystalline phase and its magnetic properties was investigated. The obtained nanoparticles showed an increase in average particle size of about 10 nm per pH unit for the magnetite phase leading to 6.9 ± 0.4 nm, 18 ± 3 nm and 28 ± 5 nm for pH 8, 9 and 10 respectively. Goethite was initially formed by an olation mechanism at room temperature, followed by a slow transformation into magnetite over a 24 h period, as tracked by X-ray diffraction. In another set of experiments where the reaction temperatures were varied, magnetite was obtained directly by the oxolation mechanism at temperatures above 45 °C. The optimization of the experimental parameters led to superparamagnetic nanoparticles with a high saturation magnetization of 82 A m2 kg−1 at 300 K when synthesized at pH 9.

방사광을 이용한 FeV2O4스피넬 산화물의 덩치상태와 분말상태의 전자구조 차이 연구

연 x선 광흡수 분광법(soft x-ray absorption spectroscopy: XAS)과 연 x선 자기 원편광 이색성(soft x-ray magnetic circular dichroism: XMCD)을 이용하여 스피넬 준강자성 산화물인 <TEX>$FeV_2O_4$</TEX>의 전자 구조를 연구하였다. Fe 2p XAS와 V 2p XAS 측정으로 부터 <TEX>$FeV_2O_4$</TEX>에서 Fe 이온과 V이온의 고유한 원자가는 각각 약 <TEX>$Fe^{2.3+}$</TEX>의 혼합원자가 상태와 약 <TEX>$V^{3+}$</TEX>의 상태임을 알 수 있었다. 실험적으로 측정된 Fe 2p XMCD의 신호는 거의 <TEX>$Fe^{2+}$</TEX> 상태에서 기인하였으며, <TEX>$Fe^{3+}$</TEX> 상태는 Fe 2p XMCD의 신호에 거의 기여하지 않는다는 사실이 발견되었다. 그러므로 <TEX>$FeV_2O_4$</TEX>의 자성 특성을 결정함에 있어서 자기적으로 정렬된 <TEX>$Fe^{2+}$</TEX> 상태 이온들이 중요한 역할을 한다고 생각된다. The electronic structure of ferrimagnetic spinel oxide of <TEX>$FeV_2O_4$</TEX> has been investigated by employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). The Fe 2p and V 2p XAS spectra show that the valence states of Fe and V ions are <TEX>${\sim}Fe^{2.3+}$</TEX> mixed-valent states and <TEX>${\sim}V^{3+}$</TEX> states, respectively. In Fe 2p XMCD spectra, finite XMCD signals are observed for divalent <TEX>$Fe^{2+}$</TEX> states only, but not for <TEX>$Fe^{3+}$</TEX> states. This finding indicates that the magnetic moments of <TEX>$Fe^{2+}$</TEX> ions are ordered ferromagnetically but that those of <TEX>$Fe^{3+}$</TEX> ions are cancelled, implying that <TEX>$Fe^{2+}$</TEX> ions play an important role in determining magnetic properties of <TEX>$FeV_2O_4$</TEX>.

Dissolution of titanomagnetite and sulphidization in sediments from Lake Kinneret, Israel

SUMMARY Magnetic extracts obtained from sediment cores recovered from Lake Kinneret, Israel, were subjected to comprehensive scanning electron microscope and in-line energy dispersive X-ray spectroscopy analyses. A variety of ferrimagnetic iron oxides and iron sulphide particles were identified, along with apparently non-magnetic iron sulphides. The majority of the iron oxides are titanomagnetites that have undergone pervasive dissolution, and in many cases were only preserved as skeletal, 3-D lattices of ilmenite lamellae. Often the spaces between the submicron ilmenite lamellae are empty. Also sponge-like dissolution features are observed in some residual titanomagnetite grains. Another group of titanomagnetite grains is characterized by superficial shrinkage-cracks, which indicate low-temperature maghemitization. In some cases, these cracks appear to be where dissolution started. Most titanomagnetites contain impurities of Al, Mg, Si and Mn on the order of 1 per cent. Chromium-magnetites, with minor Ti, Mg and Al content on the order of a few percent, but without Mn, were also found. Chromium-magnetites mostly occur as octahedra in a well-preserved state, which indicates that they are less prone to dissolution. Magnetite spherules of 40–60 μm in size, which were mostly hollow, were only found in material collected from the outer zone of the core section that was in contact with the steel core barrel. These spherules were not found in material collected from the centre of the core. They are therefore interpreted as contaminants that were produced during fabrication of the steel core barrel. Iron sulphides are present as pyrite, either as larger aggregates of cubic crystals, each of up to 20 μm in size, or as 5–10 μm framboidal aggregates, consisting mostly about 0.3 μm idiomorphic octahedra. The cubic pyrite crystals have heterogeneous compositions. Pure pyrite should be non-magnetic, but even aggregates of up to 150 μm in size were magnetically separated. They probably therefore contain a magnetic core of greigite or overgrown titanomagnetite. The latter possibility is supported by observations of residual titanomagnetites with individual pyrite crystals residing directly on their surfaces, or filling space between ilmenite lamellae. Irregular aggregates of flaky, submicron iron sulphides were also found, which are interpreted to be greigite. The greigite has a low degree of visible crystallization. Pyrite and/or greigite grains were found inside the aggregates, or in agglomerates with organic remnants. Together, visual observations and elemental analyses provide clear evidence of pervasive dissolution of primary titanomagnetite and concurrent sulphidization of sediments from Lake Kinneret.

Ultrathin oxide films and interfaces for electronics and spintronics

Oxides have become a key ingredient for new concepts of electronic devices. To a large extent, this is due to the profusion of new physics and novel functionalities arising from ultrathin oxide films and at oxide interfaces. We present here a perspective on selected topics within this vast field and focus on two main issues. The first part of this review is dedicated to the use of ultrathin films of insulating oxides as barriers for tunnel junctions. In addition to dielectric non-magnetic epitaxial barriers, which can produce tunneling magnetoresistances in excess of a few hundred percent, we pay special attention to the possibility of exploiting the multifunctional character of some oxides in order to realize ‘active’ tunnel barriers. In these, the conductance across the barrier is not only controlled by the bias voltage and/or the electrodes magnetic state, but also depends on the barrier ferroic state. Some examples include spin-filtering effects using ferro- and ferrimagnetic oxides, and the possibility of realizing hysteretic, multi-state junctions using ferroelectric barriers. The second part of this review is devoted to novel states appearing at oxide interfaces. Often completely different from those of the corresponding bulk materials, they bring about novel functionalities to be exploited in spintronics and electronics architectures. We review the main mechanisms responsible for these new properties (such as magnetic coupling, charge transfer and proximity effects) and summarize some of the most paradigmatic phenomena. These include the formation of high-mobility two-dimensional electron gases at the interface between insulators, the emergence of superconductivity (or ferromagnetism) at the interface between non-superconducting (or non-ferromagnetic) materials, the observation of magnetoelectric effects at magnetic/ferroelectric interfaces or the effects of the interplay and competing interactions at all-oxide ferromagnetic/superconducting interfaces. Finally, we link up the two reviewed research fields and emphasize that the tunneling geometry is particularly suited to probe novel interface effects at oxide barrier/electrode interfaces. We close by giving some directions toward tunneling devices exploiting novel oxide interfacial phenomena.

Magnetosome-like ferrimagnetic iron oxide nanocubes for highly sensitive MRI of single cells and transplanted pancreatic islets.

For ultrasensitive magnetic resonance imaging (MRI), magnetic nanoparticles with extremely high r2 relaxivity are strongly desired. Magnetosome-like nanoparticles were prepared by coating polyethylene glycol-phospholipid (PEG-phospholipid) onto ferrimagnetic iron oxide nanocubes (FIONs). FIONs exhibited a very high relaxivity (r2) of 324mM(-1)s(-1), allowing efficient labeling of various kinds of cells. The magnetic resonance (MR) imaging of single cells labeled with FIONs is demonstrated not only in vitro but also in vivo. Pancreatic islet grafts and their rejection could be imaged using FIONs on a 1.5T clinical MRI scanner. The strong contrast effect of FIONs enabled MR imaging of transplanted islets in small rodents as well as in large animals. Therefore, we expect that MR imaging of pancreatic islet grafts using FIONs has the potentials for clinical applications. Furthermore, FIONs will enable highly sensitive noninvasive assessment after cell transplantation.

Studies on Microstructural and Thermophysical properties of polymer nanocomposite based on polyphenylene oxide and Ferrimagnetic iron oxide

Nanocomposites of polyphenylene oxide (PPO) filled with nanoparticles of organically modified γ-Fe 2O 3, in varied concentration from 0 to 20 wt. %, were prepared. Thermal stability of these nanocomposites was evaluated by thermo-gravimetric analysis (TGA) and their dimensional stability was measured at sub-ambient as well as at elevated temperatures by thermo-mechanical analysis (TMA). The glass transition temperature ( T g ) of the nanocomposites, measured by differential scanning calorimeter (DSC), was found to decrease with increasing weight fraction of γ-Fe 2O 3. Phase morphology of the nanocomposites was analyzed by scanning electron microscope (SEM). The distribution of γ-Fe 2O 3 in PPO matrix was studied by determining the iron using a X-ray energy dispersive spectroscope (EDX) attached to the SEM. These analyses reveal that the nanoparticles of γ-Fe 2O 3 with an average diameter of 20 nm were dispersed uniformly in the PPO matrix and also that there was very good matrix-filler adhesion. A detailed morphological study using a Gatan hot stage attachment with the SEM showed that there was no change in the surface morphology from ambient to high temperature up to 280 °C, beyond which segregation of the nanoparticles took place. Measurements by vibrational sample magnetometer (VSM) showed that the degree of saturation magnetization increased with increasing filler concentration from 0% to 10 wt. % of γ-Fe 2O 3. The magnetic nanocomposites, in general, also showed very good mechanical strength and high temperature resistance.

A magnetic zeolitic nanocomposite from occlusion of silica-coated iron species by crystalline titanosilicate-1

This paper examines the preparation of novel magnetic zeolitic nanocomposites from the occlusion of silica-coated iron species by crystalline titanosilicate-1. The results revealed that well-crystallized TS-1 could be synthesized in the presence of silica-hematite nanoparticles. Each as-made nanocomposite particle exhibited a compact and monolithic ‘brick-like’ morphology with a size of ca. 400 nm × 200 nm × 200 nm. The non-magnetic hematite (iron oxide) in such an as-made nanocomposite can be reduced by hydrogen to produce ferrimagnetic iron oxides and ferromagnetic elemental iron. The resultant nanocomposite consists of TS-1 as outer shell, which occludes a small portion of silica-iron species as the core with a total magnetization value of 3.7 emu/g. The silica coating and size of hematite nanoparticles, the presence of ammonium carbonate as the crystallization-mediating agent for nucleation and growth of TS-1 are critical factors when preparing such nanocomposites.

Mineralogical, Chemical, and Physical Characterization of Synthetic Al-Substituted Maghemites (γ−Fe2−xAlxO3)

AbstractMaghemite (γ-Fe2O3) is a ferrimagnetic Fe oxide commonly found in tropical and subtropical soils, especially in the topsoil where it is usually a product of burning. Isomorphic substitution (IS) of the Fe in maghemite by different metals (mainly Al3+) can modify its mineralogical and chemical attributes, and these modifications may be important to understanding the formation and properties of this mineral in soils and sediments. The objective of this work was to evaluate the crystallochemical alterations of synthetic, Al-substituted maghemites prepared by the precipitation of magnetites from alkaline aqueous media containing FeSO4·7H2O with increasing amounts of Al2(SO4)3·7H2O to obtain hypothetical Al3+ for Fe3+ substitutions ranging from 0.0 to 40.0 mol %. The Al-substituted magnetites were washed and dried, and then heated to 250ºC for 4 h to form yellowish red maghemites that were characterized by total chemical analysis, X-ray diffraction, specific surface area (SSA), mass-specific magnetic susceptibility, infrared spectroscopy, transmission electronic microscopy, and color. Increasing Al3+ substitution to an experimental maximum of 15.9 mol % decreased both the a0 dimension of the cubic unit cell (a0 = 0.8339 − 396.157 × 10−16 Al, r2 = 0.99) and the mean crystallite dimension (MCD = 76.4–3.15Al, r2 = 0.79) of the maghemites. With the decrease in MCD came a more yellowish color, an increase in SSA, and a decrease in crystallinity as measured through extraction of the samples with acid ammonium oxalate. The mass-specific magnetic susceptibility of the maghemites increased with Al3+ substitution up to 5.3 mol % and then decreased with further replacement of Fe by Al. Solid-phase aluminum in excess of 16 mol % substitution appeared to occur as a separate, poorly crystalline phase that was X-ray amorphous.

Neutron Powder Diffraction Studies of Magnetic Quasi-degenerated Oxides with Competing Degrees of Freedom

Neutron powder diffraction has been extensively used during last years to address a wide diversity of problems in the field of Strongly Correlated Oxides. Very rich phase diagrams are a common feature of materials formed by metal-oxygen bonds with seemingly simple structures, originating from strong electron-correlations and involving spin, charge, orbital, and lattice degrees of freedom. Competing energy terms do not always favor conventional itinerant Bloch states, and make possible quasi-degenerate configurations that render these systems prone to self-organization of electrons into superstructures, or nano- and mesoscopic inhomogeneous states, or to offer giant responses. During the last years, our main research activity using neutrons has been focused on the structure-properties relationship of magnetic and electronic oxides with competing degrees of freedom: narrow-band oxides with metal-insulator transitions, materials with colossal magnetoresistance, manganites, half-metallic ferrimagnetic oxides, nickelates, vanadates, cobaltites, charge and orbital ordered phases, exotic phases in degenerated magnetic materials, etc.

Synthesis, structural study and magnetic properties of TbFeMnO 5

We describe the preparation and characterization of a new ferrimagnetic oxide of composition TbFeMnO 5. It has been prepared by a soft-chemistry procedure, involving the thermal treatment at moderate temperatures (600 °C) of citrate precursors, subsequently annealed at 900 °C under high oxygen pressure (200 bar). The crystallographic and magnetic structures have been studied by neutron powder diffraction (NPD) experiments, in complement with magnetization and susceptibility measurements. TbFeMnO 5 is an orthorhombic, Pbam space group; the crystal structure contains infinite chains of Mn 4+O 6 edge-sharing octahedra running along the c axis and interconnected by Fe 3+O 5 pyramids and TbO 8 units. Some anti-site disorder is observed from the NPD refinements: about 9% of the 4 f octahedral sites are occupied by Fe 3+ cations and about 18% of the pyramidal 4 h positions contain Mn 4+. These structural features are confirmed by Mössbauer spectroscopy: two sites for Fe 3+ are identified; one of them corresponds to almost regular octahedra (at 4 f positions), characterized by nearly equal Mn/Fe–O distances of 1.906Å at RT (from NPD data), giving a quadrupole doublet in the Mössbauer spectra at RT; the second contributes to a more intensive doublet corresponding to a distorted square pyramid Fe 3+O 5 (at 4 h sites), for which NPD data demonstrates an axial distortion with three sets of Mn/Fe–O distances at 1.981(4), 1.851(5) and 1.944(3) Å. Both doublets are broadened by the Fe/Mn disorder over these sites. TbFeMnO 5 undergoes long-range magnetic ordering below T C ≈ 175 K , as shown from magnetization, NPD and Mössbauer spectroscopy data. The propagation vector k = 0 defines a ferrimagnetic structure that initially concerns the Mn 4+ and Fe 3+ cations, in a magnetic arrangement defined by the basis vectors ( 0 , 0 , F z ) and ( 0 , 0 , F z ′ ) respectively. The Tb 3+ sublattice is ordered at 2 K with a spin arrangement given by ( 0 , 0 , F z ″ ) . The refined magnetic moments at this temperature are 2.66 ( 12 ) μ B for the Mn 4+, − 0.8 ( 2 ) μ B for the Fe 3+ and − 2.0 ( 3 ) μ B for the Tb 3+ cations.

Oxides, Oxides, and More Oxides: High-κ Oxides, Ferroelectrics, Ferromagnetics, and Multiferroics

We review and critique the recent developments on multifunctional oxide materials, which are gaining a good deal of interest. Recongnizing that this is a vast area, the focus of this treatment is mainly on high-κ dielectric, ferroelectric, magnetic, and multiferroic materials. Also, we consider ferrimagnetic oxides in the context of the new, rapidly developing field of negative-index metamaterials. This review is motivated by the recent resurgence of interest in complex oxides owing to their coupling of electrical, magnetic, thermal, mechanical, and optical properties, which make them suitable for a wide variety of applications, including heat, motion, electric, and magnetic sensors; tunable and compact microwave passive components; surface acoustic wave devices; nonlinear optics; and nonvolatile memory, and pave the way for designing multifunctional devices and unique applications in spintronics and negative refraction-index media. For most of the materials treated here, structural and physical properties, preparation methods accompanied by particulars of synthesis of thin films, devices based on them, and some projections into their future applications are discussed.