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1

Spin-glass-like freezing and enhanced magnetization in ultra-small CoFe2O4 nanoparticles.  

PubMed

The magnetic properties of ultra-small (3 nm) CoFe(2)O(4) nanoparticles have been investigated by DC magnetization measurements as a function of temperature and magnetic field. The main features of the magnetic behaviour are blocking of non-interacting particle moments (zero-field-cooled magnetization T(max) approximately 40 K), a rapid increase of saturation magnetization (up to values higher than for the bulk material) at low T and an increase in anisotropy below 30 K due to the appearance of exchange bias. The low temperature behaviour is determined by a random freezing of surface spins. Localized spin-canting and cation distribution between the two sublattices of the spinel structure account quantitatively for the observed increase in saturation magnetization. PMID:20203355

Peddis, D; Cannas, C; Piccaluga, G; Agostinelli, E; Fiorani, D

2010-03-26

2

Ethanol Sensor Using Undoped And Mn-Doped CoFe2O4 Nanoparticles  

NASA Astrophysics Data System (ADS)

Room temperature ferromagnetism and an increase in saturation magnetization due to Mn-doping are observed in CoFe2O4 nanoparticles. The ethanol sensitivity of undoped and Mn-doped (3 at.%) CoFe2O4 nanoparticles were experimented at ambient temperature using optical fiber based on evanescent wave adsorption phenomenon. By modifying the clad exposure to gas vapor, the sensitivities were calculated to be 0.07 and 0.12 counts/ppm for undoped and Mn-doped CoFe2O4 nanoparticles respectively, showing significant enhancement in ethanol sensitivity for Mn-doped sample.

Devi, P. Indra; Rajkumar, N.; Ramachandran, K.

2011-07-01

3

High coercivity of oleic acid capped CoFe2O4 nanoparticles at room temperature.  

PubMed

High coercivity (9.47 kOe) has been obtained for oleic acid capped chemically synthesized CoFe(2)O(4) nanoparticles of crystallite size approximately 20 nm. X-ray diffraction analysis confirms the formation of spinel phase in these nanoparticles. Thermal annealing at various temperatures increases the particle size and ultimately shows bulk like properties at particle size approximately 56 nm. The nature of bonding of oleic acid with CoFe(2)O(4) nanoparticles and amount of oleic acid in the sample is determined by Fourier transform infrared spectroscopy and thermogrvimetric analysis, respectively. The Raman analysis suggests that the samples are under strain due to capping molecules. Cation distribution in the sample is studied using Mossbauer spectroscopy. Oleic acid concentration dependent studies show that the amount of capping molecules plays an important role in achieving such a high coercivity. On the basis of above observations, it has been proposed that very high coercivity (9.47 kOe) is the result of the magnetic anisotropy, strain, and disorder of the surface spins developed by covalently bonded oleic acid to the surface of CoFe(2)O(4) nanoparticles. PMID:19522478

Limaye, Mukta V; Singh, Shashi B; Date, Sadgopal K; Kothari, Deepti; Reddy, V Raghavendra; Gupta, Ajay; Sathe, Vasant; Choudhary, Ram Jane; Kulkarni, Sulabha K

2009-07-01

4

Alcohol dependent production of Fe3O4 and CoFe2O4 nanoparticles.  

PubMed

Commonly available alcohols of varying lengths and degree of branching were used to synthesize iron oxide, Fe3O4, and cobalt iron oxide, CoFe2O4, nanoparticles by means of a simple solvothermal decomposition of iron (III) acetylacetonates and cobalt (II) acetylacetonates. Depending on the solvent employed resulting Fe3O4 and CoFe2O4 nanoparticles ranged in size from approximately 5-16 nm and approximately 4-8 nm, respectively. All alcohols utilized resulted in the formation of nanoparticles with a spinel crystal structure, with the exception of methanol. Use of tert-butanol and phenol resulted in nearly spherical agglomerations of individual nanoparticles ranging between 100-250 nm. The resulting structures and morphologies of all samples were confirmed by X-ray diffraction and electron microscopy. Mass specific moments are reported based on SQUID magnetometry, and ranged from 57.5(5)-76.4(3) emu/g for Fe3O4 and 47.7(7)-67.0(4) emu/g CoFe2O4. PMID:23862521

Yocum, Brandon J; Ekiert, Thomas F; Alexander, Max D; O'Malley, Matthew J

2013-06-01

5

Magnetic properties and morphology of block copolymer templated ferrimagnetic CoFe2O4 nanoparticles  

Microsoft Academic Search

We synthesized the block copolymer of poly(norbornene-dicarboxcylic acid) and poly(norbornene) at room temperature, using ring opening metathesis polymerization. We then templated the CoFe2O4 nanoparticles within the polymer matrix, utilizing the self-assembled nature of the block copolymer. We used transmission electron microscopy, superconducting quantum interference device magnetometry, and X-ray powder diffraction to investigate the morphology and magnetic properties of the nanocomposites.

Sufi R. Ahmed; Satish B. Ogale; Peter Kofinas

2003-01-01

6

Electron paramagnetic resonance, magnetic and electrical properties of CoFe2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

CoFe2O4 nanoparticles were prepared by solution combustion method. The nanoparticle are characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). PXRD reveals single phase, cubic spinel structure with Fd3¯m (227) space group. SEM micrograph shows the particles are agglomerated and porous in nature. Electron paramagnetic resonance spectrum exhibits a broad resonance signal g=2.150 and is attributed to super exchange between Fe3+ and Co2+. Magnetization values of CoFe2O4 nanoparticle are lower when compared to the literature values of bulk samples. This can be attributed to the surface spin canting due to large surface-to-volume ratio for a nanoscale system. The variation of dielectric constant, dielectric loss, loss tangent and AC conductivity of as-synthesized nano CoFe2O4 particles at room temperature as a function of frequency has been studied. The magnetic and dielectric properties of the samples show that they are suitable for electronic and biomedical applications.

Jnaneshwara, D. M.; Avadhani, D. N.; Daruka Prasad, B.; Nagabhushana, B. M.; Nagabhushana, H.; Sharma, S. C.; Shivakumara, C.; Rao, J. L.; Gopal, N. O.; Ke, Shyue-Chu; Chakradhar, R. P. S.

2013-08-01

7

Synthesis and characterization of magnetic composites based on cis-polyisoprene and CoFe2O4 nanoparticles.  

PubMed

CoFe2O4 nanoparticles were obtained by the co-precipitation method. They were further modified by the adsorption of ricinoleic acid (RA). The non-modified and modified CoFe2O4/RA nanoparticles were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman, and Fourier transform infrared (FTIR) spectroscopy. The modified particles present a mean diameter < 20 nm. The adsorption of RA on the CoFe2O4 surface is characterized by the IR absorptions of the RA while in the Raman spectrum the predominant signals are those from the CoFe2O4. The cis-polyisoprene (PI) composite was prepared by dissolving PI in cyclohexane followed by the addition of a magnetic fluid based on CoFe2O4/RA nanoparticles dispersed in cyclohexane. After solvent evaporation a magnetic composite was obtained and characterized by AFM, Raman, and FTIR measurements. AFM images show uniformly CoFe2O4/RA particles distributed in the PI matrix. Raman spectra obtained for the composites reveal the characteristic Raman peaks of PI and CoFe2O4 nanoparticles. PMID:19504891

Jacintho, Guilherme V M; Kosaka, Priscila M; Petri, Denise F S; Suarez, Paulo A Z; Rubim, Joel C

2009-06-01

8

Tuning of magnetic properties of CoFe2O4 nanoparticles through charge transfer effect  

NASA Astrophysics Data System (ADS)

Herein, we report the microscopic origin of surfactant modified magnetic properties of nearly monodispersed CoFe2O4 nanoparticles (NPs). Surface modification is carried out with four surfactants having ?-acceptor/?-donor head group along with different chain-length. Upon functionalization, magnetic NPs show a maximum 65.61% increase in coercivity and 78.24% decrease in magnetization as compared to the bare one. Furthermore, ?-donor head group surfactant modified CoFe2O4 NPs show higher coercivity and magnetization with respect to ?-acceptor head group surfactant modified NPs and with the increase in chain-length of the surfactant, coercivity of NPs enhances slightly. These consequences are explained in context of crystal field splitting energy and steric hindrance offered by the surfactant.

Rakshit, Rupali; Mandal, Madhuri; Pal, Monalisa; Mandal, Kalyan

2014-03-01

9

Colossal reduction in Curie temperature due to finite-size effects in CoFe2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

In this talk I will show the tremendous size effect on the ordering transition temperature, TO, in samples of CoFe2O4 nanoparticles with diameters ranging from 1 to 9 nm. Samples were characterized by HRTEM and XRD analyses and show a bimodal particle size distribution centered at 3 nm and around 6 nm for ``small'' and ``large'' particles, respectively. The results and their interpretation are derived from studies of the magnetization dependence of the samples on temperature at low and high magnetic fields and relaxation times using both DC and AC fields. The large particles show a typical superparamagnetic behavior with blocking temperatures, TB, arround 100K and a Curie temperature, TC, above room temperature. The small particles, however, show a colossal reduction of their magnetic ordering temperature and display paramagnetic behavior down to about 10K. At lower temperatures these small particles are blocked and show both exchange and anisotropy field values above 5T. The order of magnitude reduction in TO demonstrates a heretofore unreported magnetic behavior for ultrasmall nanoparticles of CoFe2O4, suggesting its further study as an advanced material.

Tejada, Javier; Lopez-Dominguez, Victor; Hernandez, Joan Manel; Ziolo, Ronald F.

2013-03-01

10

Size selected synthesis of CoFe2O4 nanoparticles prepared in a chitosan matrix  

NASA Astrophysics Data System (ADS)

In this paper we report the synthesis and magnetic properties of CoFe2O4 nanoparticles. The nanoparticles with sizes ranging from 6 to 20 nm were prepared in a chitosan matrix. Size selection was achieved by introducing a nonionic surfactant Tween-X, where X={20, 60, 80, and 85}. Aqueous dispersions of Tween-X show micelles with increasing hydrodynamic sizes as X increases. Mössbauer spectroscopy measurements at 300 K show superparamagnetic behavior for the small particles, changing gradually to a blocked magnetic regime as the particle size increases. Magnetization measurements at 300 K show increasing values for the ratio Mr/MHmax and coercive fields (Hc).

Gurgel, A. L.; Soares, J. M.; Chaves, D. S.; Chaves, D. S.; Xavier, M. M.; Morales, M. A.; Baggio-Saitovitch, E. M.

2010-05-01

11

Size-dependent magnetic properties of CoFe2O4 nanoparticles prepared in polyol.  

PubMed

Highly crystalline CoFe(2)O(4) nanoparticles with different diameters ranging from 2.4 to 6.1 nm have been synthesized by forced hydrolysis in polyol. The size can be controlled through adjusting the nominal water/metal molar ratio. X-ray diffraction, transmission electron microscopy, x-ray absorption spectroscopy and (57)Fe Mössbauer spectrometry were employed to investigate the structure and the microstructure of the particles produced. Magnetic measurements performed on these particles show that they are superparamagnetic with a size-dependent blocking temperature. At 5 K, high saturation magnetization (~85 emu g(-1)) approaching that of the bulk was found for the larger particles, whereas a very large coercivity (14.5 kOe) is observed for the 3.5 nm sized particles. PMID:22119894

Artus, Mathieu; Tahar, Lotfi Ben; Herbst, Frédéric; Smiri, Leila; Villain, Françoise; Yaacoub, Nader; Grenèche, Jean-Marc; Ammar, Souad; Fiévet, Fernand

2011-12-21

12

CoFe2O4 magnetic nanoparticles as a peroxidase mimic mediated chemiluminescence for hydrogen peroxide and glucose.  

PubMed

This communication presents a new peroxidase mimic of CoFe(2)O(4) nanoparticles evaluated by the luminol-based chemiluminescent (CL) reaction. This offers a new method for evaluation and screening of the nanoparticles-based enzyme mimetics. PMID:21892508

Shi, Wenbing; Zhang, Xiaodan; He, Shaohui; Huang, Yuming

2011-10-14

13

Feasibility of TEOS coated CoFe2O4 nanoparticles to a GMR biosensor agent for single molecular detection.  

PubMed

Magnetic properties of 200 nm ferrimagnetic CoFe2O4 nanoparticles before and after coating with TEOS were explored and compared to soft ferrimagnetic MgFe2O4 nanoparticles (200 nm) to evaluate the feasibility as an in-vitro GMR SV (giant magnetoresistance spin-valve) biosensor agent for single molecular detection (SMD). It was found that the magnetic degradation (or variation) of TEOS coated CoFe2O4 and MgFe2O4 nanoparticles are dominantly affected by the chemical dispersion process, which is carried out in the oleic acid (OA), oleylamine (OL), or OA+OL surfactant, before starting major coating process. In addition, the TEOS coating thickness controlled by TEOS concentration and pH level in the buffer solution prominently influenced on the magnetic degradation of TEOS coated nanoparticles. According to the experimental analysis results, the magnetic degradation of TEOS coated nanoparticles is mainly attributed to the variation of particle dipole interaction caused by the degree of particle aggregation depending on TEOS coating process conditions. The TEOS coated CoFe2O4 nanoparticles exhibited a higher magnetic stability for a GMR biosensor agent, e.g., small variation of remnant magnetization, saturation magnetization and magnetic coercivity, than that of MgFe2O4 nanoparticles at the different coating process conditions. The physical and chemical analysis confirmed that this is primarily due to its higher magnetic anisotropy. The experimentally verified high biocompatibility as well as the stably maintained magnetic properties of TEOS coated CoFe2O4 nanoparticles demonstrate that CoFe2O4 nanoparticles can be considered as one of the promising ferrimagnetic nanoparticle sensor agent for an SMD GMR SV biosensor. PMID:21446410

Tang, Shao Qiang; Moon, Seung Je; Park, Ki Ho; Paek, Sun Ha; Chung, Kyung-Won; Bae, Seongtae

2011-01-01

14

A transmission electron microscopy study of CoFe2O4 ferrite nanoparticles in silica aerogel matrix using HREM and STEM imaging and EDX spectroscopy and EELS.  

PubMed

Magnetic nanocomposite materials consisting of 5 and 10 wt% CoFe2O4 nanoparticles in a silica aerogel matrix have been synthesized by the sol-gel method. For the CoFe2O4-10wt% sample, bright-field scanning transmission electron microscopy (BF STEM) and high-resolution transmission electron microscopy (HREM) images showed distinct, rounded CoFe2O4 nanoparticles, with typical diameters of roughly 8 nm. For the CoFe2O4-5wt% sample, BF STEM images and energy dispersive X-ray (EDX) measurements showed CoFe2O4 nanoparticles with diameters of roughly 3 +/- 1 nm. EDX measurements indicate that all nanoparticles consist of stoichiometric CoFe2O4, and electron energy-loss spectroscopy measurements from lines crossing nanoparticles in the CoFe2O4-10wt% sample show a uniform composition within nanoparticles, with a precision of at best than +/-0.5 nm in analysis position. BF STEM images obtained for the CoFe2O4-10wt% sample showed many "needle-like" nanostructures that typically have a length of 10 nm and a width of 1 nm, and frequently appear to be attached to nanoparticles. These needle-like nanostructures are observed to contain layers with interlayer spacing 0.33 +/- 0.1 nm, which could be consistent with Co silicate hydroxide, a known precursor phase in these nanocomposite materials. PMID:20199712

Falqui, Andrea; Corrias, Anna; Wang, Peng; Snoeck, Etienne; Mountjoy, Gavin

2010-04-01

15

Cationic distribution and spin canting in CoFe2O4 nanoparticles.  

PubMed

CoFe(2)O(4) nanoparticles (D(NPD) ~6 nm), prepared by a thermal decomposition technique, have been investigated through the combined use of dc magnetization measurements, neutron diffraction, and (57)Fe Mössbauer spectrometry under high applied magnetic field. Despite the small particle size, the value of saturation magnetization at 300 K (M(s) ?= 70 A m(2) kg(-1)) and at 5 K (M(s) ?= 100 A m(2) kg(-1)) are rather close to the bulk values, making the samples prepared with this method attractive for biomedical applications. Neutron diffraction measurements indicate the typical ferrimagnetic structure of the ferrites, showing an inversion degree (?(NPD) = 0.74) that is in very good agreement with cationic distribution established from low temperature (10 K) Mössbauer measurements in high magnetic field (?(moss) = 0.76). In addition, the in-field Mössbauer spectrum shows the presence of a non-collinear spin structure in both A and B sublattices. The results allow us to explain the high value of saturation magnetization and provide a better insight into the complex interplay between cationic distribution and magnetic disorder in ferrimagnetic nanoparticles. PMID:21983141

Peddis, D; Yaacoub, N; Ferretti, M; Martinelli, A; Piccaluga, G; Musinu, A; Cannas, C; Navarra, G; Greneche, J M; Fiorani, D

2011-10-26

16

Magnetic properties and magnetic relaxation in a suspension of CoFe2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

We present a study of dynamic magnetic properties of superparamagnetic CoFe2O4 nanoparticles of average size 5.9 nm suspended in an organic liquid. The relaxation times of the particle magnetic moments are found to be strongly dependent on the size of the particles, and also considerably dependent on interparticle interactions. Besides the lower frequency peak, an additional much faster relaxation is observed in the frequency dependence of the imaginary part of the ac magnetic susceptibility below the freezing point of the liquid. It is found that a large contribution to the magnetic relaxation of the lower frequency peak originates from the particles of dimensions 6.3-5.1 nm with interparticle interactions in the range 25-82 K, which correspond to nearer-neighbor particles. Much faster relaxation indicates that its significant part arises from the particles of dimensions 5.8-5.0 nm with interactions in the range 1-52 K which include also more distant neighbors.

Babi?-Stoji?, B.; Jokanovi?, V.; Milivojevi?, D.; Jagli?i?, Z.; Makovec, D.; Jovi?, N.; Marinovi?-Cincovi?, M.

2013-06-01

17

Surfactant-assisted route to fabricate CoFe2O4 individual nanoparticles and spherical assemblies.  

PubMed

A surfactant-assisted route in aqueous media has been shown to be suitable to prepare either individual primary CoFe(2)O(4) nanocrystals or secondary spherical nanoporous assemblies with a high surface area. The formation of primary nanoparticles or of spherical assemblies is found to be dependent on the presence of the surfactant and on the particle size, but is shown that the nanoparticle-surfactant interface plays a dominant role. The size of the primary CoFe(2)O(4) particles is controlled by the type of salt, the synthesis temperature and the concentration of the precursors. A detailed characterization evidences the shape and size of the primary particles, the way in which the primary particles assemble and their features in terms of morphological, textural and magnetic properties. PMID:20045115

Cannas, Carla; Ardu, Andrea; Peddis, Davide; Sangregorio, Claudio; Piccaluga, Giorgio; Musinu, Anna

2010-03-15

18

Synthesis and characterization of CoFe 2O 4 magnetic nanoparticles prepared by temperature-controlled coprecipitation method  

Microsoft Academic Search

Magnetic nanoparticles of cobalt ferrite (CoFe2O4) have been synthesized in a homogeneous aqueous solution without any template and subsequent heat treatment. The average particle size could be varied in the range of 2–14nm by controlling coprecipitation temperature of Co2+ and Fe3+ ions in alkaline solution although the size distribution is pretty wide. As the precipitation temperature increased in the range

Yeong Il Kim; Don Kim; Choong Sub Lee

2003-01-01

19

Influence of particle size and temperature on the dielectric properties of CoFe2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

The objective of this study was to establish the dielectric properties of CoFe2O4 nanoparticles with particle sizes that varied from 28.6 to 5.8 nm. CoFe2O4 nanoparticles were synthesized using a chemical coprecipitation method. The particle sizes were calculated according to the Scherrer formula using X-ray diffraction (XRD) peaks, and the particle size distribution curves were constructed by using field-emission scanning electron microscopy (FESEM) images. The dielectric permittivity and loss tangents of the samples were determined in the frequency range of 1 kHz to 1 MHz and in the temperature range of 300 to 10 K. Both the dielectric permittivity and the loss tangent were found to decrease with increasing frequency and decreasing temperature. For the smallest CoFe2O4 nanoparticle size, the dielectric permittivity and loss tangent exhibited their highest and lowest values, respectively. This behavior is very useful for materials used in devices that operate in the microwave or radio frequency ranges.

Rathore, Deepshikha; Kurchania, Rajnish; Pandey, R. K.

2014-04-01

20

Synthesis of patterned nanogold and mesoporous CoFe2O4 nanoparticle assemblies and their application in clinical immunoassays.  

PubMed

Herein, we describe a facile and feasible synthesis method for patterning nanogold particles onto magnetic mesoporous CoFe(2)O(4) nanostructures (Au-MMNs) by using poly(vinyl pyrrolidone) (PVP) as cross-linker. Initially, mesoporous CoFe(2)O(4) nanoparticles were initially synthesized with a thermal decomposition method by using mesoporous silica nanoparticles as templates, and then nanometre-sized gold particles were produced through the in situ reduction of the Au(III) on the PVP-functionalized CoFe(2)O(4). The as-prepared Au-MMNs were characterized by transmission electron microscopy (TEM), N(2) adsorption-desorption isotherms, UV-visible adsorption spectrometer, vibrating sample magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS). Furthermore, we also demonstrate the conjugation capacity of the synthesized Au-MMNs toward biomolecules by using quartz crystal microbalance (QCM), and the possible application in the electrochemical immunoassays. Experimental results indicated that the resulting Au-MMNs display good conjugation capability toward the biomolecules, and excellent analytical properties for determination of target molecules. PMID:21465042

Liu, Bingqian; Li, Qunfang; Zhang, Bing; Cui, Yuling; Chen, Huafeng; Chen, Guonan; Tang, Dianping

2011-05-01

21

Non-equilibrium cation distribution and enhanced spin disorder in hollow CoFe2O4 nanoparticles.  

PubMed

We present magnetic properties of hollow and solid CoFe(2)O(4) nanoparticles that were obtained by annealing of Co(33)Fe(67)/CoFe(2)O(4) (core/shell) nanoparticles. Hollow nanoparticles were polycrystalline whereas the solid nanoparticles were mostly single crystal. Electronic structure studies were performed by photoemission which revealed that particles with hollow morphology have a higher degree of inversion compared to solid nanoparticles and the bulk counterpart. Electronic structure and the magnetic measurements show that particles have uncompensated spins. Quantitative comparison of saturation magnetization (M(S )), assuming bulk Néel type spin structure with cationic distribution, calculated from quantitative XPS analysis, is presented. The thickness of uncompensated spins is calculated to be significantly large for particles with hollow morphology compared to solid nanoparticles. Both morphologies show a lack of saturation up to 7 T. Moreover magnetic irreversibility exists up to 7 T of cooling fields for the entire temperature range (10-300 K). These effects are due to the large bulk anisotropy constant of CoFe(2)O(4) which is the highest among the cubic spinel ferrites. The effect of the uncompensated spins for hollow nanoparticles was investigated by cooling the sample in large fields of up to 9 T. The magnitude of horizontal shift resulting from the unidirectional anisotropy was more than three times larger than that of solid nanoparticles. As an indication signature of uncompensated spin structure, 11% vertical shift for hollow nanoparticles is observed, whereas solid nanoparticles do not show a similar shift. Deconvolution of the hysteresis response recorded at 300 K reveals the presence of a significant paramagnetic component for particles with hollow morphology which further confirms enhanced spin disorder. PMID:22810351

Jaffari, G Hassnain; Ceylan, A; Bui, Holt P; Beebe, Thomas P; Ozcan, S; Shah, S Ismat

2012-08-22

22

Dependence of magnetic properties on crystallite size of CoFe2O4 nanoparticles synthesised by auto-combustion method  

Microsoft Academic Search

Cobalt ferrite (CoFe2O4) nanoparticles were prepared through an auto-combustion method. The results of XRD show that the crystallite size of CoFe2O4 nanoparticles increases from 57 to 105 nm with a slight change in lattice constant as the annealing temperature increases from 300 to 1200°C. The magnetic measurements by vibrating sample magnetometer (VSM) show that Ms increases monotonously by increasing the

Y. Liu; Y. Zhang; J. D. Feng; C. F. Li; J. Shi; R. Xiong

2009-01-01

23

Growth dominant co-precipitation process to achieve high coercivity at room temperature in CoFe2O4 nanoparticles  

Microsoft Academic Search

Applications of CoFe2O4 are limited due to the lack of synthesis technique to produce monodispersed, single domain and high coercivity (Hc) nanoparticles. Here, we describe the growth dominant co-precipitation process to achieve high Hc, with moderate magnetization at room temperature (RT) in CoFe2O4 nanoparticles. It is well known that the particle size is closely related to the relative interdependence between

C. N. Chinnasamy; B. Jeyadevan; O. Perales-Perez; K. Shinoda; K. Tohji; A. Kasuya

2002-01-01

24

Synthesis, structural, dielectric, magnetic and optical properties of Cr substituted CoFe2O4 nanoparticles by co-precipitation method  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles of chromium substituted cobalt ferrite (CoFe2?xCrxO4) were prepared by the co-precipitation method for different concentrations (x=0.0, 0.1, 0.2 and 0.3) of chromium (Cr) and were annealed at 600 °C for 3 h. Formation of single phase cubic spinel structure was confirmed by X-ray diffraction analysis and the average crystallite size was in the range of 15–23 nm. Studies on the energy dispersive spectroscopy confirm the presence of Cr in Cr substituted CoFe2O4 nanoparticles. Transmission electron microscopy observations revealed that CoFe2O4 and Cr substituted CoFe2O4 nanoparticles are uniformly distributed and not highly agglomerated. Dielectric properties such as dielectric constant (??) and dielectric loss (??) of prepared nanoparticles were investigated as a function of frequency and temperature. The dielectric study reveals that dielectric constant and dielectric loss are higher for Cr substituted CoFe2O4 than the corresponding value of pure CoFe2O4 nanoparticles. Studies on magnetic properties revealed that the saturation magnetization of samples decreases with increasing Cr concentration and lies in the range of 69.67–42.71 emu/g for the prepared samples. Strong red emission and weak blue and UV emissions are observed from the fluorescence spectral analysis of the prepared pure and Cr substituted CoFe2O4 nanoparticles.

Vadivel, M.; Ramesh Babu, R.; Sethuraman, K.; Ramamurthi, K.; Arivanandhan, M.

2014-08-01

25

Surface magnetic anisotropy of CoFe2O4 nanoparticles with a giant low-temperature hysteresis  

NASA Astrophysics Data System (ADS)

Ferrimagnetic nanoparticles of CoFe2O4 about 4-16 nm in diameter were synthesized by pyrolysis of a mixture of Fe and Co acetylacetonates. The field dependences of magnetization and hysteresis loops were investigated in magnetic fields up to 4000 kA/m at various temperatures from 4.2 to 500 K. A considerable contribution, positive or negative depending on the temperature, of ``surface'' anisotropy to the effective magnetic anisotropy of the nanoparticles was observed. A correlation was found between the magnetic properties that represent the specificity of small particles, namely, between ``surface'' anisotropy, magnetization, and high-field susceptibility.

Mozul', K. A.; Ol'khovik, L. P.; Sizova, Z. I.; Bludov, A. N.; Pashchenko, V. A.; Baumer, V. N.; Vashchenko, V. V.; Kolosov, M. O.; Kryshtal', A. P.; Prodanov, M. F.

2013-04-01

26

Unusually high coercivity and critical single-domain size of nearly monodispersed CoFe2O4 nanoparticles  

Microsoft Academic Search

Nearly monodispersed CoFe2O4 nanoparticles with average sizes between 8 and 100 nm were synthesized by using seed-mediated growth dominant coprecipitation and modified oxidation methods. X-ray diffraction and Mössbauer spectroscopy analyses confirmed the spinel phase and a stoichiometric composition of (Co0.25Fe0.75)[Co0.75Fe1.25]O4 for powders with different particle diameters. Rotational hysteresis loss (Wr) analysis showed an average switching field (Hp) of 17 kOe

C. N. Chinnasamy; B. Jeyadevan; K. Shinoda; K. Tohji; D. J. Djayaprawira; M. Takahashi; R. Justin Joseyphus; A. Narayanasamy

2003-01-01

27

A study of oleic acid-based hydrothermal preparation of CoFe 2 O 4 nanoparticles  

Microsoft Academic Search

Nearly monodisperse, well crystalline, superparamagnetic CoFe2O4 nanoparticles with diameter of 6 nm were synthesized in oleic acid–water–pentanol system at 180 °C. Hydrothermal procedure,\\u000a as an efficient and environment friendly alternative to organic decomposition methods, was investigated by variation of reaction\\u000a conditions, and the particle formation mechanism was finally proposed (i.e., hydrolysis of metal oleates in organic phase,\\u000a with size of the particles

Anton Repko; Daniel Niž?anský; Jana Poltierová-Vejpravová

28

Immobilization of glucose oxidase using CoFe 2O 4\\/SiO 2 nanoparticles as carrier  

Microsoft Academic Search

Aminated-CoFe2O4\\/SiO2 magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. Glucose oxidase (GOD) was immobilized on CoFe2O4\\/SiO2 NPs via cross-linking with glutaraldehyde (GA). The optimal immobilization condition was achieved with 1% (v\\/v) GA, cross-linking time of 3h, solution pH of 7.0 and 0.4mg GOD (in 3.0mg carrier). The immobilized GOD showed maximal catalytic activity at pH

Hai Wang; Jun Huang; Chao Wang; Dapeng Li; Liyun Ding; Yun Han

2011-01-01

29

Synthesis and characterization of CoFe2O4 ferrite nanoparticles obtained by an electrochemical method.  

PubMed

Uniform size cobalt ferrite nanoparticles have been synthesized in one step using an electrochemical technique. Synthesis parameters such as the current density, temperature and stirring were optimized to produce pure cobalt ferrite. The nanoparticles have been investigated by means of magnetic measurements, Mössbauer spectroscopy, x-ray powder diffraction and transmission electron microscopy. The average size of the electrosynthesized samples was controlled by the synthesis parameters and this showed a rather narrow size distribution. The x-ray analysis shows that the CoFe(2)O(4) obtained presents a totally inverse spinel structure. The magnetic properties of the stoichiometric nanoparticles show ferromagnetic behavior at room temperature with a coercivity up to 6386 Oe and a saturation magnetization of 85 emu g(-1). PMID:22894928

Mazarío, E; Herrasti, P; Morales, M P; Menéndez, N

2012-09-01

30

Adsorption of sulfur dioxide by CoFe2O4 spinel ferrite nanoparticles and corresponding changes in magnetism.  

PubMed

Adsorption of sulfur dioxide on 10 nm CoFe(2)O(4) spinel ferrite nanoparticles was examined. Adsorption loadings of sulfur dioxide at breakthrough conditions were determined to be approximately 0.62 mol/kg, which is significant given the 150 m(2)/g surface area of the nanoparticles. Adsorption proceeds through a chemisorption mechanism with sulfur dioxide forming a sulfate upon adsorption on the particle surface, which leads to a 23% decrease in the remnant magnetization, a 20% decrease in the saturation magnetization, and a 9% decrease in the coercivity of the magnetic nanoparticles. Adsorbent materials that provide a magnetic signal when adsorption occurs could have broad implications on adsorption-based separations. PMID:22400990

Glover, T Grant; Sabo, Daniel; Vaughan, Lisa A; Rossin, Joseph A; Zhang, Z John

2012-04-01

31

Synthesis and Magnetic Properties of Nearly Monodisperse CoFe2O4Nanoparticles Through a Simple Hydrothermal Condition  

PubMed Central

Nearly monodisperse cobalt ferrite (CoFe2O4) nanoparticles without any size-selection process have been prepared through an alluring method in an oleylamine/ethanol/water system. Well-defined nanospheres with an average size of 5.5 nm have been synthesized using metal chloride as the law materials and oleic amine as the capping agent, through a general liquid–solid-solution (LSS) process. Magnetic measurement indicates that the particles exhibit a very high coercivity at 10 K and perform superparamagnetism at room temperature which is further illuminated by ZFC/FC curves. These superparamagnetic cobalt ferrite nanomaterials are considered to have potential application in the fields of biomedicine. The synthesis method is possible to be a general approach for the preparation of other pure binary and ternary compounds.

2010-01-01

32

Synthesis and Magnetic Properties of Nearly Monodisperse CoFe2O4Nanoparticles Through a Simple Hydrothermal Condition.  

PubMed

Nearly monodisperse cobalt ferrite (CoFe2O4) nanoparticles without any size-selection process have been prepared through an alluring method in an oleylamine/ethanol/water system. Well-defined nanospheres with an average size of 5.5 nm have been synthesized using metal chloride as the law materials and oleic amine as the capping agent, through a general liquid-solid-solution (LSS) process. Magnetic measurement indicates that the particles exhibit a very high coercivity at 10 K and perform superparamagnetism at room temperature which is further illuminated by ZFC/FC curves. These superparamagnetic cobalt ferrite nanomaterials are considered to have potential application in the fields of biomedicine. The synthesis method is possible to be a general approach for the preparation of other pure binary and ternary compounds. PMID:20672131

Li, Xing-Hua; Xu, Cai-Ling; Han, Xiang-Hua; Qiao, Liang; Wang, Tao; Li, Fa-Shen

2010-01-01

33

Magnetic interactions in silica coated nanoporous assemblies of CoFe2O4 nanoparticles with cubic magnetic anisotropy.  

PubMed

Magnetic interactions in silica coated spherical nanoporous assemblies of CoFe(2)O(4) nanoparticles have been investigated by low temperature field dependent remanent magnetization (M(DCD) and M(IRM)) and magnetization relaxation measurements. The synthesis procedure leads to the formation of spherical aggregates of about 50-60 nm in diameter composed of hexagonal shaped nanocrystals with shared edges. The negative deviation from the non-interacting case in the Henkel plot indicates the predominance of dipole-dipole interactions favouring the demagnetized state, although the presence of exchange interactions in the porous system cannot be excluded. The activation volume, derived from time dependent magnetization measurements, turns out to be comparable with the particle physical volume, thus indicating, in agreement with static and dynamic irreversible magnetization measurements, that the magnetization reversal actually involves individual crystals. PMID:20622300

Laureti, S; Varvaro, G; Testa, A M; Fiorani, D; Agostinelli, E; Piccaluga, G; Musinu, A; Ardu, A; Peddis, D

2010-08-01

34

Controlling phase formation in solids: rational synthesis of phase separated Co@Fe2O3 heteroparticles and CoFe2O4 nanoparticles.  

PubMed

A wet chemical approach from organometallic reactants allowed the targeted synthesis of Co@Fe(2)O(3) heterodimer and CoFe(2)O(4) ferrite nanoparticles. They display magnetic properties that are useful for magnetic MRI detection. PMID:21748171

Nakhjavan, Bahar; Tahir, Muhammad Nawaz; Panthöfer, Martin; Gao, Haitao; Gasi, Teuta; Ksenofontov, Vadim; Branscheid, Robert; Weber, Stefan; Kolb, Ute; Schreiber, Laura Maria; Tremel, Wolfgang

2011-08-21

35

Immobilization of glucose oxidase using CoFe 2O 4/SiO 2 nanoparticles as carrier  

NASA Astrophysics Data System (ADS)

Aminated-CoFe 2O 4/SiO 2 magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. Glucose oxidase (GOD) was immobilized on CoFe 2O 4/SiO 2 NPs via cross-linking with glutaraldehyde (GA). The optimal immobilization condition was achieved with 1% (v/v) GA, cross-linking time of 3 h, solution pH of 7.0 and 0.4 mg GOD (in 3.0 mg carrier). The immobilized GOD showed maximal catalytic activity at pH 6.5 and 40 °C. After immobilization, the GOD exhibited improved thermal, storage and operation stability. The immobilized GOD still maintained 80% of its initial activity after the incubation at 50 °C for 25 min, whereas free enzyme had only 20% of initial activity after the same incubation. After kept at 4 °C for 28 days, the immobilized and free enzyme retained 87% and 40% of initial activity, respectively. The immobilized GOD maintained approximately 57% of initial activity after reused 7 times. The KM (Michaelis-Menten constant) values for immobilized GOD and free GOD were 14.6 mM and 27.1 mM, respectively.

Wang, Hai; Huang, Jun; Wang, Chao; Li, Dapeng; Ding, Liyun; Han, Yun

2011-04-01

36

Spectroscopic signature of the superparamagnetic transition and surface spin disorder in CoFe2O4 nanoparticles.  

PubMed

Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials. To investigate confinement in combination with strong magnetoelastic interactions, we measured the infrared vibrational properties of CoFe(2)O(4) nanoparticles and compared our results to trends in the coercivity over the same size range and to the response of the bulk material. Remarkably, the spectroscopic response is sensitive to the size-induced crossover to the superparamagnetic state, which occurs between 7 and 10 nm. A spin-phonon coupling analysis supports the core-shell model. Moreover, it provides an estimate of the magnetically disordered shell thickness, which increases from 0.4 nm in the 14 nm particles to 0.8 nm in the 5 nm particles, demonstrating that the associated local lattice distortions take place on the length scale of the unit cell. These findings are important for understanding finite length scale effects in this and other magnetic oxides where magnetoelastic interactions are important. PMID:22540958

Sun, Qi-C; Birkel, Christina S; Cao, Jinbo; Tremel, Wolfgang; Musfeldt, Janice L

2012-06-26

37

Phase evaluation of Li+ substituted CoFe2O4 nanoparticles, their characterizations and magnetic properties  

NASA Astrophysics Data System (ADS)

Li+ substituted CoFe2O4 with the chemical formula Li3xCoFe2-xO4 were synthesized by sol-gel auto combustion method. The synthesized samples were annealed at 600 °C for 4 h. X-ray diffraction data were used to evaluate the structure of the prepared samples. Spinel ferrite phase of CoFe2O4 changes to ordered like lithium ferrite phase with increase in Li+ substitution. Lattice constant increases whereas particle size found to decrease with Li+ substitution. Infrared spectroscopy also confirmed the phase transition of CoFe2O4 after the incorporation of lithium ions. Substitution of Li+ ions for Fe3+ caused a decrease in the saturation magnetization from 69.59 emu/g to 47.71 emu/g and the coercivity increased from 647 Oe to 802 Oe. Resistivity and dielectric properties shows inverse relation to each other.

Kadam, R. H.; Alone, Suresh T.; Mane, Maheshkumar L.; Biradar, A. R.; Shirsath, Sagar E.

2014-04-01

38

Synthesis of magnetic spinel ferrite CoFe2O4 nanoparticles from ferric salt and characterization of the size-dependent superparamagnetic properties  

Microsoft Academic Search

The CoFe 2 O 4 nanoparticles have been synthesized by using a stable ferric salt of FeCl 3 with a micellar microemulsion method. The normal micelles are formed by sodium dodecyl sulfate (NaDS) in aqueous solutions. The mean size of the nanoparticles can be controlled from less than 4 nm to about 10 nm through controlling the concentrations of the

Chao Liu; Adam J. Rondinone; Z. John

2000-01-01

39

CoFe2O4 nanoparticles as oxidase mimic-mediated chemiluminescence of aqueous luminol for sulfite in white wines.  

PubMed

Recently, the intrinsic enzyme-like activity of nanoparticles (NPs) has become a growing area of interest. However, the analytical applications of the NP-based enzyme mimetic are mainly concentrated on their peroxidase-like activity; no attempts have been made to investigate the analytical applications based on the oxidase mimic activities of NPs. For the first time, we report that CoFe(2)O(4) NPs were found to possess intrinsic oxidase-like activity and could catalyze luminol oxidation by dissolved oxygen to produce intensified chemiluminescence (CL). The effect of sulfite on CoFe(2)O(4) NP oxidase mimic-mediated CL of aqueous luminol was investigated. It is very interesting that when adding sulfite to the luminol-CoFe(2)O(4) system, the role of sulfite in the luminol-CoFe(2)O(4) NP-sulfite system depends on its concentration. At a relatively low concentration level, sulfite presents an inhibition effect on the luminol-CoFe(2)O(4) NP system. However, it does have an enhancement effect at a higher concentration level. Investigations on the effect of the solution pH and luminol and CoFe(2)O(4) NP concentrations on the kinetic characteristics of the studied CL system in the presence of trace sulfite suggested that the enhancement and inhibition of the luminol-CoFe(2)O(4) NP-sulfite CL system also depended on the solution pH. It seems that the concentrations of luminol and CoFe(2)O(4) NPs did not influence the CL pathway. The possible mechanism of the luminol-CoFe(2)O(4) NP-sulfite CL system was also discussed. On this basis, a flow injection chemiluminescence method was established for the determination of trace sulfite in this study. Under the optimal conditions, the proposed system could respond down to 2.0 × 10(-8) M sulfite. The method has been applied to the determination of trace sulfite in white wine samples with satisfactory results. The results given by the proposed method are in good agreement with those given by the standard titration method. PMID:23289402

Zhang, Xiaodan; He, Shaohui; Chen, Zhaohui; Huang, Yuming

2013-01-30

40

The effect of annealing on phase evolution, microstructure and magnetic properties of Mn substituted CoFe2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

Manganese substituted CoFe2O4 nanoparticles has been prepared by a simple evaporation method and auto combustion method. The role of annealing temperature on phase, particle size and morphology of Mn-Co ferrite nanoparticles were determined by X-ray diffraction, and transmission electron microscopy (TEM). The lowest size of particles (~3 nm) is obtained by auto combustion method. The annealing effect creates a vital change in magnetic properties which is studied by using vibrating sample magnetometer (VSM). These spinel ferrites are decomposed to ?-Fe2O3 after annealing above 550 °C in air. However, ?-Fe2O3 phase was slowly vanished after ferrites annealing above 900 °C. The effect of this secondary phase on the structural and magnetic properties of Mn substituted cobalt ferrite nanoparticles is also discussed.

Ranjith Kumar, E.; Jayaprakash, R.; Prakash, T.

2014-05-01

41

Comparison of the magnetic, radiolabeling, hyperthermic and biodistribution properties of hybrid nanoparticles bearing CoFe2O4 and Fe3O4 metal cores  

NASA Astrophysics Data System (ADS)

Metal oxide nanoparticles, hybridized with various polymeric chemicals, represent a novel and breakthrough application in drug delivery, hyperthermia treatment and imaging techniques. Radiolabeling of these nanoformulations can result in new and attractive dual-imaging agents as well as provide accurate in vivo information on their biodistribution profile. In this paper a comparison study has been made between two of the most promising hybrid core-shell nanosystems, bearing either magnetite (Fe3O4) or cobalt ferrite (CoFe2O4) cores, regarding their magnetic, radiolabeling, hyperthermic and biodistribution properties. While hyperthermic properties were found to be affected by the metal-core type, the radiolabeling ability and the in vivo fate of the nanoformulations seem to depend critically on the size and the shell composition.

Psimadas, D.; Baldi, G.; Ravagli, C.; Comes Franchini, M.; Locatelli, E.; Innocenti, C.; Sangregorio, C.; Loudos, G.

2014-01-01

42

Engineered spin-valve type magnetoresistance in Fe3O4-CoFe2O4 core-shell nanoparticles  

NASA Astrophysics Data System (ADS)

Naturally occurring spin-valve-type magnetoresistance (SVMR), recently observed in Sr2FeMoO6 samples, suggests the possibility of decoupling the maximal resistance from the coercivity of the sample. Here we present the evidence that SVMR can be engineered in specifically designed and fabricated core-shell nanoparticle systems, realized here in terms of soft magnetic Fe3O4 as the core and hard magnetic insulator CoFe2O4 as the shell materials. We show that this provides a magnetically switchable tunnel barrier that controls the magnetoresistance of the system, instead of the magnetic properties of the magnetic grain material, Fe3O4, and thus establishing the feasibility of engineered SVMR structures.

Anil Kumar, P.; Ray, Sugata; Chakraverty, S.; Sarma, D. D.

2013-09-01

43

Comparison of the magnetic, radiolabeling, hyperthermic and biodistribution properties of hybrid nanoparticles bearing CoFe2O4 and Fe3O4 metal cores.  

PubMed

Metal oxide nanoparticles, hybridized with various polymeric chemicals, represent a novel and breakthrough application in drug delivery, hyperthermia treatment and imaging techniques. Radiolabeling of these nanoformulations can result in new and attractive dual-imaging agents as well as provide accurate in vivo information on their biodistribution profile. In this paper a comparison study has been made between two of the most promising hybrid core-shell nanosystems, bearing either magnetite (Fe3O4) or cobalt ferrite (CoFe2O4) cores, regarding their magnetic, radiolabeling, hyperthermic and biodistribution properties. While hyperthermic properties were found to be affected by the metal-core type, the radiolabeling ability and the in vivo fate of the nanoformulations seem to depend critically on the size and the shell composition. PMID:24334365

Psimadas, D; Baldi, G; Ravagli, C; Comes Franchini, M; Locatelli, E; Innocenti, C; Sangregorio, C; Loudos, G

2014-01-17

44

Size-regulated group separation of CoFe2O4 nanoparticles using centrifuge and their magnetic resonance contrast properties.  

PubMed

Magnetic nanoparticle (MNP)-based magnetic resonance imaging (MRI) contrast agents (CAs) have been the subject of extensive research over recent decades. The particle size of MNPs varies widely and is known to influence their physicochemical and pharmacokinetic properties. There are two commonly used methods for synthesizing MNPs, organometallic and aqueous solution coprecipitation. The former has the advantage of being able to control the particle size more effectively; however, the resulting particles require a hydrophilic coating in order to be rendered water soluble. The MNPs produced using the latter method are intrinsically water soluble, but they have a relatively wide particle size distribution. Size-controlled water-soluble MNPs have great potential as MRI CAs and in cell sorting and labeling applications. In the present study, we synthesized CoFe2O4 MNPs using an aqueous solution coprecipitation method. The MNPs were subsequently separated into four groups depending on size, by the use of centrifugation at different speeds. The crystal shapes and size distributions of the particles in the four groups were measured and confirmed by transmission electron microscopy and dynamic light scattering. Using X-ray diffraction analysis, the MNPs were found to have an inverse spinel structure. Four MNP groups with well-selected semi-Gaussian-like diameter distributions were obtained, with measured T2 relaxivities (r2) at 4.7 T and room temperature in the range of 60 to 300 mM-1s-1, depending on the particle size. This size regulation method has great promise for applications that require homogeneous-sized MNPs made by an aqueous solution coprecipitation method. Any group of the CoFe2O4 MNPs could be used as initial base cores of MRI T2 CAs, with almost unique T2 relaxivity owing to size regulation. The methodology reported here opens up many possibilities for biosensing applications and disease diagnosis. PACS: 75.75.Fk, 78.67.Bf, 61.46.Df. PMID:24004536

Kang, Jongeun; Lee, Hyunseung; Kim, Young-Nam; Yeom, Areum; Jeong, Heejeong; Lim, Yong Taik; Hong, Kwan Soo

2013-01-01

45

Synthesis and magnetic properties of cobalt ferrite (CoFe 2O 4) nanoparticles prepared by wet chemical route  

Microsoft Academic Search

Magnetic nanoparticles of cobalt ferrite have been synthesized by wet chemical method using stable ferric and cobalt salts with oleic acid as the surfactant. X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) confirmed the formation of single-phase cobalt ferrite nanoparticles in the range 15–48nm depending on the annealing temperature and time. The size of the particles increases with annealing temperature

K. Maaz; Arif Mumtaz; S. K. Hasanain; Abdullah Ceylan

2007-01-01

46

Synthesis and magnetic properties of CoFe2O4 spinel ferrite nanoparticles doped with lanthanide ions  

Microsoft Academic Search

Lanthanide ions have been doped into cobalt spinel ferrites using an oil-in-water micellar method to form CoLn0.12Fe1.88O4 nanoparticles with Ln=Ce, Sm, Eu, Gd, Dy, or Er. Doping with lanthanide ions (LnIII) modulates the magnetic properties of cobalt spinel ferrite nanoparticles. In particular cases of Gd3+ or Dy3+ ions, a dramatic increase in the blocking temperature and coercivity is observed. Indeed,

Myrtil L. Kahn; Z. John Zhang

2001-01-01

47

Synthesis and magnetic properties of CoFe2O4 spinel ferrite nanoparticles doped with lanthanide ions  

NASA Astrophysics Data System (ADS)

Lanthanide ions have been doped into cobalt spinel ferrites using an oil-in-water micellar method to form CoLn0.12Fe1.88O4 nanoparticles with Ln=Ce, Sm, Eu, Gd, Dy, or Er. Doping with lanthanide ions (LnIII) modulates the magnetic properties of cobalt spinel ferrite nanoparticles. In particular cases of Gd3+ or Dy3+ ions, a dramatic increase in the blocking temperature and coercivity is observed. Indeed, the introduction of only 4% of Gd3+ ions increases the blocking temperature ~100 K and the coercivity 60%. Initial studies on the magnetic properties of these doped nanoparticles clearly demonstrate that the relationship between the modulation of magnetic properties and the nature of doped LnIII ions is interesting but very complex.

Kahn, Myrtil L.; Zhang, Z. John

2001-06-01

48

The effective peroxidase-like activity of chitosan-functionalized CoFe2O4 nanoparticles for chemiluminescence sensing of hydrogen peroxide and glucose.  

PubMed

Here, we report a highly simple and general protocol for functionalization of the CoFe(2)O(4) NPs with chitosan polymers in order to make CoFe(2)O(4) NPs disperse and stable in solution. The functionalized CoFe(2)O(4) NPs (denoted as CF-CoFe(2)O(4) NPs) were characterized by scanning electron microscope (SEM), thermogravimetric (TG), X-ray diffraction (XRD) and FT-IR spectra. It was found that the CoFe(2)O(4) NPs were successfully decorated and uniformly dispersed on the surface of chitosan without agglomeration. The CF-CoFe(2)O(4) NPs were found to increase greatly the radiation emitted during the CL oxidation of luminol by hydrogen peroxide. Results of ESR spin-trapping experiments demonstrated that the CF-CoFe(2)O(4) NPs showed catalytic ability to H(2)O(2) decomposition into ?OH radicals. On this basis, a highly sensitive and rapid chemiluminescent method was developed for hydrogen peroxide in water samples and glucose in blood samples. Under optimum conditions, the proposed method allowed the detection of H(2)O(2) in the range of 1.0 × 10(-9) to 4.0 × 10(-6) M and glucose in the range of 5.0 × 10(-8) to 1.0 × 10(-5) M with detectable H(2)O(2) as low as 500 pM and glucose as low as 10 nM, respectively. This proposed method has been successfully applied to detect H(2)O(2) in environmental water samples and glucose in serum samples with good accuracy and precision. PMID:22258160

Fan, Yingwei; Huang, Yuming

2012-03-01

49

CoFe2O4 magnetic nanoparticles as a highly active heterogeneous catalyst of oxone for the degradation of diclofenac in water.  

PubMed

A magnetic nanoscaled catalyst cobalt ferrite (CoFe2O4) was successfully prepared and used for the activation of oxone to generate sulfate radicals for the degradation of diclofenac. The catalyst was characterized by transmission electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The effects of calcination temperature, initial pH, catalyst and oxone dosage on the degradation efficiency were investigated. Results demonstrated that CoFe2O4-300 exhibited the best catalytic performance and almost complete removal of diclofenac was obtained in 15 min. The degradation efficiency increased with initial pH decreasing in the pH range of 5-9. The increase of catalyst and oxone dosage both had the positive effect on the degradation of diclofenac. Moreover, CoFe2O4 could retain high degradation efficiency even after being reused for five cycles. Finally, the major diclofenac degradation intermediates were identified and the primary degradation pathways were proposed. PMID:24140535

Deng, Jing; Shao, Yisheng; Gao, Naiyun; Tan, Chaoqun; Zhou, Shiqing; Hu, Xuhao

2013-11-15

50

Unique magnetic properties and magnetization reversal process of CoFe2O4 nanotubes fabricated by electrospinning.  

PubMed

CoFe(2)O(4) nanotubes have been directly fabricated by single-capillary spinneret electrospinning. The external diameter of the CoFe(2)O(4) nanotubes ranges from 60 nm to 160 nm. The morphology and structure characterizations show that individual CoFe(2)O(4) nanotubes are made of CoFe(2)O(4) nanocrystals stacking along the nanotubes with no preferred growth directions and these individual nanocrystals are single crystal with a cubic spinel structure. Each nanocrystal was shown to be a single magnetic domain. The magnetic measurements show that the coercivity (H(c)) of the CoFe(2)O(4) nanotubes decreases from 10?400 Oe at 5 K to 300 Oe at 360 K. The CoFe(2)O(4) nanotubes have a spin reorientation (SR) at 5 K, which is different from CoFe(2)O(4) nanorods and nanoparticles. Based on the observed morphology and crystal structure, a micromagnetic model, "chain-of-rings", is developed to interpret the magnetic behavior of the CoFe(2)O(4) nanotubes. The theoretical coercivity (534 Oe) is in good agreement with the experimental results (509 Oe). It is believed that our work should open a new route to prepare various magnetic ferrite nanotubes and is significant for expanding the application of CoFe(2)O(4) into the new fields. PMID:22622489

Fu, Jiecai; Zhang, Junli; Peng, Yong; Zhao, Jianguo; Tan, Guoguo; Mellors, Nigel J; Xie, Erqing; Han, Weihua

2012-07-01

51

Exchange coupling behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite  

NASA Astrophysics Data System (ADS)

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 3.0 kOe at room temperature and 50 K. The mean diameter of CoFe2O4 particles is about 16 nm. 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 100 nm. The magnetization of the nanocomposite showed a hysteresis loop that is characteristic of exchange coupled systems. A maximum energy product (BH)max of 1.22 MGOe 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.

Leite, G. C. P.; Chagas, E. F.; Pereira, R.; Prado, R. J.; Terezo, A. J.; Alzamora, M.; Baggio-Saitovitch, E.

2012-09-01

52

Controlled synthesis of monodisperse CoFe2O4 nanoparticles by the phase transfer method and their catalytic activity on methylene blue discoloration with H2O2  

NASA Astrophysics Data System (ADS)

Monodisperse spinel CoFe2O4 nanoparticles have been synthesized through the solvothermal-assisted phase transfer method using aqueous soluble metal salts as starting materials and sodium oleate (SO) as the phase-transfer agent. The as-synthesized nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, infrared spectroscopy, vibrating sample magnetometry, ultraviolet and visible spectrophotometry and Mössbauer spectrum. The results revealed that the as-obtained nanoparticles have a cubic spinel structure and an average diameter of 2-6 nm. It was found that SO played an important role during the transfer of the hydrophilic inorganic precursor from aqueous phase to the organic phase. On the basis of the experimental results, a possible mechanism for the formation of the nanoparticles was proposed. Surface functionalization of the as-prepared nanoparticles was conducted to render the hydrophobic nanoparticles water-soluble, which makes the nanoparticles suitable for catalytic applications. The nanoparticles showed catalytic activity in the oxidation of methylene blue with H2O2 as an oxidizing agent.

Feng, X.; Mao, G. Y.; Bu, F. X.; Cheng, X. L.; Jiang, D. M.; Jiang, J. S.

2013-10-01

53

Magnetic CoFe2O4/carbon nanotubes composites: fabrication, microstructure and magnetic response  

NASA Astrophysics Data System (ADS)

By combining the unique microstructure of carbon nanotubes (CNTs) with the good magnetism of CoFe2O4 ferrites, CoFe2O4/CNTs nanocomposites were prepared by the solvothermal method for the application of targeting therapy and tumor hyperthermia. X-ray diffraction (XRD), thermal gravity analysis (TGA), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) were introduced to study the influence of the solvothermal temperature, time and the CNTs content on the microstructure and magnetic properties of CoFe2O4/CNTs nanocomposites. The diameter of CoFe2O4 nanoparticles coating on the surface of CNTs and the saturation magnetization (Ms) increased with the solvothermal temperature. CoFe2O4/CNTs nanocomposites prepared at 180°C, 200°C and 220°C exhibited superparamagnetism at room temperature, while the samples prepared at 240°C and 260°C presented ferromagnetism. And the solvothermal time and CNTs content slightly affected the microstructure and magnetic properties, Ms and coercivity (Hc) increased slightly with the increasing solvothermal time and the decreasing CNTs content.

Wang, Panfeng; Xu, Jingcai; Han, Yanbing; Hong, Bo; Jin, Hongxiao; Jin, Dingfeng; Peng, Xiaoling; Li, Jing; Ge, Hongliang; Wang, Xinqing

2014-05-01

54

Low-Temperature Preparation of Superparamagnetic CoFe2O4 Microspheres with High Saturation Magnetization  

Microsoft Academic Search

Based on a low-temperature route, monodispersed CoFe2O4 microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction\\/photoelectron spectroscopy, scanning\\/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe2O4 MSs with narrow size distribution can be tuned from over 200 to ~330 nm.

Hong Lei Yuan; Yong Qiang Wang; Shao Min Zhou; Li Sheng Liu; Xi Liang Chen; Shi Yun Lou; Rui Jian Yuan; Yao Ming Hao; Ning Li

2010-01-01

55

Magnetic structure of CoFe2O4  

Microsoft Academic Search

Up to now, the cubic spinel CoFe2O4 was assumed to have a collinear ferrimagnetic structure; however a High Field Mössbauer Study (HFMS) recently evidenced for canting angles at both A and B iron sites. In order to have a coherent view on the CoFe2O4 magnetic structure, we performed high field magnetic measurements and neutron diffraction experiments on the same powdered

J. Teillet; F. Bouree; R. Krishnan

1993-01-01

56

Hollow glass microspheres coated with CoFe 2O 4 and its microwave absorption property  

NASA Astrophysics Data System (ADS)

Spinel CoFe 2O 4 coating on the surface of hollow glass microspheres of low density was synthesized by co-precipitation method. The phase structures, morphologies, particle size, shell thickness, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDS). The results show that CoFe 2O 4 coating on hollow glass microspheres can be achieved, and the coating layers are constituted by CoFe 2O 4 nanoparticles of mean size ca. 10 nm. The as-synthesized powder materials were uniformly dispersed into the phenolic cement, then the mixture was pasted on metal plate with the area of 200 mm×200 mm as the test plate. The test of microwave absorption was carried out by the radar-absorbing materials (RAM) reflectivity far field radar cross-section (RCS) method. The results indicate that the coated CoFe 2O 4/hollow glass microspheres composites can be applied in lightweight and strong absorption microwave absorbers.

Fu, Wuyou; Liu, Shikai; Fan, Wenhua; Yang, Haibin; Pang, Xiaofen; Xu, Jing; Zou, Guangtian

2007-09-01

57

Magnetic Properties of CoFe2O4 Nanopillars  

NASA Astrophysics Data System (ADS)

Ferrimagnetic CoFe2O4 spontaneously forms nanopillars embedded in a BaTiO3 or BiFeO3 matrix during thin film growth by pulsed laser deposition. Such thin film nanostructures show three dimensional heteroepitaxy. All the films have a large uniaxial magnetic anisotropy with an easy axis normal to the film plane. It is calculated that stress anisotropy is the main contribution to the anisotropy field. We studied the magnetic behavior of the CoFe2O4 nanopillars formed at different growth temperatures, with different film thickness and on various substrates.

Zheng, Haimei; Zavaliche, F.; Schlom, D.

2005-03-01

58

A facile thermal decomposition route to synthesise CoFe2O4 nanostructures  

NASA Astrophysics Data System (ADS)

The synthesis of CoFe2O4 nanoparticles has been achieved by a simple thermal decomposition method from an inorganic precursor, cobalt ferrous cinnamate hydrazinate (CoFe2(cin)3(N2H4)3) which was obtained by a novel precipitation method from the corresponding metal salts, cinnamic acid and hydrazine hydrate. The precursor was characterized by hydrazine and metal analyses, infrared spectral analysis and thermo gravimetric analysis. Under appropriate annealing, CoFe2(cin)3(N2H4)3 yielded CoFe2O4 nanoparticles, which were characterized for their size and structure using X-Ray diffraction (XRD), high resolution transmission electron microscopic (HRTEM), selected area electron diffraction (SAED) and scanning electron microscopic (SEM) techniques.

Kalpanadevi, K.; Sinduja, C. R.; Manimekalai, R.

2014-01-01

59

CoFe2O4 nanostructures with high coercivity  

NASA Astrophysics Data System (ADS)

Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite (CoFe2O4). We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600 °C for 2 h in Ar gas forming arrays of cobalt ferrite nanowires inside the AAT. The morphology of the ferrite before and after annealing was observed using a field-emission scanning electron microscope. The crystallographic structure of the nanowires was analyzed using x-ray diffraction and transmission electron microscopy. The magnetization was measured by a superconducting quantum interference device. The coercivity of the annealed ferrite in the form of nanowires is significantly larger than that of the separate ferrite nanoparticles in the pores. This effect is due to the clustering of nanoparticles when the organic solvent is removed by high-temperature annealing as well as an improvement in the crystallininty of the ferrite by reduction of defects. The Faraday spectra of the nanowires were measured before and after annealing. A significant peak was observed at 725 nm. The nanowire/AAT composite material had a Verdet constant of 0.1 min/(Oe cm) at the peak. It is important to mention that not only the properties but also the form of the material-a regular array of pillars-may be important for microelectronic or information storage applications.

Jung, J.-S.; Lim, J.-H.; Choi, K.-H.; Oh, S.-L.; Kim, Y.-R.; Lee, S.-H.; Smith, D. A.; Stokes, K. L.; Malkinski, L.; O'Connor, C. J.

2005-05-01

60

Particles size effects of single domain CoFe 2O 4 on suspensions stability  

NASA Astrophysics Data System (ADS)

Single domain magnetic CoFe 2O 4 nanoparticles with spinel structure were prepared by the coprecipitation method. Particles with size of 16, 20, 40 and 60 nm were synthesized by sintering the precursor at 500, 600, 800 and 900 °C, respectively. The magnetic hysteresis measurement of CoFe 2O 4 particles showed that particles were single domain particles with similar saturation magnetization (˜300 emu/cm 3) at room temperature. The zeta potential study of suspensions (CoFe 2O 4-acetylacetone system) with various particle sizes showed the suspension systems had similar zeta potential values (˜40 mV). The effects of magnetic particle size on the suspension stability characterized by electrophoretic deposition yields and sediment volumes were studied. The suspension stability decreased with an increase in particle size and a flocculation threshold of particle radius a was found at 30 nm. A suspension stability theory approaching to the phenomenon was established. The theory based on the DLVO theory was developed by introducing an extra magnetic interaction force. Dormann model was adopted, in which the magnetic interactions of two spherical nanoparticles were investigated in terms of dipole-dipole interactions. Compared to DLVO, suspension's physical parameters not only zeta potential ? and the Debye length 1/ ?, but also particles' radius a brought about stable to flocculation transition in the theory.

Jian, Gang; Fu, Qiuyun; Zhou, Dongxiang

2012-03-01

61

Low-Temperature Preparation of Superparamagnetic CoFe2O4 Microspheres with High Saturation Magnetization  

PubMed Central

Based on a low-temperature route, monodispersed CoFe2O4 microspheres (MSs) were fabricated through aggregation of primary nanoparticles. The microstructural and magnetic characteristics of the as-prepared MSs were characterized by X-ray diffraction/photoelectron spectroscopy, scanning/transmitting electron microscopy, and vibrating sample magnetometer. The results indicate that the diameters of CoFe2O4 MSs with narrow size distribution can be tuned from over 200 to ~330 nm. Magnetic measurements reveal these MSs exhibit superparamagnetic behavior at room temperature with high saturation magnetization. Furthermore, the mechanism of formation of the monodispersed CoFe2O4 MSs was discussed on the basis of time-dependent experiments, in which hydrophilic PVP plays a crucial role.

2010-01-01

62

High frequency study of core-shell reusable CoFe2O4-ZnO nanospheres  

NASA Astrophysics Data System (ADS)

Recently, coated nanoshells combined with magnetic nanoparticles and cancer-cell-specific antibodies have been used to develop a multifunctional platform for simultaneously diagnosing and treating cancer, via magnetic resonance imaging and photothermal therapy. For this application, core-shell nano-spheres with a low resonance frequency (low GHz range) in a strong applied field are required. In this aspect, ferromagnetic resonance experiment is an important tool for determining the dynamic properties of nano-materials. Magnetic field dependence of resonance frequency (fr) and linewidths (?ƒ and ?H) for both the ZnO coated and uncoated CoFe2O4 hollow spheres are studied using a vector network analyzer. As compared to uncoated CoFe2O4 hollow sphere, ZnO coated CoFe2O4 showed reduced resonance frequency, larger ?ƒ and ?H, reduced gyromagnetic ratio and effective fields. The experimental results are confirmed with the effective medium theory.

Kuanr, Bijoy K.; Veerakumar, V.; Mishra, S. R.; Wilson, Armstrong M.; Kuanr, Alka V.; Camley, R. E.; Celinski, Z.

2014-05-01

63

CoFe2O4-TiO2 and CoFe2O4-ZnO thin film nanostructures elaborated from colloidal chemistry and atomic layer deposition.  

PubMed

CoFe(2)O(4)-TiO(2) and CoFe(2)O(4)-ZnO nanoparticles/film composites were prepared from directed assembly of colloidal CoFe(2)O(4) in a Langmuir-Blodgett monolayer and atomic layer deposition (ALD) of an oxide (TiO(2) or ZnO). The combination of these two methods permits the use of well-defined nanoparticles from colloidal chemistry, their assembly on a large scale, and the control over the interface between a ferrimagnetic material (CoFe(2)O(4)) and a semiconductor (TiO(2) or ZnO). Using this approach, architectures can be assembled with a precise control from the Angstrom scale (ALD) to the micrometer scale (Langmuir-Blodgett film). The resulting heterostructures present well-calibrated thicknesses. Electron microscopy and magnetic measurement studies give evidence that the size of the nanoparticles and their intrinsic magnetic properties are not altered by the various steps involved in the synthesis process. Therefore, the approach is suitable to obtain a layered composite with a quasi-monodisperse layer of ferrimagnetic nanoparticles embedded in an ultrathin film of semiconducting material. PMID:21067161

Clavel, Guylhaine; Marichy, Catherine; Willinger, Marc-Georg; Ravaine, Serge; Zitoun, David; Pinna, Nicola

2010-12-01

64

Magnetic Properties of CoFe2O4 Nanopillars  

Microsoft Academic Search

Ferrimagnetic CoFe2O4 spontaneously forms nanopillars embedded in a BaTiO3 or BiFeO3 matrix during thin film growth by pulsed laser deposition. Such thin film nanostructures show three dimensional heteroepitaxy. All the films have a large uniaxial magnetic anisotropy with an easy axis normal to the film plane. It is calculated that stress anisotropy is the main contribution to the anisotropy field.

Haimei Zheng; F. Zavaliche; D. Schlom

2005-01-01

65

Controlling role of pH and temperature on CoFe2O4 nanostructures produced by hydrothermal synthesis.  

PubMed

The hydrothermal synthesis (HS) of CoFe2O4 nanoparticles (NPs) has been investigated as a function of reaction temperature and pH, using complementary characterisation techniques of transmission electron microscopy and X-ray diffractometry. The HS of CoFe2O4 NPs (< 25 nm) at pH - 8 proceeded through the formation and dissolution of intermediate Fe(OH)3 and [FeCo3(OH)8]+ x [Cl- x H2O]- phases with increasing reaction temperature. In contrast, HS of CoFe2O4 NPs (< 50 nm) at pH - 12 resulted in the formation of additional intermediate Co(OH)2, CoOOH and alpha-FeOOH phases, with residual alpha-Fe2O3 present in the final reaction product. This research demonstrates the size and phase purity of the CoFe2O4 NPs may be controlled through the formation and dissolution of the intermediate phases at various pH values in the alkaline pH regime. PMID:23421290

Almeida, Trevor P; Fay, Mike; Zhu, Yanqiu; Brown, Paul D

2012-11-01

66

Synthesis and characterization of superparamagnetic CoFe2O4/MWCNT hybrids for tumor-targeted therapy.  

PubMed

Owing to their great potentialities of carbon nanotubes (CNTs)-based magnetic nano-composites, numerous applications of them have been found in nanotechnology, integrated functional system, and in medicine. Herein, nearly monodisperse CoFe2O4 nanoparticles have been deposited on multi-walled carbon nanotubes (MWCNTs) by high-temperature hydrolysis and inorganic polymerization of ionic Co(II) and Fe(III) salts and MWCNTs in a polyol solution. X-ray diffraction, energy-dispersive X-ray spectrometry and transmission electron microscopy were used to characterize the final products. The average size of CoFe2O4 nanoparticles and their coverage density on MWCNTs can be adjusted to some extent by altering the reaction parameters. A proposed formation mechanism of the magnetic hybrids is presented. Magnetic measurements showed that the hybrids were superparamagnetic at room temperature and their saturation magnetization could be fine tuned by changing the loading of CoFe2O4 nanoparticles on the MWCNTs. PMID:23646722

Sun, Chuanyu; Liu, Yong; Ding, Weihong; Gou, Yuancheng; Xu, Ke; Xia, Guowei; Ding, Qiang

2013-01-01

67

Conduction mechanism and gas sensing properties of CoFe2O4 nanocomposite thick films for H2S gas.  

PubMed

Nanocrystalline 10 wt% Ni and 0.2 wt% Sm doped CoFe(2)O(4) was prepared by sol-gel citrate method and calcined at different temperatures. The CoFe(2)O(4) nanoparticles were characterized by X-ray diffraction (XRD), electrical properties were studied by impedance analysis. The XRD of CoFe(2)O(4) shows cubic structure with grain growth of 40 nm. The ac conductivity was studied for the sample 10 wt% Ni and 0.2 wt% Sm doped CoFe(2)O(4) calcined at 650°C, at temperature range from 100 to 700°C over a wide range of frequencies from 50 Hz to 200 kHz. The result indicates that the ac conductivity depend on temperature, frequency and concentration of dopant. Nanocrystalline 10 wt% Ni and 0.2 wt% Sm doped CoFe(2)O(4) was found to be good H(2)S sensor with high sensitivity and selectivity. PMID:22284478

Bodade, Anjali B; Bodade, Archana B; Wankhade, H G; Chaudhari, G N; Kothari, D C

2012-01-30

68

Nanolamellar Magnetoelectric BaTiO3-CoFe2O4 Bicrystal.  

National Technical Information Service (NTIS)

Here, we report a spontaneously formed nanolamellar BaTiO3-CoFe2O4 bicrystal. (110) interfaces join the BaTiO3 and CoFe2O4 single crystalline periodically arranged lamellae that have a common (111) direction. The superlattice of approximately 2 nm wavelen...

M. Laver M. Wuttig S. Ren

2009-01-01

69

ZnO supported CoFe2O4 nanophotocatalysts for the mineralization of Direct Blue 71 in aqueous environments.  

PubMed

In this study, an attempt was made to render both the magnetic and photocatalytic properties in a semiconductor material to enhance the efficiency of degradation and recycling possibility of magnetic nanophotocatalysts. CoFe2O4 and CoFe2O4 loaded ZnO nanoparticles were prepared by a simple co-precipitation method and characterized using various analytical tools and in addition to check its visible light assisted photocatalytic activity. CoFe2O4/ZnO nanocatalyst coupled with acceptor, peroxomonosulphate (PMS) showed 1.69-fold enhancement in Direct Blue 71 (triazo dye; DB71) mineralization within 5h. The accomplished enrichment in decolorization was due to the production of more number of non-selective and active free radicals at the catalyst surface. PMID:23523908

Sathishkumar, Panneerselvam; Pugazhenthiran, Nalenthiran; Mangalaraja, Ramalinga Viswanathan; Asiri, Abdullah M; Anandan, Sambandam

2013-05-15

70

Magnetic and elastic properties of CoFe2O4- polydimethylsiloxane magnetically oriented elastomer nanocomposites  

NASA Astrophysics Data System (ADS)

Magnetic elastic structured composites were prepared by using CoFe2O4 ferromagnetic and superparamagnetic nanoparticles as fillers in polydimethylsiloxane (PDMS) matrixes, which were cured in the presence of a uniform magnetic field. Cobalt-iron oxide nanoparticles of three different average sizes (between 2 and 12 nm) were synthesized and characterized. The smallest nanoparticles presented superparamagnetic behavior, with a blocking temperature of approximately 75 K, while larger particles are already blocked at room temperature. Macroscopically structured-anisotropic PDMS-CoFe2O4 composites were obtained when curing the dispersion of the nanoparticles in the presence of a uniform magnetic field (0.3 T). The formation of the particle's chains (needles) orientated in the direction of the magnetic field was observed only when loading with the larger magnetically blocked nanoparticles. The SEM images show that the needles are formed by groups of nanoparticles which retain their original average size. The Young's moduli of the structured composites are four times larger when measured along the oriented needles than in the perpendicular direction. Magnetization (VSM) and ferromagnetic resonance curves of the structured composites were determined as a function of the relative orientation between the needles and the probe field. The remanence magnetization was 30% higher when measured parallel to the needles, while the coercive field remains isotropic. These observations are discussed in terms of the individual nanoparticle's properties and its aggregation in the composites.

Soledad Antonel, P.; Jorge, Guillermo; Perez, Oscar E.; Butera, Alejandro; Gabriela Leyva, A.; Martín Negri, R.

2011-08-01

71

Strain-induced high coercivity in CoFe2O4 powders  

Microsoft Academic Search

Three cobalt ferrite (CoFe2O4) powders were used as starting materials for mechanical milling. A mechanical milling for a short time resulted in a relatively large residual strain and a high density of defects in the micrometer-sized CoFe2O4 powders. High coercivities (up to 5.1 kOe) were achieved in these samples, probably due to the stress anisotropy and pinning effects. A relatively

B. H. Liu; J. Ding

2006-01-01

72

Formation Mechanism and Shape Control of Monodisperse Magnetic CoFe2O4 Nanocrystals  

Microsoft Academic Search

The formation mechanism and shape control of monodisperse magnetic cobalt ferrite (CoFe2O4) nanocrystals produced by thermolysis of a stoichiometric Co2+Fe2 3+-oleate complex in organic solution has been investigated. Synthesis of the pure ternary CoFe2O4 inverse spinel phase, without formation of any intermediate binary cobalt and iron oxides, is favored by the close thermal decomposition temperature of the Co2+-oleate and Fe3+-oleate

Ningzhong Bao; Liming Shen; Wei An; Prahallad Padhan; C. Heath Turner; Arunuba Gupta

2009-01-01

73

Preparation and photocatalytic properties of nanometer-sized magnetic TiO2/SiO2/CoFe2O4 composites.  

PubMed

Magnetic TiO2/SiO2/CoFe2O4 nanoparticles (TiO2/SCFs) were prepared by a sol-gel process in a reverse microemulsion combined with solvent-thermal technique. TiO2/SCFs were characterized by Fourier transform infrared spectrometry, thermogravimetric analysis-differential scanning calorimetry, X-ray diffraction, Raman spectrometry, TEM, BET specific surface area measurement, and magnetic analysis. Structure analyses indicated that TiO2/SCFs presented a core-shell structure with TiO2 uniformly coating on SiO2/CoFe2O4 nanomagnets (SCFs) and typical ferromagnetic hysteresis. TiO2/SCFs showed larger specific surface area and better photocatalytic activities than TiO2 and TiO2/CoFe2O4 photocatalysts prepared by the same method. The doping interaction between TiO2 and CoFe2O4 reduced thanks to the inert SiO2 mesosphere. PMID:22413361

Li, Hansheng; Zhang, Yaping; Wu, Qin; Wang, Xitao; Liu, Changhao

2011-11-01

74

Deposition of luminescent Y2O3:Eu3+ on ferromagnetic mesoporous CoFe2O4@mSiO2 nanocomposites.  

PubMed

Luminescent Y2O3:Eu(3+) particles have been deposited on the surface of ferromagnetic mesoporous CoFe2O4@mSiO2 nanoparticles by a co-precipitation method, obtaining multifunctional CoFe2O4@mSiO2@Y2O3:Eu(3+) nanocomposites. XRD, SEM, TEM, EDX, XPS, N2-adsorption-desorption, FT-IR, VSM and PL were used to characterized the samples. The results reveal that the nanocomposites display typical mesoporous characteristics with high surface areas (BET), large pore volumes and core-shell structures. The composites show ferromagnetic properties and red luminescence from the (5)D0-(7)F2 transition at 610 nm. The size and the magnetic and luminescence properties of the composites could be tuned by systematically varying the experimental parameters, such as the annealing temperature, the mass ratio of CoFe2O4@mSiO2 to Y2O3:Eu(3+), and the volume of TEOS. A possible quenching mechanism of the luminescent Y2O3:Eu(3+) by the ferromagnetic CoFe2O4 is proposed. The high BET and large pore volume may give the composite potential application in controlled drug release. PMID:24741669

Ren, Xiaozhen; Tong, Lizhu; Chen, Xiaodong; Ding, Hong; Yang, Xuwei; Yang, Hua

2014-06-14

75

Electrical properties and phase transition of CoFe2O4 nanocrystals under pressure  

NASA Astrophysics Data System (ADS)

The electric resistance CoFe2O4 nanocrystals of different sizes, obtained by the coprecipitation method was investigated under pressure up to 20 GPa in a diamond anvil cell at ambient temperature. The experimental results indicate that the phase transition (from the spinel to a tetragonal structure) takes place at 7.5 and 12.5 GPa for 6 and 80 nm, nanocrystals, respectively, in agreement with the prediction of scaling theory of the phase transition of nanocrystals. The relatively low transition pressure for CoFe2O4 is related to the high d-electron coupling between magnetic ions and to the small band gap in CoFe2O4 as compared to the other spinel ferrites. These results are discussed in terms of decreasing band gap with increasing pressure. The smaller the size of nanocrystals, the higher the phase transition pressure. The resistance of CoFe2O4 nanocrystal decreases exponentially under pressure, according to R~exp(-CP), where C=0.7634 GPa-1 for large nanocrystals (80 nm) and C=0.5124 GPa-1 for CoFe2O4 of 6 nm.

Wu, Zhenyu; Bao, Zhongxing; Cao, Li; Liu, Cuixia; Li, Qianshu; Xie, Sishen; Zou, Bingsuo

2003-06-01

76

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films.  

PubMed

Transition metal ferrites such as CoFe2O4, possessing a large magnetostriction coefficient and high Curie temperature (Tc > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0-3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 ?m. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe2O4 polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization (Ms). An enhancement of the effective permittivity and saturation magnetization of the CoFe2O4-P(VDF-HFP) films was observed and directly compared with CoFe2O4-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe2O4-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of Ms up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe2O4-P(VDF-HFP) sample. PMID:24004499

Liu, Xiaohua; Liu, Shuangyi; Han, Myung-Geun; Zhao, Lukas; Deng, Haiming; Li, Jackie; Zhu, Yimei; Krusin-Elbaum, Lia; O'Brien, Stephen

2013-01-01

77

Formation Mechanism and Shape Control of Monodisperse Magnetic CoFe2O4 Nanocrystals  

SciTech Connect

The formation mechanism and shape control of monodisperse magnetic cobalt ferrite (CoFe2O4) nanocrystals produced by thermolysis of a stoichiometric Co2+Fe2 3+-oleate complex in organic solution has been investigated. Synthesis of the pure ternary CoFe2O4 inverse spinel phase, without formation of any intermediate binary cobalt and iron oxides, is favored by the close thermal decomposition temperature of the Co2+-oleate and Fe3+-oleate precursors. For reaction temperatures between 250 and 320 ?C, the nucleation and growth dynamics dictate the size and shape evolution of the nanocrystals. Prenucleation of CoFe2O4 occurs at 250-300 ?C but without any growth of nanocrystals, because the monomer concentration is lower than the critical nucleation concentration. For temperatures in the range of 300-320 ?C,which is above the thermolysis temperature of the mixed Co2+Fe2 3+-oleate complex, the monomer concentration increases rapidly resulting in homogeneous nucleation. Atomic clusters of CoFe2O4 with size<2 nm are initially formed at 314 ?C that then grow rapidly when the temperature is raised to 320 ?C in less than a minute. The shape of the CoFe2O4 nanocrystals can be reproducibly controlled by prolonging the aging time at 320 ?C, evolving from initial spherical, to spherical-to-cubic, cubic, corner-grown cubic, or starlike shapes. Thus, with careful choice of reaction parameters, such as the precursor concentration and the heating rate, it is possible to achieve large-scale synthesis of shape-controlled monodisperse CoFe2O4 nanocrystals with high yield.

Bao, Ningzhong; Shen, Liming; An, Wei; Padhan, Prahallad; Turner, C. H.; Gupta, Arunuba

2009-07-28

78

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films  

NASA Astrophysics Data System (ADS)

Transition metal ferrites such as CoFe2O4, possessing a large magnetostriction coefficient and high Curie temperature ( T c > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0-3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 ?m. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe2O4 polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization ( M s). An enhancement of the effective permittivity and saturation magnetization of the CoFe2O4-P(VDF-HFP) films was observed and directly compared with CoFe2O4-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe2O4-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of M s up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe2O4-P(VDF-HFP) sample.

Liu, Xiaohua; Liu, Shuangyi; Han, Myung-Geun; Zhao, Lukas; Deng, Haiming; Li, Jackie; Zhu, Yimei; Krusin-Elbaum, Lia; O'Brien, Stephen

2013-09-01

79

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films  

PubMed Central

Transition metal ferrites such as CoFe2O4, possessing a large magnetostriction coefficient and high Curie temperature (Tc > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0–3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 ?m. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe2O4 polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization (Ms). An enhancement of the effective permittivity and saturation magnetization of the CoFe2O4-P(VDF-HFP) films was observed and directly compared with CoFe2O4-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe2O4-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of Ms up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe2O4-P(VDF-HFP) sample.

2013-01-01

80

Strain induced magnetic anisotropy in highly epitaxial CoFe2O4 thin films  

NASA Astrophysics Data System (ADS)

Cobalt ferrite (CoFe2O4) thin films were epitaxially grown on (001) SrTiO3 and (001) MgO by laser molecular beam epitaxy. Microstructural studies indicate that the CoFe2O4 grown on (001) SrTiO3 with compressive strain are c-oriented island growth mode with rough surface morphology, whereas the films on (001) MgO with tensile strain become c oriented with layer-by-layer mode. Magnetic property studies reveal that the compressive strained CoFe2O4 films on (001) SrTiO3 can significantly enhance out-of-plane magnetization (190 emu/cm3) with a large coercivity (3.8 kOe). In contrast, the tensile strained CoFe2O4 films on (001) MgO exhibit weak magnetic anisotropy. These results suggest that strong magnetic anisotropy is highly dependent on the lattice mismatch induced strain.

Huang, W.; Zhu, J.; Zeng, H. Z.; Wei, X. H.; Zhang, Y.; Li, Y. R.

2006-12-01

81

Interface states in CoFe2O4 spin-filter tunnel junctions  

NASA Astrophysics Data System (ADS)

Spin-filter tunneling is a promising way to generate highly spin-polarized current, a key component for spintronics applications. In this paper we explore the tunneling conductance across the spin-filter material CoFe2O4 interfaced with Au electrodes, a geometry which provides nearly perfect lattice matching at the CoFe2O4/Au(001) interface. Using density functional theory calculations we demonstrate that interface states play a decisive role in controlling the transport spin polarization in this tunnel junction. For a realistic CoFe2O4 barrier thickness, we predict a tunneling spin polarization of about -60%. We show that this value is lower than what is expected based solely on considerations of the spin-polarized band structure of CoFe2O4, and therefore that these interface states can play a detrimental role. We argue that this is a rather general feature of ferrimagnetic ferrites and could make an important impact on spin-filter tunneling applications.

Lukashev, Pavel V.; Burton, J. D.; Smogunov, Alexander; Velev, Julian P.; Tsymbal, Evgeny Y.

2013-10-01

82

Structural and Raman scattering study of Ni-doped CoFe2O4  

NASA Astrophysics Data System (ADS)

Raman scattering measurements were made on polycrystalline CoFe2O4 and Co0.5Ni0.5Fe2O4 ferrites as prepared by solid-state reaction route. Rietveld refined X-ray diffraction pattern confirmed the formation of single-phase and both of the samples perfectly indexed in cubic spinel structure with Fd3m space group. Slight reduction in the lattice parameter of Co0.5Ni0.5Fe2O4 has been observed as compared to CoFe2O4. From Raman scattering spectra, a shoulder like feature has been observed in both of the compounds reveals that octahedral site is occupied by Co, Ni and Fe ions and tetrahedral site is occupied by only Fe ion.

Kumar, Ashwini; Dar, Mashkoor A.; Sharma, Poorva; Varshney, Dinesh

2014-04-01

83

The cooling rate dependence of cation distributions in CoFe2O4  

NASA Technical Reports Server (NTRS)

The room-temperature cation distributions in bulk CoFe2O4 samples, cooled at rates between less than 0.01 and about 1000 C/sec, have been determined using Mossbauer spectroscopy in an 80-kOe magnetic field. With increasing cooling rate, the quenched structure departs increasingly from the mostly ordered cation distribution ordinarily observed at room temperature. However, the cation disorder appears to saturate just short of a random distribution at very high cooling rates. These results are interpreted in terms of a simple relaxation model of cation redistribution kinetics. The disordered cation distributions should lead to increased magnetization and decreased coercivity in CoFe2O4.

De Guire, Mark R.; O'Handley, Robert C.; Kalonji, Gretchen

1989-01-01

84

Synthesis and characterization of CoFe2O4/polyaniline nanocomposites for electromagnetic interference applications.  

PubMed

The Cobalt ferrite (CoFe2O4) powders were synthesized by Co-precipitation method. The as prepared ferrite powders were incorporated into a polyaniline matrix at various volumetric ratios. The as prepared composites of ferrite and polyaniline powders were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM). The particle size of CoFe2O4 is found to be 20 nm. The saturation magnetization (M(s)) of all the composites was found to be decreasing with decrease of ferrite content, while coercivity (H(c)) remained at the value corresponding to pure cobalt ferrite nanopowders. The complex permittivity (epsilon' and epsilon") and permeability (mu' and mu") of composite samples were measured in the range of 1 MHz to 1.1 GHz. The value of epsilon' and mu' found to be increased with ferrite volume concentration. PMID:24738398

Praveena, K; Srinath, S

2014-06-01

85

Multiferroic BaTiO3-CoFe2O4 Nanostructures  

Microsoft Academic Search

We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO3 (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The

H. Zheng; J. Wang; S. E. Lofland; Z. Ma; L. Mohaddes-Ardabili; T. Zhao; L. Salamanca-Riba; S. R. Shinde; S. B. Ogale; F. Bai; D. Viehland; Y. Jia; D. G. Schlom; M. Wuttig; A. Roytburd; R. Ramesh

2004-01-01

86

Fabrication and characterization of cobalt ferrite (CoFe 2O 4) nanofibers by electrospinning  

Microsoft Academic Search

By sol–gel process and electrospinning method, cobalt ferrite\\/polyvinyl acetate (PVAc) composite fiber was obtained. Cobalt ferrite (CoFe2O4) nanofibers were synthesized by calcination of the cobalt ferrite\\/polyvinyl acetate (PVAc) composite fiber with several temperatures. The nanofibers were characterized by SEM, FT-IR, XRD and EXAFS. The diameter of nanofibers was slightly decreased with increasing the calcination temperature. The fibers calcined at 800°C

Young-Wan Ju; Jae-Hyun Park; Hong-Ryun Jung; Sung-June Cho; Wan-Jin Lee

2008-01-01

87

Noncollinear magnetic structure of CoFe2O4 small particles  

Microsoft Academic Search

The magnetic structure of small CoFe2O4 particles has been investigated as a function of the particle size. Samples (in the 10–100 nm size range and up) were prepared by chemical precipitation followed by a heat treatment at relatively low temperatures. Mo¨ssbauer spectra of the 57Fe nuclei, obtained with a longitudinal magnetic applied field, unambiguously establish that a noncollinear structure exists

K. Haneda; A. H. Morrish

1988-01-01

88

Coupling interaction in multiferroic BaTiO3 CoFe2O4 nanostructures  

Microsoft Academic Search

Recent experimental results (Zheng et al 2004 Science 303 661) have shown that a 1-3-type BaTiO3-CoFe2O4 composite film exhibited a strong coupling between the ferroelectric and ferromagnetic order parameters. The coupling interaction in the nanostructured multiferroic film could be different from that in a bulk composite because there exists a giant residual stress\\/strain in the film. In this paper, by

Gang Liu; Ce-Wen Nan; Z. K. Xu; Haydn Chen

2005-01-01

89

Synthesis of nanocrystalline spinel CoFe 2O 4 via a polymer-pyrolysis route  

Microsoft Academic Search

Nanocrystalline CoFe2O4 spinel ferrites were synthesized via the pyrolysis of polyacrylate salt precursors prepared by in situ polymerization of metal salts and acrylic acid. The pyrolytic behaviors of the polymeric precursors were analyzed by use of simultaneous thermogravimetric and differential thermal analysis (TG-DTA). The structural characteristics of the calcined products were obtained by powder X-ray diffraction (XRD), infrared spectroscopy (IR)

Xian-Ming Liu; Shao-Yun Fu; Hong-Mei Xiao; Chuan-Jun Huang

2005-01-01

90

Multiferroic BaTiO3-CoFe2O4 Nanostructures.  

PubMed

We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO3 (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The films are epitaxial in-plane as well as out-of-plane with self-assembled hexagonal arrays of CoFe2O4 nanopillars embedded in a BaTiO3 matrix. The CoFe2O4 nanopillars have uniform size and average spacing of 20 to 30 nanometers. Temperature-dependent magnetic measurements illustrate the coupling between the two order parameters, which is manifested as a change in magnetization at the ferroelectric Curie temperature. Thermodynamic analyses show that the magnetoelectric coupling in such a nanostructure can be understood on the basis of the strong elastic interactions between the two phases. PMID:14752158

Zheng, H; Wang, J; Lofland, S E; Ma, Z; Mohaddes-Ardabili, L; Zhao, T; Salamanca-Riba, L; Shinde, S R; Ogale, S B; Bai, F; Viehland, D; Jia, Y; Schlom, D G; Wuttig, M; Roytburd, A; Ramesh, R

2004-01-30

91

Physicochemical Properties of Spray-Deposited CoFe2O4 Thin Films  

NASA Astrophysics Data System (ADS)

Cobalt ferrite thin films are deposited onto quartz glass substrates by chemical spray pyrolysis technique at different substrate temperatures using ferric nitrate and cobalt nitrate as precursors. Thermogravimetric analysis (TGA) study indicates the formation of CoFe2O4 by decomposition of cobalt and ferric nitrates after 800 °C. X-ray diffraction studies reveal that annealed films are polycrystalline in nature and exhibit spinel cubic crystal structure. Crystallite size varies from 39 to 44 nm with the substrate temperatures. Direct optical band gap energy of CoFe2O4 thin films is found to be 2.57 eV. The AFM images show that roughness and grain size of the CoFe2O4 thin film are about 9 and 138 nm, respectively. The measured DC resistivity of the deposited thin films indicates that as temperature increases the resistivity decreases indicating the semiconductor nature of the films. Decrease in dielectric constant (?') and loss tangent (tan?) has been observed with frequency and attains the constant value at higher frequencies. The AC conductivity of cobalt ferrite thin films increases with increase in frequency. Thus, the prepared films show normal dielectric performance of the spinel ferrite thin film. Room-temperature complex impedance spectra show the incomplete semicircles as films exhibit high resistance values at lower frequencies.

Bagade, A. A.; Ganbavle, V. V.; Rajpure, K. Y.

2014-05-01

92

Preparation and magnetic study of the CoFe2O4-CoFe2 nanocomposite powders  

Microsoft Academic Search

Ferri-ferromagnetic nanocomposites CoFe2O4-CoFe2 were prepared via reduction of the cobalt ferrite CoFe2O4 into a hydrogen atmosphere and by heat treatments. This preparation method yielded powders with relative volume fraction of CoFe2O4 and CoFe2 in the range 0-0.91. The structure and the room temperature magnetization of the samples were analyzed by X-ray diffraction, scanning electron microscope (SEM) and transmission electron microscope

F. de Assis Olimpio Cabral; F. L. de Araujo Machado; José Humberto de Araujo; João Maria Soares; Alexandre Ricalde Rodrigues; Armando Araujo

2008-01-01

93

Magnetoelectric behavior of BaTiO3 films directly grown on CoFe2O4 ceramics  

Microsoft Academic Search

BaTiO3 films were grown on highly dense CoFe2O4 ceramics via pulsed laser deposition. Microstructural characterization showed that polycrystalline BaTiO3 thin films with grain size of about 70 nm were grown on the CoFe2O4 ceramics. BaTiO3 films showed good ferroelectric feature. An obvious magnetoelectric response, which had the same bias-dependent trend as the piezomagnetic coupling coefficient of CoFe2O4 ceramics, was observed

Jing Wang; Yi Zhang; Jing Ma; Yuanhua Lin; C. W. Nan

2008-01-01

94

Three-dimensional heteroepitaxy in self-assembled BaTiO3-CoFe2O4 nanostructures  

Microsoft Academic Search

Self-assembled BaTiO3-CoFe2O4 complex oxide nanostructures have been synthesized by pulsed laser deposition. A single ceramic target with a molar ratio of 0.62BaTiO3-0.38CoFe2O4 was used. Spinel CoFe2O4 and perovskite BaTiO3 phases spontaneously separated during heteroepitaxial growth on a single-crystal SrTiO3 (001) substrate. The nanostructures are epitaxial in-plane as well as out-of-plane, with CoFe2O4 nanopillar arrays embedded in a BaTiO3 matrix. The

H. Zheng; J. Wang; L. Mohaddes-Ardabili; M. Wuttig; L. Salamanca-Riba; D. G. Schlom; R. Ramesh

2004-01-01

95

The effect of molar composition of Co2+ to structure and magnetic properties of CoFe2O4  

NASA Astrophysics Data System (ADS)

The powder sample of CoFe2O4 have been successfully prepared by a sol gel method with different Co2+ contents to study the effect of addition of percentage molar composition of Co2+ to its crystal structure and magnetic characteristics of CoFe2O4. The crystal structure of CoFe2O4 was measured by X-ray diffraction. Magnetization and their hysteresis properties were measured by vibrating sample magnetometer to investigate remnant magnetization, coercive field and uniaxial anisotropy field. The quality of crystal and magnetic properties of CoFe2O4 samples decrease with increasing the percentage molar composition of Co2+.

Saragi, T.; Syakir, N.; Nainggolan, T. H.; Alboin, C.; Risdiana

2013-09-01

96

Magnetic Nanocheckerboards with Tunable Sizes in the Mn-Doped CoFe2O4 Spinel  

Microsoft Academic Search

In the Mn-doped CoFe2O4 spinel, a highly ordered array of two types of rectangular nanorods, ˜300 nm in length and a few nanometer in size, is achieved through chemical phase separation mediated by cooperative Jahn-Teller distortions. At room temperature, the magnetic nanorods with composition close to CoFe2O4 interlace with the paramagnetic counterparts and form a highly organized checkerboard pattern in

Chenglin Zhang; C. M. Tseng; C. H. Chen; S. Yeo; Y. J. Choi; S.-W. Cheong

2008-01-01

97

Microstructural evolution and its influence on the magnetic properties of CoFe2O4 powders during mechanical milling  

Microsoft Academic Search

A high coercivity of up to 5.1 kOe was induced in a large-grained CoFe2O4 powder after milling for a short time 1.5 h. It was found that the initial grain particle size played an important role in the microstructural evolution and in the magnetic properties of the milled CoFe2O4 materials. The milling-induced microstructural evolution was analyzed using x-ray diffraction and

B. H. Liu; J. Ding; Z. L. Dong; C. B. Boothroyd; J. H. Yin; J. B. Yi

2006-01-01

98

High-yield synthesis and characterization of monodisperse sub-microsized CoFe 2O 4 octahedra  

Microsoft Academic Search

In this study, sub-microsized CoFe2O4 octahedra with a high yield are synthesized via a simple hydrothermal route under mild conditions. The as-prepared products are characterized by conventional techniques of XRD, SEM, TEM, ED and HR-TEM. The results show that the as-synthesized sample exhibits octahedral morphology with a narrow size distribution. The edge size of CoFe2O4 octahedra is estimated to be

Xian-Ming Liu; Shao-Yun Fu; Lu-Ping Zhu

2007-01-01

99

Electronic structure and optical band gap of CoFe2O4 thin films  

NASA Astrophysics Data System (ADS)

Electronic structure and optical band gap of CoFe2O4 thin films grown on (001) oriented LaAlO3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explained by the quantum size effect and misfit dislocation. Such results provide interesting insights for the growth of spinel phases.

Ravindra, A. V.; Padhan, P.; Prellier, W.

2012-10-01

100

Observation of surface effects in La-doped CoFe2O4/SiO2 nanocomposites  

NASA Astrophysics Data System (ADS)

In magnetism of nanoparticles, surface spin effects play a key role. The so-called spin canting at the surface leads either to lowering of saturation magnetization, or even to lack of saturation in high magnetic fields. The value of the saturation magnetization depends on cation distribution within the spinel network and on the spin canting angles. We have investigated structure and magnetic behavior of CoFe2O4 nanoparticles doped with La (Co1-xLaxFe2O4, x = 0.05 - 0.5 and CoLaxFe2-xO4, x = 0.05 - 0.2) embedded in amorphous silica matrix prepared by a sol-gel method. The samples were characterized using X-ray diffraction and TEM. The zero-field cooled and field cooled measurements of magnetization showed that the blocking temperature is well above the room temperature. The high coercivity was observed (up to 2 T at 10 K) and no saturation of the magnetization even in applied field of 7 T was obtained, suggesting considerable spin canting effects. Finally, the Mossbauer spectroscopy under magnetic field and down to low temperature was performed to determine the cation distribution and the spin canting angles.

Burianova, Simona; Poltierova Vejpravova, Jana; Holec, Petr; Niznansky, Daniel; Plocek, Jiri

2011-03-01

101

Accommodation of transformation strains in transverse multiferroic nanostructures CoFe2O4-PbTiO3  

NASA Astrophysics Data System (ADS)

Variable-temperature x-ray diffraction was used to investigate the internal strains that arise from a ferroelectric phase transition in self-assembled multiferroic nanostructures CoFe2O4-PbTiO3 on (001) SrTiO3. The constraints from CoFe2O4 suppressed the c/a ratio in tetragonal PbTiO3 (without affecting its Curie temperature) while the expansion of the out-of-plane lattice parameter in PbTiO3 upon the transition induced tensile out-of-plane strain in CoFe2O4. The transformation strain was partly relieved by the 90° twin domains in PbTiO3 which reduced the net deformation of the component phases. Significant fractions of both c- and a-domains were observed despite the nanoscale of PbTiO3 in the composite films.

Levin, Igor; Slutsker, Julia; Li, Jianhua; Tan, Zhuopeng; Roytburd, Alexander L.

2007-08-01

102

A first-principles study of magnetostrictions of Fe3O4 and CoFe2O4  

NASA Astrophysics Data System (ADS)

Effects of charge ordering in the octahedral sites of Fe3O4 and CoFe2O4 on their magnetostrictions are investigated using the density functional theory plus U approach. Precise description of charge ordering was found to be crucial in determining only band-gaps of Fe3O4 and CoFe2O4, but not other physical properties such as lattice constant, magnetic moment, and magnetostriction. And Co configuration in CoFe2O4 is important in determining its magnetostriction; the most stable configuration results in substantially enhanced magnetostriction (-245 ppm), compared to that (-25 ppm) of Fe3O4, in consistent with experiments.

Odkhuu, Dorj; Taivansaikhan, Purev; Yun, Won Seok; Hong, Soon Cheol

2014-05-01

103

Nonlinear strain dependence of magnetic anisotropy in CoFe2O4 films on MgO(001) substrates  

NASA Astrophysics Data System (ADS)

CoFe2O4 films were deposited on MgO(001) substrates using pulsed laser deposition with various laser energy densities. We found that the CoFe2O4 films were grown in the (001) orientation and that the lattice constant of the CoFe2O4 films was dependent on the laser energy densities. Perpendicular magnetic anisotropy (PMA) was observed, but the lattice strain dependence was not consistent with the phenomenological model in which the PMA is in proportion to the lattice strain. The lattice strain dependence of PMA was compared with an electron theory in which the spin-orbit interaction and the tetragonal crystal field in the electronic state of a single Co ion are considered. The experimental result does not contradict with the calculation, which shows that the magnetic anisotropy is not proportional to the lattice strain and asymmetric in respect to negative and positive lattice strain.

Tanaka, M. A.; Harada, K.; Takemura, M.; Mibu, K.; Inoue, J.

2014-05-01

104

Nanogranular BaTiO3-CoFe2O4 thin films deposited by pulsed laser ablation  

NASA Astrophysics Data System (ADS)

Detailed structural and magnetic measurements were performed on nanostructured composite thin films of cobalt ferrite (CoFe2O4-magnetostrictive) dispersed in a barium titanate (BaTiO3-piezoelectric) matrix, with different CoFe2O4 concentrations (ranging from x=20% to x=70%). The films were deposited by laser ablation on platinum covered Si(100). Their structure was studied by x-ray diffraction and Raman spectroscopy. The magnetic properties were measured with a superconducting quantum inteference device magnetometer. The nanocomposite films were polycrystalline and composed by a mixture of tetragonal-BaTiO3 and CoFe2O4 with the cubic spinel structure. The lattice parameter of the CoFe2O4 phase varied from 8.26 A? (x=20%) to 8.35 A? (x=70%), and, compared with bulk CoFe2O4, it was under compressive stress that relaxed as its concentration progressively increased. In the tetragonal-BaTiO3 phase, the lattice parameter a was contracted relative to the bulk phase and decreases with x. The lattice parameter c increased from 4.088 A? (x=20%) to 4.376 A? (x=70%), so that the BaTiO3 c axes were increasingly expanded as the quantity of the barium titanate phase was reduced. This behavior was the opposite of that observed in CoFe2O4. The magnetic measurements showed that the coercive fields decreased from 6.6 kOe (x=20%) to 2.3 kOe (x=70%), which was attributed to the progressive relaxation of the stress in the films as well as to the increase of particle agglomeration in bigger polycrystalline clusters with increasing cobalt ferrite concentration. For higher temperatures T=300 K, the reduction of magnetocrystalline anisotropy induced a strong reduction of the coercive field.

Barbosa, J.; Almeida, B. G.; Mendes, J. A.; Rolo, A. G.; Araújo, J. P.; Sousa, J. B.

2007-05-01

105

Electrophoretic Deposition of CoFe2O4 Nanograins Dispersed in a Laser Ablated BaTiO3 Matrix  

Microsoft Academic Search

Thin film nanocomposites composed by CoFe2O4 grains, deposited by electrophoresis, and subsequently covered by a laser ablation deposited BaTiO3 layer, were prepared with different cobalt ferrite concentrations (x). The cobalt ferrite phase was under a compressive strain that relaxed as the CoFe2O4 concentration increased. Consequently, a blueshift of the Raman peaks of CoFe2O4 was observed, that decreased with increasing x.

J. G. Barbosa; M. R. Pereira; C. Moura; J. A. Mendes; B. G. Almeida

2011-01-01

106

Magnetoelectric CoFe2O4-lead zirconate titanate thick films prepared by a polyvinylpyrrolidone-assisted sol-gel method  

Microsoft Academic Search

Magnetoelectric CoFe2O4-PZT (lead zirconate titanate) films as thick as 1 mum have been prepared by spin coating using a PZT sol-gel solution containing polyvinylpyrrolidone and CoFe2O4 powder. X-ray diffraction result reveals that there exists no chemical reaction or phase diffusion between the CoFe2O4 and PZT phases. The scanning electron microscopy observation confirms that the composite thick film is crack-free and

Jian-Guo Wan; Hao Zhang; Xiuwei Wang; Dengyu Pan; Jun-Ming Liu; Guanghou Wang

2006-01-01

107

CoFe2O4/buffer layer ultrathin heterostructures on Si(001)  

NASA Astrophysics Data System (ADS)

Epitaxial films of ferromagnetic CoFe2O4 (CFO) were grown by pulsed laser deposition on Si(001) buffered with ultrathin yttria-stabilized zirconia (YSZ) layers in a single process. Reflection high-energy electron diffraction was used to monitor in real time the crystallization of YSZ, allowing the fabrication of epitaxial YSZ buffers with thickness of about 2 nm. CFO films, with thicknesses in the 2-50 nm range were subsequently deposited. The magnetization of the CFO films is close to the bulk value. The ultrathin CFO/YSZ heterostructures have very flat morphology (0.1 nm roughness) and thin interfacial SiOx layer (about 2 nm thick) making them suitable for integration in tunnel (e.g., spin injection) devices.

Bachelet, R.; de Coux, P.; Warot-Fonrose, B.; Skumryev, V.; Fontcuberta, J.; Sánchez, F.

2011-10-01

108

Magnetoelectric relaxation in rhombohedral LiNbO3-CoFe2O4  

NASA Astrophysics Data System (ADS)

We demonstrate a magnetoelectric nanocomposite, LiNbO3-CoFe2O4 (LNO-CFO), consisting of rhombohedral R3c LNO and R3m CFO phases. It is characterized by a maximum inverse magnetoelectric coefficient of 6.5 Oe cm.V-1 measured in a 106 V/m electric field, and a magnetic field dependent Vogel-Fulcher-like relaxation characterized by a relaxation time ?=?0exp(-?H/k(Tm-TvfH)), ?0=29.66 s, ?H=1.06 eV, TvfH represents the magnetic field-dependent Vogel-Fulcher temperature. The activation energy equals the activation energy of oxygen vacancy diffusion in niobate-based crystals. The room temperature electric field-induced magnetization change relaxes as ?=18.05 s.

Han, Yemei; Liu, Yueying; Zavalij, Peter; Salamanca-Riba, Lourdes; Cantando, Elizabeth; Bergstrom, Richard; Li, Lingxia; Wuttig, Manfred

2012-06-01

109

A novel nonenzymatic hydrogen peroxide sensor based on LaNi0.5Ti0.5O3/CoFe2O4 modified electrode.  

PubMed

A novel nonenzymatic hydrogen peroxide (H(2)O(2)) sensor based on LaNi(0.5)Ti(0.5)O(3)/CoFe(2)O(4) nanoparticles modified glassy carbon electrode (LNT-CFO/GCE) was proposed. Perovskite-type nanocomposite oxide LaNi(0.5)Ti(0.5)O(3)/CoFe(2)O(4) was synthesized by sol-gel method and characterized by X-ray diffraction and transmission electron microscopy. The electrochemical properties of the modified electrode were studied by cyclic voltammetry and amperometry, which showed an excellent electrocatalytic activity for the oxidation of H(2)O(2). Under the optimum conditions, the linear response was obtained in the range of 0.1 ?M to 8.2 mM, with the correlation coefficient of 0.997. The sensitivity of the modified electrode was calculated to be 3.21 ?A ?M(-1) cm(-2) and the detection limit was 23 nM (based on the S/N=3). PMID:21917429

Ye, Daixin; Xu, Yanhong; Luo, Liqiang; Ding, Yaping; Wang, Yulong; Liu, Xiaojuan; Xing, Lijun; Peng, Jinwei

2012-01-01

110

A facile synthesis of encapsulated CoFe2O4 into carbon nanofibres and its application as conversion anodes for lithium ion batteries  

NASA Astrophysics Data System (ADS)

CoFe2O4 nanoparticles anchored into in-situ formed carbon nanofibres were synthesized by a simple solvent-free and template-free pyrolysis-oxidation process and have been investigated as a promising anode material for Li-ion batteries. Ferrocene and cobaltocene as precursor materials, act as both metal and carbon sources. Carbon contents in the composite can be easily adjusted by varying oxidation conditions. The as-prepared composites show a high and stable capacity. More than 700 mAh g-1 based on the total mass of the as-prepared composite was obtained in the composite with 36% carbon content after long-term cycling of 250 cycles. The superior electrochemical properties are suggested to be benefited from the synergistic effects by combining CoFe2O4 and carbon and also their intimate contact developed in the synthetic process. This work opens a facile and broadly applicable way for fabrication and utilization of metal oxide/mixed metal oxide-carbon composites for Li-ion batteries.

Ren, Shuhua; Zhao, Xiangyu; Chen, Ruiyong; Fichtner, Maximilian

111

Enhancement in magnetoelectric response in CoFe2O4-BaTiO3 heterostructure  

Microsoft Academic Search

CoFe2O4-BaTiO3 heterostructure was epitaxially grown on the (001)-SrTiO3 substrate via pulsed laser deposition, in which the bottom BaTiO3 layer epitaxially grown on the substrate acts as a buffer layer and effectively reduces the coherent constraint in the magnetic layer arising from the substrate. Microstructure studies from x-ray diffraction and electron microscopies showed good coherent epitaxy thin films of the (001)-CoFe2O4

Yi Zhang; Chaoyong Deng; Jing Ma; Yuanhua Lin; Ce-Wen Nan

2008-01-01

112

Directional solidification and interface structure of BaTiO3-CoFe2O4 eutectic  

Microsoft Academic Search

The directional solidification and the interface structure of BaTiO3-CoFe2O4 eutectic grown by the floating zone melting method were investigated. The microstructure of the eutectic were found to consist grains of lamellar or fibrous morphology. Two types of crystal structures of BaTiO3 were observed for different growth conditions. The orientation relationships between BaTiO3 and CoFe2O4 (the spinel-type crystal structure) are a)

J. Echigoya; S. Hayashi; Y. Obi

2000-01-01

113

Multiferroic nanoparticulate Bi3.15Nd0.85Ti3O12-CoFe2O4 composite thin films prepared by a chemical solution deposition technique  

Microsoft Academic Search

Multiferroic xBi3.15Nd0.85Ti3O12-(1-x)CoFe2O4 composite thin films with x=0.5, 0.6, and 0.7 were fabricated on Pt\\/Ti\\/SiO2\\/Si(100) substrates by a chemical solution deposition technique. X-ray diffraction shows that there are no other phases but bismuth-layered perovskite Bi3.15Nd0.85Ti3O12 and spinel CoFe2O4 phases in the films. Scanning electron microscopy reveals that CoFe2O4 aggregates locally into nanoparticles and embeds in the Bi3.15Nd0.85Ti3O12 matrix. The composite films

X. L. Zhong; J. B. Wang; M. Liao; G. J. Huang; S. H. Xie; Y. C. Zhou; Y. Qiao; J. P. He

2007-01-01

114

Directed Self-Assembly of Epitaxial CoFe2O4-BiFeO3 Multiferroic Nanocomposites.  

National Technical Information Service (NTIS)

CoFe2O4 (CFO) BiFeO3 (BFO) nanocomposites are an intriguing option for future memory and logic technologies due to the magnetoelectric properties of the system. However, these nanocomposites form with CFO pillars randomly located within a BFO matrix, maki...

H. Liu J. Lu M. Khokhlov R. Comes R. Kasica

2012-01-01

115

Effect of nanodisperse ferrite cobalt (CoFe2O4) particles on contractile reactions in guinea pigs airways.  

PubMed

The effect of nanopowder CoFe(2)O(4)on contractile responses of smooth-muscle segments of guinea pigs airways was studied by mechanography. Both in vivo inhalation of nanopowder aerosol or in vitro application of nanopowder to isolated airway segments increased the amplitude of contractile responses to histamine and potentiated the dilatory reaction to adrenergic salbutamol. PMID:21113462

Kapilevich, L V; D'yakova, E Yu; Nosarev, A V; Zaitseva, T N; Petlina, Z R; Ogorodova, L M; Ageev, B G; Magaeva, A A; Itin, V I; Terekhova, O G

2010-07-01

116

Wintersweet-flower-like CoFe2O4/MWCNTs hybrid material for high-capacity reversible lithium storage.  

PubMed

CoFe(2)O(4)/multiwalled carbon nanotubes (MWCNTs) hybrid materials were synthesized by a hydrothermal method. Field emission scanning electron microscopy and transmission electron microscopy analysis confirmed the morphology of the as-prepared hybrid material resembling wintersweet flower "buds on branches", in which CoFe(2)O(4) nanoclusters, consisting of nanocrystals with a size of 5-10 nm, are anchored along carbon nanotubes. When applied as an anode material in lithium ion batteries, the CoFe(2)O(4)/MWCNTs hybrid material exhibited a high performance for reversible lithium storage. In particular, the hybrid anode material delivered reversible lithium storage capacities of 809, 765, 539, and 359 mA h g(-1) at current densities of 180, 450, 900, and 1800 mA g(-1), respectively. The superior performance of CoFe(2)O(4)/MWCNTs hybrid materials could be ascribed to the synergistic pinning effect of the wintersweet-flower-like nanoarchitecture. This strategy could also be applied to synthesize other metal oxide/CNTs hybrid materials as high-capacity anode materials for lithium ion batteries. PMID:22593078

Wang, Ying; Park, Jinsoo; Sun, Bing; Ahn, Hyojun; Wang, Guoxiu

2012-08-01

117

FTIR and UV-vis diffuse reflectance spectroscopy studies of the wet chemical (WC) route synthesized nano-structure CoFe2O4 from CoCl2 and FeCl3  

NASA Astrophysics Data System (ADS)

Nano-structure CoFe2O4 has been fabricated by wet chemical route using CoCl2 and FeCl3 as simple precursors. The prepared nano-structure samples was calcined at 600 °C and characterized by fourier transform infrared spectra (FTIR), UV-vis diffuse reflectance spectroscopy (DRS), X-ray powder diffractometry (XRD), and field emission scanning electron microscopy (FESEM). X-ray diffraction patterns confirmed the presence of the spinel phases with average crystallite sizes of 47 nm. Field emission scanning electron microscopy investigations showed spherical morphology of nanoparticles with average particle size of 46 nm. The FTIR spectra of CoFe2O4 nanoparticles showed absorption bands at about 594 cm-1 and 401 cm-1 due to the stretching vibrations of Co-O and Fe-O respectively. Investigation of the optical properties of the produced nano-structure CoFe2O4 confirmed its semiconducting properties by revealing two optical band gaps at 1.4 and 2.0 eV.

Habibi, Mohammad Hossein; Parhizkar, Hadi Janan

2014-06-01

118

FTIR and UV-vis diffuse reflectance spectroscopy studies of the wet chemical (WC) route synthesized nano-structure CoFe2O4 from CoCl2 and FeCl3.  

PubMed

Nano-structure CoFe2O4 has been fabricated by wet chemical route using CoCl2 and FeCl3 as simple precursors. The prepared nano-structure samples was calcined at 600°C and characterized by fourier transform infrared spectra (FTIR), UV-vis diffuse reflectance spectroscopy (DRS), X-ray powder diffractometry (XRD), and field emission scanning electron microscopy (FESEM). X-ray diffraction patterns confirmed the presence of the spinel phases with average crystallite sizes of 47nm. Field emission scanning electron microscopy investigations showed spherical morphology of nanoparticles with average particle size of 46nm. The FTIR spectra of CoFe2O4 nanoparticles showed absorption bands at about 594cm(-1) and 401cm(-1) due to the stretching vibrations of Co-O and Fe-O respectively. Investigation of the optical properties of the produced nano-structure CoFe2O4 confirmed its semiconducting properties by revealing two optical band gaps at 1.4 and 2.0eV. PMID:24637270

Habibi, Mohammad Hossein; Parhizkar, Hadi Janan

2014-06-01

119

On the strain coupling across vertical interfaces of switchable BiFeO3-CoFe2O4 multiferroic nanostructures  

NASA Astrophysics Data System (ADS)

In magnetoelectrically coupled CoFe2O4-BiFeO3 nanostructures vertical and lateral lattice parameters of both phases are determined. We find that the in-plane lattice parameter of CoFe2O4 is fully relaxed whereas it presents compressive strain along the out-of-plane direction. Although the CoFe2O4-BiFeO3 interface is semicoherent, CoFe2O4 out-of-plane lattice strain is not relaxed after selective removal of the matrix and thus it is of nonelastic origin. In spite of the absence of elastic residual strain caused by CoFe2O4-BiFeO3 interfaces, the two phases are mechanically coupled as demonstrated by the electrical switching of the magnetization.

Dix, N.; Muralidharan, R.; Guyonnet, J.; Warot-Fonrose, B.; Varela, M.; Paruch, P.; Sánchez, F.; Fontcuberta, J.

2009-08-01

120

Conduction mechanism in BiFeO3-CoFe2O4 columnar nanostructure  

NASA Astrophysics Data System (ADS)

Multiferroic materials, which possess interaction between more than one ferroic ordering parameters, had attracted great scientific and technological interests. Among the bi-phase magneto-electric nanostructures, BiFeO3-CoFe2O4 (BFO-CFO) is a model system with ferroelectricity and ferrimagnetism coupling to each other through stress mediation. In this study, we investigated the electron transport behavior and the leakage-current mechanism in high quality nano-composite BFO-CFO thin films. The CFO nanopillars were heteroepitaxially embedded in a BFO matrix grown on SrTiO3 substrates. Macroscopic vertical transport result showed the interface limit model was the dominant mechanism of the large leakage. Local conduction in epitaxial BFO-CFO nanostructures was studied by conducting atomic force microscope (C-AFM) while the nature of band structure variation was demonstrated by scanning tunneling microscope (STM). This study provides a basic explanation of leakage mechanism in self-assembled composite material system.

Chen, Yi-Chun; Heish, Ying-Hui; Liang, Chen-Wei; Liou, Jia-Ming; Chiu, Ya-Ping; He, Qing; Zhan, Qian; Chu, Ying-Hao

2012-02-01

121

Tuning the formation and functionalities of ultrafine CoFe2O4 nanocrystals via interfacial coherent strain  

NASA Astrophysics Data System (ADS)

Complex oxide nanocrystals with a spinel structure show their remarkable optical, electronic, mechanical, thermal, and magnetic properties. In this study, we present a simple yet versatile strategy to grow self-assembled epitaxial CoFe2O4 nanocrystals with well-controlled size (less than 10 nm) and single orientation. CoFe2O4 nanocrystals were fabricated via phase separation in a BiFeO3-CoF2O4 ultrathin film by pulsed laser deposition. The coherent strain at the BiFeO3-CoF2O4 interface suppressed the growth of the nanocrystals regardless of substrate temperatures. This strain also resulted in the ferromagnetic anisotropy and interesting conducting behaviors of ultrafine CFO nanocrystals.

Hsieh, Ying-Hui; Kuo, Ho-Hung; Liao, Sheng-Chieh; Liu, Heng-Jui; Chen, Ying-Jiun; Lin, Hong-Ji; Chen, Chien-Te; Lai, Chih-Huang; Zhan, Qian; Chueh, Yu-Lun; Chu, Ying-Hao

2013-06-01

122

Strong in-plane magnetic anisotropy in (111)-oriented CoFe2O4 thin film  

NASA Astrophysics Data System (ADS)

The perfect (111)-oriented CoFe2O4 thin films were grown on Pt(111)/Si substrate by pulsed laser deposition technique at substrate temperature of 600 °C. The optimum oxygen pressure was found to be 10 mTorr based on structural and magnetic properties. The film grown at 10 mTorr has the highest (111)-orientation degree and magnetization. The films are under in-plane tensile stress due to the residual thermal strain which is thickness-dependent. It was found that the (111)-oriented CoFe2O4 thin film demonstrates the strong in-plane magnetic anisotropy which results from orientation as well as the stress-induced magnetic anisotropy.

Khodaei, M.; Seyyed Ebrahimi, S. A.; Park, Yong Jun; Ok, Jong Mok; Kim, Jun Sung; Son, Junwoo; Baik, Sunggi

2013-08-01

123

Tuning the formation and functionalities of ultrafine CoFe2O4 nanocrystals via interfacial coherent strain.  

PubMed

Complex oxide nanocrystals with a spinel structure show their remarkable optical, electronic, mechanical, thermal, and magnetic properties. In this study, we present a simple yet versatile strategy to grow self-assembled epitaxial CoFe2O4 nanocrystals with well-controlled size (less than 10 nm) and single orientation. CoFe2O4 nanocrystals were fabricated via phase separation in a BiFeO3-CoF2O4 ultrathin film by pulsed laser deposition. The coherent strain at the BiFeO3-CoF2O4 interface suppressed the growth of the nanocrystals regardless of substrate temperatures. This strain also resulted in the ferromagnetic anisotropy and interesting conducting behaviors of ultrafine CFO nanocrystals. PMID:23732994

Hsieh, Ying-Hui; Kuo, Ho-Hung; Liao, Sheng-Chieh; Liu, Heng-Jui; Chen, Ying-Jiun; Lin, Hong-Ji; Chen, Chien-Te; Lai, Chih-Huang; Zhan, Qian; Chueh, Yu-Lun; Chu, Ying-Hao

2013-07-21

124

Quantitative determination of anisotropic magnetoelectric coupling in BiFeO3-CoFe2O4 nanostructures  

NASA Astrophysics Data System (ADS)

The transverse and longitudinal magnetoelectric susceptibilities (MES) were quantitatively determined for (001) heteroepitaxial BiFeO3-CoFe2O4 nanostructures. Both of these MES values were sharply enhanced at magnetic fields below 6 kOe and revealed asymmetric line shapes with respect to the dc magnetic field, demonstrating the strain-induced magnetoelectric effect. The maximum transverse MES, which reached as high as ~60 mV/cm Oe, was about five times larger than the longitudinal MES. This observation signifies that transverse magnetostriction of the CoFe2O4 nanopillars is enhanced more than the bulk value due to preferred magnetic domain alignment along the [001] direction coming from compressive, heteroepitaxial strain.

Oh, Yoon Seok; Crane, S.; Zheng, H.; Chu, Y. H.; Ramesh, R.; Kim, Kee Hoon

2010-08-01

125

Quantitative determination of anisotropic magnetoelectric coupling in BiFeO3-CoFe2O4 nanostructures  

Microsoft Academic Search

The transverse and longitudinal magnetoelectric susceptibilities (MES) were quantitatively determined for (001) heteroepitaxial BiFeO3-CoFe2O4 nanostructures. Both of these MES values were sharply enhanced at magnetic fields below 6 kOe and revealed asymmetric line shapes with respect to the dc magnetic field, demonstrating the strain-induced magnetoelectric effect. The maximum transverse MES, which reached as high as ~60 mV\\/cm Oe, was about

Yoon Seok Oh; S. Crane; H. Zheng; Y. H. Chu; R. Ramesh; Kee Hoon Kim

2010-01-01

126

Epitaxial growth of the CoFe 2O 4 film on SrTiO 3 and its characterization  

NASA Astrophysics Data System (ADS)

Cobalt ferrite (CoFe 2O 4) thin film is epitaxially grown on (0 0 1) SrTiO 3 (STO) by laser molecular beam epitaxy (LMBE). The growth modes of CoFe 2O 4 (CFO) film are found to be sensitive to laser repetition, the transitions from layer-by-layer mode to Stranski-Krastanov (SK) mode and then to island mode occur at the laser repetition of 3 and 5 Hz at 700 °C, respectively. The X-ray diffraction (XRD) results show that the CFO film on (0 0 1) SrTiO 3 is compressively strained by the underlying substrate and exhibits high crystallinity with a full-width at half-maximum of 0.86°. Microstructural studies indicate that the as-deposited CFO film is c-oriented island structure with rough surface morphology and the magnetic measurements reveal that the compressive strained CoFe 2O 4 film exhibits an enhanced out-of-plane magnetization (190 emu/cm 3) with a large coercivity (3.8 kOe).

Huang, W.; Zhou, L. X.; Zeng, H. Z.; Wei, X. H.; Zhu, J.; Zhang, Y.; Li, Y. R.

2007-03-01

127

High-pressure x-ray diffraction and Raman spectroscopic studies of the tetragonal spinel CoFe2O4  

Microsoft Academic Search

In situ x-ray diffraction and Raman spectroscopy have been carried out to pressures of 93.6 and 63.2 GPa, respectively, to explore the pressure-induced phase transformation of CoFe2O4 spinel. CoFe2O4 adopts a distorted tetragonal spinel structure at one atmosphere. At a pressure of ˜32.5 GPa, both x-ray diffraction and Raman spectroscopy indicate that CoFe2O4 transforms to the orthorhombic CaFe2O4 structure, which

Zhongwu Wang; R. T. Downs; V. Pischedda; R. Shetty; S. K. Saxena; C. S. Zha; Y. S. Zhao; D. Schiferl; A. Waskowska

2003-01-01

128

Role of spinel substrate in the morphology of BiFeO3-CoFe2O4 epitaxial nanocomposite films  

Microsoft Academic Search

Epitaxial thin films of BiFeO3-CoFe2O4 composite were grown on spinel MgAl2O4 substrates with a (001) orientation. The composite formed an intriguing nanogrid structure where perovskite BiFeO3 forms linear mounds embedded in a matrix of spinel CoFe2O4. The structure makes a stark distinction with similar composite films on (001) perovskite SrTiO3 substrates where CoFe2O4 forms nanopillars surrounded by a BiFeO3 matrix.

Ilan Stern; Jibao He; Xiaolan Zhou; Punam Silwal; Ludi Miao; Jose Marcelo Vargas; Leonard Spinu; Dae Ho Kim

2011-01-01

129

Could microwave induced catalytic oxidation (MICO) process over CoFe2O4 effectively eliminate brilliant green in aqueous solution?  

PubMed

In this study, we adopted the chemical co-precipitation (CP) method and sol-gel method followed by calcination at temperatures of 100-900°C for 12h to synthesize CoFe2O4 materials, which were further characterized by TEM, XRD and XPS techniques. The properties of CoFe2O4 materials were evaluated in a microwave (MW) induced catalytic oxidation (MICO) process for the elimination of brilliant green (BG). The results showed that: (1) the removal rates of BG gradually decreased over a series of CoFe2O4 materials prepared by CP method and calcinated with 100-700°C (except 900°C) for 12h within three reuse cycles; for comparison, no removal of BG was obtained over CoFe2O4 synthesized by sol-gel method and CoFe2O4-900 (CP); (2) no hydroxyl radicals were captured with salicylic acid used as molecular probe in the MICO process; (3) MW irradiation enhanced the release of residual NaOH within the microstructure of CoFe2O4 and further discolored BG, because BG is sensitive to pH; (4) granular activated carbon (GAC), an excellent MW-absorbing material possessing higher dielectric loss tangent compared to that of a series of CoFe2O4 materials, could not remove BG in suspensions at a higher efficiency, even if the loading amount was 20 g L(-1). Accordingly, MICO process over CoFe2O4 materials and GAC could not effectively eliminate BG in suspensions. PMID:24220199

Ju, Yongming; Wang, Xiaoyan; Qiao, Junqin; Li, Guohua; Wu, You; Li, Yuan; Zhang, Xiuyu; Xu, Zhencheng; Qi, Jianying; Fang, Jiande; Dionysiou, Dionysios D

2013-12-15

130

Influence of grain size dispersion on the magnetic properties of nanogranular BaTiO3-CoFe2O4 thin films.  

PubMed

Thin film nanogranular composites of cobalt ferrite (CoFe2O4) dispersed in a barium titanate (BaTiO3) matrix were deposited by laser ablation with different cobalt ferrite concentrations (x). Their structural and magnetic properties were characterized. The films were polycrystalline and composed by a mixture of tetragonal-BaTiO3 and CoFe2O4 with the cubic spinel structure. A slight (111) barium titanate phase orientation and (311) CoFe2O4 phase orientation were observed. The lattice parameter of the CoFe2O4 was always smaller than the bulk value indicating that the cobalt ferrite was under compressive stress. From atomic force microscopy a broad distribution of grain sizes was observed in the nanocomposites, with a significant amount of smaller grains (<40 nm) from the CoFe2O4 phase. The magnetic measurements show an increase of the magnetic moment from the low concentration region where the magnetic grains are more isolated and their magnetic interaction is small, towards the bulk value for higher CoFe2O4 content in the films. A corresponding decrease of coercive field with increasing cobalt ferrite concentration was also observed, due to the higher inter-particle magnetic interaction (and reduced stress) of the agglomerated grains. PMID:19504912

Barbosa, J; Almeida, B G; Mendes, J A; Leitão, D; Araújo, J P

2009-06-01

131

Multiferroic behavior and impedance spectroscopy of bilayered BiFeO3\\/CoFe2O4 thin films  

Microsoft Academic Search

Lead-free bilayered multiferroic thin films consisting of BiFeO3 (BFO) and CoFe2O4 (CFO) layers with different thicknesses were grown on SrRuO3-coated Pt\\/TiO2\\/SiO2\\/Si substrates by radio frequency sputtering. The effects of constituent layer thicknesses on the ferroelectric and magnetic behavior have been studied. The physical behaviors are shown to strongly depend on the thicknesses of the constituent layers. BFO (220 nm)\\/CFO (30

Jiagang Wu; John Wang

2009-01-01

132

Thickness dependence of the magnetoelastic effect of CoFe2O4 films grown on piezoelectric substrates  

NASA Astrophysics Data System (ADS)

Epitaxial CoFe2O4 (CFO) films of varying thickness were grown on piezoelectric Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrates. The magnetic anisotropy of the CFO films is controlled by the piezoelectric in-plane strain imposed by the substrate constraint during application of an electric field. We find that the strain-induced change of the remanent magnetization is constant at large thickness, but drops significantly below ~100 nm. This thickness dependence of the magnetoelastic effect is shown not to be caused by a variation of the as-grown strain state.

Rus, S. F.; Herklotz, A.; Roth, R.; Schultz, L.; Dörr, K.

2013-07-01

133

Tuning of the magnetostrictive properties of CoFe2O4 by Mn substitution for Co  

Microsoft Academic Search

Marked changes in the magnetostriction of CoFe2O4 in the substitution of\\u000a Mn for Co has been observed. The magnetostriction parallel to the\\u000a applied field direction decreases with increasing Mn content, whereas\\u000a the magnetostriction perpendicular to the field showed a marked increase\\u000a for 10\\\\% of the Mn substitution. The observed magnetostrictive\\u000a properties are correlated with the magnetic properties. The results\\u000a suggest

Shekhar D. Bhame; P. A. Joy

2006-01-01

134

Local Dielectric Measurements of BaTiO3-CoFe2O4 Nanocomposites Through Microwave Microscopy  

Microsoft Academic Search

We report on linear and non-linear dielectric property measurements of BaTiO3\\u000a- CoFe2O4 (BTO-CFO) ferroelectro-magnetic nano-composites and pure BaTiO3 and\\u000aCoFe2O4 samples with Scanning Near Field Microwave Microscopy. The permittivity\\u000ascanning image with spatial resolution on the micro-meter scale shows that the\\u000anano-composites have very uniform quality with an effective dielectric constant\\u000a\\\\epsilon_r = 140 +\\/- 6.4 at 3.8 GHz

Yi Qi; H. Zheng; R. Ramesh; Steven M. Anlage

2006-01-01

135

Preparation of CoFe2O4 Spin Valves and Improvement of Their Magnetoresistance Property by Postannealing  

Microsoft Academic Search

We have fabricated spin valves which had the simple structure of Si\\/SiO2\\/CoFe2O4 (40 nm)\\/Co (2 nm)\\/Cu (2 nm)\\/Co (4 nm) by rf-magnetron sputtering at room temperature. A hard magnetic and insulating Co-ferrite film was used as a pinning layer. As-deposited films showed a high sheet resistance of 36.3 Omega\\/square and a magnetoresistance (MR) ratio of 4.5%. The MR property of

Hiroshi Naganuma; Soichiro Okamura; Hiroshi Sakakima; Tadashi Shiosaki

2003-01-01

136

Synthesis and magnetic characterization of novel CoFe 2O 4–BiFeO 3 nanocomposites  

Microsoft Academic Search

The novel mixed spinel–perovskite nanocomposites of xCoFe2O4(1?x)BiFeO3 (x=0.1, 0.2, 0.3, 0.4) have been prepared by sol–gel technique. The structure and morphology of the composites were examined by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction (ED). The XRD and TEM results showed that the composites consisted of spinel CoFe2O4 and perovskite BiFeO3 after annealing at a

Xian-Ming Liu; Shao-Yun Fu; Chuan-Jun Huang

2005-01-01

137

Directed self-assembly of epitaxial CoFe2O(4)-BiFeO3 multiferroic nanocomposites.  

PubMed

CoFe(2)O(4) (CFO)-BiFeO(3) (BFO) nanocomposites are an intriguing option for future memory and logic technologies due to the magnetoelectric properties of the system. However, these nanocomposites form with CFO pillars randomly located within a BFO matrix, making implementation in devices difficult. To overcome this, we present a technique to produce patterned nanocomposites through self-assembly. CFO islands are patterned on Nb-doped SrTiO(3) to direct the self-assembly of epitaxial CFO-BFO nanocomposites, producing square arrays of CFO pillars. PMID:22486737

Comes, Ryan; Liu, Hongxue; Khokhlov, Mikhail; Kasica, Richard; Lu, Jiwei; Wolf, Stuart A

2012-05-01

138

CoFe2O4 and/or Co3Fe7 loaded porous activated carbon balls as a lightweight microwave absorbent.  

PubMed

In order to prepare a lightweight and efficient microwave absorbent, porous activated carbon balls (PACB) were used to load Fe(3+) and Co(2+) ions, because the PACB carrier has a high specific surface area of 800 m(2) g(-1) and abundant pores, including micropores and macropores. The loaded Fe(3+) and Co(2+) ions in the PACB composite were transformed into magnetic CoFe2O4 and/or Co3Fe7 particles during subsequent heat-treatment under an Ar atmosphere. According to the XRD and SEM results, the magnetic particles were embedded in the PACB macropores and showed different crystalline phases and morphologies after heat-treatment. CoFe2O4 flakes with spinel structure were obtained at approximately 450 °C, and were then transformed into loose quasi-spheres between 500 °C and 600 °C, where CoFe2O4 and Co3Fe7 coexisted because of the partial reduction of CoFe2O4. Co3Fe7 microspheres appeared above 700 °C. The density of the magnetic PACB composites was in the range of 2.2-2.3 g cm(-3). The as-synthesized PACB composites exhibited excellent microwave absorbability, which was mainly attributed to the magnetism of CoFe2O4 and Co3Fe7, as well as the presence of graphitized carbon. The minimum reflection loss value of the CoFe2O4-Co3Fe7-PACB composite reached -32 dB at 15.6 GHz, and the frequency of microwave absorption obeyed the quarter-wavelength matching model, showing a good match between dielectric loss and magnetic loss. The microwave reflection loss (RL) value could be modulated by adjusting the composition and thickness of the PACB composite absorbent. PACB composites with CoFe2O4-Co3Fe7 are a promising candidate for lightweight microwave absorption materials. PMID:24829135

Li, Guomin; Wang, Liancheng; Li, Wanxi; Ding, Ruimin; Xu, Yao

2014-06-28

139

Band gap hierarchy of single crystal CoFe2O4 thin films from optical absorption spectroscopy  

NASA Astrophysics Data System (ADS)

Thin film materials have a wide variety of applications and also serve as an useful bridge between bulk single crystals and the nanoscale. In this work, we report temperature-dependent optical absorption spectroscopy of single crystal CoFe2O4 thin-films along with complimentary electronic structure analysis. This magnetic insulator has one of the highest Curie temperature among complex oxides and potentially useful in areas such as spintronics. Similar to its Nickel analogue,footnotetextQ.C. Sun, H. Sims, D.Mazumdar, J.X.Ma, B. Holinswoth, K.O'Neal, G.Kim, W.H.Butler, A.Gupta, and J.Musfeldt (accepted to Phys. Rev. B). our work reveals CoFe2O4 to be an indirect band gap material (1.2 eV) with a direct gap much higher (2.8eV) at 300K. These gap values are robust down to 4.2K. Electronically, both chemical tuning and inversion fraction are found to be important factors in lowering of the band gap compared to NiFe2O4.

Holinsworth, Brian; Sims, Hunter; Mazumdar, Dipanjan; Sun, Qi; Yurtisigi, Mehmet; Sarker, Sanjoy; Gupta, Arun; Butler, Bill; Musfeldt, Janice

2013-03-01

140

Magnetic studies of CoFe2O4/SiO2 aerogel and xerogel nanocomposites.  

PubMed

The evolution of the structural and magnetic properties of nanocomposites formed by cobalt ferrite particles dispersed in xerogel and aerogel silica matrices (CoFe2O4/SiO2) have been studied as a function of the temperature of preparation and the amount of ferrite dispersed in the matrix. Wet samples with different amounts of CoFe2O4 in SiO2 matrix were prepared by sol-gel process in monolithic form. Xerogel and aerogel samples were prepared by controlled and hypercritical drying, respectively, and heated at various temperatures between 300 and 1100 degrees C. Superparamagnetic behavior has been observed by magnetization studies at room temperature for xerogels prepared at low temperature. Aerogel samples showed significant superparamagnetic fractions for all thermal treatment temperatures as determined by Mössbauer spectroscopy. Magnetization of the nanocomposites at 10 KOe applied field varied from 1 to 19 emu/g and the coercivity from 90 to 2320 Oe, respectively, for the different morphologies and textures of the analyzed material. The results show that besides the magnetization and coercivity depend on crystallite size, parameters such as ferrite content, porosity and drying conditions greatly influence the nanocomposite magnetic behavior. PMID:19908477

da Silva, J B; Mohallem, N D S; Sinnecker, E; Novak, M A; Alburquerque, A S; Ardisson, J D; Macedo, W A

2009-10-01

141

Deposition of epitaxial BiFeO3/CoFe2O4 nanocomposites on (001) SrTiO3 by combinatorial pulsed laser deposition  

NASA Astrophysics Data System (ADS)

BiFeO3/CoFe2O4 (BFO/CFO) nanocomposites were grown on SrTiO3 by pulsed laser deposition using a combinatorial method in which Bi1.2FeO3 and CoFe2O4 targets are alternately ablated. The films had the same vertically nanostructured morphology as thin films prepared by ablation of a single target, consisting of epitaxial CoFe2O4 pillars in a BiFeO3 matrix. In a series of samples synthesized with a compositional spread, the out-of-plane magnetic anisotropy and the out-of-plane compressive strain of the CoFe2O4 pillars increased with decreasing volume fraction, and the anisotropy agreed with the value predicted from the strain state and magnetoelastic coefficients of CoFe2O4. These results show the dominant effect of magnetoelastic anisotropy in determining the magnetic hysteresis of the nanocomposite.

Aimon, Nicolas M.; Hun Kim, Dong; Kyoon Choi, Hong; Ross, C. A.

2012-02-01

142

Synthesis, structure, and magnetic studies on the CoFe2O4-BiFeO3 nanocomposite films with different number of CoFe2O4 layers  

NASA Astrophysics Data System (ADS)

The multiferroic heterostructures consisting of CoFe2O4 (CFO)-BiFeO3 (BFO) layers with increasing the number of CFO layers (2, 4, 6 and 8) have been grown on LaNiO3 buffered Si (1 0 0) substrate by a simple sol-gel spin-coating route. X-ray diffraction (XRD) shows that the CFO and BFO phases have been successfully retained in the heterostructures and the films are polycrystalline. The high resolution transmission electron microscope (HRTEM) images show the clear interplanar distances and the interface between the two phases. The magnetization (M) versus field (H) loops reveal that, with increasing the CFO layers, the magnetization of CFO-BFO films will be enhanced. The Ms, Mr and Hc of the composite film with 8 CFO layers are measured to be the largest values of 1304 emu/cm3, 562 emu/cm3 and 2074 Oe, respectively.

Liu, Y. Q.; Zhang, B.; Wu, Y. H.; Zhang, J.; Li, D.; Liu, Y.; Wei, M. B.; Yang, J. H.

2013-09-01

143

Selectable spontaneous polarization direction and magnetic anisotropy in BiFeO3-CoFe2O4 epitaxial nanostructures.  

PubMed

We demonstrate that epitaxial strain engineering is an efficient method to manipulate the ferromagnetic and ferroelectric properties in BiFeO(3)-CoFe(2)O(4) columnar nanocomposites. On one hand, the magnetic anisotropy of CoFe(2)O(4) is totally tunable from parallel to perpendicular controlling the CoFe(2)O(4) strain with proper combinations of substrate and ferroelectric phase. On the other hand, the selection of the used substrate allows the growth of the rhombohedral bulk phase of BiFeO(3) or the metastable nearly tetragonal one, which implies a rotation of the ferroelectric polar axis from [111] to close to the [001] direction. Remarkably, epitaxy is preserved and interfaces are semicoherent even when lattice mismatch is above 10%. The broad range of sustainable mismatch suggests new opportunities to assemble epitaxial nanostructures combining highly dissimilar materials with distinct functionalities. PMID:20666444

Dix, Nico; Muralidharan, Rajaram; Rebled, Jose-Manuel; Estradé, Sonia; Peiró, Francesca; Varela, Manuel; Fontcuberta, Josep; Sánchez, Florencio

2010-08-24

144

Magnetic properties of nanocrystalline CoFe 2O 4 synthesized by modified citrate-gel method  

NASA Astrophysics Data System (ADS)

Nanocrystalline CoFe 2O 4 with an average grain size of about 40 nm was successfully prepared by a modified citrate-gel method. At temperatures of 3 and 300 K, the measured coercive fields are 0.43 and 0.07 T and the magnetizations at 7 T are 89 and 83 emu/g, respectively. At room temperature, the longitudinal and transversal magnetostriction values are -130 and 70 ppm, respectively. The contribution of a disordered magnetic phase was detected by the occurrence of a peak in the ac-susceptibilities curves at around 250 K. The temperature dependence of the field-cooled and zero field-cooled low-field magnetization showed a larger irreversibility below this temperature. This disordered phase behaves like a spin-glass, which is coexisting with the ferrimagnetically ordered main phase

Sato Turtelli, R.; Duong, Giap V.; Nunes, W.; Grössinger, R.; Knobel, M.

145

Magnetic Properties of Liquid-Phase Sintered CoFe2O4 for Application in Magnetoelastic and Magnetoelectric Transducers  

PubMed Central

Cobalt ferrite is a ferrimagnetic magnetostrictive ceramic that has potential application in magnetoelastic and magnetoelectric transducers. In this work, CoFe2O4 was obtained using a conventional ceramic method and Bi2O3 was used as additive in order to obtain liquid-phase sintered samples. Bi2O3 was added to the ferrite in amounts ranging from 0.25 mol% to 0.45 mol% and samples were sintered at 900 °C and 950 °C. It was observed the presence of Bi-containing particles in the microstructure of the sintered samples and the magnetostriction results indicated microstructural anisotropy. It was verified that it is possible to get dense cobalt ferrites, liquid-phase sintered, with relative densities higher than 90% and with magnetostriction values very close to samples sintered without additives.

de Brito, Vera Lucia Othero; Cunha, Stephanie Ala; Lemos, Leonardo Violim; Nunes, Cristina Bormio

2012-01-01

146

Multiferroic nanoparticulate Bi3.15Nd0.85Ti3O12-CoFe2O4 composite thin films prepared by a chemical solution deposition technique  

NASA Astrophysics Data System (ADS)

Multiferroic xBi3.15Nd0.85Ti3O12-(1-x)CoFe2O4 composite thin films with x=0.5, 0.6, and 0.7 were fabricated on Pt/Ti/SiO2/Si(100) substrates by a chemical solution deposition technique. X-ray diffraction shows that there are no other phases but bismuth-layered perovskite Bi3.15Nd0.85Ti3O12 and spinel CoFe2O4 phases in the films. Scanning electron microscopy reveals that CoFe2O4 aggregates locally into nanoparticles and embeds in the Bi3.15Nd0.85Ti3O12 matrix. The composite films exhibit both good ferroelectric and magnetic properties at room temperature, as well as distinct magnetoelectric coupling behaviors, which are comparable with those of multiferroic composite films with conventional Pb-based ferroelectric as a ferroelectric component.

Zhong, X. L.; Wang, J. B.; Liao, M.; Huang, G. J.; Xie, S. H.; Zhou, Y. C.; Qiao, Y.; He, J. P.

2007-04-01

147

Chemical tuning of the optical band gap in spinel ferrites: CoFe2O4 vs NiFe2O4  

NASA Astrophysics Data System (ADS)

We measured the optical properties of epitaxial CoFe2O4 thin films and compared our findings with complementary electronic structure calculations and similar studies on the Ni analog. Our work reveals CoFe2O4 to be an indirect band gap material (1.2 eV, X --> ? in the spin-down channel) with a direct gap at 2.7 eV. The latter is robust up to 800 K. Compared to NiFe2O4, the indirect gap is ~0.5 eV lower, a difference we discuss in terms of size and covalency effects in spinel ferrites.

Holinsworth, B. S.; Mazumdar, D.; Sims, H.; Sun, Q.-C.; Yurtisigi, M. K.; Sarker, S. K.; Gupta, A.; Butler, W. H.; Musfeldt, J. L.

2013-08-01

148

Modification of Ferroelectric Properties of BaTiO3-CoFe2O4 Multiferroic Composite Thin Film by Application of Magnetic Field  

Microsoft Academic Search

We prepared BaTiO3-CoFe2O4 composite thin film on (La0.5Sr0.5)CoO3\\/CeO2\\/YSZ\\/Si(100) substrate by pulsed laser deposition. Simultaneous epitaxial growths of BaTiO3 and CoFe2O4 were achieved. Reciprocal space map measurement revealed that the lattice parameters of BaTiO3 parallel and perpendicular to the substrate are 0.4239 and 0.4060 nm, respectively. The fact that both lattice parameters are larger than those of the bulk (a =

Shigeki Sawamura; Naoki Wakiya; Naonori Sakamoto; Kazuo Shinozaki; Hisao Suzuki

2008-01-01

149

Synthesis and characterization of SrFe 12O 19\\/CoFe 2O 4 nanocomposites with core-shell structure  

Microsoft Academic Search

SrFe12O19\\/CoFe2O4 nanocomposites with core-shell structure were successfully synthesized with two-step coprecipitation method. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Raman spectroscopy, vibrating sample magnetometer (VSM) and radar absorbing material reflectivity far field radar cross-section method, respectively. XRD and TEM results show that CoFe2O4 shell is obtained on the surface of SrFe12O19. And Raman spectra confirm

Liuyang Zhang; Zuowei Li

2009-01-01

150

Controlled growth of monodisperse self-supported superparamagnetic nanostructures of spherical and rod-like CoFe2O4 nanocrystals.  

PubMed

Novel shape- and structural-controlled superparamagnetic nanostructures composed of self-supported spherical and rod-like CoFe(2)O(4) colloidal nanocrystals have been prepared by thermolysis of a stoichiometric Co(2+)Fe(2)(3+)-oleate complex in organic solution with periodic injection of hexane for controlling the nucleation, assembly, and growth of the nuclei. PMID:19691318

Bao, Ningzhong; Shen, Liming; Wang, Yu-Hsiang A; Ma, Jianxing; Mazumdar, Dipanjan; Gupta, Arunava

2009-09-16

151

Exchange Coupling and Spin-Flip Transition of CoFe2O4/alpha-Fe2O3 Bilayered Films.  

National Technical Information Service (NTIS)

CoFe2O4/alpha-Fe2O3 (ferrimagnetic/antiferromagnetism) bilayered films were prepared on alpha-Al2O3(102) single-crystalline substrates by helicon plasma sputtering. A well-crystallized epitaxial alpha-Fe2O3(102) layer was formed on the substrate, while Co...

J. Takada M. Nakanishi T. Fujii T. Yano

2001-01-01

152

Direct formation of reusable TiO2/CoFe2O4 heterogeneous photocatalytic fibers via two-spinneret electrospinning.  

PubMed

A reusable photocatalytic TiO2/CoFe2O4 composite nanofiber was directly formed by using a vertical two-spinneret electrospinning process and sol-gel method, followed by heat treatment at 550 degrees C for 2 h. The high photocatalytic activity of the composite nanofibers depends on the good morphology of the fibers and the appropriate calcination temperature. The crystal structure and magnetic properties of the fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The photocatalytic activity of the TiO2/CoFe2O4 fibers was investigated through ultraviolet-visible absorbance following the photo-oxidative decomposition of phenol. Meanwhile, the presence of CoFe2O4 not only broadens the response region of visible light, but also enhances the absorbance of UV light. Furthermore, these fibers displayed photocatalytic activity associated with magnetic activity of CoFe2O4 ferrites, allowing easy separated of the photocatalysts after the photo-oxidative process and effectively avoided the secondary pollution of the treated water. PMID:22755080

Li, Cong-Ju; Wang, Jiao-Na; Wang, Bin; Gong, Jian Ru; Lin, Zhang

2012-03-01

153

A contribution to the investigation of fine-particle solid solutions between cubic iron sesquioxide ?Fe2O3and cobalt ferrite CoFe2O4  

Microsoft Academic Search

The authors give the chemical, morphological, crystallographic, and magnetic properties of solid solutions between cubic iron sesquioxide ?Fe2O3and cobalt ferrite CoFe2O4obtained as fine particles by a new preparation method. This method gives the whole range of compositions and allows shifting of the magnetic and morphological features in a direction suitable for magnetic recording applications.

PAUL MOLLARD; A. Collomb; J. Devenyi; A. Rousset

1975-01-01

154

Investigation of nanocrystalline CoFe2O4 by positron annihilation lifetime spectroscopy  

Microsoft Academic Search

Nanoparticles of cobalt ferrite prepared by the co-precipitation method with crystallite size varying from 4.7 to 41 nm have been characterized by positron annihilation lifetime spectroscopy. Three lifetime components are fitted to the lifetime data. The shortest lifetime component is attributed to the delocalized positron lifetime shortened by defect trapping. The intermediate lifetime is assigned to the positron annihilation in

S. Bandyopadhyay; A. Roy; D. Das; S. S. Ghugre; J. Ghose

2003-01-01

155

Controlled synthesis and magnetic properties of bimagnetic spinel ferrite CoFe2O4 and MnFe2O4 nanocrystals with core-shell architecture.  

PubMed

A combination of hard phase CoFe(2)O(4) and soft phase MnFe(2)O(4) as the bimagnetic nanocrystals in a core-shell architecture has been synthesized, and their magnetic properties have been systematically studied. Both HRTEM and EDS results confirmed the formation of bimagnetic core-shell structured nanocrystals. On the basis of the systematic and comparative studies of the magnetic properties of a mechanical mixture of pure CoFe(2)O(4) and MnFe(2)O(4) nanocrystals, chemically mixed Co(1-x)Mn(x)Fe(2)O(4) nanocrystals, and bimagnetic core-shell CoFe(2)O(4)@MnFe(2)O(4) and MnFe(2)O(4)@CoFe(2)O(4) nanocrystals, the bimagnetic core-shell nanocrystals show very unique magnetic properties, such as the blocking temperature and coercivity. Our results show that the coercivity correlates with the volume fraction of the soft phase as the theoretical hard-soft phase model has suggested. Furthermore, switching the hard phase CoFe(2)O(4) from the core to the shell shows great changes in the coercivity of the nanocrystals. The bimagnetic core-shell nanocrystals evidently demonstrate the rational design capability to separately control the blocking temperature and the coercivity in magnetic nanocrystals by varying the materials, their combination, and the volume ratio between the core and the shell and by switching hard or soft phase materials between the core and shell. Such controls via a bimagnetic core-shell architecture are highly desirable for magnetic nanocrystals in various applications. PMID:22621435

Song, Qing; Zhang, Z John

2012-06-20

156

Enhanced magnetostrictive properties of CoFe2O4 synthesized by an autocombustion method  

Microsoft Academic Search

The magnetostrictive properties of sintered cobalt ferrite derived from\\u000a nanocrystalline powders synthesized by three different low-temperature\\u000a methods (citrate, coprecipitation and autocombustion) and the\\u000a high-temperature ceramic method have been compared. A strong dependence\\u000a of the magnetostrictive strain is observed on the initial morphology of\\u000a the ferrite particles and the microstructure of the final sintered\\u000a product. The nanoparticles synthesized by the autocombustion

S. D. Bhame; P. A. Joy

2007-01-01

157

Crossover of uniaxial magnetic anisotropy direction mediated by interfacial strain of CoFe2O4 films  

NASA Astrophysics Data System (ADS)

This study examined the deposition temperature-dependent magnetic anisotropy of CoFe2O4 films grown on Al2O3(0001) substrates using pulsed-laser deposition. X-ray diffraction revealed all films to have a <111> orientation except for the films grown at room temperature, which exhibited amorphous characteristics. Furthermore, the films deposited between 350 °C and 550 °C exhibited out-of-plane tensile strain even though, which was relieved as the deposition temperature increased. On the other hand, film deposited at 650 °C showed out-of-plane compressive strain. The in-plane and out-of-plane magnetic hysteresis loops, which were measured at room temperature, showed a decreased out-of-plane anisotropy when the deposition temperature was increased. Simple uniaxial magnetic anisotropy energy calculations based on the experimental data showed a direct correlation between the uniaxial magnetic anisotropy direction and stress of the films. X-ray photoelectron spectroscopy revealed variations in the cation distribution according to the deposition temperature.

Cho, C.-W.; Lee, D. Y.; Bae, J. S.; Park, S.

2014-11-01

158

Epitaxial Bi5Ti3FeO15-CoFe2O4 pillar-matrix multiferroic nanostructures.  

PubMed

Epitaxial self-assembled ferro(i)magnetic spinel (CoFe2O4 (CFO)) and ferroelectric bismuth layered perovskite (Bi5Ti3FeO15 (BTFO)) pillar-matrix nanostructures are demonstrated on (001) single-crystalline strontium titanate substrates. The CFO remains embedded in the BTFO matrix as vertical pillars (?50 nm in diameter) up to a volume fraction of 50%. Piezoresponse force microscopy experiments evidence a weak out-of-plane and a strong in-plane ferroelectricity in the BTFO phase, despite previously reported paraelectricity along the c-axis in a pure BTFO film. Phenomenological Landau-Ginzburg-Devonshire-based thermodynamic computations show that the radial stress induced by the CFO nanopillars can influence these ferroelectric phases, thus signifying the importance of the nanopillars. The CFO pillars demonstrate robust ferromagnetic hysteresis loops with little degradation in the saturation magnetization (ca. 4 ?B/f.u.). Thus BTFO-CFO nanocomposites show significant promise as a lead-free magnetoelectric materials system. PMID:24215598

Imai, Akira; Cheng, Xuan; Xin, Huolin L; Eliseev, Eugene A; Morozovska, Anna N; Kalinin, Sergei V; Takahashi, Ryota; Lippmaa, Mikk; Matsumoto, Yuji; Nagarajan, Valanoor

2013-12-23

159

Molecular Beam Epitaxial Growth and Properties of CoFe2O4 on MgO(001)  

SciTech Connect

We have grown single-crystal Co ferrite (CoFe2O4) on MgO(001) by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE), and have characterized the composition, structure, surface morphology, and magnetic properties by a number of methods The as-grown OPA-MBE material forms a perfect inverse spinel, in which all Co is in the? formal oxidation state, and occupies octahedral sites within the cation sublattice. The OPA-MBE film surfaces are very flat, with mean roughnesses of only a few A, and exhibit large, stable magnetic domains. The measured moment per unit volume is 250 emu/cm3, and the saturation magnetization for films in the 1000A film thickness range is {approx}60% of that of bulk Co ferrite. The material also exhibits strain-dependent magnetic anisotropy that can be understood by considering the various contributions to the total magnetic energy. The overall quality of epitaxial Co ferrite grown on MgO by OPA-MBE is superior in every respect to that obtained using pulsed laser deposition as the growth method.

Chambers, Scott A.; Farrow, Robin F.; Maat, S.; Toney, M.; Folks, L.; Catalano, J.G.; Trainor, T.P.; Brown, G.E. Jr.

2002-04-01

160

Multiferroic behavior and impedance spectroscopy of bilayered BiFeO3/CoFe2O4 thin films  

NASA Astrophysics Data System (ADS)

Lead-free bilayered multiferroic thin films consisting of BiFeO3 (BFO) and CoFe2O4 (CFO) layers with different thicknesses were grown on SrRuO3-coated Pt/TiO2/SiO2/Si substrates by radio frequency sputtering. The effects of constituent layer thicknesses on the ferroelectric and magnetic behavior have been studied. The physical behaviors are shown to strongly depend on the thicknesses of the constituent layers. BFO (220 nm)/CFO (30 nm) bilayered thin film demonstrated much improved ferroelectric and ferromagnetic behavior (2Pr=144.2 ?C/cm2, 2Ec=778.0 kV/cm, Ms=61.2 emu/cm3, and Hc=200.8 Oe) as compared to those of the single layer BFO thin film. The dielectric behavior and conductivity of BFO (220 nm)/CFO (30 nm) bilayered thin film were investigated as a function of both temperature (in the range of 294-534 K) and frequency (in the range of 10-1-106 Hz), where an activation energy of ~1.11 eV for dielectric relaxation was demonstrated. From the conductivity behavior, an activation energies of ~0.98 eV was derived for dc conductivity are, implying that oxygen vacancies are involved in the conduction of the BFO (220 nm)/CFO (30 nm) bilayered film.

Wu, Jiagang; Wang, John

2009-06-01

161

Nucleation of electroactive ?-phase poly(vinilidene fluoride) with CoFe2O4 and NiFe2O4 nanofillers: a new method for the preparation of multiferroic nanocomposites  

NASA Astrophysics Data System (ADS)

Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials. In this paper we report on the nucleation of the electroactive ?-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe2O4 and NiFe2O4 nanoparticles in order to prepare poly(vinylidene fluoride)/ferrite nanocomposite for multiferroic and magnetoelectric applications,. The dispersed ferrite nanofiller particles strongly enhance the nucleation of the ?-phase of the polymer matrix. In this way, magnetoelectric polymer nanocomposites can be processed avoiding the usual ?- to ?-phase transformation by stretching of the polymer matrix.

Martins, P.; Costa, C. M.; Lanceros-Mendez, S.

2011-04-01

162

First-principles calculation of magnetoelastic coefficients and magnetostriction in the spinel ferrites CoFe2O4 and NiFe2O4  

NASA Astrophysics Data System (ADS)

We present calculations of magnetostriction constants for the spinel ferrites CoFe2O4 and NiFe2O4 using density functional theory within the GGA+U approach. Special emphasis is devoted to the influence of different possible cation distributions on the B-site sublattice of the inverse spinel structure on the calculated elastic and magnetoelastic constants. We show that the resulting symmetry lowering has only a negligible effect on the elastic constants of both systems as well as on the magnetoelastic response of NiFe2O4, whereas the magnetoelastic response of CoFe2O4 depends more strongly on the specific cation arrangement. In all cases our calculated magnetostriction constants are in good agreement with available experimental data. Our work thus paves the way for more detailed first-principles studies regarding the effect of stoichiometry and cation inversion on the magnetostrictive properties of spinel ferrites.

Fritsch, Daniel; Ederer, Claude

2012-07-01

163

Magnetoelectric nano-Fe3O4/CoFe2O4?PbZr0.53Ti0.47O3 composite  

NASA Astrophysics Data System (ADS)

A new magnetoelectric hybrid device composed of a nanoparticulate magnetostrictive iron oxide-cobalt ferrite film on a piezoelectric lead zirconic titanate crystal serving as both substrate and straining medium is described. Nano-Fe3O4/CoFe2O4 particles, ranging from 5 to 42 nm, were prepared using a variation of the sol-gel method. A small electric field, 5-10 kV cm-1, applied at the coercive field of the nano-Fe3O4/CoFe2O4 component modulates the film magnetization up to 10% of the saturation magnetization of ferrite. At the smallest particle size of 5 nm, the coercive field is as low as 25 Oe and the inverse MEE voltage coefficient is as high as (10.1 V/cm Oe)-1.

Ren, Shenqiang; Wuttig, Manfred

2008-02-01

164

Enhanced photoluminescence of core-shell CoFe2O4/SiO2/Y2O3:Eu3+ composite by remanent magnetization  

NASA Astrophysics Data System (ADS)

A core-shell cobalt ferrite/silicon dioxide/europium ion-doped Y2O3 (CoFe2O4/SiO2/Y2O3:Eu3+) composite was synthesized by a facile layer-by-layer method. Magnetization of the composite under an external magnetic field of approximately 0.25 T enhanced the photoluminescence (PL) intensity by 56%. The remanent magnetization of the CoFe2O4 core increased the excited charge-transfer transition between O2- and Eu3+ in the Y2O3:Eu3+ shell, thus enhancing the probability of radiative transition (5D0?7F2) of Eu3+ ions and leading to enhanced PL. Remanent magnetization is a noncontact, easy-to-operate technique with high growth amplitude and potential for practical application for smart display devices.

Jia, Yanmin; Zhou, Zhihua; Wei, Yongbin; Wu, Zheng; Wang, Haihang; Chen, Jianrong; Zhang, Yihe; Liu, Yongsheng

2013-12-01

165

Magnetization-induced enhancement of photoluminescence in core-shell CoFe2O4@YVO4:Eu3+ composite  

NASA Astrophysics Data System (ADS)

After the core-shell CoFe2O4@YVO4:Eu3+ composite synthesized through a facile sol-gel method was magnetized under an external magnetic field of 0.25 T for 4 h, an enhancement of ˜56% in photoluminescence intensity was observed. The remanent magnetization of the CoFe2O4 core increases the intensity of the excited charge transfer transition of VO43- group in YVO4:Eu3+ shell, which may enhance the probability related to the Eu3+ radiative transition 5D0-7F2, yielding to a high photoluminescence. The obvious remanent-magnetization-induced enhancement in photoluminescence is helpful in developing excellent magnetic/luminescent material for the practical display devices.

Jia, Yanmin; Zhou, Zhihua; Wei, Yongbin; Wu, Zheng; Chen, Jianrong; Zhang, Yihe; Liu, Yongsheng

2013-12-01

166

dc and high frequency magnetic properties of nanopatterned CoFe2O4 arrays fabricated using sol-gel precursors  

NASA Astrophysics Data System (ADS)

Nanostructures of ferromagnetic oxides having Curie temperatures above room temperature have potential for applications in memory devices and future spin-based electronic applications. In this article, we report on the dc and high frequency magnetic properties of arrays of elliptical CoFe2O4 nanopillars, covering a large area, fabricated by combined electron beam lithography, and a sol-gel based chemical route. The nanopillars were successfully fabricated on insulating oxidized silicon substrates and on epitaxial thin films of ferroelectric BiFeO3. We performed magnetic force microscopy and ferromagnetic resonance spectroscopy on the arrays to probe their magnetic properties. Due to the possible existence of dominant pinning sites, the CoFe2O4 nanopillars are not single-domain even at nanometer size scales.

Sheet, Goutam; Cunliffe, Alexandra R.; Offerman, Erik J.; Folkman, Chad M.; Eom, Chang-Beom; Chandrasekhar, Venkat

2010-05-01

167

Magnetism of CoFe2O4 ultrathin films on MgAl2O4 driven by epitaxial strain  

NASA Astrophysics Data System (ADS)

We report on the correlations between magnetic anisotropy and strain state in CoFe2O4 ultrathin films grown on MgAl2O4(100) and MgAl2O4(111) substrates. By local strain analysis using the geometric phase method, a significant in-plane compressive strain is observed for the (001) orientation while a full relaxation is detected for the (111) orientation. The relaxation process in CoFe2O4(111) layers induces interface dislocations and a large amount of antiphase boundaries while a pseudomorphic growth is observed for the (001) direction, decreasing significantly the density of antiphase boundaries. By comparing the magnetoelastic energy terms, the correlation between strain state and resultant magnetization is discussed.

Gatel, C.; Warot-Fonrose, B.; Matzen, S.; Moussy, J.-B.

2013-08-01

168

Role of epitaxial strain on the magnetic structure of Fe-doped CoFe2O4  

NASA Astrophysics Data System (ADS)

The magnetic structure of Fe-doped CoFe2O4 (Co1-xFe2+xO4) grown on MgO (0 0 1) and SrTiO3 (0 0 1) substrates is studied with superconducting quantum interference device magnetometry and soft x-ray magnetic spectroscopies. X-ray and electron diffraction show that the choice of substrate has large effects on the strain, crystal structure and surface morphology of Co1-xFe2+xO4 thin films. Samples grown on MgO have small, coherent strains and surfaces that are nearly atomically flat, whereas films grown on SrTiO3 have large tensile strains and surfaces terminated with islands, which indicate the presence of a large density of misfit dislocations. These differences in structural properties correlate with the large differences seen in the magnetic structure; samples grown on SrTiO3 have larger magnetic moments and increased anisotropies compared to those grown on MgO. Most strikingly, the large magnetic spin and orbital moments found in the films grown on SrTiO3 suggest a suppression of anti-phase boundary formation, which we attribute to the large compressive lattice mismatch and the formation of misfit dislocations during the film growth in order to relieve the epitaxial strain. This results in the films grown on SrTiO3 having magnetic properties that are more similar to bulk Co1-xFe2+xO4 than those grown on MgO, demonstrating that epitaxial strain can result in large changes in the magnetic structure of Co1-xFe2+xO4.

Moyer, J. A.; Kumah, D. P.; Vaz, C. A. F.; Arena, D. A.; Henrich, V. E.

2013-11-01

169

Fabrication and Electrical Measurements of CoFe2O4 Nanopillars in a BiFeO3 matrix  

NASA Astrophysics Data System (ADS)

Coupling between ferromagnetic and ferroelectric ordering has recently stimulated many scientific and technological interests. This ``coupling'', would provide an additional degree of freedom in the design of micro and nano-electronic devices such as actuators, transducers, or memories. Unfortunately, the clamping effect of the substrate negates any such magnetoelectric coupling through elastic interactions which evident in a multilayer structures. Therefore our focus is directed towads the design of a novel vertically aligned oxide nano-structures, which will allow us to switch the magnetic domains by applying the electric field and vice versa. These nano-structures will also be used as model system to understand the physics of order parameter coupling in ferrroelctric and ferromagnetic systems. We have fabricated ferromagnetic nanopillar arrays of CoFe2O4 (CFO), surrounded by a ferroelectric BiFeO3 (BFO) and BaTiO3 matrix. 90^0 off-axis sputtering is used to deposit SrRuO3 (SRO), followed by CFO on single surface TiO2-terminated SrTiO3 (001) substrates. SRO provides a good lattice match and electrode capabilities for the subsequent deposition of CFO. E-beam patterning defines pillar dimensions and spacing, while ion milling etches down to the SRO layer. The pillar dimensions range between 100 nm and 500 nm in diameter and are spaced 0.5 to 1 ?m apart. Atomic force microscopy and scanning electron microscopy measurements confirm the structure of the pillars following the pattering and etching steps. The BFO ferroelectric matrix is then deposited by on-axis sputtering. Fabrication of these pillars along with piezo force micrcroscopy and magnetic force microscopy was used to understand the microstructure and domain switching. The detailed scanning probe measurements of domain switching in these novel oxide nanostructures will be discussed.

Rutherford, Scott; Das, Rasmi; Ke, Xianglin; Ruzmetov, Dmitry; Kim, Dong-Min; Hyub Baek, Seung; Rzchowski, Mark; Eom, Chang-Beom

2006-03-01

170

Core shell particles consisting of cobalt ferrite and silica as model ferrofluids [CoFe 2O 4–SiO 2 core shell particles  

Microsoft Academic Search

Nearly monodisperse core shell particles consisting of a magnetic core of cobalt ferrite (CoFe2O4) and a shell of silica (SiO2) are prepared via a modified Stöber synthesis. The core shell structure is confirmed by TEM, the size distribution of the whole particles was determined by means of photon correlation spectroscopy and small angle X-ray scattering. Due to charged surface groups

Joachim Wagner; Tina Autenrieth; Rolf Hempelmann

2002-01-01

171

Influence of a metallic or oxide top layer in epitaxial magnetic bilayers containing CoFe2O4(111) tunnel barriers  

Microsoft Academic Search

We investigate the interaction of CoFe2O4(111) tunnel barriers with Co and Fe3O4 electrodes in light of their potential as room temperature spin filters. The question of the exchange coupling that often prohibits the independent switching between a magnetic tunnel barrier and its magnetic electrode is addressed, as is the difference between an oxide\\/metal and oxide\\/oxide system. Our study of the

A. V. Ramos; J.-B. Moussy; M.-J. Guittet; M. Gautier-Soyer; C. Gatel; P. Bayle-Guillemaud; B. Warot-Fonrose; E. Snoeck

2007-01-01

172

Impedance spectroscopy of multiferroic PbZrxTi1-xO3\\/CoFe2O4 layered thin films  

Microsoft Academic Search

The electrical properties of ferroelectric Pb(Zr,Ti)O3 (PZT) and ferromagnetic CoFe2O4 (CFO) thin film multilayers (MLs) fabricated by pulsed laser deposition technique has been studied by impedance and modulus spectroscopy. The effect of various PZT\\/CFO configurations having three, five, and nine layers has been systematically investigated. The transmission electron microscopy images revealed that the ML structures were at least partially diffused

N. Ortega; Ashok Kumar; P. Bhattacharya; S. B. Majumder; R. S. Katiyar

2008-01-01

173

Controllable phase connectivity and magnetoelectric coupling behavior in CoFe2O4 Pb(Zr,Ti)O3 nanostructured films  

Microsoft Academic Search

Magnetoelectric CoFe2O4-Pb(Zr,Ti)O3 nanostructured films with various phase connectivity patterns were prepared by a pulsed laser deposition method. It was found that the microstructure as well as the phase connectivity pattern of the film varied remarkably with the variation of phase content ratio. All composite nanofilms exhibit evident ferromagnetic and ferroelectric characteristics, as well as distinct magnetoelectric coupling behavior upon increasing

Jian-guo Wan; Yuyan Weng; Yujie Wu; Zhengyu Li; Jun-ming Liu; Guanghou Wang

2007-01-01

174

Evidence for first-order nature of the ferromagnetic transition in Ni, Fe, Co, and CoFe2O4  

Microsoft Academic Search

Nearly all ferromagnetic transitions have been considered to be continuous or second order, and the most typical examples are the ferromagnetic transitions in Ni, Fe, Co, and CoFe2O4 . However, by precise measurement with electrical resistivity or impedance and differential scanning calorimetry, we show clear evidence for the first-order nature of these ``second-order transitions''---a small thermal hysteresis and latent heat.

Sen Yang; Xiaobing Ren; Xiaoping Song

2008-01-01

175

Thickness and coupling effects in bilayered multiferroic CoFe2O4\\/Pb(Zr0.52Ti0.48)O3 thin films  

Microsoft Academic Search

Four CoFe2O4\\/Pb(Zr0.52Ti0.48)O3 (CFO\\/PZT) bilayered thin films with increasing PZT constituent layer thicknesses have been fabricated in order to investigate the optimized PZT layer thickness and the thickness effect on the magnetic and ferroelectric behaviors of the heterolayered multiferroic thin films. These heterostructured thin films were fabricated via a combined route of spin coating and rf sputtering. Both magnetic CFO and

C. H. Sim; A. Z. Z. Pan; J. Wang

2008-01-01

176

LETTER TO THE EDITOR: Cation migration and magnetic ordering in spinel CoFe2O4 powder: micro-Raman scattering study  

Microsoft Academic Search

Micro-Raman scattering was used to characterize spinel CoFe2O4 at high temperature up to 870 K and under an external magnetic field up to 6.0 kOe. It was found that the rapid increase in the linewidth of the Raman modes was related to the inter-site cation migration starting at ~390 K. A red-shift of the Raman peaks induced by the magnetic

T. Yu; Z. X. Shen; Y. Shi; J. Ding

2002-01-01

177

Experimental evidence of the spin dependence of electron reflections in magnetic CoFe2O4/Au/Fe3O4 trilayers  

NASA Astrophysics Data System (ADS)

An original epitaxial system consisting of two ferrimagnetic insulator layers ( CoFe2O4 and Fe3O4 ) separated by a nonmagnetic metallic layer (Au) has been grown. The transport properties in the current in plane geometry indicate that the conduction of the CoFe2O4/Au/Fe3O4 trilayer takes place within the thin metallic layer. The giant magnetoresistance (GMR) observed (2.6% at 10K ) is associated to the switching from a parallel to an antiparallel configuration of the magnetization of the two ferrite layers and corresponds to the spin dependence of electron reflection at the interfaces with a large contribution of specular reflections. The increase of the GMR (5% at 10K ) in the symmetrical interface CoFe2O4/Fe3O4/Au/Fe3O4 system and the effect of the interface roughness on the GMR confirm the presence of this spin-dependent specular reflection.

Snoeck, E.; Gatel, Ch.; Serra, R.; Benassayag, G.; Moussy, J.-B.; Bataille, A. M.; Pannetier, M.; Gautier-Soyer, M.

2006-03-01

178

High-pressure x-ray diffraction and Raman spectroscopic studies of the tetragonal spinel CoFe2O4  

NASA Astrophysics Data System (ADS)

In situ x-ray diffraction and Raman spectroscopy have been carried out to pressures of 93.6 and 63.2 GPa, respectively, to explore the pressure-induced phase transformation of CoFe2O4 spinel. CoFe2O4 adopts a distorted tetragonal spinel structure at one atmosphere. At a pressure of ˜32.5 GPa, both x-ray diffraction and Raman spectroscopy indicate that CoFe2O4 transforms to the orthorhombic CaFe2O4 structure, which remains stable to at least 93.6 GPa. The bulk modulus (K0) of the tetragonal and the high-pressure polymorphs were calculated to be 94(12) and 145(16) GPa, respectively, with K'?4. Upon release of pressure the orthorhombic phase persists and appears to be structurally metastable. At zero pressure, laser induced heating leads to a significant transformation back to the tetragonal phase. The high-pressure orthorhombic phase at one atmosphere is 14.7% denser than the tetragonal phase.

Wang, Zhongwu; Downs, R. T.; Pischedda, V.; Shetty, R.; Saxena, S. K.; Zha, C. S.; Zhao, Y. S.; Schiferl, D.; Waskowska, A.

2003-09-01

179

A large low field colossal magnetoresistance in the La0.7Sr0.3MnO3 and CoFe2O4 combined system  

Microsoft Academic Search

La0.7Sr0.3MnO3 and CoFe2O4 samples have been prepared by a sol-gel process. A mixture of the two samples was annealed at 800 °C and the scanning electron micrograph shows large CoFe2O4 grains well surrounded by La0.7Sr0.3MnO3 grains. The powder x-ray diffraction patterns indicate no evidence of reaction between the La0.7Sr0.3MnO3 and CoFe2O4. The resistivity of the combined sample (with 20 wt%

Chun-Hua Yan; Zhi-Gang Xu; Tao Zhu; Zhe-Ming Wang; Fu-Xiang Cheng; Yun-Hui Huang; Chun-Sheng Liao

2000-01-01

180

Ferromagnetic, ferroelectric and dielectric properties of Pb(Zr0.53Ti0.47)O3\\/CoFe2O4 multiferroic composite thick films  

Microsoft Academic Search

Pb(Zr0.53Ti0.47)O3\\/CoFe2O4 (abbreviated as PZT\\/CFO) multiferroic composite thick films have been prepared on the Pt\\/Ti\\/SiO2\\/Si substrate by using a hybrid sol-gel process. The thick films were finally annealed at 650 °C in air and the ferromagnetic, ferroelectric and dielectric properties of these films were investigated. Both the PZT pervoskite phase and the CFO spinel phase were detected from x-ray diffraction. The

W. Chen; Z. H. Wang; W. Zhu; O. K. Tan

2009-01-01

181

Strain relaxation and enhanced perpendicular magnetic anisotropy in BiFeO3:CoFe2O4 vertically aligned nanocomposite thin films  

NASA Astrophysics Data System (ADS)

Self-assembled BiFeO3:CoFe2O4 (BFO:CFO) vertically aligned nanocomposite thin films have been fabricated on SrTiO3 (001) substrates using pulsed laser deposition. The strain relaxation mechanism between BFO and CFO with a large lattice mismatch has been studied by X-ray diffraction and transmission electron microscopy. The as-prepared nanocomposite films exhibit enhanced perpendicular magnetic anisotropy as the BFO composition increases. Different anisotropy sources have been investigated, suggesting that spin-flop coupling between antiferromagnetic BFO and ferrimagnetic CFO plays a dominant role in enhancing the uniaxial magnetic anisotropy.

Zhang, Wenrui; Jian, Jie; Chen, Aiping; Jiao, Liang; Khatkhatay, Fauzia; Li, Leigang; Chu, Frank; Jia, Quanxi; MacManus-Driscoll, Judith L.; Wang, Haiyan

2014-02-01

182

Multiferroic Properties of CoFe2O4\\/PbZr0.52Ti0.48O3 Composite Ceramics  

Microsoft Academic Search

The xCoFe2O4-(1?x)PbZr0.52Ti0.48O3 (PZT) composite ceramics with x = 0.1, 0.2 and 0.3 have been prepared by solid state reaction method. X-ray diffraction result reveals that no chemical reaction or phase diffusion between the CoFe2O4 and PZT phases exists in the composites. The composites exhibited ferroelectric as well as magnetic characteristics at room temperature. The distribution of the ferroelectric and magnetic

Xiaobo Wu; Wei Cai; Yi Kan; Pan Yang; Yunfei Liu; Huifeng Bo; Xiaomei Lu; Jinsong Zhu

2009-01-01

183

Synthesis, structure, and magnetic studies on self-assembled BiFeO3-CoFe2O4 nanocomposite thin films  

Microsoft Academic Search

Self-assembled (0.65)BiFeO3-(0.35)CoFe2O4 (BFO-CFO) nanostructures were deposited on SrTiO3 (001) and (111) substrates by pulsed laser deposition at various temperatures from 500 to 800 °C. The crystal phases and the lattice strain for the two different substrate orientations have been determined and compared. The films grow epitaxial on both substrates but separation of the spinel and perovskite crystallites, without parasitic phases,

R. Muralidharan; N. Dix; V. Skumryev; M. Varela; F. Sánchez; J. Fontcuberta

2008-01-01

184

Dielectric and Magnetoelectric Characterization of CoFe2O4\\/Sr0.5Ba0.5Nb2O6 Composites  

Microsoft Academic Search

Magnetoelectric composites were created through incorporating dispersed CoFe2O4 ferromagnetic grains into a Sr0.5Ba0.5Nb2O6 relaxor ferroelectric matrix. The two phases are chemically compatible and coexist in the dense, sintered composites. Unlike other relaxors, the Sr0.5Ba0.5Nb2O6-containing composites can be electrically poled. The apparent dielectric constant is enhanced by the conductivity in the ferrite phase and the space charge at the phase interface.

X. M. Chen; Y. H. Tang; I.-W. Chen; Z. C. Xu; S. Y. Wu

2004-01-01

185

Reaction kinetic, magnetic and microwave absorption studies of SrFe 12 O 19 \\/CoFe 2 O 4 ferrite nanocrystals  

Microsoft Academic Search

Mixture of cobalt ferrite and strontium hexaferrite nanocrystals i.e. SrFe12O19\\/CoFe2O4 exhibiting super paramagnetic nature were synthesized by modified flux method. The resulting precursors were heat treated\\u000a (HT) at 900 and 1200°C for 4 h in nitrogen atmosphere. During heat treatment, transformation proceeds as instantaneous rate\\u000a of nucleation and three dimensional growth with activation energy of 135.835 kJ\\/mole. The hysteresis loops

Sachin Tyagi; Himanshu B. Baskey; R. C. Agarwala; Vijaya Agarwala; T. C. Shami

2011-01-01

186

Direct measurement of magnetoelectric exchange in self-assembled epitaxial BiFeO3-CoFe2O4 nanocomposite thin films  

NASA Astrophysics Data System (ADS)

We report the direct measurement of a magnetoelectric (ME) exchange between magnetostrictive CoFe2O4 nanopillars in a piezoelectric BiFeO3 matrix for single-layer nanocomposite epitaxial thin films grown on (001) SrTiO3 substrates with SrRuO3 bottom electrodes. The ME coefficient was measured by a magnetic cantilever method and had a maximum value of ~20 mV/cm Oe. The films possessed saturation polarization (60 ?C/cm2) and magnetization (410 emu/cc) properties equivalent to bulk values, with typical hysteresis loops.

Yan, Li; Xing, Zengping; Wang, Zhiguang; Wang, Tao; Lei, Guangyin; Li, Jiefang; Viehland, D.

2009-05-01

187

Local probing of magnetoelectric coupling and magnetoelastic control of switching in BiFeO3-CoFe2O4 thin-film nanocomposite  

NASA Astrophysics Data System (ADS)

We report on the combination of piezoresponse force microscopy (PFM), magnetic force microscopy, and local ferroelectric switching with magnetic field for the study of a thin-film magnetoelectric (ME) nanocomposite. The collection of PFM under an applied variable magnetic field within a polycrystalline perovskite-spinel BiFeO3-CoFe2O4 (BFO-CFO) 0-3 type thin-film nanocomposite enables quantitative and proximal measurement of magnetoelastic strain-driven ME response. Combination of measurement of the as-grown strain state with local measurements of microstructure and macroscopic magnetization permits local mapping of ME coupling.

Yan, Feng; Chen, Guannan; Lu, Li; Finkel, Peter; Spanier, Jonathan E.

2013-07-01

188

Direct measurement of magnetoelectric exchange in self-assembled epitaxial BiFeO3-CoFe2O4 nanocomposite thin films  

Microsoft Academic Search

We report the direct measurement of a magnetoelectric (ME) exchange between magnetostrictive CoFe2O4 nanopillars in a piezoelectric BiFeO3 matrix for single-layer nanocomposite epitaxial thin films grown on (001) SrTiO3 substrates with SrRuO3 bottom electrodes. The ME coefficient was measured by a magnetic cantilever method and had a maximum value of ~20 mV\\/cm Oe. The films possessed saturation polarization (60 muC\\/cm2)

Li Yan; Zengping Xing; Zhiguang Wang; Tao Wang; Guangyin Lei; Jiefang Li; D. Viehland

2009-01-01

189

Magneto-optic material selectivity in self-assembled BiFeO3-CoFe2O4 biferroic nanostructures  

NASA Astrophysics Data System (ADS)

Material selective sensitivity of a magneto-optical polar Kerr effect to magnetic contributions from different inclusions in self-organized magnetic nanostructures is presented. The method is supported by modeling of the magneto-optic response based on the effective medium approximation and by hysteresis loop measurement of the multiferroic BiFeO3-CoFe2O4 self-assembled nanostructure. Magneto-optic selective sensitivity is demonstrated and explained as an effect of different complex diagonal and off-diagonal permittivity tensor elements of two materials.

Postava, K.; Hrabovský, D.; Životský, O.; Pištora, J.; Dix, N.; Muralidharan, R.; Caicedo, J. M.; Sánchez, F.; Fontcuberta, J.

2009-04-01

190

Visualization of magnetic domain structure changes induced by interfacial strain in CoFe2O4/BaTiO3 heterostructures  

NASA Astrophysics Data System (ADS)

We visualized the evolution of the magnetic domain structure in CoFe2O4 films on different structural phases of BaTiO3 substrates with {0?0?1} orientation, using variable temperature magnetic force microscopy. When BaTiO3 underwent transitions from rhombohedral to orthorhombic to and from orthorhombic to tetragonal structures with increasing temperature, only local variations to the magnetic domains were observed. At the BaTiO3 tetragonal-cubic transition however, the magnetic domain size increased by 75% with an overall decrease in stray field contrast (33% decrease) because of reorientation of the magnetization to the in-plane directions. The reorientation of magnetization during the tetragonal to cubic phase transition of BaTiO3 was induced by release of asymmetric interfacial strain between the CoFe2O4 film and the BaTiO3 substrate, as non-uniformly distributed a and c surface ferroelectric domains in the BaTiO3 tetragonal phase disappeared at the paraelectric BaTiO3 cubic phase transition. Strain analysis based on macroscopic magnetization measurements was correlated with the microscopic magnetic domain structure to help understand the coupling in two-phase multiferroicheterostructure mediated by interfacial strain.

Pan, Mengchun; Hong, Seungbum; Guest, Jeffrey R.; Liu, Yuzi; Petford-Long, Amanda

2013-02-01

191

Electric in-plane polarization in multiferroic CoFe2O4/BaTiO3 nanocomposite tuned by magnetic fields  

NASA Astrophysics Data System (ADS)

Ferrimagnetic CoFe2O4 nanopillars embedded in a ferroelectric BaTiO3 matrix are an example for a two-phase magnetoelectrically coupled system. They operate at room temperature and are free of any resource-critical rare-earth element, which makes them interesting for potential applications. Prior studies succeeded in showing strain-mediated coupling between the two subsystems. In particular, the electric properties can be tuned by magnetic fields and the magnetic properties by electric fields. Here we take the analysis of the coupling to a new level utilizing soft X-ray absorption spectroscopy and its associated linear dichroism. We demonstrate that an in-plane magnetic field breaks the tetragonal symmetry of the (1,3)-type CoFe2O4/BaTiO3 structures and discuss it in terms of off-diagonal magnetostrictive-piezoelectric coupling. This coupling creates staggered in-plane components of the electric polarization, which are stable even at magnetic remanence due to hysteretic behaviour of structural changes in the BaTiO3 matrix. The competing mechanisms of clamping and relaxation effects are discussed in detail.

Schmitz-Antoniak, Carolin; Schmitz, Detlef; Borisov, Pavel; de Groot, Frank M. F.; Stienen, Sven; Warland, Anne; Krumme, Bernhard; Feyerherm, Ralf; Dudzik, Esther; Kleemann, Wolfgang; Wende, Heiko

2013-06-01

192

Multiferroic CoFe2O4-Pb(Zr(0.52)Ti(0.48))O3 core-shell nanofibers and their magnetoelectric coupling.  

PubMed

Multiferroic CoFe(2)O(4)-Pb(Zr(0.52)Ti(0.48))O(3) core-shell nanofibers have been synthesized by coaxial electrospinning in combination with a sol-gel process. The core-shell configuration of nanofibers has been verified by scanning electron microscopy and transmission electron microscopy, and the spinel structure of CoFe(2)O(4) and perovskite structure of Pb(Zr(0.52)Ti(0.48))O(3) have been confirmed by X-ray diffraction and selected area electron diffraction. The multiferroic properties of core-shell nanofibers have been demonstrated by magnetic hysteresis and piezoresponse force microscopy, and their magnetoelectric coupling has been confirmed by evolution of piezoresponse under an external magnetic field, showing magnetically induced ferroelectric domain switching and changes in switching characteristics. The lateral magnetoelectric coefficient is estimated to be 2.95 × 10(4) mV/cmOe, two orders of magnitude higher than multiferroic thin films of similar composition. PMID:21643573

Xie, Shuhong; Ma, Feiyue; Liu, Yuanming; Li, Jiangyu

2011-08-01

193

INHOMOGENEITY INDUCED CONDUCTIVITY FLUCTUATION IN YBa2Cu3O7-?/BaTiO3-CoFe2O4 COMPOSITE  

NASA Astrophysics Data System (ADS)

Polycrystalline (1-x)YBa2Cu3O7-y + xBaTiO3-CoFe2O4(x = 0.0, 0.2, 0.4, 0.6 wt.%) superconductors were prepared by solid state route. XRD analysis reveals no significant change in "b" parameter and increase in "a" and "c" parameters. SEM micrographs show no change in grain size of the samples. With the increase of BaTiO3-CoFe2O4 (BTO-CFO) addition it has been analyzed that the superconducting transition temperatures (Tc) determined from standard four-probe method was decreased and dropped sharply with higher wt.% addition. Excess conductivity fluctuation analysis using Aslamazov-Larkin model fitting reveals transition of two dominant regions (2D and 3D) above Tc. The decrease in 2D-3D crossover temperature TLD (Lawerence-Doniach temperature) in the mean field region has been observed as a consequent dominance of 3D region to increase in wt.% in the composite. The increasing value of ?wl and ?0 and the decreasing trend in the value of zero-resistance critical temperature (Tc0) indicates that the connectivity between grains decreases gradually with the addition of magneto-electric composite BTO-CFO.

Sahoo, Mousumibala; Behera, Dhrubananda

2013-08-01

194

Epitaxial strain-induced changes in the cation distribution and resistivity of Fe-doped CoFe2O4  

NASA Astrophysics Data System (ADS)

The distribution of cations in Fe-doped cobalt ferrite (Co1-xFe2+xO4) is investigated as a function of epitaxial strain through x-ray absorption measurements of samples grown on SrTiO3, MgO, and CoCr2O4-buffered MgAl2O4 (001). In agreement with recent theoretical calculations, compressive (tensile) strain results in the films having a larger (smaller) degree of cation inversion for iron doping levels up to x = 0.62. Measurements of the resistivity further conclude that the degree of cation inversion has a direct effect on the size of the bandgap for stoichiometric CoFe2O4, an effect that is reduced as the iron doping level is increased.

Moyer, J. A.; Kumah, D. P.; Vaz, C. A. F.; Arena, D. A.; Henrich, V. E.

2012-07-01

195

Ti diffusion in (001) SrTiO3-CoFe2O4 epitaxial heterostructures: blocking role of a MgAl2O4 buffer.  

PubMed

Titanium diffusion from (001) SrTiO3 (STO) substrates into CoFe2O4 (CFO) films grown using pulsed laser deposition is reported. To elucidate the reasons for Ti interdiffusion, a comparative study of CFO films grown on MgAl2O4 (MAO) and STO substrates, buffered by thin STO and MAO layers, has been made. It is shown that whereas bottom STO layers always result in Ti migration, a thin MAO layer, only 8 nm thick, is effective in blocking it. We argue that this success relies on the lower mobility of Ti ions in the MAO lattice compared to that of CFO. This result should contribute to the development of high quality epitaxial heterostructures of dissimilar complex oxides. PMID:24068072

Rebled, J M; Foerster, M; Estradé, S; Rigato, F; Kanamadi, C; Sánchez, F; Peiró, F; Fontcuberta, J

2013-11-01

196

Magnetic anisotropy in composite CoFe2O4-BiFeO3 ultrathin films grown by pulsed-electron deposition  

NASA Astrophysics Data System (ADS)

Many works have demonstrated perpendicular magnetic anisotropy in CoFe2O4-BiFeO3 (CFO-BFO) composites, which is commonly believed to originate from out-of-plane compressive strain in the CFO pillars due to the lattice mismatch with the BFO matrix. Others have shown that the pillar-matrix interface in similar NiFe2O4-BFO composites is fully relaxed. To study the origin of the magnetic anisotropy, composite films were grown on SrTiO3 with thicknesses ranging from 13 to 150 nm via pulsed electron deposition. In-plane compressive strain in the pillars is found for thinner samples, which induces in-plane magnetoelastic anisotropy. A model for the origin of this previously unreported strain is proposed and the results are contrasted with the thicker composite films found in the literature.

Comes, Ryan; Khokhlov, Mikhail; Liu, Hongxue; Lu, Jiwei; Wolf, Stuart A.

2012-04-01

197

Large converse magnetoelectric effect in Na0.5Bi0.5TiO3-CoFe2O4 lead-free multiferroic composites  

NASA Astrophysics Data System (ADS)

Lead-free multiferroic composites of ferroelectric, Na0.5Bi0.5TiO3 (NBT) and ferrimagnetic, CoFe2O4 (CFO) were synthesized by the solid-state sintering method and a systematic study of structural, magnetic, and magnetoelectric properties was undertaken. X-ray diffraction and field emission scanning electron microscopy displayed the formation of single phase for parent phases and the presence of both phases in the composites. Magnetic properties were investigated using a vibrating sample magnetometer (VSM) and ferromagnetic resonance (FMR) measurements at room temperature. Strong magnetoelectric (ME) coupling was demonstrated by an electric field tunable FMR field shift. A large value of converse ME coefficient 109 Oe-cm kV-1 was observed for NBT/CFO 70/30 composite. Furthermore, these lead-free multiferroic composites exhibiting a large converse magnetoelectric effect at room temperature provide great opportunities for electrostatically tunable devices at microwave frequencies.

Narendra Babu, S.; Malkinski, Leszek

2012-04-01

198

Temperature dependent phonon Raman scattering of highly a-axis oriented CoFe2O4 inverse spinel ferromagnetic films grown by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Lattice vibrations of highly a-axis oriented CoFe2O4 (CFO) films have been investigated by Raman scattering in the temperature range of 80-873 K. The five phonon modes T1g(2), T1g(3), Eg, A1g(1), A1g(2), and their evolutions can be uniquely distinguished. It was found that an electron transfer between Co2+ and Fe3+ cations occurs in octahedral sites at about 173 K. The structure disorder in the CFO films appears with increasing the temperature, which indicates the cation migration between tetrahedral and octahedral sites. The phenomena suggest the structural transformation trend from inverse spinel to normal spinel at the elevated temperatures.

Liao, Y. Y.; Li, Y. W.; Hu, Z. G.; Chu, J. H.

2012-02-01

199

Luminol-silver nitrate chemiluminescence enhancement induced by cobalt ferrite nanoparticles.  

PubMed

CoFe(2)O(4) nanoparticles (NPs) could stimulate the weak chemiluminescence (CL) system of luminol and AgNO(3), resulting in a strong CL emission. The UV-visible spectra, X-ray photoelectron spectra and TEM images of the investigated system revealed that AgNO(3) was reduced by luminol to Ag in the presence of CoFe(2)O(4) NPs and the formed Ag covered the surface of CoFe(2)O(4) NPs, resulting in CoFe(2)O(4)-Ag core-shell nanoparticles. Investigation of the CL reaction kinetics demonstrated that the reaction among luminol, AgNO(3) and CoFe(2)O(4) NPs was fast at the beginning and slowed down later. The CL spectra of the luminol - AgNO(3) - CoFe(2)O(4) NPs system indicated that the luminophor was still an electronically excited 3-aminophthalate anion. A CL mechanism has been postulated. When the CoFe(2)O(4) NPs were injected into the mixture of luminol and AgNO(3), they catalyzed the reduction of AgNO(3) by luminol to produce luminol radicals and Ag, which immediately covered the CoFe(2)O(4) NPs to form CoFe(2)O(4)-Ag core-shell nanoparticles, and the luminol radicals reacted with the dissolved oxygen, leading to a strong CL emission. With the continuous deposition of Ag on the surface of CoFe(2)O(4) NPs, the catalytic activity of the core-shell nanoparticles was inhibited and a decrease in CL intensity was observed and also a slow growth of shell on the nanoparticles. PMID:21400653

Shi, Wenbing; Wang, Hui; Huang, Yuming

2011-01-01

200

Preparation and Dielectric Characteristics of Semitransparent CoFe2O4-P(VDF-TrFE) Nanocomposite Films  

NASA Astrophysics Data System (ADS)

Polymer-ceramic nanocomposites play an important role in embedded capacitors. However, polymer-ceramic dielectrics are limited for commercial applications due to their low transmittance, poor adhesion, and poor thermal stress reliability at high filler loadings. Thus, materials design and processing is critical to prepare films with improved dielectric properties and low filler loading. In this work, we use a spin coating-assisted method to fabricate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]-CoFe2O4 (CFO) nanocomposite films. Magnetic CFO nanoparticles in the size range of 10 nm to 40 nm were successfully synthesized using a hydrothermal process. The dispersion of the nanoparticles, the dielectric properties, and the transmittance of the nanocomposite films were studied. The dielectric constant of the nanocomposite films increased by about 45% over the frequency range of 100 Hz to 1 MHz, compared with that of pristine P(VDF-TrFE) film. Optical measurements indicated that the transmittance of the films remains above 60% in the visible range, indicating a relatively low content of CFO in the polymer matrix. Our experimental results suggest that spin coating-assisted dispersion may be a promising route to fabricate dielectric polymer-ceramic nanocomposite films of controllable thickness.

Dong, Wen; Guo, Yiping; Liu, Yun; Liu, Hezhou; Li, Hua

2013-04-01

201

Study on the growth and interfacial strain of CoFe 2O 4/BaTiO 3 bilayer films  

NASA Astrophysics Data System (ADS)

CoFe 2O 4/BaTiO 3 bilayer films were epitaxially deposited on SrTiO 3 substrates by laser molecular beam epitaxy (LMBE). The growth process of the bilayer films was in-situ monitored by reflection high-energy electron diffraction (RHEED). Sixty nanometer thick-BTO layer was firstly fabricated in a layer-by-layer growth mode with an atomic smooth surface. CFO films with a varying thickness ranging from 5 to 60 nm were subsequently deposited on BTO-coated STO substrates. The different growth behaviors of CFO films were observed due to the lattice mismatch strain. Between two short stages of the growth mode transforming, a long duration with Stransky and Krastonov growth mode was maintained. Strainfully relaxed CFO film in the island growth mode was finally formed. High-resolution X-ray diffraction (HRXRD) was used to further analyze the strain effect. It was found that the tensile stress imposed on BTO by CFO was strengthened with increasing the thickness of CFO films, which could lessen the distortion of BTO by counteracting the compressive stress caused by STO substrates. The strengthened tensile stress weakened the ferroelectric property of BTO films by reducing structural tetragonality, which was demonstrated by polarization-electric ( P- E) measurement.

Zhu, J.; Zhou, L. X.; Huang, W.; Li, Y. Q.; Li, Y. R.

2009-06-01

202

Engineered magnetic shape anisotropy in BiFeO3-CoFe2O4 self-assembled thin films.  

PubMed

We report growth of various phase architectures of self-assembled BiFeO3-CoFe2O4 (BFO-CFO) thin films on differently oriented SrTiO3 (STO) substrates. CFO forms segregated square, stripe, and triangular nanopillars embedded in a coherent BFO matrix on (001)-, (110)-, and (111)-oriented STO substrates, respectively. Nanostructures with an aspect ratio of up to 5:1 with a prominent magnetic anisotropy were obtained on both (001) and (110) STO along out-of-plane and in-plane directions. Magnetic easy axis rotation from in-plane to out-of-plane directions was realized through aspect ratio control. An intractable in-plane anisotropy was fixed in CFO on (111) STO due to the triangular shape of the ferromagnetic phase nanopillars. These studies established a detailed relationship of magnetic anisotropy with specific shape and dimensions of ordered magnetic arrays. The results suggest a way to effectively control the magnetic anisotropy in patterned ferromagnetic oxide arrays with tunable shape, aspect ratio, and elastic strain conditions of the nanostructures. PMID:23473343

Wang, Zhiguang; Li, Yanxi; Viswan, Ravindranath; Hu, Bolin; Harris, Vincent G; Li, Jiefang; Viehland, Dwight

2013-04-23

203

Effects of inhomogeneous strain on the magnetization behavior of magnetic nanostructures in BiFeO3/CoFe2O4 composite  

NASA Astrophysics Data System (ADS)

In CoFe2O4/BiFeO3 (CFO/BFO) nanostructured thin films, where ferromagnetic nanopillars are embedded in a ferroelectric matrix, electric field induced rotation of the easy axis of the ferrimagnetic nanopillars has been demonstrated experimentally [Zavaliche et al. 2005]. However, for applications where the magnetic pillars would be used to store information, electric control of the magnetization has to be acheived at the scale of a single pillar, without disturbing the neighbors, and the effects of local strain on the magnetic reversal is therefore of interest. We carried out finite element simulations of the strain state of an arrangement of CFO pillars when the BFO matrix surrounding one of them is under piezoelectric strain. Because of stress relaxation at the top free surface of the thin film, the strain is highly inhomogeneous along the pillar. The position-dependent strain was imported into a micromagnetic simulation, giving a position-dependant magnetoelasticity, to predict the switching behavior of the CFO pillars and estimate the feasibility of electric control of a single magnetic bit in this system. The reversal of the pillars was found to be highly incoherent, showing that the pillars cannot be treated as a macrospin.

Aimon, Nicolas; Mascaro, Mark; Liu, Frank; Buehler, Markus; Ross, Caroline

2012-02-01

204

The Nanostructure Formation and Growth Evolution of Ferroelectric/Ferromagnetic BiFeO3-CoFe2O4 Thin Films  

NASA Astrophysics Data System (ADS)

We have investigated the mechanism of the self-assembly of BiFeO3-CoFe2O4 (BFO-CFO) ferroelectric/ferromagnetic thin film nanostructures using high-resolution transmission electron microscopy. We discuss the formation of the CFO columnar structure during the deposition process. The BFO-CFO thin films were deposited on SrTiO3 (001) single crystal substrates using pulsed laser deposition at a substrate temperature of 700 ^oC and deposition rate of around 5nm/min. In the early stages of growth, CFO domains form with dome like island shape and are covered by a BFO layer. After approximately 10 mins of continuous deposition, the nanocomposite rearranges and diffusion dominates to form a self-assembly of faceted CFO columns that extend to the surface of the film. These columns show pyramidal-like faceted shape and are embedded in the BFO matrix. A few atomic layers of BFO lie at the interface between the CFO columnar structures and the substrate. This layer helps relax the misfit strain between CFO and STO. The magnetic properties of the nanocomposite samples will also be presented.

Young, Sheng Yu; Salamanca-Riba, Lourdes G.; Zheng, Haimei

2006-03-01

205

Synthesis, structure, and magnetic studies on self-assembled BiFeO3-CoFe2O4 nanocomposite thin films  

NASA Astrophysics Data System (ADS)

Self-assembled (0.65)BiFeO3-(0.35)CoFe2O4 (BFO-CFO) nanostructures were deposited on SrTiO3 (001) and (111) substrates by pulsed laser deposition at various temperatures from 500 to 800 °C. The crystal phases and the lattice strain for the two different substrate orientations have been determined and compared. The films grow epitaxial on both substrates but separation of the spinel and perovskite crystallites, without parasitic phases, is only obtained for growth temperatures of around 600-650 °C. The BFO crystallites are out-of-plane expanded on STO(001), whereas they are almost relaxed on (111). In contrast, CFO crystallites grow out-of-plane compressed on both substrates. The asymmetric behavior of the cell parameters of CFO and BFO is discussed on the basis of the role of the epitaxial stress caused by the substrate and the spinel-perovskite interfacial stress. It is concluded that interfacial stress dominates the elastic properties of CFO crystallites and thus it may play a fundamental on the interface magnetoelectric coupling in these nanocomposites.

Muralidharan, R.; Dix, N.; Skumryev, V.; Varela, M.; Sánchez, F.; Fontcuberta, J.

2008-04-01

206

Structural, microstructural and magnetic properties of NiFe 2 O 4 , CoFe 2 O 4 and MnFe 2 O 4 nanoferrite thin films  

NASA Astrophysics Data System (ADS)

The structural, microstructural and magnetic properties of nanoferrite NiFe 2O 4 (NF), CoFe 2O 4 (CF) and MnFe 2O 4 (MF) thin films have been studied. The coating solution of these ferrite films was prepared by a chemical synthesis route called sol-gel combined metallo-organic decomposition method. The solution was coated on Si substrate by spin coating and annealed at 700 °C for 3 h. X-ray diffraction pattern has been used to analyze the phase structure and lattice parameters. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to show the nanostructural behavior of these ferrites. The values of average grain's size from SEM are 44, 60 and 74 nm, and from AFM are 46, 61 and 75 nm, respectively, measured for NF, CF and MF ferrites. At room temperature, the values of saturation magnetization, Ms˜50.60, 33.52 and 5.40 emu/cc, and remanent magnetization, Mr˜14.33, 15.50 and 1.10 emu/cc, respectively, are observed for NF, CF and MF. At low temperature measurements of 10 K, the anisotropy of ferromagnetism is observed in these ferrite films. The superparamagnetic/paramagnetic behavior is also confirmed by ?'( T) curves of AC susceptibility by applying DC magnetizing field of 3 Oe. The temperature dependent magnetization measurements show the magnetic phase transition temperature.

Chand Verma, Kuldeep; Pratap Singh, Virender; Ram, Mast; Shah, Jyoti; Kotnala, R. K.

2011-12-01

207

Synthysis of Ultrasmall Ultrabright Photostable Yellow Luminescent SI Nanoparticles  

Microsoft Academic Search

We have synthesized ultrasmall yellow luminescent Si nanoparticles that are ultrabright under uv single photon excitation or under two-photon near infrared excitation. The brightness is comparable to that of rhodamine dye molecules. Monte Carlo quantum calculations yield a Si66 prototype structure. Previously we synthesized ultrabright blue luminescent particles (Si29 prototype). Direct imaging of single particles using transmission electron microscopy and

Gennadiy Belomoin; Nick Barry; Adam Smith; Osman Akcakir; Laila Abuhassan; Enrico Gratton; Munir Nayfeh

2001-01-01

208

Magnetoelectric coupling of multilayered Pb(Zr0.52Ti0.48)O3-CoFe2O4 film by piezoresponse force microscopy under magnetic field  

NASA Astrophysics Data System (ADS)

Multiferroic Pb(Zr0.52Ti0.48)O3-CoFe2O4-Pb(Zr0.52Ti0.48)O3 (PCP) laminated film has been synthesized by sol-gel process and spin coating, with the spinel structure of CoFe2O4 and perovskite structure of Pb(Zr0.52Ti0.48)O3 verified by x-ray diffraction. The good multiferroic properties of PCP film have been confirmed by ferroelectric and magnetic hysteresis loops, with leakage current substantially reduced. The local magnetoelectric coupling has been verified using piezoresponse force microscopy under external magnetic field, showing magnetically induced evolution of piezoresponse and ferroelectric switching characteristics, with piezoresponse amplitude reduced and coercive voltage increased. Such technique will be useful in characterizing local magnetoelectric (ME) couplings for a wide range of multiferroic materials.

Xie, S. H.; Liu, Y. M.; Ou, Y.; Chen, Q. N.; Tan, X. L.; Li, J. Y.

2012-10-01

209

Magnetic properties of (CoFe2O4)x:(CeO2)1-x vertically aligned nanocomposites and their pinning properties in YBa2Cu3O7-? thin films  

NASA Astrophysics Data System (ADS)

Vertically aligned nanocomposites (VAN) combined ferrimagnetic CoFe2O4 with non-magnetic CeO2 ((CoFe2O4)x:(CeO2)1-x) in different phase ratios (x = 10%, 30% to 50%) have been grown by a pulsed laser deposition technique. Various unique magnetic domain structures form based on the VAN compositions and growth conditions. Anisotropic and tunable ferrimagnetic properties have been demonstrated. These ordered ferrimagnetic nanostructures have been incorporated into YBa2Cu3O7-? thin films as both cap and buffer layers to enhance the flux pinning properties of the superconducting thin films. The results suggest that the ordered magnetic VAN provides effective pinning centers by both defect and magnetic nanoinclusions.

Huang, Jijie; Tsai, Chen-Fong; Chen, Li; Jian, Jie; Khatkhatay, Fauzia; Yu, Kaiyuan; Wang, Haiyan

2014-03-01

210

Dependence of Site Occupancy and Structural and Electrical Properties on Successive Replacement of Co by Zn in CoFe2O4  

NASA Astrophysics Data System (ADS)

The crystal structure and cation distribution at particular sites in the crystal lattice play the primary role in determining the properties of nanocrystalline transition-metal oxide materials. Nanocrystalline ferrite particles of Co1- x Zn x Fe2O4 with x varying from 0.0 to 1.0 were synthesized by a coprecipitation method. Samples synthesized at the reaction temperature of 70°C were sintered at 600°C for 3 h. The face-centered cubic (FCC) spinel structure of the synthesized particles was confirmed by x-ray diffraction patterns. The grain sizes calculated from the most intense peak (311) using the Scherrer equation were found to be in the range from 10 nm to 35 nm. Extended x-ray absorption fine-structure and x-ray absorption near-edge structure spectroscopy is a powerful tool for structural study of metal oxide materials. These techniques are element specific and sensitive to the local structure. These techniques were used at Fe, Co, and Zn K-edges to investigate the cation distribution in the crystal structure. The dependence of the electrical transport properties on the shift in the crystal structure due to successive replacement of Co by Zn in CoFe2O4 was examined. Direct-current (dc) electrical conduction measurements were carried out as a function of temperature from 313 K to 700 K. Activation energy values indicated the polaron hopping conduction mechanism. The alternating-current (ac) electrical transport properties were studied by measuring the dielectric constant as a function of frequency. A regular shift?in the electrical properties was observed depending upon the cation distribution.

Akram, M.; Anis-ur-Rehman, M.

2014-02-01

211

Magnetic, magnetoelectric and dielectric behavior of CoFe2O4-Pb(Fe1/2Nb1/2)O3 particulate and layered composites  

NASA Astrophysics Data System (ADS)

Magnetic, magnetoelectric and dielectric properties of multiferroic CoFe2O4-Pb(Fe1/2Nb1/2)O3 composites prepared as bulk ceramics were compared with those of tape cast and cofired laminates consisting of alternate ferrite and relaxor layers. X-ray diffraction analysis and Scanning Electron Microscope observations of ceramic samples revealed two-phase composition and fine grained microstructure with uniformly distributed ferrite and relaxor phases. High and broad maxima of dielectric permittivity attributed to dielectric relaxation were found for ceramic samples measured in a temperature range from -55 to 500 °C at frequencies 10 Hz-2 MHz. Magnetic hysteresis, zero-field cooled (ZFC) and field cooled (FC) curves, and dependencies of magnetization on temperature for both magnetoelectric composites were measured with a vibrating sample magnetometer in an applied magnetic field up to 80 kOe at 4-400 K. The hysteresis loops obtained for composites are typical of a mixture of the hard magnetic material with a significant amount of the paramagnet. The bifurcation of ZFC-FC magnetizations observed for both composites implies spin-glass behavior. Magnetoelectric properties at room temperature were investigated as a function of dc magnetic field (0.3-7.2 kOe) and frequency (10 Hz-10 kHz) of ac magnetic field. Both types of composites exhibit a distinct magnetoelectric effect. Maximum values of magnetoelectric coefficient attained for the layered composites exceed 200 mV/(cm Oe) and are almost three times higher than those for particulate composites.

Kulawik, J.; Szwagierczak, D.; Guzdek, P.

2012-09-01

212

Synthesis of ultrasmall platinum nanoparticles and structural relaxation.  

PubMed

We report the synthesis of ligand-protected, ultrasmall Pt nanoparticles of ?1nm size via a one-phase wet chemical method. Using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), we determined the mass of the nanoparticles to be ?8kDa. Characterization of the Pt nanoparticles was further carried out by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), optical absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS). Interestingly, we observed a large structural relaxation in the 8kDa nanoparticles (i.e. lattice parameter elongation by +10%) compared to bulk platinum. XPS analysis revealed a positive shift of Pt 4f core level energy by approximately +1eV compared with bulk Pt, indicating charge transfer from Pt to S atom of the thiolate ligand on the particle. Compared to bulk Pt, the 5d band of Pt nanoparticles is narrower and shifts to higher binding energy. Overall, the ?1nm ultrasmall Pt nanoparticles exhibit quite distinct differences in electronic and structural properties compared to their larger counterparts and bulk Pt. PMID:24703677

Liu, Chao; Li, Gao; Kauffman, Douglas R; Pang, Guangsheng; Jin, Rongchao

2014-06-01

213

Adsorption of cobalt ferrite nanoparticles within layer-by-layer films: a kinetic study carried out using quartz crystal microbalance.  

PubMed

The paper reports on the successful use of the quartz crystal microbalance technique to assess accurate kinetics and equilibrium parameters regarding the investigation of in situ adsorption of nanosized cobalt ferrite particles (CoFe(2)O(4)--10.5 nm-diameter) onto two different surfaces. Firstly, a single layer of nanoparticles was deposited onto the surface provided by the gold-coated quartz resonator functionalized with sodium 3-mercapto propanesulfonate (3-MPS). Secondly, the layer-by-layer (LbL) technique was used to build multilayers in which the CoFe(2)O(4) nanoparticle-based layer alternates with the sodium sulfonated polystyrene (PSS) layer. The adsorption experiments were conducted by modulating the number of adsorbed CoFe(2)O(4)/PSS bilayers (n) and/or by changing the CoFe(2)O(4) nanoparticle concentration while suspended as a stable colloidal dispersion. Adsorption of CoFe(2)O(4) nanoparticles onto the 3-MPS-functionalized surface follows perfectly a first order kinetic process in a wide range (two orders of magnitude) of nanoparticle concentrations. These data were used to assess the equilibrium constant and the adsorption free energy. Alternatively, the Langmuir adsorption constant was obtained while analyzing the isotherm data at the equilibrium. Adsorption of CoFe(2)O(4) nanoparticles while growing multilayers of CoFe(2)O(4)/PSS was conducted using colloidal suspensions with CoFe(2)O(4) concentration in the range of 10(-8) to 10(-6) (moles of cobalt ferrite per litre) and for different numbers of cycles n = 1, 3, 5, and 10. We found the adsorption of CoFe(2)O(4) nanoparticles within the CoFe(2)O(4)/PSS bilayers perfectly following a first order kinetic process, with the characteristic rate constant growing with the increase of CoFe(2)O(4) nanoparticle concentration and decreasing with the rise of the number of LbL cycles (n). Additionally, atomic force microscopy was employed for assessing the LbL film roughness and thickness. We found the film thickness increasing from about 20 to 120 nm while shifting from 3 to 10 CoFe(2)O(4)/PSS bilayers, using the 8.9 × 10(-6) (moles of cobalt ferrite per litre) suspension. PMID:22025281

Alcantara, Gustavo B; Paterno, Leonardo G; Afonso, André S; Faria, Ronaldo C; Pereira-da-Silva, Marcelo A; Morais, Paulo C; Soler, Maria A G

2011-12-28

214

Effect of the CoFe2O4 thin film thickness on multiferroic property of (00l)-oriented Pb(Zr0.5Ti0.5)O3/CoFe2O4/Pb(Zr0.5Ti0.5)O3 trilayer structure  

NASA Astrophysics Data System (ADS)

In this study, we have fabricated (00l)-oriented Pb(Zr0.5Ti0.5)O3/CoFe2O4/Pb(Zr0.5Ti0.5)O3 (PZT/CFO/PZT) trilayer thin films on LaNiO3 coated substrates by dual-cathode rf sputtering system. The thicknesses of top and bottom PZT thin films were fixed at 100 nm but those of the CFO interlayer were 40, 80, and 120 nm, respectively. The x-ray diffraction showed well-defined PZT and CFO peaks with (00l) orientation, and large grains with columnar structure were observed by field-emission scanning electron microscopy. Hard-magnetic M-H loop with a saturation magnetization of ~235 emu/cm3 and ferroelectric hysteresis curve with saturation polarization of ~40.1 ?C/cm2 were measured at room temperature for the PZT/CFO (120 nm)/PZT trilayer thin films. Due to the low-resistance CFO interlayer in series with the PZT layers, the ferroelectric property does not significantly vary with the CFO interlayer thickness. In contrast, the possibility of the existence of nonmagnetic interfacial layer at the CFO/PZT interface causes the reduction of the magnetization. Both of the good magnetic and ferroelectric responses suggest that the (00l)-oriented PZT/CFO/PZT trilayer thin film is a promising magnetoeletric material for study.

Lin, Rueijer; Liao, Jeng-Hwa; Hung, Lung-Jie; Wu, Tai-Bor

2008-04-01

215

Magnetoelectric CoFe2O4\\/Pb(Zr0.52Ti0.48)O3 double-layer thin film prepared by pulsed-laser deposition  

Microsoft Academic Search

Double-layer magnetoelectric CoFe2O4 (CFO)\\/Pb(Zr0.52Ti0.48)O3 (PZT) nanocomposite thin film was prepared via a pulsed-laser deposition. X-ray diffraction showed that there are no other phases but PZT and CFO phases in the film. The smooth film surface was obtained after depositing the CFO and PZT layers. The double-layer thin film exhibits both good ferromagnetic and electric properties, as well as a magnetoelectric

Jian-Ping Zhou; Hongcai He; Zhan Shi; Ce-Wen Nan

2006-01-01

216

Enhanced magnetoelectric properties in Pb(Zr,Ti)O3-CoFe2O4 layered thin films with LaNiO3 as a buffer layer  

Microsoft Academic Search

Conductive LaNiO3 thin films were prepared via a simple solution method to be used as both a buffer layer and a bottom electrode layer, on which Pb(Zr,Ti)O3-CoFe2O4 bi-layered films were also deposited by a similar solution method. The results showed that the LaNiO3 buffer layer could induce a different preferential orientation for the Pb(Zr,Ti)O3 layer in the composite films and

H. C. He; J. Ma; Y. H. Lin; C. W. Nan

2009-01-01

217

Effect of sample shape on the zero-field-cooled magnetization behavior: comparative studies on NiFe2O4, CoFe2O4 and SrFe12O19  

Microsoft Academic Search

The zero-held-cooled (ZFC) magnetization behavior of powders and\\u000a sintered solid pieces having arbitrary shapes and sizes of three\\u000a different ferrimagnetic oxides, NiFe2O4, CoFe2O4 and SrFe12O19, has been\\u000a compared to distinguish the contribution from magnetocrystalline and\\u000a shape anisotropies on the general characteristics of the ZFC\\u000a magnetization curves. It is observed that the general shape of the ZFC\\u000a magnetization curve is mainly

PA Joy; S. K Date

2000-01-01

218

A novel nanostructure and multiferroic properties in Pb(Zr0.52Ti0.48)O3\\/CoFe2O4 nanocomposite films grown by pulsed-laser deposition  

Microsoft Academic Search

Multiferroic nanocomposite thin films containing Pb(Zr0.52Ti0.48)O3 (PZT) and CoFe2O4(CFO) with a novel nanostructure are deposited on (1 0 0)-oriented Nb-doped SrTiO3 (STO) substrates by pulsed-laser deposition. Structural characterizations show that only PZT and CFO phases exist in the composite films, and the perovskite-structured PZT nano-pyramids with diameters of 50-100 nm are randomly embedded in the spinel-structured polycrystalline CFO matrix. Ferroelectric

J. X. Zhang; J. Y. Dai; W. Lu; H. L. W. Chan; B. Wu; D. X. Li

2008-01-01

219

Influence of relative thickness on multiferroic properties of bilayered Pb(Zr0.52Ti0.48)O3-CoFe2O4 thin films  

Microsoft Academic Search

Multiferroic bilayered thin films consisting of Pb(Zr0.52Ti0.48)O3 (PZT) and CoFe2O4 (CFO) layers of different relative thicknesses were prepared on a general Pt\\/Ti\\/SiO2\\/Si substrate via a simple solution processing. The influence of the thickness fraction on their properties including ferroelectric, ferromagnetic, and magnetoelectric properties in the PZT-CFO bilayered thin films was investigated. Our results showed that the thickness fractions (or relative

Hong-Cai He; Jing Ma; Yuanhua Lin; C. W. Nan

2008-01-01

220

Orientation-dependent multiferroic properties in Pb(Zr0.52Ti0.48)O3-CoFe2O4 nanocomposite thin films derived by a sol-gel processing  

Microsoft Academic Search

Bilayered multiferroic nanocomposite films of preferentially oriented Pb(Zr0.52Ti0.48)O3 (PZT) and CoFe2O4 (CFO) were prepared on general Pt\\/Ti\\/SiO2\\/Si substrate via a simple solution processing. Different annealing processings resulted in different preferential orientations for the PZT layers in the bilayered thin films, on which the dependence of properties, including ferroelectric, ferromagnetic, and magnetoelectric properties, in the PZT-CFO nanocomposite thin films was investigated.

Hong-Cai He; Jing Ma; Jing Wang; Ce-Wen Nan

2008-01-01

221

Effects of magnetic cobalt ferrite nanoparticles on biological and artificial lipid membranes  

PubMed Central

Background The purpose of this work is to provide experimental evidence on the interactions of suspended nanoparticles with artificial or biological membranes and to assess the possibility of suspended nanoparticles interacting with the lipid component of biological membranes. Methods 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid vesicles and human red blood cells were incubated in suspensions of magnetic bare cobalt ferrite (CoFe2O4) or citric acid (CA)-adsorbed CoFe2O4 nanoparticles dispersed in phosphate-buffered saline and glucose solution. The stability of POPC giant unilamellar vesicles after incubation in the tested nanoparticle suspensions was assessed by phase-contrast light microscopy and analyzed with computer-aided imaging. Structural changes in the POPC multilamellar vesicles were assessed by small angle X-ray scattering, and the shape transformation of red blood cells after incubation in tested suspensions of nanoparticles was observed using scanning electron microscopy and sedimentation, agglutination, and hemolysis assays. Results Artificial lipid membranes were disturbed more by CA-adsorbed CoFe2O4 nanoparticle suspensions than by bare CoFe2O4 nanoparticle suspensions. CA-adsorbed CoFe2O4-CA nanoparticles caused more significant shape transformation in red blood cells than bare CoFe2O4 nanoparticles. Conclusion Consistent with their smaller sized agglomerates, CA-adsorbed CoFe2O4 nanoparticles demonstrate more pronounced effects on artificial and biological membranes. Larger agglomerates of nanoparticles were confirmed to be reactive against lipid membranes and thus not acceptable for use with red blood cells. This finding is significant with respect to the efficient and safe application of nanoparticles as medicinal agents.

Drasler, Barbara; Drobne, Damjana; Novak, Sara; Valant, Janez; Boljte, Sabina; Otrin, Lado; Rappolt, Michael; Sartori, Barbara; Iglic, Ales; Kralj-Iglic, Veronika; Sustar, Vid; Makovec, Darko; Gyergyek, Saso; Hocevar, Matej; Godec, Matjaz; Zupanc, Jernej

2014-01-01

222

Synthysis of Ultrasmall Ultrabright Photostable Yellow Luminescent SI Nanoparticles  

NASA Astrophysics Data System (ADS)

We have synthesized ultrasmall yellow luminescent Si nanoparticles that are ultrabright under uv single photon excitation or under two-photon near infrared excitation. The brightness is comparable to that of rhodamine dye molecules. Monte Carlo quantum calculations yield a Si66 prototype structure. Previously we synthesized ultrabright blue luminescent particles (Si29 prototype). Direct imaging of single particles using transmission electron microscopy and electron diffraction measurements show atomically resolved silicon planes. A small number of the particles and dye molecules were immobilized in agarose gel or on a quartz substrate. Emission from single stationary particles is readily detectable. "Parking" the excitation beam, focused to an average intensity as high as 1MW/cm2, on stationery particles shows that they, unlike the dye molecules, are photostable and do not blink, hence paving the way for their use as fluorescent biomedical labels.

Belomoin, Gennadiy; Barry, Nick; Smith, Adam; Akcakir, Osman; Abuhassan, Laila; Gratton, Enrico; Nayfeh, Munir

2001-03-01

223

Oxide and hydrogen capped ultrasmall blue luminescent Si nanoparticles  

SciTech Connect

We dispersed electrochemical etched silicon into a colloid of ultrasmall ultrabright Si nanoparticles. Direct imaging using transmission electron microscopy shows particles of {approx}1 nm in diameter, and infrared and electron photospectroscopy show that they are passivated with hydrogen. Under 350 nm excitation, the luminescence is dominated by an extremely strong blue band at 390 nm. We replace hydrogen by a high-quality ultrathin surface oxide cap by self-limiting oxidation in H{sub 2}O{sub 2}. Upon capping, the excitation efficiency drops, but only by a factor of 2, to an efficiency still two-fold larger than that of fluorescein. Although of slightly lower brightness, capped Si particles have superior biocompatability, an important property for biosensing applications. (c) 2000 American Institute of Physics.

Belomoin, Gennadiy [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States); Therrien, Joel [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States); Nayfeh, Munir [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, 1110 W. Green Street, Urbana, Illinois 61801 (United States)

2000-08-07

224

Strong magnetoelectric coupling in sol-gel derived multiferroic (Pb0.76Ca0.24)TiO3-CoFe2O4 composite films  

NASA Astrophysics Data System (ADS)

A multilayer heterostructure composite thin films consisting of alternating layers (Pb0.76Ca0.24)TiO3 (PCT) and CoFe2O4 (CFO) were grown on Pt/Ti/SiO2/Si(100) substrate by a sol-gel process. X-ray measurements indicated high quality of crystallization of both PCT and CFO layers. The magnetic and ferroelectric properties of the composite were investigated. Well-defined polarization vs. electric field (P-E) and magnetic hysteresis (M-H) loops were obtained. A strong magnetoelectric (ME) response was observed in the sample which was subjected to an alternating magnetic field, and a high ME voltage coefficient ?E = 870 mV/Oe cm was obtained for the composite thin films when applied magnetic field parallel to the sample plane.

Cheng, T. D.; Tang, X. G.; Wang, Yu; Chan, H. L. W.

2012-10-01

225

Molecularly stabilised ultrasmall gold nanoparticles: synthesis, characterization and bioactivity  

NASA Astrophysics Data System (ADS)

Gold nanoparticles (AuNPs) are widely used as contrast agents in electron microscopy as well as for diagnostic tests. Due to their unique optical and electrical properties and their small size, there is also a growing field of potential applications in medical fields of imaging and therapy, for example as drug carriers or as active compounds in thermotherapy. Besides their intrinsic optical properties, facile surface decoration with (bio)functional ligands renders AuNPs ideally suited for many industrial and medical applications. However, novel AuNPs may have toxicological profiles differing from bulk and therefore a thorough analysis of the quantitative structure-activity relationship (QSAR) is required. Several mechanisms are proposed that cause adverse effects of nanoparticles in biological systems. Catalytic generation of reactive species due to the large and chemically active surface area of nanomaterials is well established. Because nanoparticles approach the size of biological molecules and subcellular structures, they may overcome natural barriers by active or passive uptake. Ultrasmall AuNPs with sizes of 2 nm or less may even behave as molecular ligands. These types of potential interactions would imply a size and ligand-dependent behaviour of any nanomaterial towards biological systems. Thus, to fully understand their QSAR, AuNPs bioactivity should be analysed in biological systems of increasing complexity ranging from cell culture to whole animal studies.

Leifert, Annika; Pan-Bartnek, Yu; Simon, Ulrich; Jahnen-Dechent, Willi

2013-06-01

226

Molecularly stabilised ultrasmall gold nanoparticles: synthesis, characterization and bioactivity.  

PubMed

Gold nanoparticles (AuNPs) are widely used as contrast agents in electron microscopy as well as for diagnostic tests. Due to their unique optical and electrical properties and their small size, there is also a growing field of potential applications in medical fields of imaging and therapy, for example as drug carriers or as active compounds in thermotherapy. Besides their intrinsic optical properties, facile surface decoration with (bio)functional ligands renders AuNPs ideally suited for many industrial and medical applications. However, novel AuNPs may have toxicological profiles differing from bulk and therefore a thorough analysis of the quantitative structure-activity relationship (QSAR) is required. Several mechanisms are proposed that cause adverse effects of nanoparticles in biological systems. Catalytic generation of reactive species due to the large and chemically active surface area of nanomaterials is well established. Because nanoparticles approach the size of biological molecules and subcellular structures, they may overcome natural barriers by active or passive uptake. Ultrasmall AuNPs with sizes of 2 nm or less may even behave as molecular ligands. These types of potential interactions would imply a size and ligand-dependent behaviour of any nanomaterial towards biological systems. Thus, to fully understand their QSAR, AuNPs bioactivity should be analysed in biological systems of increasing complexity ranging from cell culture to whole animal studies. PMID:23743952

Leifert, Annika; Pan-Bartnek, Yu; Simon, Ulrich; Jahnen-Dechent, Willi

2013-07-21

227

Synthesis of monodisperse FeCo nanoparticles by reductive salt-matrix annealing.  

PubMed

We report here a novel synthetic method to prepare monodisperse air-stable FeCo nanoparticles with average sizes of 8, 12 and 20 nm. CoFe2O4 nanoparticles of different sizes were first synthesized by a chemical solution method. The as-synthesized CoFe2O4 nanoparticles were then mixed with ball-milled NaCl powders and heated to 400-500?° C in forming gas (Ar 93%+H2 7%). The salt powder worked as a separating medium that prevents the CoFe2O4 nanoparticles from agglomerating during the heat treatment while the forming gas reduces the CoFe2O4 nanoparticles to FeCo nanoparticles. Monodisperse FeCo nanoparticles were recovered by dissolving the NaCl in water and subsequently washing with ethanol and acetone. Structural analyses confirmed that FeCo nanoparticles retained the same size as their oxide precursors. The size of the FeCo nanoparticles can be well tuned by controlling the size of the CoFe2O4 nanoparticles. The saturation magnetization of FeCo nanoparticles is size dependent and increases with size. PMID:23912629

Poudyal, Narayan; Chaubey, Girija S; Rong, Chuan-Bing; Cui, Jun; Liu, J Ping

2013-08-30

228

Synthesis of monodisperse FeCo nanoparticles by reductive salt-matrix annealing  

NASA Astrophysics Data System (ADS)

We report here a novel synthetic method to prepare monodisperse air-stable FeCo nanoparticles with average sizes of 8, 12 and 20 nm. CoFe2O4 nanoparticles of different sizes were first synthesized by a chemical solution method. The as-synthesized CoFe2O4 nanoparticles were then mixed with ball-milled NaCl powders and heated to 400-500?° C in forming gas (Ar 93%+H2 7%). The salt powder worked as a separating medium that prevents the CoFe2O4 nanoparticles from agglomerating during the heat treatment while the forming gas reduces the CoFe2O4 nanoparticles to FeCo nanoparticles. Monodisperse FeCo nanoparticles were recovered by dissolving the NaCl in water and subsequently washing with ethanol and acetone. Structural analyses confirmed that FeCo nanoparticles retained the same size as their oxide precursors. The size of the FeCo nanoparticles can be well tuned by controlling the size of the CoFe2O4 nanoparticles. The saturation magnetization of FeCo nanoparticles is size dependent and increases with size.

Poudyal, Narayan; Chaubey, Girija S.; Rong, Chuan-Bing; Cui, Jun; Liu, J. Ping

2013-08-01

229

Application of hydrophobically modified water-soluble polymers for the dispersion of hydrophobic magnetic nanoparticles in aqueous media.  

PubMed

Hydrophobically modified water-soluble polymers (HMWSPs), comprised of a poly(sodium methacrylate) (PMANa) or poly(sodium acrylate) (PANa) backbone and pendent dodecyl methacrylate (DMA) or dodecyl acrylamide (DAAm) chains, respectively, were synthesized. The hydrophobic content of the copolymers, P(MANa-co-DMA) and P(ANa-co-DAAm), is in the range of 0 to 25 mol%, while their weight-average molar mass varies from ?10?000 up to ?75?000. Their self-assembly behavior in dilute aqueous solution was followed through Nile Red probing, DLS and TEM measurements. The critical micelle concentration (CMC) is mainly controlled by the hydrophobic content and not the molar mass of the copolymers. Above CMC, spherical and large-compound micelles are identified by DLS and TEM. Moreover, oleylamine coated CoFe2O4 nanoparticles (CoFe2O4@OAm MNPs) of 9.4 nm with a saturation magnetization Ms = 85 emu g(-1) were solvothermally prepared. The hydrophobic CoFe2O4@OAm MNPs were successfully encapsulated into the hydrophobic cores of the structures formed by the copolymers above CMC through a solvent mixing procedure, and in that way hydrophilic CoFe2O4@HMWSP nanohybrids resulted. For comparison purposes, two alternate phase transfer approaches were also used to convert CoFe2O4@OAm MNPs to hydrophilic ones: (a) addition of a coating layer by cetyltrimethyl ammonium bromide (CTAB) and (b) by the ligand exchange procedure with 2,3-dimercaptosuccinic acid (DMSA). NMR transverse relaxivity measurements of the aqueous suspensions of CoFe2O4@P(ANa-co-DAAm), CoFe2O4@CTAB and CoFe2O4@DMSA were recorded and the r2 relaxivity was determined. CoFe2O4@CTAB demonstrated the highest r2 relaxivity of 554.0 mM(-1) s(-1), while CoFe2O4@P(ANa-co-DAAm) and CoFe2O4@DMSA showed lower values of 313.6 mM(-1) s(-1) and 76.3 mM(-1) s(-1), respectively. PMID:24759871

Iatridi, Zacharoula; Georgiadou, Violetta; Menelaou, Melita; Dendrinou-Samara, Catherine; Bokias, Georgios

2014-05-20

230

Anatase TiO 2 nanolayer coating on cobalt ferrite nanoparticles for magnetic photocatalyst  

Microsoft Academic Search

TiO2\\/CoFe2O4 composite nanoparticles with a core–shell structure have been obtained. The core CoFe2O4 nanoparticles were synthesized via co-precipitation method, and the shell TiO2 nanocrystals were derived via sol–gel technology followed by heat-treatment at 450 °C. The morphology and the crystalline structure of composite nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction, respectively. The as-prepared composite particles can

Wuyou Fu; Haibin Yang; Minghua Li; Minghui Li; Nan Yang; Guangtian Zou

2005-01-01

231

Confirmation of disordered structure of ultrasmall CdSe nanoparticles from X-ray atomic pair distribution function analysis.  

PubMed

The atomic pair distribution function (PDF) analysis of X-ray powder diffraction data has been used to study the structure of small and ultra-small CdSe nanoparticles. A method is described that uses a wurtzite and zinc-blende mixed phase model to account for stacking faults in CdSe particles. The mixed-phase model successfully describes the structure of nanoparticles larger than 2 nm yielding a stacking fault density of about 30%. However, for ultrasmall nanoparticles smaller than 2 nm, the models cannot fit the experimental PDF showing that the structure is significantly modified from that of larger particles and the bulk. The observation of a significant change in the average structure at ultra-small size is likely to explain the unusual properties of the ultrasmall particles such as their white light emitting ability. PMID:23525376

Yang, Xiaohao; Masadeh, Ahmad S; McBride, James R; Božin, Emil S; Rosenthal, Sandra J; Billinge, Simon J L

2013-06-14

232

Ultra-small platinum and gold nanoparticles by arc plasma deposition  

NASA Astrophysics Data System (ADS)

Ultra-small (<2 nm) nanoparticles of platinum and gold were produced by arc plasma deposition (APD) in a systematic way and the deposition behavior was studied. Nanoparticles were deposited on two dimensional amorphous carbon and amorphous titania thin films and characterized by transmission electron microscopy (TEM). Deposition behavior of nanoparticles by APD was studied with discharge voltage (V), discharge condenser capacitance (C), and the number of plasma pulse shots (n) as controllable parameters. The average size of intrinsic nanoparticles generated by APD process was as small as 0.9 nm and deposited nanoparticles began to have crystal structures from the particle size of about 2 nm. V was the most sensitive parameter to control the size and coverage of generated nanoparticles compared to C and n. Size of APD deposited nanoparticles was also influenced by the nature of evaporating materials and substrates.

Kim, Sang Hoon; Jeong, Young Eun; Ha, Heonphil; Byun, Ji Young; Kim, Young Dok

2014-04-01

233

Synthesis, Characterization and Direct Intracellular Imaging of Ultrasmall and Uniform Glutathione-Coated Gold Nanoparticles  

PubMed Central

Gold nanoparticles (AuNPs) with core sizes below 2 nm and compact ligand shells constitute versatile platforms for the development of novel reagents in nanomedicine. Due to their ultrasmall size, these AuNPs are especially attractive in applications requiring delivery to crowded intracellular spaces in the cytosol and nucleus. For eventual use in vivo, ultrasmall AuNPs should ideally be monodisperse, since small variations in size may affect how they interact with cells and behave in the body. Here we report the synthesis of ultrasmall, uniform 144-atom AuNPs protected by p-mercaptobenzoic acid (Au144(pMBA)60) followed by ligand exchange with glutathione (GSH). Quantitative scanning transmission electron microscopy (STEM) reveals that the resulting GSH-coated AuNPs (Au(GSH)) have a uniform mass distribution with cores that contain 134 gold atoms on average. Particle size dispersity is analyzed by analytical ultracentrifugation, giving a narrow distribution of apparent hydrodynamic diameter of 4.0 ± 0.6 nm. To evaluate the nanoparticles' intracellular fate, the cell penetrating peptide TAT is attached non-covalently to Au(GSH), which is confirmed by fluorescence quenching and isothermal titration calorimetry. HeLa cells are then incubated with both Au(GSH) and the Au(GSH)-TAT complex, and imaged without silver enhancement of the AuNPs in unstained thin sections by STEM. This imaging approach enables unbiased detection and quantification of individual ultrasmall nanoparticles and aggregates in the cytoplasm and nucleus of the cells.

Morgan, Jeffrey T.; Brown, Patrick H.; Adams, April; Mudiyanselage, Pushpa; Zhang, Guofeng; Ackerson, Christopher J.; Kruhlak, Michael J.

2013-01-01

234

Synthesis and coating of cobalt ferrite nanoparticles: a first step toward the obtainment of new magnetic nanocarriers.  

PubMed

Monodisperse and stable cobalt ferrite (CoFe2O4) nanoparticles (5.4 nm) have been produced, coated with mono- and difunctional phosphonic and hydroxamic acids, and fully characterized (using thermogravimetric analysis (TGA), dynamic light scattering (DLS), IR spectroscopy, transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) measurements). Cobalt leakage of the coated nanoparticles has been also studied. Magnetic measurements show the possible applications in hyperthermia at low frequencies, and for this reason, water-soluble coated CoFe2O4 can be seen as a first step toward the obtainment of novel systems for biomagnetic applications. PMID:17335257

Baldi, Giovanni; Bonacchi, Daniele; Franchini, Mauro Comes; Gentili, Denis; Lorenzi, Giada; Ricci, Alfredo; Ravagli, Costanza

2007-03-27

235

Cellular distribution and degradation of cobalt ferrite nanoparticles in Balb/3T3 mouse fibroblasts.  

PubMed

The effect of the concentration of cobalt ferrite (CoFe(2)O(4)) nanoparticles (NPs) on their intracellular location and distribution has been explored by synchrotron radiation X-ray and fluorescence microscopy (SR-XRF) monitoring the evolution of NPs elemental composition as well. In cells exposed to low concentrations of CoFe(2)O(4) NPs, the NPs preferentially segregate in the perinuclear region preserving their initial chemical content. At concentrations exceeding 500 ?M the XRF spectra indicate the presence of Co and Fe also in the nuclear region, accompanied by sensible changes in the cellular morphology. The increase of the Co/Fe ratio measured in the nuclear compartment indicates that above certain concentrations the CoFe(2)O(4) NPs intracellular distribution could be accompanied by biodegradation resulting in Co accumulation in the nucleus. PMID:21925252

Marmorato, Patrick; Ceccone, Giacomo; Gianoncelli, Alessandra; Pascolo, Lorella; Ponti, Jessica; Rossi, François; Salomé, Murielle; Kaulich, Burkhard; Kiskinova, Maya

2011-11-30

236

Fabrication and Characterization of Cobalt Iron Oxide Nanoparticles by a Reverse Micelle Process  

NASA Astrophysics Data System (ADS)

The preparation of CoFe2O4 nanoparticles in Igepal CO-520-cyclohexane-water reverse micelle solutions has been studied. Transmission electron microscopy and X-ray diffraction pattern analyses revealed the resultant particles to be CoFe2O4. The average size and distribution of synthesized particles calcined at 6000C for 2 hrs were in the range of 30 to 70 nm and broaden, respectively. The phase of synthesized particles was crystalline. The magnetic behavior of the synthesized particles was ferromagnetism. The effects of synthesis parameters, such as the molar ratio of water to surfactant and calcination temperature, are discussed.

Bae, D. S.

2013-12-01

237

Unconventional route to encapsulated ultrasmall gold nanoparticles for high-temperature catalysis.  

PubMed

Ultrasmall gold nanoparticles (us-AuNPs, <3 nm) have been recently recognized as surprisingly active and extraordinarily effective green catalysts. Their stability against sintering during reactions, however, remains a serious issue for practical applications. Encapsulating such small nanoparticles in a layer of porous silica can dramatically enhance the stability, but it has been extremely difficult to achieve using conventional sol-gel coating methods due to the weak metal/oxide affinity. In this work, we address this challenge by developing an effective protocol for the synthesis of us-AuNP@SiO2 single-core/shell nanospheres. More specifically, we take an alternative route by starting with ultrasmall gold hydroxide nanoparticles, which have excellent affinity to silica, then carrying out controllable silica coating in reverse micelles, and finally converting gold hydroxide particles into well-protected us-AuNPs. With a single-core/shell configuration that prevents sintering of nearby us-AuNPs and amino group modification of the Au/SiO2 interface that provides additional coordinating interactions, the resulting us-AuNP@SiO2 nanospheres are highly stable at high temperatures and show high activity in catalytic CO oxidation reactions. A dramatic and continuous increase in the catalytic activity has been observed when the size of the us-AuNPs decreases from 2.3 to 1.5 nm, which reflects the intrinsic size effect of the Au nanoparticles on an inert support. The synthesis scheme described in this work is believed to be extendable to many other ultrasmall metal@oxide nanostructures for much broader catalytic applications. PMID:24984223

Zhang, Tingting; Zhao, Hongyu; He, Shengnan; Liu, Kai; Liu, Hongyang; Yin, Yadong; Gao, Chuanbo

2014-07-22

238

Surface-functionalized ultrasmall superparamagnetic nanoparticles as magnetic delivery vectors for camptothecin.  

PubMed

Drug-nanoparticle conjugates: The anticancer drug camptothecin (CPT) was covalently linked at the surface of ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) via a linker, allowing drug release by cellular esterases. Nanoparticles were hierarchically built to achieve magnetically-enhanced drug delivery to human cancer cells and antiproliferative activity.The linking of therapeutic drugs to ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) allowing intracellular release of the active drug via cell-specific mechanisms would achieve tumor-selective magnetically-enhanced drug delivery. To validate this concept, we covalently attached the anticancer drug camptothecin (CPT) to biocompatible USPIOs (iron oxide core, 9-10 nm; hydrodynamic diameter, 52 nm) coated with polyvinylalcohol/polyvinylamine (PVA/aminoPVA). A bifunctional, end-differentiated dicarboxylic acid linker allowed the attachment of CPT to the aminoPVA as a biologically labile ester substrate for cellular esterases at one end, and as an amide at the other end. These CPT-USPIO conjugates exhibited antiproliferative activity in vitro against human melanoma cells. The intracellular localization of CPT-USPIOs was confirmed by transmission electron microscopy (iron oxide core), suggesting localization in lipid vesicles, and by fluorescence microscopy (CPT). An external static magnetic field applied during exposure increased melanoma cell uptake of the CPT-USPIOs. PMID:19347834

Cengelli, Feride; Grzyb, Justyna A; Montoro, Auxia; Hofmann, Heinrich; Hanessian, Stephen; Juillerat-Jeanneret, Lucienne

2009-06-01

239

Synthesis and characterization of ultra-small superparamagnetic iron oxide nanoparticles thinly coated with silica  

NASA Astrophysics Data System (ADS)

Ultra-small superparamagnetic iron oxide nanoparticles were synthesized by co-precipitation of iron chloride salts with ammonia and then encapsulated with thin (~2 nm) layers of silica. The particles have been characterized for size, diffraction pattern, surface charge, and magnetic properties. This rapid and economical synthesis has a number of industrial applications; however, the silica-coated particles have been optimized for use in medical applications such as magnetic resonance contrast agents and biosensors, and in DNA capturing, bioseparation and enzyme immobilization.

Bumb, A.; Brechbiel, M. W.; Choyke, P. L.; Fugger, L.; Eggeman, A.; Prabhakaran, D.; Hutchinson, J.; Dobson, P. J.

2008-08-01

240

Magnetocaloric effect in ferrite nanoparticles  

Microsoft Academic Search

A comparative study of the magnetocaloric effect (MCE) is reported in two different types of chemically synthesized magnetic nanoparticle systems—cobalt ferrite and manganese zinc ferrite with mean size around 5 and 15nm, respectively. While CoFe2O4 nanoparticles were synthesized using co-precipitation, the Mn0.68Zn0.25Fe2.07O4 (MZFO) nanoparticles were prepared by reverse micelle technique using AOT as surfactant. Our results indicate that the change

P. Poddar; J. Gass; D. J. Rebar; S. Srinath; H. Srikanth; S. A. Morrison; E. E. Carpenter

2006-01-01

241

Use of a polyol liquid collection medium to obtain ultrasmall magnetic nanoparticles by laser pyrolysis.  

PubMed

The present work addresses the main bottleneck in the synthesis of magnetic nanoparticles by laser pyrolysis. Since the introduction of laser pyrolysis for the production of nanoparticles nearly three decades ago, this method has been repeatedly presented as a highly promising alternative, on account of two main characteristics: (i) its flexibility, since nanoparticles can be formed from a wide variety of precursors in both gas and liquid phase, and (ii) its continuous nature, avoiding the intrinsic variability of batch processing. However, the results reported to date invariably show considerable aggregation of the obtained nanoparticles, which strongly limits their application in most fields. In this work, we have been able to circumvent this problem by collecting the particles in a polyol liquid medium. This method prevents the formation of aggregates and renders a uniform distribution of well dispersed ultrasmall nanoparticles (<4 nm) in a water-compatible solvent. We consider that the effectiveness of this novel collection method for the production of well-dispersed magnetic nanoparticles will be of high interest to a wide range of scientists working in the nanoparticle synthesis field and may enable new applications wherever there is a strict requirement for non-agglomerated nanoparticles. PMID:23037862

Martínez, G; Malumbres, A; Mallada, R; Hueso, J L; Irusta, S; Bomatí-Miguel, O; Santamaría, J

2012-10-26

242

Ultrasmall gold nanoparticles as carriers for nucleus-based gene therapy due to size-dependent nuclear entry.  

PubMed

The aim of this study was to determine the size-dependent penetration ability of gold nanoparticles and the potential application of ultrasmall gold nanoparticles for intranucleus delivery and therapy. We synthesized gold nanoparticles with diameters of 2, 6, 10, and 16 nm and compared their intracellular distribution in MCF-7 breast cancer cells. Nanoparticles smaller than 10 nm (2 and 6 nm) could enter the nucleus, whereas larger ones (10 and 16 nm) were found only in the cytoplasm. We then investigated the possibility of using ultrasmall 2 nm nanoparticles as carriers for nuclear delivery of a triplex-forming oligonucleotide (TFO) that binds to the c-myc promoter. Compared to free TFO, the nanoparticle-conjugated TFO was more effective at reducing c-myc RNA and c-myc protein, which resulted in reduced cell viability. Our result demonstrated that the entry of gold nanoparticles into the cell nucleus is critically dependent on the size of the nanoparticles. We developed a strategy for regulating gene expression, by directly delivering TFOs into the nucleus using ultrasmall gold nanoparticles. More importantly, guidelines were provided to choose appropriate nanocarriers for different biomedical purposes. PMID:24824865

Huo, Shuaidong; Jin, Shubin; Ma, Xiaowei; Xue, Xiangdong; Yang, Keni; Kumar, Anil; Wang, Paul C; Zhang, Jinchao; Hu, Zhongbo; Liang, Xing-Jie

2014-06-24

243

Ultrasmall, Water-Soluble Magnetite Nanoparticles with High Relaxivity for Magnetic Resonance Imaging  

PubMed Central

Ultrasmall (3, 4, 5, and 6 nm), water-soluble Fe3O4 magnetic nanoparticles were synthesized in diethylene glycol (DEG) via a facile one-pot reaction. Hydrodynamic size and relaxation time measurements did not show particle aggregation when Fe3O4 nanoparticles were dispersed in phosphate buffered saline, fetal bovine serum, or calf bovine serum for 1 week. Furthermore, the new Fe3O4 nanoparticles tolerated high salt concentrations (?1 M NaCl) and a wide pH range from 5 to 11. Surface modification of the nanoparticles with poly(ethylene glycol) bis(carboxymethyl) ether (HOOC-PEG-COOH, 600 g/mol) was accomplished through a ligand-exchange reaction. The effects of PEG modification on magnetization and relaxivity of the Fe3O4 nanoparticles were investigated, and the results indicate that the increase in transverse relaxivity after PEG modification may be due to the increased volume of slowly diffusing water surrounding each nanoparticle. In vitro experiments showed that the DEG- and PEG-coated Fe3O4 nanoparticles have little effect on NIH/3T3 cell viability.

Hu, Fengqin; MacRenaris, Keith W.; Waters, Emily A.; Liang, Taiyang; Schultz-Sikma, Elise A.; Eckermann, Amanda L.; Meade, Thomas J.

2014-01-01

244

Ultrasmall sub-10 nm near-infrared fluorescent mesoporous silica nanoparticles.  

PubMed

Ultrasmall sub-10 nm nanoprobes and carriers are of significant interest due to their favorable biodistribution characteristics in in vivo experiments. Here we describe the one-pot synthesis of PEGylated mesoporous silica nanoparticles with a single pore, tunable sizes around 9 nm and narrow size distributions that can be labeled with near-infrared dye Cy5.5. Particles are characterized by a combination of transmission electron microscopy, dynamic light scattering, fluorescence correlation spectroscopy, optical spectroscopy, nuclear magnetic resonance spectroscopy, and nitrogen sorption/desorption measurements. The possibility to distinguish an "inside" and "outside" may render these particles an interesting subject for further studies in sensing, drug delivery, and theranostics applications. PMID:22830608

Ma, Kai; Sai, Hiroaki; Wiesner, Ulrich

2012-08-15

245

Differential hERG ion channel activity of ultrasmall gold nanoparticles  

PubMed Central

Understanding the mechanism of toxicity of nanomaterials remains a challenge with respect to both mechanisms involved and product regulation. Here we show toxicity of ultrasmall gold nanoparticles (AuNPs). Depending on the ligand chemistry, 1.4-nm-diameter AuNPs failed electrophysiology-based safety testing using human embryonic kidney cell line 293 cells expressing human ether-á-go-go-Related gene (hERG), a Food and Drug Administration-established drug safety test. In patch-clamp experiments, phosphine-stabilized AuNPs irreversibly blocked hERG channels, whereas thiol-stabilized AuNPs of similar size had no effect in vitro, and neither particle blocked the channel in vivo. We conclude that safety regulations may need to be reevaluated and adapted to reflect the fact that the binding modality of surface functional groups becomes a relevant parameter for the design of nanoscale bioactive compounds.

Leifert, Annika; Pan, Yu; Kinkeldey, Anne; Schiefer, Frank; Setzler, Julia; Scheel, Olaf; Lichtenbeld, Hera; Schmid, Gunter; Wenzel, Wolfgang; Jahnen-Dechent, Willi; Simon, Ulrich

2013-01-01

246

Detection of luminescent single ultrasmall silicon nanoparticles using fluctuation correlation spectroscopy  

SciTech Connect

We dispersed electrochemical etched Si into a colloid of ultrasmall blue luminescent nanoparticles, observable with the naked eye, in room light. We use two-photon near-infrared femtosecond excitation at 780 nm to record the fluctuating time series of the luminescence, and determine the number density, brightness, and size of diffusing fluorescent particles. The luminescence efficiency of particles is high enough such that we are able to detect a single particle, in a focal volume, of 1 pcm3. The measurements yield a particle size of 1 nm, consistent with direct imaging by transmission electron microscopy. They also yield an excitation efficiency under two-photon excitation two to threefold larger than that of fluorescein. Detection of single particles paves the way for their use as labels in biosensing applications. (c) 2000 American Institute of Physics.

Akcakir, O. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Therrien, J. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Belomoin, G. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Barry, N. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Muller, J. D. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Gratton, E. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Nayfeh, M. [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

2000-04-03

247

Ultrasmall superparamagnetic iron oxide nanoparticle prelabelling of human neural precursor cells.  

PubMed

Stem cells prelabelled with iron oxide nanoparticles can be visualised using magnetic resonance imaging (MRI). This technique allows for noninvasive long-term monitoring of migration, integration and stem cell fate following transplantation into living animals. In order to determine biocompatibility, the present study investigated the biological impact of introducing ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) into primary human fetal neural precursor cells (hNPCs) in vitro. USPIOs with a mean diameter of 10-15 nm maghemite iron oxide core were sterically stabilised by 95% methoxy-poly(ethylene glycol) (MPEG) and either 5% cationic (NH2) end-functionalised, or 5% Rhodamine B end-functionalised, polyacrylamide. The stabilising polymer diblocks were synthesised by reversible addition-fragmentation chain transfer (RAFT) polymerisation. Upon loading, cellular viability, total iron capacity, differentiation, average distance of migration and changes in intracellular calcium ion concentration were measured to determine optimal loading conditions. Taken together we demonstrate that prelabelling of hNPCs with USPIOs has no significant detrimental effect on cell biology and that USPIOs, when utilised at an optimised dosage, are an effective means of noninvasively tracking prelabelled hNPCs. PMID:24726535

Eamegdool, Steven S; Weible, Michael W; Pham, Binh T T; Hawkett, Brian S; Grieve, Stuart M; Chan-ling, Tailoi

2014-07-01

248

In vitro studies on ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid for T2 MRI contrast agent.  

PubMed

Ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid have been investigated as possible constituents of aqueous ferrofluids for biomedical applications and especially for MRI contrast agent. The structural characteristics and the size of the nanoparticles have been analyzed as well as the magnetic properties. In order to evaluate any possible capabilities as a contrast agent, the relaxation time, T2, of hydrogen protons in the colloidal solutions of nanoparticles have been measured in order to gain information on the relaxation behavior compared to other MRI contrast agents. The in vitro cytotoxicity of the obtained magnetic nanoparticles of iron oxide coated with gummic acid was investigated by two separate methods (MTT and FACS analysis) and by using three different normal and transformed cell lines. Our results showed that the synthesized nanoparticles had no toxic effect on any of the cell lines used. PMID:19693403

Rabias, I; Pratsinis, H; Drossopoulou, G; Fardis, M; Maris, T; Boukos, N; Tsotakos, N; Kletsas, D; Tsilibary, E; Papavassiliou, G

2007-01-01

249

In vitro studies on ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid for T2 MRI contrast agent  

PubMed Central

Ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid have been investigated as possible constituents of aqueous ferrofluids for biomedical applications and especially for MRI contrast agent. The structural characteristics and the size of the nanoparticles have been analyzed as well as the magnetic properties. In order to evaluate any possible capabilities as a contrast agent, the relaxation time, T2, of hydrogen protons in the colloidal solutions of nanoparticles have been measured in order to gain information on the relaxation behavior compared to other MRI contrast agents. The in vitro cytotoxicity of the obtained magnetic nanoparticles of iron oxide coated with gummic acid was investigated by two separate methods (MTT and FACS analysis) and by using three different normal and transformed cell lines. Our results showed that the synthesized nanoparticles had no toxic effect on any of the cell lines used.

Rabias, I.; Pratsinis, H.; Drossopoulou, G.; Fardis, M.; Maris, T.; Boukos, N.; Tsotakos, N.; Kletsas, D.; Tsilibary, E.; Papavassiliou, G.

2007-01-01

250

Differential magnetic catch and release: analysis and separation of magnetic nanoparticles.  

PubMed

This article reports the purification and separation of magnetic nanoparticle mixtures using differential magnetic catch and release (DMCR). This method applies a variable magnetic flux orthogonal to the flow direction in an open tubular capillary to trap and controllably release magnetic nanoparticles. Magnetic moments of 8, 12, and 17 nm diameter CoFe2O4 nanoparticles are calculated using the applied magnetic flux and experimentally determined force required to trap 50% of the particle sample. Balancing the relative strengths of the drag and magnetic forces enables separation and purification of magnetic CoFe2O4 nanoparticle samples with <20 nm diameters. Samples were characterized by transmission electron microscopy to determine the average size and size dispersity of the sample population. DMCR is further demonstrated to be useful for separation of a magnetic nanoparticle mixture, resulting in samples with narrowed size distributions. PMID:19891452

Beveridge, Jacob S; Stephens, Jason R; Latham, Andrew H; Williams, Mary Elizabeth

2009-12-01

251

Enhanced magnetism and ferroelectricity in epitaxial Pb(Zr0.52Ti0.48)O3/CoFe2O4/La0.7Sr0.3MnO3 multiferroic heterostructures grown using dual-laser ablation technique  

NASA Astrophysics Data System (ADS)

PbZr0.52Ti0.48O3/CoFe2O4/La0.7Sr0.3MnO3 (PZT/CFO/LSMO) and PZT/LSMO heterostructures were grown on single-crystal MgO (100) substrates using the dual-laser ablation technique. X-ray diffraction confirmed the epitaxial relationship between the layers in the heterostructures. Magnetization measurements showed in-plane uniaxial magnetic anisotropy in PZT/CFO/LSMO with enhanced saturation magnetization of 288 emu/cm3 as compared to 244 emu/cm3 for PZT/LSMO. With the introduction of the hard magnetic CFO, the low coercivity of PZT/LSMO increased from 0.1 kOe to 1.4 kOe. Polarization measurements showed well-saturated square hysteresis loops for PZT/CFO/LSMO with enhanced remanent polarization (Pr) values of 69 ?C/cm2 at a coercive field (Ec) of 88 kV/cm as compared to Pr = 51 ?C/cm2 at Ec = 39 kV/cm for PZT/LSMO. The improved hard ferromagnetic and ferroelectric properties in PZT/CFO/LSMO as compared to PZT/LSMO make it desirable for multiferroic device applications.

Mukherjee, Devajyoti; Hordagoda, Mahesh; Lampen, Paula; Phan, Manh-Huong; Srikanth, Hariharan; Witanachchi, Sarath; Mukherjee, Pritish

2014-05-01

252

Influence of the morphology of ferrite nanoparticles on the directed assembly into magnetically anisotropic hierarchical structures.  

PubMed

The effect of the morphology of ferrite nanoparticles on their assembly in a magnetic field was studied. Thin BaFe12O19 nanoplatelets were compared with isotropic, spherical or octahedral, CoFe2O4 nanoparticles, all of which were synthesized hydrothermally. The nanoplatelets and nanoparticles assembled into a variety of hierarchical structures from stable suspensions during the "drop deposition" and drying in a magnetic field. The alignment of the nanoparticles in the magnetic field was observed in situ with an optical microscope. The morphologies of the nanoparticles and the subsequent assemblies were observed with transmission and scanning electron microscopes, respectively. The magnetic properties of the nanoparticles and the assemblies were measured with a vibrating-sample magnetometer. The BaFe12O19 nanoplatelets aligned in the plane of the substrate and formed several-micrometers-thick, ordered films with a magnetic alignment of approximately 90%. The CoFe2O4 nanoparticles assembled into thick, dense columns with a height of several hundreds of micrometers and showed a magnetic alignment of up to 60%. The differences in the morphologies and the magnetic alignments between the BaFe12O19 and CoFe2O4 hierarchical structures could be explained in terms of the differences in the shape and magnetocrystalline structure of the specific nanoparticles. PMID:24841592

Lisjak, Darja; Jenuš, Petra; Mertelj, Alenka

2014-06-10

253

Oleylamine as a beneficial agent for the synthesis of CoFe?O? nanoparticles with potential biomedical uses.  

PubMed

The multifunctional role of oleylamine (OAm) as a versatile and flexible reagent in synthesis as well as a desired surface ligand for the synthesis of CoFe2O4 nanoparticles (NPs) is described. CoFe2O4 NPs were prepared by a facile, reproducible and scalable solvothermal approach in the presence of pure OAm. By monitoring the volume of OAm, different shapes of NPs, spherical and truncated, were formed. The syntheses led to high yields of monodispersed and considerably small (9-11 nm) CoFe2O4 NPs with enhanced magnetization (M(s) = 84.7-87.5 emu g(-1)). The resulting hydrophobic CoFe2O4 NPs were easily transferred to an aqueous phase through the formation of reverse micelles between the hydrophobic chains of OAm and cetyltrimethylammonium bromide (CTAB) and transverse relaxivities (r2) were measured. The spherical NPs had a greater effect on water proton relaxivity (r2 = 553 mM(-1) s(-1)) at an applied magnetic field of 11.7 T. The NPs became fluorescent probes by exploiting the presence of the double bond of OAm in the middle of the molecule; a thiol-ene "click" reaction with the fluorophore bovine serum albumin (FITC-BSA) was achieved. The labeled/biofunctionalized CoFe2O4 NPs interacted with cancer (HeLa and A549) and non-cancer cell lines (MRC5 and dental MSCS) and cell viability was estimated. A clear difference of toxicity between the cancer and non-cancer cells was observed while low cytotoxicity in living cells was supported. Confocal laser microscopy showed that NPs entered the cell membranes and were firstly localized close to them provoking a membrane expansion and were further accumulated perinuclearly without entering the nuclei. PMID:24604256

Georgiadou, Violetta; Kokotidou, Chrysoula; Le Droumaguet, Benjamin; Carbonnier, Benjamin; Choli-Papadopoulou, Theodora; Dendrinou-Samara, Catherine

2014-05-01

254

Near-field light concentration of ultra-small metallic nanoparticles for absorption enhancement in a-Si solar cells  

NASA Astrophysics Data System (ADS)

Near-field light concentration from plasmonic nanostructures was predicted to significantly improve solar cell conversion efficiency since the inception of plasmonic solar cells. However the challenge remains in designing effective nanostructures for useful near-field enhancement much exceeding the detrimental ohmic loss and light blockage losses in solar cells. We propose and demonstrate ultra-small (a few nanometers) gold nanoparticles integrated in amorphous silicon solar cells between the front electrode and the photoactive layer. Significant enhancements in both the photocurrent (14.1%) and fill factor (12.3%) have been achieved due to the strong plasmonic near-field concentration and the reduced contact resistance, respectively.

Cai, Boyuan; Jia, Baohua; Shi, Zhengrong; Gu, Min

2013-03-01

255

Relaxation behavior study of ultrasmall superparamagnetic iron oxide nanoparticles at ultralow and ultrahigh magnetic fields.  

PubMed

Ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) have attracted attention because of their current and potential usefulness as contrast agents for magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR). USPIOs are usually used for their significant capacity to produce predominant proton relaxation effects, which result in signal reduction. However, most previous studies that utilized USPIOs have been focused on the relaxation behavior at commonly used magnetic fields of clinical MRI systems (typically 1-3 T). In this paper, magnetic relaxation processes of protons in water surrounding the USPIOs are studied at ultralow (?10 mT) and ultrahigh magnetic fields (14.1 T). USPIOs used in our experiments were synthesized with a core size of 6 nm, and transferred from organic to water by ligand exchange. The proton spin-lattice relaxation time (T(1)) and spin-spin relaxation time (T(2)) were investigated at ultralow (212 ?T for T(2) and 10 mT for T(1)) and at 14.1 T with different iron concentrations. At all of the fields, there is a linear relationship between the inverse of relaxation times and the iron concentration. The spin-spin relaxivity (r(2)) at 14.1 T is much larger than that value of the ultralow field. At ultralow field, however, the spin-lattice relaxivity (r(1)) is larger than the r(1) at ultrahigh field. The results provide a perspective on potential in vivo and in vitro applications of USPIOs in ultralow and ultrahigh field NMR and MRI. PMID:21972868

Wang, Wei; Dong, Hui; Pacheco, Victor; Willbold, Dieter; Zhang, Yi; Offenhaeusser, Andreas; Hartmann, Rudolf; Weirich, Thomas E; Ma, Peixiang; Krause, Hans-Joachim; Gu, Zhongwei

2011-12-15

256

Highly accessible catalytic sites on recyclable organosilane-functionalized magnetic nanoparticles: An alternative to functionalized porous silica catalysts  

Microsoft Academic Search

Diaminosilane-functionalized cobalt spinel ferrite (CoFe2O4) magnetic nanoparticles are synthesized and used as efficient heterogeneous base catalysts for the Knoevenagel condensation of aromatic and heteroaromatic aldehydes with malononitrile. The magnetic nanoparticle catalyst is characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and nitrogen physisorption measurements. Quantitative conversion of the reactants is achieved

Nam T. S. Phan; Christopher W. Jones

2006-01-01

257

Ultrasmall Sn nanoparticles embedded in nitrogen-doped porous carbon as high-performance anode for lithium-ion batteries.  

PubMed

In this Letter, we reported on the preparation and Li-ion battery anode application of ultrasmall Sn nanoparticles (?5 nm) embedded in nitrogen-doped porous carbon network (denoted as 5-Sn/C). Pyrolysis of Sn(Salen) at 650 °C under Ar atmosphere was carried out to prepare N-doped porous 5-Sn/C with the BET specific surface area of 286.3 m(2) g(-1). The 5-Sn/C showed an initial discharge capacity of 1014 mAh g(-1) and a capacity retention of 722 mAh g(-1) after 200 cycles at the current density of 0.2 A g(-1). Furthermore, a reversible capacity of ?480 mAh g(-1) was obtained at much higher current density of 5 A g(-1). The remarkable electrochemical performance of 5-Sn/C was attributed to the effective combination of ultrasmall Sn nanoparticles, uniform distribution, and porous carbon network structure, which simultaneously solved the major problems of pulverization, loss of electrical contact, and particle aggregation facing Sn anode. PMID:24328829

Zhu, Zhiqiang; Wang, Shiwen; Du, Jing; Jin, Qi; Zhang, Tianran; Cheng, Fangyi; Chen, Jun

2014-01-01

258

Chemisorption of cyanogen chloride by spinel ferrite magnetic nanoparticles.  

PubMed

Spinel ferrite magnetic nanoparticles, MnFe2O4, NiFe2O4, and CoFe2O4, were synthesized and used as gas-phase adsorbents for the removal of cyanogen chloride from dry air. Fixed-bed adsorption breakthrough experiments show adsorption wave behavior at the leading edge of the breakthrough curve that is not typical of physically adsorbed species. Fourier transform infrared spectroscopy (FTIR) results indicate that CK is reacting with the spinel ferrite surface and forming a carbamate species. The reaction is shown to be a function of the hydroxyl groups and adsorbed water on the surface of the particles as well as the metallic composition of the particles. The surface reaction decreases the remnant and saturation magnetism of the MnFe2O4 and CoFe2O4 particles by approximately 25%. PMID:23540752

Glover, T Grant; DeCoste, Jared B; Sabo, Daniel; Zhang, Z John

2013-05-01

259

Synthesis of core/shell spinel ferrite/carbon nanoparticles with enhanced cycling stability for lithium ion battery anodes  

NASA Astrophysics Data System (ADS)

Monodispersed core/shell spinel ferrite/carbon nanoparticles are formed by thermolysis of metal (Fe3+, Co2+) oleates followed by carbon coating. The phase and morphology of nanoparticles are characterized by x-ray diffraction and transmission electron microscopy. Pure Fe3O4 and CoFe2O4 nanoparticles are initially prepared through thermal decomposition of metal-oleate precursors at 310?°C and they are found to exhibit poor electrochemical performance because of the easy aggregation of nanoparticles and the resulting increase in the interparticle contact resistance. In contrast, uniform carbon coating of Fe3O4 and CoFe2O4 nanoparticles by low-temperature (180?°C) decomposition of malic acid allowed each nanoparticle to be electrically wired to a current collector through a conducting percolative path. Core/shell Fe3O4/C and CoFe2O4/C nanocomposite electrodes show a high specific capacity that can exceed 700 mAh g-1 after 200 cycles, along with enhanced cycling stability.

Jin, Yun-Ho; Seo, Seung-Deok; Shim, Hyun-Woo; Park, Kyung-Soo; Kim, Dong-Wan

2012-03-01

260

Synthesis of core/shell spinel ferrite/carbon nanoparticles with enhanced cycling stability for lithium ion battery anodes.  

PubMed

Monodispersed core/shell spinel ferrite/carbon nanoparticles are formed by thermolysis of metal (Fe3+, Co2+) oleates followed by carbon coating. The phase and morphology of nanoparticles are characterized by x-ray diffraction and transmission electron microscopy. Pure Fe3O4 and CoFe2O4 nanoparticles are initially prepared through thermal decomposition of metal–oleate precursors at 310 degrees C and they are found to exhibit poor electrochemical performance because of the easy aggregation of nanoparticles and the resulting increase in the interparticle contact resistance. In contrast, uniform carbon coating of Fe3O4 and CoFe2O4 nanoparticles by low-temperature (180 degrees C) decomposition of malic acid allowed each nanoparticle to be electrically wired to a current collector through a conducting percolative path. Core/shell Fe3O4/C and CoFe2O4/C nanocomposite electrodes show a high specific capacity that can exceed 700 mAh g(-1) after 200 cycles, along with enhanced cycling stability. PMID:22414887

Jin, Yun-Ho; Seo, Seung-Deok; Shim, Hyun-Woo; Park, Kyung-Soo; Kim, Dong-Wan

2012-03-30

261

Effect of light on the magnetic properties of cobalt ferrite nanoparticles  

Microsoft Academic Search

We report variations in the coercivity of CoFe2O4 nanoparticles as a function of particle size, temperature and light intensity. For 30 nm particles, this change in was 2300 Oe at 10 K, 120 Oe at 170 K, for a light intensity of under 2 milliwatts. The remanent magnetization was nearly unchanged by illumination. A simple model of optical absorption followed

Anit K. Giri; Kelly Pellerin; Wanida Pongsaksawad; Monica Sorescu; Sara A. Majetich

2000-01-01

262

Thiol-functionalized silica colloids, grains, and membranes for irreversible adsorption of metal(oxide) nanoparticles  

Microsoft Academic Search

Thiol-functionalization is described for silica surfaces from diverging origin, including commercial silica nanoparticles and Stöber silica as well as silica structures provided by porous glasses and novel polymer-templated silica membranes. The functionalization allows in all cases for the irreversible binding of metal(oxide) particles from a solution. Examples are the adsorption of CoFe2 O4 particles for the preparation of magnetizable silica

E. Maria Claesson; Albert P. Philipse

2007-01-01

263

Finite size and surface effects on the magnetic properties of cobalt ferrite nanoparticles  

Microsoft Academic Search

Cobalt ferrite, CoFe2O4, nanoparticles in the size range 2–15 nm have been prepared using a non-aqueous solvothermal method. The magnetic studies\\u000a indicate a superparamagnetic behavior, showing an increase in the blocking temperatures (ranging from 215 to more than 340 K)\\u000a with the particle size, D\\u000a TEM. Fitting M versus H isotherms to the saturation approach law, the anisotropy constant, K, and the

C. Vázquez-Vázquez; M. A. López-Quintela; M. C. Buján-Núñez; J. Rivas

2011-01-01

264

Ultra-small Fe3O4 nanoparticle decorated graphene nanosheets with superior cyclic performance and rate capability  

NASA Astrophysics Data System (ADS)

Advanced anode materials for next generation lithium ion batteries have attracted great interest due to the ever increasing demand for powerful, light-weight, and compact electrical devices. In this work, graphene nanosheets decorated with ultra-small Fe3O4 nanoparticles (USIO/G) were synthesized via a facile hydrothermal method. Compared with other reported Fe3O4-based anode composites, USIO/G demonstrated superior cyclic ability and excellent rate capability owing to its ultra-small size of active lithium storage sites, Fe3O4, with an average diameter less than 5 nm. Furthermore, graphene nanosheets played an important role in the overall electrochemical performance of the composite by enhancing the electrical conductivity, forming a flexible network, and providing extra lithium storage sites. The obtained composites were tested for electrochemical performance for a total number of 2120 cycles: a rate capability test with current densities ranged from 90 to 7200 mA g-1 for 920 cycles, followed by a cycling test at 1800 mA g-1 for 1200 cycles. For the rate capability test, steady reversible capacities were delivered under each current density with final reversible capacities of 1177, 1096, 833, 488, 242, and 146 mA h g-1 at 90, 180, 900, 1800, 3600, and 7200 mA g-1, respectively. The subsequent cyclic test demonstrated the superior cyclic stability of USIO/G and a reversible capacity of 437 mA h g-1 at the 2120th cycle was delivered.Advanced anode materials for next generation lithium ion batteries have attracted great interest due to the ever increasing demand for powerful, light-weight, and compact electrical devices. In this work, graphene nanosheets decorated with ultra-small Fe3O4 nanoparticles (USIO/G) were synthesized via a facile hydrothermal method. Compared with other reported Fe3O4-based anode composites, USIO/G demonstrated superior cyclic ability and excellent rate capability owing to its ultra-small size of active lithium storage sites, Fe3O4, with an average diameter less than 5 nm. Furthermore, graphene nanosheets played an important role in the overall electrochemical performance of the composite by enhancing the electrical conductivity, forming a flexible network, and providing extra lithium storage sites. The obtained composites were tested for electrochemical performance for a total number of 2120 cycles: a rate capability test with current densities ranged from 90 to 7200 mA g-1 for 920 cycles, followed by a cycling test at 1800 mA g-1 for 1200 cycles. For the rate capability test, steady reversible capacities were delivered under each current density with final reversible capacities of 1177, 1096, 833, 488, 242, and 146 mA h g-1 at 90, 180, 900, 1800, 3600, and 7200 mA g-1, respectively. The subsequent cyclic test demonstrated the superior cyclic stability of USIO/G and a reversible capacity of 437 mA h g-1 at the 2120th cycle was delivered. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr01826a

Chen, Yu; Song, Bohang; Lu, Li; Xue, Junmin

2013-07-01

265

Ultra-small Fe3O4 nanoparticle decorated graphene nanosheets with superior cyclic performance and rate capability.  

PubMed

Advanced anode materials for next generation lithium ion batteries have attracted great interest due to the ever increasing demand for powerful, light-weight, and compact electrical devices. In this work, graphene nanosheets decorated with ultra-small Fe3O4 nanoparticles (USIO/G) were synthesized via a facile hydrothermal method. Compared with other reported Fe3O4-based anode composites, USIO/G demonstrated superior cyclic ability and excellent rate capability owing to its ultra-small size of active lithium storage sites, Fe3O4, with an average diameter less than 5 nm. Furthermore, graphene nanosheets played an important role in the overall electrochemical performance of the composite by enhancing the electrical conductivity, forming a flexible network, and providing extra lithium storage sites. The obtained composites were tested for electrochemical performance for a total number of 2120 cycles: a rate capability test with current densities ranged from 90 to 7200 mA g(-1) for 920 cycles, followed by a cycling test at 1800 mA g(-1) for 1200 cycles. For the rate capability test, steady reversible capacities were delivered under each current density with final reversible capacities of 1177, 1096, 833, 488, 242, and 146 mA h g(-1) at 90, 180, 900, 1800, 3600, and 7200 mA g(-1), respectively. The subsequent cyclic test demonstrated the superior cyclic stability of USIO/G and a reversible capacity of 437 mA h g(-1) at the 2120(th) cycle was delivered. PMID:23765405

Chen, Yu; Song, Bohang; Lu, Li; Xue, Junmin

2013-08-01

266

Evaluation of uptake and transport of cationic and anionic ultrasmall iron oxide nanoparticles by human colon cells  

PubMed Central

Nanoparticles (NPs) are in clinical use or under development for therapeutic imaging and drug delivery. However, relatively little information exists concerning the uptake and transport of NPs across human colon cell layers, or their potential to invade three-dimensional models of human colon cells that better mimic the tissue structures of normal and tumoral colon. In order to gain such information, the interactions of biocompatible ultrasmall superparamagnetic iron oxide nanoparticles (USPIO NPs) (iron oxide core 9–10 nm) coated with either cationic polyvinylamine (aminoPVA) or anionic oleic acid with human HT-29 and Caco-2 colon cells was determined. The uptake of the cationic USPIO NPs was much higher than the uptake of the anionic USPIO NPs. The intracellular localization of aminoPVA USPIO NPs was confirmed in HT-29 cells by transmission electron microscopy that detected the iron oxide core. AminoPVA USPIO NPs invaded three-dimensional spheroids of both HT-29 and Caco-2 cells, whereas oleic acid-coated USPIO NPs could only invade Caco-2 spheroids. Neither cationic aminoPVA USPIO NPs nor anionic oleic acid-coated USPIO NPs were transported at detectable levels across the tight CacoReady™ intestinal barrier model or the more permeable mucus-secreting CacoGoblet™ model.

Kenzaoui, Blanka Halamoda; Vila, Maya R; Miquel, Josep M; Cengelli, Feride; Juillerat-Jeanneret, Lucienne

2012-01-01

267

Luminescent ultra-small gold nanoparticles obtained by ion implantation in silica  

NASA Astrophysics Data System (ADS)

The room temperature photoluminescence properties of ultra-small Au nanoclusters (made by 5–10 atoms) obtained by ion implantation in silica are presented. The results show a broad and intense luminescent emission in three different spectral regions around 750 nm, 980 nm and 1150 nm. The luminescence properties of the molecule-like Au clusters have been also correlated to the energy-transfer process to Er3+ ions in Au–Er co-implanted silica samples. A partial quenching of the 980 nm component is observed due to the Er3+ absorption level at 980 nm that acts as a de-excitation channel through which the photon energy is transferred from the Au nanoclusters to the Er ions, eventually producing the Er-related emission at 1.5 microns.

Cesca, T.; Maurizio, C.; Kalinic, B.; Scian, C.; Trave, E.; Battaglin, G.; Mazzoldi, P.; Mattei, G.

2014-05-01

268

Biofunctionalized, phosphonate-grafted, ultrasmall iron oxide nanoparticles for combined targeted cancer therapy and multimodal imaging.  

PubMed

A novel, inexpensive biofunctionalization approach is adopted to develop a multimodal and theranostic nanoagent, which combines cancer-targeted magnetic resonance/optical imaging and pH-sensitive drug release into one system. This multifunctional nanosystem, based on an ultrasmall superparamagnetic iron oxide (USPIO) nanocore, is modified with a hydrophilic, biocompatible, and biodegradable coating of N-phosphonomethyl iminodiacetic acid (PMIDA). Using appropriate spacers, functional molecules, such as rhodamine B isothiocyanate, folic acid, and methotrexate, are coupled to the amine-derivatized USPIO-PMIDA support with the aim of endowing simultaneous targeting, imaging, and intracellular drug-delivering capability. For the first time, phosphonic acid chemistry is successfully exploited to develop a stealth, multifunctional nanoprobe that can selectively target, detect, and kill cancer cells overexpressing the folate receptor, while allowing real-time monitoring of tumor response to drug treatment through dual-modal fluorescence and magnetic resonance imaging. PMID:19856326

Das, Manasmita; Mishra, Debasish; Dhak, Prasanta; Gupta, Satyajit; Maiti, Tapas Kumar; Basak, Amit; Pramanik, Panchanan

2009-12-01

269

PEG-nanolized ultrasmall selenium nanoparticles overcome drug resistance in hepatocellular carcinoma HepG2 cells through induction of mitochondria dysfunction  

PubMed Central

Gray selenium (Se) is one of the most widely used Se sources with very limited biocompatibility and bioactivity. In the present study, a simple method for the preparation of ultrasmall selenium nanoparticles (SeNPs) through direct nanolization of gray selenium by polyethylene glycol (PEG) was demonstrated. Monodisperse and homogeneous PEG-SeNPs with ultrasmall diameters were successfully prepared under optimized conditions. The products were characterized using various microscopic and spectroscopic methods, and the results suggest that the amphoteric properties of PEG and the coordination between oxygen and selenium atoms contributed to the formation of ultrasmall nanoparticles. PEG-SeNPs exhibited stronger growth inhibition on drug-resistant hepatocellular carcinoma (R-HepG2) cells than on normal HepG2 cells. Dose-dependent apoptosis was induced by PEG-SeNPs in R-HepG2 cells, as evidenced by an increase in the sub-G1 cell population. Further investigation on the underlying molecular mechanisms revealed that depletion of mitochondrial membrane potential and generation of superoxide anions contributed to PEG-SeNPs-induced apoptotic cell death in R-HepG2 cells. Our results suggest that PEG-SeNPs may be a candidate for further evaluation as a chemotherapeutic agent for drug-resistant liver cancer, and the strategy to use PEG200 as a surface decorator could be a highly efficient way to enhance the anticancer efficacy of nanomaterials.

Zheng, Shanyuan; Li, Xiaoling; Zhang, Yibo; Xie, Qiang; Wong, Yum-Shing; Zheng, Wenjie; Chen, Tianfeng

2012-01-01

270

Impact of surface coating and particle size on the uptake of small and ultrasmall superparamagnetic iron oxide nanoparticles by macrophages  

PubMed Central

Purpose Magnetic resonance imaging (MRI) using contrast agents like superparamagnetic iron oxide (SPIO) is an extremely versatile technique to diagnose diseases and to monitor treatment. This study tested the relative importance of particle size and surface coating for the optimization of MRI contrast and labeling efficiency of macrophages migrating to remote inflammation sites. Materials and methods We tested four SPIO and ultrasmall superparamagnetic iron oxide (USPIO), alkali-treated dextran magnetite (ATDM) with particle sizes of 28 and 74 nm, and carboxymethyl dextran magnetite (CMDM) with particle sizes of 28 and 72 nm. Mouse macrophage RAW264 cells were incubated with SPIOs and USPIOs, and the labeling efficiency of the cells was determined by the percentage of Berlin blue-stained cells and by measuring T2 relaxation times with 11.7-T MRI. We used trypan blue staining to measure cell viability. Results Analysis of the properties of the nanoparticles revealed that ATDM-coated 74 nm particles have a lower T2 relaxation time than the others, translating into a higher ability of MRI negative contrast agent. Among the other three candidates, CMDM-coated particles showed the highest T2 relaxation time once internalized by macrophages. Regarding labeling efficiency, ATDM coating resulted in a cellular uptake higher than CMDM coating, independent of nanoparticle size. None of these particle formulations affected macrophage viability. Conclusion This study suggests that coating is more critical than size to optimize the SPIO labeling of macrophages. Among the formulations tested in this study, the best MRI contrast and labeling efficiency are expected with ATDM-coated 74 nm nanoparticles.

Saito, Shigeyoshi; Tsugeno, Mana; Koto, Daichi; Mori, Yuki; Yoshioka, Yoshichika; Nohara, Satoshi; Murase, Kenya

2012-01-01

271

Multidentate block-copolymer-stabilized ultrasmall superparamagnetic iron oxide nanoparticles with enhanced colloidal stability for magnetic resonance imaging.  

PubMed

Ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) with diameters <5 nm hold great promise as T1-positive contrast agents for in vivo magnetic resonance imaging. However, control of the surface chemistry of USPIOs to ensure individual colloidal USPIOs with a ligand monolayer and to impart biocompatibility and enhanced colloidal stability is essential for successful clinical applications. Herein, an effective and versatile strategy enabling the development of aqueous colloidal USPIOs stabilized with well-defined multidentate block copolymers (MDBCs) is reported. The multifunctional MDBCs are designed to consist of an anchoring block possessing pendant carboxylates as multidentate anchoring groups strongly bound to USPIO surfaces and a hydrophilic block having pendant hydrophilic oligo(ethylene oxide) chains to confer water dispersibility and biocompatibility. The surface of USPIOs is saturated with multiple anchoring groups of MDBCs, thus exhibiting excellent long-term colloidal stability as well as enhanced colloidal stability at biologically relevant electrolyte, pH, and temperature conditions. Furthermore, relaxometric properties as well as in vitro and in vivo MR imaging results demonstrate that the MDBC-stabilized USPIO colloids hold great potential as an effective T1 contrast agent. PMID:24785001

Chan, Nicky; Laprise-Pelletier, Myriam; Chevallier, Pascale; Bianchi, Andrea; Fortin, Marc-André; Oh, Jung Kwon

2014-06-01

272

Solvothermal synthesis of cobalt ferrite nanoparticles loaded on multiwalled carbon nanotubes for magnetic resonance imaging and drug delivery.  

PubMed

Multiwalled carbon nanotube (MWCNT)/cobalt ferrite (CoFe(2)O(4)) magnetic hybrids were synthesized by a solvothermal method. The reaction temperature significantly affected the structure of the resultant MWCNT/CoFe(2)O(4) hybrids, which varied from 6nm CoFe(2)O(4) nanoparticles uniformly coated on the nanotubes at 180°C to agglomerated CoFe(2)O(4) spherical particles threaded by MWCNTs and forming necklace-like nanostructures at 240°C. Based on the superparamagnetic property at room temperature and high hydrophilicity, the MWCNT/CoFe(2)O(4) hybrids prepared at 180°C (MWCNT/CoFe(2)O(4)-180) were further investigated for biomedical applications, which showed a high T(2) relaxivity of 152.8 Fe mM(-1)s(-1) in aqueous solutions, a significant negative contrast enhancement effect on cancer cells and, more importantly, low cytotoxicity and negligible hemolytic activity. The anticancer drug doxorubicin (DOX) can be loaded onto the hybrids and subsequently released in a sustained and pH-responsive way. The DOX-loaded hybrids exhibited notable cytotoxicity to HeLa cancer cells due to the intracellular release of DOX. These results suggest that MWCNT/CoFe(2)O(4)-180 hybrids may be used as both effective magnetic resonance imaging contrast agents and anticancer drug delivery systems for simultaneous cancer diagnosis and chemotherapy. PMID:21664499

Wu, Huixia; Liu, Gang; Wang, Xue; Zhang, Jiamin; Chen, Yu; Shi, Jianlin; Yang, Hong; Hu, He; Yang, Shiping

2011-09-01

273

DNA hydrogel as a template for synthesis of ultrasmall gold nanoparticles for catalytic applications.  

PubMed

DNA cross-linked hydrogel was used as a matrix for synthesis of gold nanoparticles. DNA possesses a strong affinity to transition metals such as gold, which allows for the concentration of Au precursor inside a hydrogel. Further reduction of HAuCl4 inside DNA hydrogel yields well dispersed, non-aggregated spherical Au nanoparticles of 2-3 nm size. The average size of these Au nanoparticles synthesized in DNA hydrogel is the smallest reported so far for in-gel metal nanoparticles synthesis. DNA hybrid hydrogel containing gold nanoparticles showed high catalytic activity in the hydrogenation reaction of nitrophenol to aminophenol. The proposed soft hybrid material is promising as environmentally friendly and sustainable material for catalytic applications. PMID:24533931

Zinchenko, Anatoly; Miwa, Yasuyuki; Lopatina, Larisa I; Sergeyev, Vladimir G; Murata, Shizuaki

2014-03-12

274

Synthesis and magnetic behavior of ultra-small bimetallic FeCo/graphite nanoparticles  

NASA Astrophysics Data System (ADS)

FeCo-alloy graphite-coated nanoparticles with mean particle diameter under 8 nm have been synthesized following a CVD carbon-deficient method. The superior magnetic properties of FeCo-alloy nanoparticles makes them good candidates to be used as magnetic filler in magneto-polymer composites. Thanks to the protective effect of the graphite shell, FeCo nanoparticles are stable under oxygen atmosphere up to 200?° C. The as-prepared nanoparticles presented a highly long range chemically ordered core being ferromagnetic at room temperature with a saturation magnetization at room temperature close to the bulk value. After annealing at 750 K the saturation magnetization and the coercive field increase. To investigate the processes involved in the thermal treatment, the temperature dependence of the magnetization and the particle composition, size and structure have been characterized before and after annealing. Besides powder x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), a detailed study by means of advanced transmission electron microscopy (TEM) techniques has been carried out. In particular, aberration corrected scanning transmission electron microscopy (STEM), has shown that nanoparticles became faceted after the thermal treatment, as a mechanism to reach the thermodynamic equilibrium within the metastable phase. This outstanding feature, not previously reported, leads to an increase of the shape anisotropy, which in turn might be the origin of the observed increase of the coercive field after annealing.

Castrillón, M.; Mayoral, A.; Urtizberea, A.; Marquina, C.; Irusta, S.; Meier, J. G.; Santamaría, J.

2013-12-01

275

Synthesis of ultrasmall magnetic iron oxide nanoparticles and study of their colloid and surface chemistry  

PubMed Central

Colloidal nanoparticles of Fe3O4 (4 nm) were synthesized by high-temperature hydrolysis of chelated iron (II) and (III) diethylene glycol alkoxide complexes in a solution of the parent alcohol (H2DEG) without using capping ligands or surfactants: [Fe(DEG)Cl2]2- + 2[Fe(DEG)Cl3]2- + 2H2O + 2OH- ? Fe3O4 + 3H2DEG + 8Cl- The obtained particles were reacted with different small-molecule polydentate ligands, and the resulting adducts were tested for aqueous colloid formation. Both the carboxyl and ?-hydroxyl groups of the hydroxyacids are involved in coordination to the nanoparticles’ surface. This coordination provides the major contribution to the stability of the ligand-coated nanoparticles against hydrolysis.

Goloverda, Galina; Jackson, Barry; Kidd, Clayton; Kolesnichenko, Vladimir

2009-01-01

276

Hybrid melittin cytolytic Peptide-driven ultrasmall lipid nanoparticles block melanoma growth in vivo.  

PubMed

The cytolytic peptide melittin is a potential anticancer candidate that may be able to overcome tumor drug resistance due to its lytic properties. However, in vivo applications of melittin are limited due to its main side effect, hemolysis, which is especially pronounced following intravenous administration. Here, we designed a hybrid cytolytic peptide, ?-melittin, in which the N-terminus of melittin is linked to the C-terminus of an amphipathic ?-helical peptide (?-peptide) via a GSG linker. The strong ?-helical configuration allows ?-melittin to interact with phospholipids and self-assemble into lipid nanoparticles, with a high efficiency for ?-melittin encapsulation (>80%) and a strong ability to control the structure of the nanoparticle (~20 nm). This ?-melittin-based lipid nanoparticle (?-melittin-NP) efficiently shields the positive charge of melittin (18.70 ± 0.90 mV) within the phospholipid monolayer, resulting in the generation of a neutral nanoparticle (2.45 ± 0.56 mV) with reduced cytotoxicity and a widened safe dosage range. Confocal imaging data confirmed that ?-melittin peptides were efficiently released from the nanoparticles and were cytotoxic to the melanoma cells. Finally, ?-melittin-NPs were administered to melanoma-bearing mice via intravenous injection. The growth of the melanoma cells was blocked by the ?-melittin-NPs, with an 82.8% inhibition rate relative to the PBS-treated control group. No side effects of treatment were found in this study. Thus, the excellent properties of ?-melittin-NP give it potential clinical applications in solid tumor therapeutics through intravenous administration. PMID:23790040

Huang, Chuan; Jin, Honglin; Qian, Yuan; Qi, Shuhong; Luo, Haiming; Luo, Qingming; Zhang, Zhihong

2013-07-23

277

A highly effective, nontoxic T1 MR contrast agent based on ultrasmall PEGylated iron oxide nanoparticles.  

PubMed

In this study we systematically developed a potential MR T(1) contrast agent based on very small PEGylated iron oxide nanoparticles. We adjusted the size of the crystalline core providing suitable relaxometric properties. In addition, a dense and optimized PEG coating provides high stability under physiological conditions together with low cytotoxicity and low nonspecific phagocytosis into macrophage cells as a part of the reticulo endothelial system at biologically relevant concentrations. The as developed contrast agent has the lowest r(2)/r(1) ratio (2.4) at 1.41 T reported so far for PEGylated iron oxide nanoparticles as well as a r(1) relaxivity (7.3 mM(-1) s(-1)) that is two times higher compared to that of Magnevist as a typical T(1) contrast agent based on gadolinium as a clinical standard. PMID:19799448

Tromsdorf, Ulrich I; Bruns, Oliver T; Salmen, Sunhild C; Beisiegel, Ulrike; Weller, Horst

2009-12-01

278

Magnoelastic coupling in magnetic oxide nanoparticles  

NASA Astrophysics Data System (ADS)

Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials. To investigate confinement in combination with strong magnetoelastic interactions, we measured the infrared vibrational properties of MnO and CoFe2O4 nanoparticles and their parent compounds. For MnO, a charge and bonding analysis reveals that Born effective charge, local effective charge, total polarizability, and the force constant are overall lower in the nanoparticles compared to the bulk. We find that the spin-lattice coupling drops from ˜7 cm-1 in the single crystal to <1 cm-1 in the nanoparticles. For CoFe2O4, the spectroscopic response is sensitive to the size-induced crossover to the superparamagnetic state, which occurs between 7 and 10 nm, and a spin-phonon coupling analysis supports the core-shell model. Moreover, it provides an estimate of the thickness of the magnetically disordered shell, increasing from 0.4 nm in the 14 nm particles to 0.8 nm in the 5 nm particles, demonstrating that the associated local lattice distortions take place on the length scale of the unit cell. These findings are important for understanding finite length scale effects in magnetic oxides and other more complex functional oxides.

Sun, Qi; Baker, Sheila; Birkel, Christina; Seshadri, Ram; Tremel, Wolfgang; Christianson, Andrew; Musfeldt, Janice

2012-02-01

279

Synthesis of stable ultra-small Cu nanoparticles for direct writing flexible electronics  

NASA Astrophysics Data System (ADS)

In this study, pure Cu nanoparticles (NPs) have been successfully synthesized and the Cu nano-ink was prepared for direct writing on photo paper using a roller pen. The tri-sodium citrate was used as initial reducing-cum-surfactant agent followed by hydrazine as a second massive reducing agent and cetyltrimethylammonium bromide (CTAB) as extra surfactant agent. From the XRD, TEM, and HR-TEM analyses, the synthesized particles are confirmed to be Cu in spherical shape with sizes range of 2.5 ± 1.0 nm. By analyzing the FT-IR spectroscopy and TGA curves, it was found that the obtained particles capped with tri-sodium citrate and CTAB layers are stable to oxidation up to the temperature 228 °C. The reduced size and enhanced air-stability of the Cu NPs result in an improved particle density upon sintering, which is mainly responsible for the increased conductivity of the Cu patterns. The resistivity of Cu patterns sintered in Ar at 160 °C for 2 h is 7.2 ± 0.6 ?? cm, which is 4.40 times the bulk Cu resistivity. The drawn Cu lines exhibited excellent integrity and good conductivity, which were experimentally tested. Moreover, a Cu electrode and a sample RFID antenna were successfully made.

Li, Wei; Chen, Minfang

2014-01-01

280

Magnetic Characterization of Ferrite Nanoparticles  

NASA Astrophysics Data System (ADS)

Magnetic nanoparticles (NPs) of different compositions (FeO/Fe3O4, g-Fe2O3, FePt, and CoFe2O4) have been synthesized using high temperature organometallic routes described elsewhere. NPs (16.6 nm in diameter) of a mixed FeO/Fe3O4 (wuestite/magnetite) composition were prepared by thermal decomposition or iron oleate in the presence of oleic acid as a surfactant in dodocane at 370C in argon atmosphere. After the thermal treatment of the reaction solution at 200 C under air for 2 hours these NPs are transformed into maghemite (g-Fe2O3), the magnetization of which is significantly enhanced. NPs of CoFe2O4 (8 nm) have been prepared by simultaneous decomposition of Co(II) and Fe(III) acetylacetonates in the presence of oleic acid and oleylamine. The X-ray diffraction profile of these NPs is characteristic of cobalt ferrite. Alternatively, alloyed 1.8 nm FePt NPs prepared by simultaneous decomposition of Fe and Pt acetylacetonates in the reductive environment demonstrate a completely disordered structure, which is reflected in their magnetic properties. SQUID magnetometry was used to measure the magnetization of NPs at high and low temperatures. Zero-field cooling and field-cooling measurements were taken to demonstrate superparamagnetic behavior and an associated blocking temperature.

Bryan, Matthew; Sokol, Paul; Gumina, Greg; Bronstein, Lyudmila; Dragnea, Bogdan

2011-03-01

281

One-step synthesis of monodisperse, water-soluble ultra-small Fe3O4 nanoparticles for potential bio-application  

NASA Astrophysics Data System (ADS)

We report that ultra-small, monodisperse, water-dispersible magnetite (Fe3O4) nanoparticles can be synthesized by a facile one-pot approach using trisodium citrate as crystal grain growth inhibitor and stabilizer in polyol solution. The resultant Fe3O4 nanoparticles exhibit an excellent long-term colloidal stability in various buffer solutions without any modification. They are also superparamagnetic at room temperature and their magnetic property relies heavily on their size. Due to the low magnetization and good water-dispersibility, the 1.9 nm-sized Fe3O4 nanoparticles reveal a low r2/r1 ratio of 2.03 (r1 = 1.415 mM-1 s-1, r2 = 2.87 mM-1 s-1), demonstrating that they can be efficient T1 contrast agents. On the other hand, because of the excellent magnetic responsivity, the 13.8 nm-sized Fe3O4 nanoparticles can be readily modified with nitrilotriacetic acid and used to separate the protein simply with the assistance of a magnet. In addition, these Fe3O4 nanoparticles may be useful in other fields, such as hyperthermia treatment of cancer and targeted drug delivery based on their size-dependent magnetic property and excellent stability.

Shen, Li-Hua; Bao, Jian-Feng; Wang, Dong; Wang, Yi-Xiao; Chen, Zhi-Wei; Ren, Lei; Zhou, Xi; Ke, Xue-Bin; Chen, Min; Yang, An-Qi

2013-02-01

282

Bcl-2-functionalized ultrasmall superparamagnetic iron oxide nanoparticles coated with amphiphilic polymer enhance the labeling efficiency of islets for detection by magnetic resonance imaging  

PubMed Central

Based on their versatile, biocompatible properties, superparamagnetic iron oxide (SPIO) or ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles are utilized for detecting and tracing cells or tumors in vivo. Here, we developed an innoxious and concise synthesis approach for a novel B-cell lymphoma (Bcl)-2 monoclonal antibody-functionalized USPIO nanoparticle coated with an amphiphilic polymer (carboxylated polyethylene glycol monooleyl ether [OE-PEG-COOH]). These nanoparticles can be effectively internalized by beta cells and label primary islet cells, at relatively low iron concentration. The biocompatibility and cytotoxicity of these products were investigated by comparison with the commercial USPIO product, FeraSpin™ S. We also assessed the safe dosage range of the product. Although some cases showed a hypointensity change at the site of transplant, a strong magnetic resonance imaging (MRI) was detectable by a clinical MRI scanner, at field strength of 3.0 Tesla, in vivo, and the iron deposition/attached in islets was confirmed by Prussian blue and immunohistochemistry staining. It is noteworthy that based on our synthesis approach, in future, we could exchange the Bcl-2 with other probes that would be more specific for the targeted cells and that would have better labeling specificity in vivo. The combined results point to the promising potential of the novel Bcl-2-functionalized PEG-USPIO as a molecular imaging agent for in vivo monitoring of islet cells or other cells.

Yang, Bin; Cai, Haolei; Qin, Wenjie; Zhang, Bo; Zhai, Chuanxin; Jiang, Biao; Wu, Yulian

2013-01-01

283

One-pot synthesis of pegylated ultrasmall iron-oxide nanoparticles and their in vivo evaluation as magnetic resonance imaging contrast agents.  

PubMed

A well-defined copolymer poly(oligo(ethylene glycol) methacrylate-co-methacrylic acid) P(OEGMA-co-MAA) was studied as a novel water-soluble biocompatible coating for superparamagnetic iron oxide nanoparticles. This copolymer was prepared via a two-step procedure: a well-defined precursor poly(oligo(ethylene glycol) methacrylate-co-tert-butyl methacrylate), P(OEGMA-co-tBMA) (M(n) = 17300 g mol(-1); M(w)/M(n) = 1.22), was first synthesized by atom-transfer radical polymerization in the presence of the catalyst system copper(I) chloride/2,2'-bipyridyl and subsequently selectively hydrolyzed in acidic conditions. The resulting P(OEGMA-co-MAA) was directly utilized as a polymeric stabilizer in the nanoparticle synthesis. Four batches of ultrasmall PEGylated magnetite nanoparticles (i.e., with an average diameter below 30 nm) were prepared via aqueous coprecipitation of iron salts in the presence of variable amounts of P(OEGMA-co-MAA). The diameter of the nanoparticles could be easily tuned in the range 10-25 nm by varying the initial copolymer concentration. Moreover, the formed PEGylated ferrofluids exhibited a long-term colloidal stability in physiological buffer and could therefore be studied in vivo by magnetic resonance (MR) imaging. Intravenous injection into rats showed no detectable signal in the liver within the first 2 h. Maximum liver accumulation was found after 6 h, suggesting a prolongated circulation of the nanoparticles in the bloodstream as compared to conventional MR imaging contrast agents. PMID:17096542

Lutz, Jean-François; Stiller, Sabrina; Hoth, Ann; Kaufner, Lutz; Pison, Ulrich; Cartier, Régis

2006-11-01

284

Hollow magnetic microspheres obtained by nanoparticle adsorption on surfactant stabilized microbubbles.  

PubMed

We report on the stabilization of nanoparticle-decorated microbubbles for long periods of time using a synergism between a soluble surfactant and nanoparticles. The soluble surfactant is the perfluoroalkyl phosphate C8F17(CH2)2OP(O)(OH)2 (labeled F8H2Phos) and the nanoparticles (NPs) are 20-25 nm cobalt ferrite (CoFe2O4). The NP-F8H2Phos system has been studied by dynamic light scattering, dynamic magnetic susceptibility measurements and thermal gravimetric analysis. Microbubbles with diameters in the 1-20 ?m range have been stabilized in 0.1 M NaCl brine. Its presence is crucial for the long-term stabilization. The surfactant adsorbs rapidly on bubbles and slows down the bubble shrinkage. Thus, the NPs can attach to the bubble and form a hollow sphere with a rigid shell. The charge screening by NaCl favors the attachment of NPs to the bubble surface. The coverage of the bubbles by the CoFe2O4 nanoparticle layer is confirmed by thermally induced inflation-deflation experiments and the control of bubbles with a magnetic field. PMID:24909785

Kovalenko, Artem; Jouhannaud, Julien; Polavarapu, Prasad; Krafft, Marie Pierre; Waton, Gilles; Pourroy, Geneviève

2014-06-25

285

Copper(0) nanoparticles supported on silica-coated cobalt ferrite magnetic particles: cost effective catalyst in the hydrolysis of ammonia-borane with an exceptional reusability performance.  

PubMed

Herein we report the development of a new and cost-effective nanocomposite catalyst for the hydrolysis of ammonia-borane (NH(3)BH(3)), which is considered to be one of the most promising solid hydrogen carriers because of its high gravimetric hydrogen storage capacity (19.6% wt) and low molecular weight. The new catalyst system consisting of copper nanoparticles supported on magnetic SiO(2)/CoFe(2)O(4) particles was reproducibly prepared by wet-impregnation of Cu(II) ions on SiO(2)/CoFe(2)O(4) followed by in situ reduction of the Cu(II) ions on the surface of magnetic support during the hydrolysis of NH(3)BH(3) and characterized by ICP-MS, XRD, XPS, TEM, HR-TEM and N(2) adsorption-desorption technique. Copper nanoparticles supported on silica coated cobalt(II) ferrite SiO(2)/CoFe(2)O(4) (CuNPs@SCF) act as highly active catalyst in the hydrolysis of ammonia-borane, providing an initial turnover frequency of TOF = 2400 h(-1) at room temperature, which is not only higher than all the non-noble metal catalysts but also higher than the majority of the noble metal based homogeneous and heterogeneous catalysts employed in the same reaction. More importantly, they were easily recovered by using a permanent magnet in the reactor wall and reused for up to 10 recycles without losing their inherent catalytic activity significantly, which demonstrates the exceptional reusability of the CuNPs@SCF catalyst. PMID:22856878

Kaya, Murat; Zahmakiran, Mehmet; Ozkar, Saim; Volkan, Mürvet

2012-08-01

286

Comprehensive assessment of nephrotoxicity of intravenously administered sodium-oleate-coated ultra-small superparamagnetic iron oxide (USPIO) and titanium dioxide (TiO2) nanoparticles in rats.  

PubMed

As a main excretory organ, kidney is predisposed to direct/indirect injury. We addressed the potential nephrotoxic effects following expositions of healthy rats to nanoparticle (NP) loads relevant to humans in a situation of 100% bioavailability. Up to 4 weeks after administration, a single iv bolus of oleate-coated ultra-small superparamagnetic iron oxide NPs (in dose of 0.1%, 1.0% and 10.0% of LD50) or TiO2 NPs (1.0% of LD50) did not elicit decline in renal function, damage to proximal tubules, alterations in: renal histology or expression of pro-inflammatory/pro-fibrotic genes, markers of systemic or local renal micro-inflammation or oxidative damage. Antioxidant enzyme activities in renal cortex, mildly elevated at 24 h, completely restored at later time points. Data obtained by multifaceted approach enable the prediction of human nephrotoxicity during preclinical studies, and may serve as comparison for alternative testing strategies using in vitro and in silico methods essential for the NP-nephrotoxicity risk assessment. PMID:23272807

Šebeková, Katarína; Dušinská, Mária; Simon Klenovics, Kristína; Kollárová, Radana; Boor, Peter; Kebis, Anton; Staruchová, Marta; Vlková, Barbora; Celec, Peter; Hodosy, Július; Ba?iak, Ladislav; Tušková, Radka; Be?o, Milan; Tulinská, Jana; Príbojová, Jana; Bilani?ová, Dagmar; Pojana, Giulio; Marcomini, Antonio; Volkovová, Katarína

2014-03-01

287

Influence of ferrite nanoparticle type and content on the crystallization kinetics and electroactive phase nucleation of poly(vinylidene fluoride).  

PubMed

This work reports on the nucleation of the ?-phase of poly(vinylidene fluoride) (PVDF) by incorporating CoFe(2)O(4) and NiFe(2)O(4) nanoparticles, leading in this way to the preparation of magnetoelectric composites. The fraction of filler nanoparticles needed to produce the same ?- to ?-phase ratio in crystallized PVDF is 1 order of magnitude lower in the cobalt ferrite nanoparticles. The interaction between nanoparticles and PVDF chains induce the all-trans conformation in PVDF segments, and this structure then propagates in crystal growth. The nucleation kinetics is enhanced by the presence of nanoparticles, as corroborated by the increasing number of spherulites with increasing nanoparticle content and by the variations of the Avrami's exponent. Further, the decrease of the crystalline fraction of PVDF with increasing nanoparticle content indicates that an important fraction of polymer chains are confined in interphases with the filler particle. PMID:21545124

Sencadas, Vitor; Martins, Pedro; Pitães, Alexandre; Benelmekki, Maria; Gómez Ribelles, José Luis; Lanceros-Mendez, Senentxu

2011-06-01

288

Magnetic properties of CoFe2O4-BaTiO3 composites  

NASA Astrophysics Data System (ADS)

The aim of the present work is to study how the volume (lattice parameters) changes of barium titanate, induced by a phase transition, which occurs by temperature sweeps, influence magnetic behavior of cobalt ferrite in their composites via inverse magnetostrictive (Villari) effect. Structure, phase composition, and magnetic properties were investigated using X-ray diffraction, Mössbauer spectroscopy, and temperature dependence of magnetization. The tetragonal-to-orthorhombic phase transition in barium titanate occurring at ~280 K on cooling can be observed in the zero-field cooled magnetization curve. The other phase transitions, i.e., tetragonal-to-cubic transition at ~390 K and orthorhombic-to-rhombohedral transition at ~178 K, were detected neither by magnetic nor by Mössbauer measurements.

?uda, J.; Mousa, I.; David, B.; Pizúrová, N.; Tu?ek, J.; Žák, T.; Mašlá?, M.; Schneeweiss, O.

2012-10-01

289

A LOW TEMPERATURE PATH TO THE PREPARATION OF CoFe2O4 FERRITE  

Microsoft Academic Search

Ultrafine cobalt ferrite has been prepared by the decomposition of cobalt oxalate-hydrazinate complex, which is used as precursor. The preparation and thermal decomposition of the precursor have been studied using chemical, thermal, and infrared techniques. The precursor decomposes at low temperatures with the effusion of large amounts of gases. The coordination compounds used as chemical precursors have to include, ligands,

E. Chirtop; I. Mitova; R. M. Ion; M. Iliescu

290

Thermal conductivity of Zn doped CoFe2O4 ferrites  

Microsoft Academic Search

A series of samples of the type Co1-xZnxFe2O4 (x = 0.0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0) was prepared as ceramics. The existence of a single phase was confirmed by x-ray studies. The thermal conductivity and specific heat were measured at temperatures ranging from 100°C to 200°C. The thermal conductivity had a minimum value at x = 0.4,

M. I. Abd El-Ati

1994-01-01

291

CoFe2O4 polypyrrole (PPy) nanocomposites: new multifunctional materials  

Microsoft Academic Search

Spinel ferrites (iron cobalt oxide) were prepared by the microemulsion method at different temperatures and sodium dodecyl sulphate (SDS) surfactant concentrations. Subsequently, a quantity of the different samples were coated with an intrinsically conducting polymer (ICP) shell of polypyrrole. The polymer shell was synthesized by a chemical route after the ferrites particle production. By combining in a single material the

N. Murillo; E. Ochoteco; Y. Alesanco; J. A. Pomposo; J. Rodriguez; J. González; J. J. del Val; M. R. Britel; F. M. Varela-Feria; A. R. de Arellano-López

2004-01-01

292

Signature of ferroelectricity in magnetically ordered Mo-doped CoFe2O4  

Microsoft Academic Search

Coexistence of both magnetic ordering and ferroelectricity (with giant dielectric constant) have been observed for the first time in Co(Fe1-xMox)2O4 . The magnetization of Co(Fe1-xMox)2O4 ( x ranges from 0 to 0.1) was found to increase with doping concentration of Mo. The magnetic properties indicate that Mo goes into the tetrahedral site. The giant dielectric constant may be attributed to

G. D. Dwivedi; K. F. Tseng; C. L. Chan; P. Shahi; J. Lourembam; B. Chatterjee; A. K. Ghosh; H. D. Yang; Sandip Chatterjee

2010-01-01

293

Polyethylene glycol-covered ultra-small Gd2O3 nanoparticles for positive contrast at 1.5 T magnetic resonance clinical scanning  

NASA Astrophysics Data System (ADS)

The size distribution and magnetic properties of ultra-small gadolinium oxide crystals (US-Gd2O3) were studied, and the impact of polyethylene glycol capping on the relaxivity constants (r1, r2) and signal intensity with this contrast agent was investigated. Size distribution and magnetic properties of US-Gd2O3 nanocrystals were measured with a TEM and PPMS magnetometer. For relaxation studies, diethylene glycol (DEG)-capped US-Gd2O3 nanocrystals were reacted with PEG-silane (MW 5000). Suspensions were adequately dialyzed in water to eliminate traces of Gd3+ and surfactants. The particle hydrodynamic radius was measured with dynamic light scattering (DLS) and the proton relaxation times were measured with a 1.5 T MRI scanner. Parallel studies were performed with DEG-Gd2O3 and PEG-silane-SPGO (Gd2O3,< 40 nm diameter). The small and narrow size distribution of US-Gd2O3 was confirmed with TEM (~3 nm) and DLS. PEG-silane-US-Gd2O3 relaxation parameters were twice as high as for Gd-DTPA and the r2/r1 ratio was 1.4. PEG-silane-SPGO gave low r1 relaxivities and high r2/r1 ratios, less compatible with positive contrast agent requirements. Higher r1 were obtained with PEG-silane in comparison to DEG-Gd2O3. Treatment of DEG-US-Gd2O3 with PEG-silane provides enhanced relaxivity while preventing aggregation of the oxide cores. This study confirms that PEG-covered Gd2O3 nanoparticles can be used for positively contrasted MR applications requiring stability, biocompatible coatings and nanocrystal functionalization.

Fortin, Marc-André; Petoral, Rodrigo M., Jr.; Söderlind, Fredrik; Klasson, A.; Engström, Maria; Veres, Teodor; Käll, Per-Olof; Uvdal, Kajsa

2007-10-01

294

Role of oxygen defects on the magnetic properties of ultra-small Sn1-xFexO2 nanoparticles  

NASA Astrophysics Data System (ADS)

Although the role of oxygen defects in the magnetism of metal oxide semiconductors has been widely discussed, it is been difficult to directly measure the oxygen defect concentration of samples to verify this. This work demonstrates a direct correlation between the photocatalytic activity of Sn1-xFexO2 nanoparticles and their magnetic properties. For this, a series of ~2.6 nm sized, well characterized, single-phase Sn1-xFexO2 crystallites with x = 0-0.20 were synthesized using tin acetate, urea, and appropriate amounts of iron acetate. X-ray photoelectron spectroscopy confirmed the concentration and 3+ oxidation state of the doped Fe ions. The maximum magnetic moment/Fe ion, ?, of 1.6 × 10-4 ?B observed for the 0.1% Fe doped sample is smaller than the expected spin-only contribution from either high or low spin Fe3+ ions, and ? decreases with increasing Fe concentration. This behavior cannot be explained by the existing models of magnetic exchange. Photocatalytic studies of pure and Fe-doped SnO2 were used to understand the roles of doped Fe3+ ions and of the oxygen vacancies and defects. The photocatalytic rate constant k also showed an increase when SnO2 nanoparticles were doped with low concentrations of Fe3+, reaching a maximum at 0.1% Fe, followed by a rapid decrease of k for further increase in Fe%. Fe doping presumably increases the concentration of oxygen vacancies, and both Fe3+ ions and oxygen vacancies act as electron acceptors to reduce e--h+ recombination and promote transfer of electrons (and/or holes) to the nanoparticle surface, where they participate in redox reactions. This electron transfer from the Fe3+ ions to local defect density of states at the nanoparticle surface could develop a magnetic moment at the surface states and leads to spontaneous ferromagnetic ordering of the surface shell under favorable conditions. However, at higher doping levels, the same Fe3+ ions might act as recombination centers causing a decrease of both k and magnetic moment ?.

Dodge, Kelsey; Chess, Jordan; Eixenberger, Josh; Alanko, Gordon; Hanna, Charles B.; Punnoose, Alex

2013-05-01

295

Cobalt-ferrite nanoparticles: Structure, cation distributions, and magnetic properties  

NASA Astrophysics Data System (ADS)

Cobalt-ferrite nanoparticles have been synthesized in water-in-oil microemulsions (reversed micelles) with varying cation composition. The microenvironment provides a template effect that controls the size and particle shape. Transmission electron microscopy reveals that the particles are nanospheres with particle size ranging from 12 to 18 nm. X-ray diffraction results indicate that at low Co2+:Fe2+ ratio (1:10 and 1:5) in the precursor, the particles retain an essentially ferrite structure (?-Fe2O3). However, the cobalt-ferrite phase (CoFe2O4) forms upon further increase of the Co2+ content. The materials are found to exhibit superparamagnetism. The blocking temperatures and coercivities are dependent on the Co2+:Fe2+ ratio in the system.

Li, Sichu; John, Vijay T.; O'Connor, Charles; Harris, Vincent; Carpenter, Everett

2000-05-01

296

Evidence for Quantization of Mechanical Rotation of Magnetic Nanoparticles  

NASA Astrophysics Data System (ADS)

We report evidence of the quantization of the rotational motion of solid particles containing thousands of atoms. A system of CoFe2O4 nanoparticles confined inside polymeric cavities has been studied. The particles have been characterized by the x-ray diffraction, transmission electron microscopy, plasma mass spectroscopy, ferromagnetic resonance (FMR), and magnetization measurements. Magnetic and FMR data confirm the presence of particles that are free to rotate inside the cavities. Equidistant, temperature-independent jumps in the dependence of the microwave absorption on the magnetic field have been detected. This observation is in accordance with the expectation that orbital motion splits the low-field absorption line into multiple lines.

Tejada, J.; Zysler, R. D.; Molins, E.; Chudnovsky, E. M.

2010-01-01

297

Evidence for quantization of mechanical rotation of magnetic nanoparticles.  

PubMed

We report evidence of the quantization of the rotational motion of solid particles containing thousands of atoms. A system of CoFe2O4 nanoparticles confined inside polymeric cavities has been studied. The particles have been characterized by the x-ray diffraction, transmission electron microscopy, plasma mass spectroscopy, ferromagnetic resonance (FMR), and magnetization measurements. Magnetic and FMR data confirm the presence of particles that are free to rotate inside the cavities. Equidistant, temperature-independent jumps in the dependence of the microwave absorption on the magnetic field have been detected. This observation is in accordance with the expectation that orbital motion splits the low-field absorption line into multiple lines. PMID:20366623

Tejada, J; Zysler, R D; Molins, E; Chudnovsky, E M

2010-01-15

298

Grain Size Control of the Magnetic Nanoparticles by Solid State Route Modification  

NASA Astrophysics Data System (ADS)

The CoFe2O4 and NiFe2O4 nanoparticles were synthesized exploiting a co-precipitation method and afterward calcinated at 400 °C through two different experimental apparatus: a conventional muffle and rotatory oven. X-ray diffraction (XRD) analysis revealed that nanocrystalline ferrites grew with a face center cubic structure (fcc) and Fd3 m symmetry space group. XRD, transmission electron microscopy, and magnetic measurements confirmed the compositional homogeneity and the narrow size particle distribution (6-8 nm) of the sample thermally treated in a rotary oven, in all likelihood due to the sample's constant turning movement. The size of the magnetic particles is extremely important and influences the choice of a potential technological application. For this reason, our study emerges as a new and simple innovating procedure to control the size of magnetic nanoparticles.

Barreto, A. C. H.; Santiago, V. R.; Freire, R. M.; Mazzetto, S. E.; Sasaki, J. M.; Vasconcelos, I. F.; Denardin, J. C.; Mele, Giuseppe; Carbone, Luigi; Fechine, P. B. A.

2013-07-01

299

The need for stable, mono-dispersed, and biofunctional magnetic nanoparticles for one-step magnetic immunoassays  

NASA Astrophysics Data System (ADS)

We have developed a magnetic immunoassay system (MIA) using magnetic nanoparticle markers for biomolecule detection. We have magnetically characterized multi-core magnetic nanoparticles (MNPs) containing single-domain crystals of Fe3O4 and CoFe2O4 with our system using a high temperature superconducting quantum interference device as detector. We use a Helmholtz coil to excite the MNPs and study the AC-susceptibility. The data is fit to a model and information about the particle size distribution of the MNP system is extracted. We observe high stability of the unfunctionalized MNPs. However, our MIA measurements require stable functionalized MNPs. We have found a significant increase in hydrodynamic size of the functionalized MNP systems in the course of just a few days caused by agglomeration behaviour. Separate measurements performed at Imego AB with their AC-Susceptometer, DynoMAG®, confirm these findings. Without stable, functionalized MNPs MIAs of this kind are impossible.

Öisjöen, F.; Schneiderman, J. F.; Astalan, A. P.; Kalabukhov, A.; Johansson, C.; Winkler, D.

2010-01-01

300

Cobalt ferrite thin films as anode material for lithium ion batteries  

Microsoft Academic Search

Spinel cobalt ferrite (CoFe2O4) thin films have been fabricated by 355nm reactive pulsed laser deposition on stainless steel substrates. XRD and SEM analyses showed that the CoFe2O4 films exhibited a polycrystalline structure and were composed of nanoparticles with an average size of 80nm. At 1C rate, the initial irreversible capacity of polycrystalline CoFe2O4 film electrode cycled between 0.01 and 3.0V

Yan-Qiu Chu; Zheng-Wen Fu; Qi-Zong Qin

2004-01-01

301

In situ synthesis of cobalt ferrite nanoparticle/polymer hybrid from a mixed Fe-Co methacrylate for magnetic hyperthermia  

NASA Astrophysics Data System (ADS)

Hyperthermic CoFe2O4 nanoparticle (CFO NP)/polymer hybrids were synthesized by hydrolysis-condensation from a complex of Co and Fe possessing methacrylate ligands. Single-crystal analysis revealed that the complex consisted of two Co and four Fe metal atoms coordinated by methacrylate and 2-methoxyethoxy groups. The complex was copolymerized with 2-hydroxyethyl methacrylate (HEMA) and the resulting copolymer was then hydrolyzed to form a CFO NP/copolymer of poly(methacrylate) and poly(2-hydroxyethyl methacrylate) hybrid. Copolymerization with HEMA enhanced the stability of the hybrid in water. The size and magnetic properties of CFO in the hybrid were controlled by adjusting the hydrolysis conditions. Moreover, the hybrid generated heat under an alternating current magnetic field; its exothermal properties depended on the magnetic properties of the hybrid, the strength of the applied field, and the CFO NP content in the agar phantom matrix.

Hayashi, Koichiro; Maeda, Kazuki; Moriya, Makoto; Sakamoto, Wataru; Yogo, Toshinobu

2012-09-01

302

Synthesis and Characterization of Nano CoFe2O4 by Low-Temperature Combustion Synthesis Using Different Fuels  

NASA Astrophysics Data System (ADS)

The combustion synthesis has been utilized to prepare nanophased powders of cobalt spinel ferrite using ODH and glycine fuels. The product was characterized by X-ray diffraction; Fourier transformed spectroscopy, scanning electron microscopy, UV-Vis absorption etc. The XRD patterns reveal spinal cubic structure. SEM profiles show the product is porous, agglomeration, irregular in shape. The crystallite size was estimated using Scherer's formula and W-H plots and show nano in size (13 nm: ODH & 36 nm: Glycine). The UV-Vis absorption shows at ~430 nm in both the samples.

Jnaneshwara, D. M.; Krishna, R. Gopala; Nagabhushana, H.; Nagabhushana, B. M.; Shivakumara, C.; Chakradhar, R. P. S.

2011-07-01

303

Magnetic structure of Fe-doped CoFe2O4 probed by x-ray magnetic spectroscopies  

NASA Astrophysics Data System (ADS)

The magnetic properties of iron-doped cobalt ferrite (Co1-xFe2+xO4) (001) thin films grown epitaxially on MgO (001) substrates are investigated by superconducting quantum interference device magnetometry and soft x-ray magnetic linear and circular dichroisms. All Co1-xFe2+xO4 (0.01 ? x ? 0.63) samples have out-of-plane magnetic easy axes and large coercive fields, unlike Fe3O4, due to a large Co2+ orbital moment. The magnetic moments for those samples are significantly reduced from their bulk values; however, as x increases, the magnetic moments tend nearer to their bulk values and increase more rapidly as x approaches 1. This reduction in magnetic moment is attributed to spin canting among the Co2+ cations, owing to a small in-plane tensile strain in the film and to an increased antiferromagnetic alignment among all the cations caused by a partially inverse spinel cubic structure and the likely presence of antiphase boundaries. Our results show that small changes in stoichiometry can lead to significant changes in the magnetic moment of Co1-xFe2+xO4, especially at large values of x.

Moyer, J. A.; Vaz, C. A. F.; Arena, D. A.; Kumah, D.; Negusse, E.; Henrich, V. E.

2011-08-01

304

Electrical and magnetic properties of multiferroic BiFeO3\\/CoFe2O4 heterostructure  

Microsoft Academic Search

To realize a magnetoelectric heterostructure with desired ferroelectric and magnetic properties, a heterostructure consisting of BiFeO3 (BFO)\\/CoFe2O4 (CFO) layers has been grown on SrRuO3 buffered Pt\\/TiO2\\/SiO2\\/Si substrate by rf sputtering. X-ray diffraction shows that the BFO and CFO phases have been successfully retained in the heterostructure. Grain growth of the CFO phase was enhanced on top of the BFO layer.

R. Y. Zheng; J. Wang; S. Ramakrishna

2008-01-01

305

Multiferroic properties of Pb(Zr,Ti)O3\\/CoFe2O4 composite thin films  

Microsoft Academic Search

In the present work we report multiferroic behavior in lead zirconate titanate (PZT)-cobalt iron oxide (CFO) composite thin films. It is found that upon annealing, the multilayered structures are intermixed at least partially, and CFO is phase separated into PZT matrix to form a composite film. The phase separation behavior has been characterized by x-ray photoelectron spectroscopy depth profiling of

N. Ortega; P. Bhattacharya; R. S. Katiyar; P. Dutta; A. Manivannan; M. S. Seehra; I. Takeuchi; S. B. Majumder

2006-01-01

306

Mechanical alloyed Ho3+ doping in CoFe2O4 spinel ferrite and understanding of magnetic nanodomains  

Microsoft Academic Search

We doped Ho3+ in CoFe1.95Ho0.05O4 spinel ferrite by mechanical alloying and subsequent annealing at different temperatures (600-1200 °C). We understood the structural and magnetic properties of the samples using X-ray diffraction, SEM, Thermal analysis (TGA and DTA), and VSM measurement. The samples have shown structural stabilization within cubic spinel phase for the annealing temperature (TAN)>=800 °C. Thermal activated grain growth

I. Panneer Muthuselvam; R. N. Bhowmik

2010-01-01

307

Magnetic properties of CoFe2O4 thin films prepared by a sol-gel method  

Microsoft Academic Search

Thin films with cobalt ferrite layers on thermally oxidized silicon wafers were fabricated by a sol-gel method. Magnetic and structural properties of the films were investigated with an x-ray diffractometer, a vibrating sample magnetometer and atomic force microscopy. The crystallization temperature for Co ferrite thin films was determined by using Mössbauer spectroscopy. Co ferrite films annealed at and above 450

Jae-Gwang Lee; Jae Yun Park; Young-Jei Oh; Chul Sung Kim

1998-01-01

308

Electrical and magnetic properties of multiferroic BiFeO3/CoFe2O4 heterostructure  

NASA Astrophysics Data System (ADS)

To realize a magnetoelectric heterostructure with desired ferroelectric and magnetic properties, a heterostructure consisting of BiFeO3 (BFO)/CoFe2O4 (CFO) layers has been grown on SrRuO3 buffered Pt/TiO2/SiO2/Si substrate by rf sputtering. X-ray diffraction shows that the BFO and CFO phases have been successfully retained in the heterostructure. Grain growth of the CFO phase was enhanced on top of the BFO layer. The heterostructure exhibits both ferroelectric and magnetic behaviors at room temperature. Its remanent polarization (2Pr) is measured to be ~146 ?C/cm2 and the coercive field (2Ec) is ~1803 kV/cm, while the saturation magnetization (2Ms) is 140 emu/cm3 and the coercive field (2Hc) is ~2.7 kOe. The leakage current behavior of the heterostructure is consistent with space charge limited conduction mechanism. While the heterostructure is promising for multiferroic behavior, it would be necessary to control the structural defects such that the leakage is minimized.

Zheng, R. Y.; Wang, J.; Ramakrishna, S.

2008-08-01

309

Enhanced magneto-optical Kerr effects in nanocrystalline Sc-doped CoFe 2O 4 thin films  

Microsoft Academic Search

Nanocrystalline CoFe2?xScxO4 (x=0–0.4) thin films were prepared on silicon substrates at reduced temperature by a sol–gel process, and the doping effects of scandium on the microstructure, magnetism and polar magneto-optical Kerr effects of the as-deposited films were examined. It was shown that the intensities of both of the Kerr rotation peaks increase with the doping content x of Sc3+. The

Biao Zhou; Yawen Zhang; Chunsheng Liao; Chunhua Yan; Liangyao Chen; Songyou Wang

2003-01-01

310

Fabrication and Electrical Measurements of CoFe2O4 Nanopillars in a BiFeO3 matrix  

Microsoft Academic Search

Coupling between ferromagnetic and ferroelectric ordering has recently stimulated many scientific and technological interests. This ``coupling'', would provide an additional degree of freedom in the design of micro and nano-electronic devices such as actuators, transducers, or memories. Unfortunately, the clamping effect of the substrate negates any such magnetoelectric coupling through elastic interactions which evident in a multilayer structures. Therefore our

Scott Rutherford; Rasmi Das; Xianglin Ke; Dmitry Ruzmetov; Dong-Min Kim; Seung Hyub Baek; Mark Rzchowski; Chang-Beom Eom

2006-01-01

311

Passing through the renal clearance barrier: toward ultrasmall sizes with stable ligands for potential clinical applications  

PubMed Central

The use of nanoparticles holds promise for medical applications, such as X-ray imaging, photothermal therapy and radiotherapy. However, the in vivo toxicity of inorganic nanoparticles raises some concern regarding undesirable side effects which prevent their further medical application. Ultrasmall sub-5.5 nm particles can pass through the barrier for renal clearance, minimizing their toxicity. In this letter we address some recent interesting work regarding in vivo toxicity and renal clearance, and discuss the possible strategy of utilizing ultrasmall nanomaterials. We propose that small hydrodynamic sized nanoclusters can achieve both nontoxic and therapeutic clinical features.

Zhang, Xiao-Dong; Yang, Jiang; Song, Sha-Sha; Long, Wei; Chen, Jie; Shen, Xiu; Wang, Hao; Sun, Yuan-Ming; Liu, Pei-Xun; Fan, Saijun

2014-01-01

312

Ferrite nanoparticles for future heart diagnostics  

NASA Astrophysics Data System (ADS)

Normally, CoFe2O4 has been known as ferromagnetic ferrite with a quite large magnetic moment. However, since we aim to inject the particles into the human body, we are also interested in ZnFe2O4 because in the human body, Fe and Zn exist, so that adding ZnFe2O4 is safer. In both cases, the nanoparticles are coated by silica in order to get rid of toxicity. Our main purpose is to test whether these nanoparticles affect the contractile function of heart cells. Our results on rat's heart cells have shown that both Zn and Co ferrites improved the contractility of heart cells. Notably, although both nanoparticles increased contraction and delayed relaxation, Co ferrites induced a greater contraction but with a slower relaxation. We can theoretically argue that the magnetization effects of the quantum dots have a considerable effect on the pulsating properties of the heart cells. Through this effect, the locally applied magnetic field is able to induce as well as turn on/off various regular beating patterns, thus, resetting the heart beatings.

Hong, Nguyen Hoa; Raghavender, A. T.; Ciftja, O.; Phan, M.-H.; Stojak, K.; Srikanth, H.; Zhang, Yin Hua

2013-08-01

313

Enhancement of the field modulation of light transmission through films of binary ferrofluids.  

PubMed

CoFe2O4 nanoparticles are ferrimagnetic and p-MgFe2O4 nanoparticles are paramagnetic. Binary ferrofluids can be synthesized by mixing CoFe2O4 ferrofluids and p-MgFe2O4 fluids in such a way that the magnetic interaction of the CoFe2O4 particles is large enough to form field-induced chainlike aggregates. The field modulation of light transmission through films of CoFe{2}O{4}-p-MgFe2O4 binary ferrofluids with different values of applied magnetic field is compared with pure CoFe2O4 ferrofluids. The experimental results revealed that the light transmission coefficient of binary ferrofluids can be more intensely modulated by an external magnetic field than pure CoFe2O4 ferrofluids. These show that in the binary ferrofluids, the field-induced structure mainly arises from the CoFe2O4 nanoparticle system and the p-MgFe2O4 nanoparticles introduce a nonlinear modulation effect, even though the microstructure of p-MgFe2O4 fluids is not affected by an applied magnetic field. Using a model of magnetic bidispersal, the enhanced field modulation of the light transmission through binary ferrofluids is explained by the coupling of geometric shadowing effects from both the CoFe2O4 and p-MgFe2O4 particle systems. PMID:20866805

Zhang, Ting-Zhen; Li, Jian; Miao, Hua; Zhang, Qing-Mei; Fu, Jun; Wen, Bang-Cai

2010-08-01

314

Embryotoxicity of cobalt ferrite and gold nanoparticles: a first in vitro approach.  

PubMed

Nanoparticles (NPs) are emerging as promising biomedical tools thanks to their peculiar characteristics. Our purpose was to investigate the embryotoxicity of cobalt ferrite and gold NPs through the Embryonic Stem Cell Test (EST). The EST is an in vitro standard assay, which permits to classify substances as strongly, weakly or non-embryotoxic. Due to the particular physical-chemical nature of nanoparticles, we introduced a modification to the standard protocol exposing the Embryonic Stem Cells (ES-D3) to nanoparticles only during the first 5 days of the assay. Moreover, we proposed a method to discriminate and compare the embryotoxicity of the substances within the weakly embryotoxic range. Our ID(50) results permit to classify cobalt ferrite nanoparticles coated with gold and silanes as non-embryotoxic. The remaining nanoparticles have been classified as weakly embryotoxic in this decreasing order: gold salt (HAuCl(4).3H(2)O)>cobalt ferrite salt (CoFe(2)O(4))>cobalt ferrite nanoparticles coated with silanes (Si-CoFe)>gold nanoparticles coated with hyaluronic acid (HA-Au). PMID:20566333

Di Guglielmo, Claudia; López, David Ramos; De Lapuente, Joaquín; Mallafre, Joan Maria Llobet; Suàrez, Miquel Borràs

2010-09-01

315

Synthesis, magnetic and optical properties of core/shell Co1-xZnxFe2O4/SiO2 nanoparticles  

PubMed Central

The optical properties of multi-functionalized cobalt ferrite (CoFe2O4), cobalt zinc ferrite (Co0.5Zn0.5Fe2O4), and zinc ferrite (ZnFe2O4) nanoparticles have been enhanced by coating them with silica shell using a modified Stöber method. The ferrites nanoparticles were prepared by a modified citrate gel technique. These core/shell ferrites nanoparticles have been fired at temperatures: 400°C, 600°C and 800°C, respectively, for 2 h. The composition, phase, and morphology of the prepared core/shell ferrites nanoparticles were determined by X-ray diffraction and transmission electron microscopy, respectively. The diffuse reflectance and magnetic properties of the core/shell ferrites nanoparticles at room temperature were investigated using UV/VIS double-beam spectrophotometer and vibrating sample magnetometer, respectively. It was found that, by increasing the firing temperature from 400°C to 800°C, the average crystallite size of the core/shell ferrites nanoparticles increases. The cobalt ferrite nanoparticles fired at temperature 800°C; show the highest saturation magnetization while the zinc ferrite nanoparticles coated with silica shell shows the highest diffuse reflectance. On the other hand, core/shell zinc ferrite/silica nanoparticles fired at 400°C show a ferromagnetic behavior and high diffuse reflectance when compared with all the uncoated or coated ferrites nanoparticles. These characteristics of core/shell zinc ferrite/silica nanostructures make them promising candidates for magneto-optical nanodevice applications.

2011-01-01

316

Synthesis, magnetic and optical properties of core/shell Co1-xZnxFe2O4/SiO2 nanoparticles.  

PubMed

The optical properties of multi-functionalized cobalt ferrite (CoFe2O4), cobalt zinc ferrite (Co0.5Zn0.5Fe2O4), and zinc ferrite (ZnFe2O4) nanoparticles have been enhanced by coating them with silica shell using a modified Stöber method. The ferrites nanoparticles were prepared by a modified citrate gel technique. These core/shell ferrites nanoparticles have been fired at temperatures: 400°C, 600°C and 800°C, respectively, for 2 h. The composition, phase, and morphology of the prepared core/shell ferrites nanoparticles were determined by X-ray diffraction and transmission electron microscopy, respectively. The diffuse reflectance and magnetic properties of the core/shell ferrites nanoparticles at room temperature were investigated using UV/VIS double-beam spectrophotometer and vibrating sample magnetometer, respectively. It was found that, by increasing the firing temperature from 400°C to 800°C, the average crystallite size of the core/shell ferrites nanoparticles increases. The cobalt ferrite nanoparticles fired at temperature 800°C; show the highest saturation magnetization while the zinc ferrite nanoparticles coated with silica shell shows the highest diffuse reflectance. On the other hand, core/shell zinc ferrite/silica nanoparticles fired at 400°C show a ferromagnetic behavior and high diffuse reflectance when compared with all the uncoated or coated ferrites nanoparticles. These characteristics of core/shell zinc ferrite/silica nanostructures make them promising candidates for magneto-optical nanodevice applications. PMID:21774807

Girgis, Emad; Wahsh, Mohamed Ms; Othman, Atef Gm; Bandhu, Lokeshwar; Rao, Kv

2011-01-01

317

Applications of ultrasmall superparamagnetic iron oxide contrast agents in the MR study of animal models  

Microsoft Academic Search

Ultrasmall superparamagnetic iron oxide nanoparticles have been widely used during the past decade as MR intravascular contrast agents in the study of animal models. Such agents enhance both T1 and T2\\/T2* relaxation, although for animal studies it is the later type of enhancement that is most commonly exploited. Their strong microscopic intravascular susceptibility effect enables the local blood volume distribution

Ed X. Wu; Haiying Tang; Jens H. Jensen

2004-01-01

318

Core/Shell and High Aspect Ratio Magnetic Oxide Nanoparticles for Antenna Applications  

NASA Astrophysics Data System (ADS)

Improved antenna gain, reduced antenna aperture size, and improved bandwidth are of interest to an increasingly mobile world. To obtain these improvements our efforts are directed at developing new magnetic oxide nanoparticle/polymer composites with modifiable permeability and permittivity and low electrical losses. Our approach consists of producing core/shell and shape controlled magnetic nanoparticles. Methods of synthesis utilize microwave and traditional heating to perform hydrothermal and solvothermal reactions. Decomposition of metal acetylacetonates is performed using various alcohols resulting in spherical nanoparticles with diameters of 8-16 nm and 3-7 nm for Fe3O4 and CoFe2O4, respectively. Microwave methods result in similar particles, but are produced in an hour or less as compared to 48 hrs via the traditional solvothermal method. Successive growths are used to produce larger monolithic particles as well as core/shell systems where exchange coupling between the core and shell is observed. Hexaferrite particles have been produced via hydrothermal synthesis, while high aspect ratio Fe3O4 nanoparticles ( 10-100 nm) produced via hydrothermal synthesis result in nanoneedles with high ?r.

Ekiert, Thomas F., Jr.; O'Malley, Matthew; Yocum, Brandon; Lippold, Jennifer; Lyle, Mallory; Griner, Angela; Flynn, Cory; Nickel, Anna; Alexander, Max D., Jr.

2012-02-01

319

Synthesis, characterization and magnetic properties of carbon nanotubes decorated with magnetic MIIFe2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

In this study, a simple, efficient and reproducible microemulsion method was applied for the successful decoration of carbon nanotubes (CNTs) with magnetic MIIFe2O4 (M = Co, Ni, Cu, Zn) nanoparticles. The structure, composition and morphology of the prepared nanocomposite materials were characterized using X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The magnetic properties were investigated by the vibrating sample magnetometer (VSM). The SEM results illustrated that large quantity of MIIFe2O4 nanoparticles were uniformly decorated around the circumference of CNTs and the sizes of the nanoparticles ranged from 15 to 20 nm. Magnetic hysteresis loop measurements revealed that all the MIIFe2O4/CNTs nanocomposites displayed ferromagnetic behavior at 300 K and can be manipulated using an external magnetic field. The CoFe2O4/CNTs nanocomposite showed maximum value of saturation magnetization which was 37.47 emu g-1. The as prepared MIIFe2O4/CNTs nanocomposites have many potential application in magnetically guided targeted drug delivery, clinical diagnosis, electrochemical biosensing, magnetic data storage and magnetic resonance imaging.

Ali, Syed Danish; Hussain, Syed Tajammul; Gilani, Syeda Rubina

2013-04-01

320

Preliminary evaluation of a 99mTc labeled hybrid nanoparticle bearing a cobalt ferrite core: in vivo biodistribution.  

PubMed

Magnetic nanoparticles have become important tools for imaging a wide range of diseases, improving drug delivery and applying hyperthermic treatment. Iron oxide based nanoparticles have been widely examined, unlike cobalt ferrite based ones. Herein, monodisperse and stable CoFe2O4 nanoparticles have been produced, coated and further stabilized using ethyl 12-(hydroxyamino)-12-oxododecanoate, poly(lactic-co-glycolic acid) and bovine serum albumin. The final product, NBRh1, was fully characterized and has been directly radiolabeled with 99mTc using SnCl1 as the reducing agent in high yields. In vitro stability and hyperthermic properties of 99mTC-NBRh1 were encouraging for further application in low frequencies hyperthermia and biomagnetic applications. In vivo evaluation followed after injection in healthy mice. The planar and SPECT imaging data as well as the biodistribution results were in accordance, showing high liver and spleen uptake as expected starting almost immediately after administration. In conclusion the preliminary results for nanoparticles bearing a cobalt ferrite core justify further investigations towards potential hyperthermic applications, drug transportation and liver or spleen imaging. PMID:22852467

Psimadas, Dimitrios; Baldi, Giovanni; Ravagli, Costanza; Bouziotis, Penelope; Xanthopoulos, Stavros; Franchini, Mauro Comes; Georgoulias, Panagiotis; Loudos, George

2012-08-01

321

Externally controlled on-demand release of anti-HIV drug using magneto-electric nanoparticles as carriers.  

PubMed

Although highly active anti-retroviral therapy has resulted in remarkable decline in the morbidity and mortality in AIDS patients, inadequately low delivery of anti-retroviral drugs across the blood-brain barrier results in virus persistence. The capability of high-efficacy-targeted drug delivery and on-demand release remains a formidable task. Here we report an in vitro study to demonstrate the on-demand release of azidothymidine 5'-triphosphate, an anti-human immunodeficiency virus drug, from 30 nm CoFe2O4@BaTiO3 magneto-electric nanoparticles by applying a low alternating current magnetic field. Magneto-electric nanoparticles as field-controlled drug carriers offer a unique capability of field-triggered release after crossing the blood-brain barrier. Owing to the intrinsic magnetoelectricity, these nanoparticles can couple external magnetic fields with the electric forces in drug-carrier bonds to enable remotely controlled delivery without exploiting heat. Functional and structural integrity of the drug after the release was confirmed in in vitro experiments with human immunodeficiency virus-infected cells and through atomic force microscopy, spectrophotometry, Fourier transform infrared and mass spectrometry studies. PMID:23591874

Nair, Madhavan; Guduru, Rakesh; Liang, Ping; Hong, Jeongmin; Sagar, Vidya; Khizroev, Sakhrat

2013-01-01

322

Developing a millifluidic platform for the synthesis of ultrasmall nanoclusters: ultrasmall copper nanoclusters as a case study.  

PubMed

The future of lab-on-a-chip devices for the synthesis of nanomaterials hinges on the successful development of high-throughput methods with better control over their size. While significant effort in this direction mainly focuses on developing "difficult to fabricate" complex microfluidic reactors, scant attention has been paid to the "easy to fabricate" and simple millifluidic systems that could provide the required control as well as high throughput. By utilizing numerical simulation of fluids within the millifluidic space at different flow rates, the results presented here show velocity profiles and residence time distributions similar to the case of microfluidics. By significantly reducing the residence time and residence time distribution, a continuous flow synthesis of ultrasmall copper nanoclusters (UCNCs) with exceptional colloidal stability is achieved. In-situ synchrotron-radiation-based X-ray absorption spectroscopy (XAS) reveal that the as-prepared clusters are about 1 nm, which is further supported by transmission electron microscopy and UV-vis spectroscopy studies. The clusters reported here are the smallest ever produced using a lab-on-a-chip platform. When supported on silica, they are found to efficiently catalyze C-H oxidation reactions, hitherto unknown to be catalyzed by Cu. This work suggests that a millifluidic platform can be an inexpensive, versatile, easy-to-use, and powerful tool for nanoparticle synthesis in general, and more specifically for ultrasmall nanoclusters (UNCs). PMID:22298499

Biswas, Sanchita; Miller, Jeffrey T; Li, Yuehao; Nandakumar, Krishnaswamy; Kumar, Challa S S R

2012-03-12

323

Ultra-small particles of iron oxide as peroxidase for immunohistochemical detection.  

PubMed

Dimercaptosuccinic acid (DMSA) modified ultra-small particles of iron oxide (USPIO) were synthesized through a two-step process. The first step: oleic acid (OA) capped Fe(3)O(4) (OA-USPIO) were synthesized by a novel oxidation coprecipitation method in H(2)O/DMSO mixing system, where DMSO acts as an oxidant simultaneously. The second step: OA was replaced by DMSA to obtain water-soluble nanoparticles. The as-synthesized nanoparticles were characterized by TEM, FTIR, TGA, VSM, DLS, EDS and UV-vis. Hydrodynamic sizes and Peroxidase-like catalytic activity of the nanoparticles were investigated. The hydrodynamic sizes of the nanoparticles (around 24.4 nm) were well suited to developing stable nanoprobes for bio-detection. The kinetic studies were performed to quantitatively evaluate the catalytic ability of the peroxidase-like nanoparticles. The calculated kinetic parameters indicated that the DMSA-USPIO possesses high catalytic activity. Based on the high activity, immunohistochemical experiments were established: using low-cost nanoparticles as the enzyme instead of expensive HRP, Nimotuzumab was conjugated onto the surface of the nanoparticles to construct a kind of ultra-small nanoprobe which was employed to detect epidermal growth factor receptor (EGFR) over-expressed on the membrane of esophageal cancer cell. The proper sizes of the probes and the result of membranous immunohistochemical staining suggest that the probes can be served as a useful diagnostic reagent for bio-detection. PMID:21454943

Wu, Yihang; Song, Mengjie; Xin, Zhuang; Zhang, Xiaoqing; Zhang, Yu; Wang, Chunyu; Li, Suyi; Gu, Ning

2011-06-01

324

Micrometric periodic assembly of magnetotactic bacteria and magnetic nanoparticles using audio tapes  

NASA Astrophysics Data System (ADS)

We report micrometric periodic assembly of live and dead magnetotactic bacteria, Magnetospirillum magneticum AMB-1, which synthesize chains of magnetic nanoparticles inside their bodies, and of superparamagnetic Fe3O4 and ferromagnetic CoFe2O4 nanoparticles in aqueous suspensions using periodically magnetized audio tapes. The distribution of the stray magnetic field at the surface of the tapes was determined analytically and experimentally by magneto-optic imaging. Calculations showed that the magnetic field close to the tape surface was of the order of 100 mT, and the magnetic field gradient was larger than 1 T mm-1. Drops of aqueous solutions were deposited on the tapes, and bacteria and particles were trapped at locations where magnetic energy is minimized, as observed using conventional optical microscopy. Suspensions of M. magneticum AMB-1 treated with formaldehyde and kanamycin were studied, and patterns of trapped dead bacteria indicated that magnetic forces dominate over self-propelling forces in these experiments, in accordance with calculated values. The behavior of the different types of samples is discussed.

Godoy, M.; Moreno, A. J.; Jorge, G. A.; Ferrari, H. J.; Antonel, P. S.; Mietta, J. L.; Ruiz, M.; Negri, R. M.; Pettinari, M. J.; Bekeris, V.

2012-02-01

325

Uptake and distribution of ultra-small anatase TiO2 Alizarin red S nanoconjugates in Arabidopsis thaliana  

PubMed Central

While few publications have documented the uptake of nanoparticles in plants, this is the first study describing uptake and distribution of the ultra-small anatase TiO2 in the plant model system Arabidopsis. We modified the nanoparticle surface with Alizarin red S and sucrose, and demonstrated that nanoconjugates traversed cell walls, entered into plant cells, and accumulated in specific subcellular locations. Optical and X-ray fluorescence microscopy co-registered the nanoconjugates in cell vacuoles and nuclei.

Kurepa, Jasmina; Paunesku, Tatjana; Vogt, Stefan; Arora, Hans; Rabatic, Bryan M.; Lu, Jinju; Wanzer, M. Beau; Woloschak, Gayle E.; Smalle, Jan A.

2010-01-01

326

Structural, Dielectric, FT-IR and Complex Impedance Properties of Cobalt Ferrite Nanoparticles  

NASA Astrophysics Data System (ADS)

Cobalt ferrite nanoparticles having the general formula CoFe2-xCuxO4 (0.0 <= x <= 0.5) were prepared by sol-gel method and characterized by using X-Ray diffraction (XRD), scanning electron microscopy (SEM ), Fourier transform infrared spectroscopy (FTIR), dielectric and impedance spectroscopy measurements. Confirmation of the single phase cubic spinel structure was made by using X-ray diffractometer. Lattice parameter `a' is found to decrease with increasing the doping contents. Debye- Scherer formula was used for finding the particle size and found in the range 30-45 nm. Morphological analysis was made by scanning electron microscopy which shows agglomerated flakes of particles having large pores on the surface. FT-IR spectra show two absorption bands assigned to the tetrahedral and octahedral complexes in the frequency range 400-600 cm-1. The variation of dielectric properties ?', V, tan? with frequency reveals that the dispersion is due to Maxwell-Wagner type of interfacial polarization. Impedance spectroscopy technique has been used to understand the conduction mechanism and to study the effect of grain and grain boundary on the electrical properties of the Cu doped CoFe2O4 ferrites.

Hashim, Mohd.; Alimuddin, Alimuddin; Ali, Sikander; Kumar, Shalendra; Kumar, Ravi

2011-11-01

327

A study of the properties of SrFe12-xCoxO19 nanoparticles  

NASA Astrophysics Data System (ADS)

In this paper, the nanoparticles of SrFe12-xCoxO19 (x=0-2) were synthesized via the sol-gel technique. The XRD results showed that all samples with x?0.5 are single-phase. It seems that the Fe3+ ions are substituted by Co2+ ions in the crystallography sites of the SrFe12O19 structure, but for the x>0.5 cases, the phase of CoFe2O4 is materialized in the samples. The DC electrical resistivity decreases with the increase of cobalt content up to level of x=0.5, but it increases on further addition of cobalt. We found that the dielectric constant and the dielectric loss for samples with x=1 and 1.2 into the pure sample (SrFe12O19), decrease as the Co2+ content increases. The variation of AC conductivity (?ac) with frequency ranging from 500 Hz to 200 KHz shows that electrical conductivity in these ferrites is mainly due to the electron hopping mechanism.

Mousavi Ghahfarokhi, S. E.; Ranjbar, F.; Zargar Shoushtari, M.

2014-01-01

328

The converse magnetoelectric characteristics of Mn and Mg doped CoFe2O4-PbTiO3 composites  

NASA Astrophysics Data System (ADS)

Electric-field-induced magnetization characteristics are demonstrated in xCo0.6Mg0.2Mn0.2Fe2O4-(1 - x) PbTiO3 (x = 0.4, 0.5, 0.6, and 0.7) composites synthesized by sol-gel method. The converse magnetoelectric effect (CME) with driving frequency in a range of 4-16 kHz was measured at room temperature. The composite of 0.6Co0.6Mg0.2Mn0.2Fe2O4-0.4PbTiO3 exhibits the maximum CME coefficient at electromechanical resonance frequency of 13 kHz. Doping Mn and Mg into CFO enhances CME coefficients and resistivity of compositions, which provide great opportunities for electric field tunable microwave devices.

Liu, Ting-ting; Wang, Zhi; Mao, Jun; Cheng, Ning-ning; Ni, Li-jun

2014-05-01

329

Influence of thermal annealing on the dielectric properties and electrical relaxation behaviour in nanostructured CoFe2O4 ferrite  

Microsoft Academic Search

Nanocrystalline cobalt ferrite particles with the grain size of 8 nm were synthesized by using the co-precipitation technique and subsequently heat treated to obtain larger grain sizes. The effect of grain size, cation distribution, frequency and temperature on their dielectric properties has been studied. The dielectric constant (?') of 8 nm grains is found to be an order of magnitude

N. Sivakumar; A. Narayanasamy; C. N. Chinnasamy; B. Jeyadevan

2007-01-01

330

On the correlation between nanoscale structure and magnetic properties in ordered mesoporous cobalt ferrite (CoFe2O4) thin films.  

PubMed

In this work, we report the synthesis of periodic nanoporous cobalt ferrite (CFO) that exhibits tunable room temperature ferrimagnetism. The porous cubic CFO frameworks are fabricated by coassembly of inorganic precursors with a large amphiphilic diblock copolymer, referred to as KLE. The inverse spinel framework boasts an ordered open network of pores averaging 14 nm in diameter. The domain sizes of the crystallites are tunable from 6 to 15 nm, a control which comes at little cost to the ordering of the mesostructure. Increases in crystalline domain size directly correlate with increases in room temperature coercivity. In addition, these materials show a strong preference for out-of-plane oriented magnetization, which is unique in a thin film system. The preference is explained by in-plane tensile strain, combined with relaxation of the out-of-plane strain through flexing of the mesopores. It is envisioned that the pores of this ferrimagnet could facilitate the formation of a diverse range of exchange coupled composite materials. PMID:20698611

Quickel, Thomas E; Le, Van H; Brezesinski, Torsten; Tolbert, Sarah H

2010-08-11

331

The crystallographic, magnetic properties of Al, Ti doped CoFe2O4 powders grown by sol-gel method  

Microsoft Academic Search

The Al and Ti doped cobalt ferrite powders, Al0.2CoFe1.8O4 and Ti0.2Co1.2Fe1.6O4, have been fabricated by the sol-gel method, and the powders' crystallographic and magnetic properties related to the annealing temperature are being studied. Using X-ray diffraction and Mössbauer spectroscopy, the formation of crystallized particles has been confirmed in Al0.2CoFe1.8O4 and Ti0.2Co1.2Fe1.6O4 ferrite powders. The Al doped cobalt ferrite, Al0.2CoFe1.8O4, has

Kwang Pyo Chae; Jae-Gwang Lee; Hyzzuck Su Kweon; Young Bae Lee

2004-01-01

332

Effects of In3+ substitution on structural properties, cation distribution and Mössbauer spectra of CoFe2O4 ferrite  

NASA Astrophysics Data System (ADS)

The use of non-destructive, high resolution technique namely Mössbauer spectroscopy is discussed in detail for the investigation of structural and magnetic properties of Fe based indium substituted cobalt ferrites. The polycrystalline samples of CoFe2-xInxO4 (x = 0.2, 0.6) were prepared by double sintering solid state reaction method. To ensure a single phase formation of the as prepared samples the X-ray diffraction (XRD) data of the powdered samples was Rietveld refined using Fd3m space group. An excellent agreement is obtained between the integrated intensity ratios of 57 Fe spectra at A- and B-sites and those calculated on the basis of cation distribution the cation distribution obtained data analysis. The results of Mössbauer spectra and cation distribution are also correlated well with magnetization versus applied field (M-H) study.

Kumar, Ravi; Pandit, Rabia; Sharma, K. K.; Kaur, Pawanpreet

2014-04-01

333

Magnetic properties of nano-crystalline Gd or Pr-substituted CoFe2O4 synthesized by the citrate precursor technique  

Microsoft Academic Search

The magnetic properties of nano-crystalline CoMxFe2-xO4 (where M=Gd and Pr and \\/x=0, 0.1 and 0.2) powders prepared by a citrate precursor technique have been studied by using vibrating sample magnetometer (VSM). The crystallite sizes of the materials were varied by altering the synthetic conditions and are within the range of a minimum of 6.8nm and a maximum of 87.5nm. The

R. N. Panda; J. C. Shih; T. S. Chin

2003-01-01

334

Sum Rules in X-Ray Resonant Raman Scattering: Recovering the Co Ground State Information in CoFe2O4 as a Test Case  

Microsoft Academic Search

We present an approach to x-ray resonant Raman scattering suitable for sum-rule analysis. In magnetic systems it gives ground state information as represented by an expansion in coupled multipoles of orbital and spin moments. The experiment is based on the angular dependence of the integrated peak intensities. In 3d transition elements one obtains information up to order 4 from the

L. Braicovich; A. Tagliaferri; G. van der Laan; G. Ghiringhelli; N. B. Brookes

2003-01-01

335

Maxwell-Wagner space charge effects on the Pb(Zr,Ti)O3-CoFe2O4 multilayers  

Microsoft Academic Search

Electrical properties of Pb(Zr0.53Ti0.47)O3\\/CoFe3O4 (PZT\\/CFO) multilayers (MLs) were investigated in the light of Maxwell-Wagner space charge effects and the data differ from those of BiFeO3\\/CoFe3O4 nanocomposites. These MLs are of special interest as weak field sensors of magnetism. These data fit the Maxwell-Wagner space charge model of Catalan et al. [Appl. Phys. Lett. 77, 3078 (2000)]. Very large temperature shifts

N. Ortega; Ashok Kumar; R. S. Katiyar; J. F. Scott

2007-01-01

336

Impact of larger rare earth Pr3+ ions on the physical properties of chemically derived PrxCoFe2-xO4 nanoparticles  

NASA Astrophysics Data System (ADS)

Rare earth Pr3+ ions with its larger ionic radii substituted CoFe2O4 nanoparticles with x ranging from 0.0 to 0.1 were synthesized by sol-gel auto-combustion chemical method. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR) and vibrating sample magnetometer (VSM) were employed to characterize the physical properties of these ferrite nanoparticles. XRD pattern reveals the formation of cubic spinel ferrite with the signature of PrFeO3 phases for x ? 0.05. SEM images show that the synthesized samples are in good homogeneity with uniformly distributed grain. The results of IR spectroscopy analysis indicated that the functional groups of cobalt spinel ferrite were formed during the sol-gel process. The cations distribution between the tetrahedral (A-site) and octahedral sites (B-site) has been estimated by XRD analysis. Room temperature magnetic measurement shows saturation magnetization and coercivity increased from 54.7 to 64.2 emu/g and 644 to 1013 Oe, respectively with the increasing Pr3+ substitution.

Pachpinde, A. M.; Langade, M. M.; Lohar, K. S.; Patange, S. M.; Shirsath, Sagar E.

2014-01-01

337

Synthesis, size and magnetic properties of controllable MnFe2O4 nanoparticles with versatile surface functionalities.  

PubMed

Size controllable MnFe2O4 superparamagnetic nanoparticles (NPs) were prepared by a solvothermal method using low-cost metal oleate as the source. The particle size, chemical composition and magnetic properties were investigated. The MnFe2O4 nanomaterials exhibit high colloidal stabilities and superparamagnetic properties, with an average particle size in the range of 2 to 10 nm by modifying the reaction condition, such as surfactant, reaction temperature and reaction time. By changing Mn(2+) to different cations, CoFe2O4, NiFe2O4, and ZnFe2O4 with different magnetic properties could be obtained. The hydrophobic MnFe2O4 NPs could also be modified with many surfactants, such as cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl benzene sulfonate (SDBS) and sodium dodecylsulfate (SDS), with the aim of achieving high zeta-potential hydrophilic bilayer-coated MnFe2O4 NPs. In addition, the water soluble MnFe2O4 magnetic NPs can be applied to the removal of Pb(ii) from waste water with good recovery under external magnetic field. PMID:24847889

Bateer, Buhe; Tian, Chungui; Qu, Yang; Du, Shichao; Yang, Ying; Ren, Zhiyu; Pan, Kai; Fu, Honggang

2014-07-14

338

Magneto-electric Nanoparticles to Enable Field-controlled High-Specificity Drug Delivery to Eradicate Ovarian Cancer Cells  

PubMed Central

The nanotechnology capable of high-specificity targeted delivery of anti-neoplastic drugs would be a significant breakthrough in Cancer in general and Ovarian Cancer in particular. We addressed this challenge through a new physical concept that exploited (i) the difference in the membrane electric properties between the tumor and healthy cells and (ii) the capability of magneto-electric nanoparticles (MENs) to serve as nanosized converters of remote magnetic field energy into the MENs' intrinsic electric field energy. This capability allows to remotely control the membrane electric fields and consequently trigger high-specificity drug uptake through creation of localized nano-electroporation sites. In in-vitro studies on human ovarian carcinoma cell (SKOV-3) and healthy cell (HOMEC) lines, we applied a 30-Oe d.c. field to trigger high-specificity uptake of paclitaxel loaded on 30-nm CoFe2O4@BaTiO3 MENs. The drug penetrated through the membrane and completely eradicated the tumor within 24 hours without affecting the normal cells.

Guduru, Rakesh; Liang, Ping; Runowicz, Carolyn; Nair, Madhavan; Atluri, Venkata; Khizroev, Sakhrat

2013-01-01

339

RGD-conjugated iron oxide magnetic nanoparticles for magnetic resonance imaging contrast enhancement and hyperthermia.  

PubMed

The purpose of this study was to develop a specific targeting magnetic nanoparticle probe for magnetic resonance imaging and therapy in the form of local hyperthermia. Carboxymethyl dextran-coated ultrasmall superparamagnetic iron oxide nanoparticles with carboxyl groups were coupled to cyclic arginine-glycine-aspartic peptides for integrin ?(v)?? targeting. The particle size, magnetic properties, heating effect, and stability of the arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide were measured. The arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide demonstrates excellent stability and fast magneto-temperature response. Magnetic resonance imaging signal intensity of Bcap37 cells incubated with arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide was significantly decreased compared with that incubated with plain ultrasmall superparamagnetic iron oxide. The preferential uptake of arginine-glycine-aspartic-ultrasmall superparamagnetic iron oxide by target cells was further confirmed by Prussian blue staining and confocal laser scanning microscopy. PMID:23796630

Zheng, S W; Huang, M; Hong, R Y; Deng, S M; Cheng, L F; Gao, B; Badami, D

2014-03-01

340

Reductive deprotection of monolayer protected nanoclusters: an efficient route to supported ultrasmall au nanocatalysts for selective oxidation.  

PubMed

The synthesis and investigation of the catalytic properties of Au nanoparticles (AuNPs) is an area of intense research. Despite much effort being made to this field, attaining both high catalytic activity and selectivity at the same time remains elusive. Herein a new mild reductive thiolate-deprotection strategy is reported to prepare nanoporous silica-supported ultrasmall AuNP catalysts that show very efficient catalytic activity and high selectivity for oxidation reactions. PMID:24425579

Das, Sayantani; Goswami, Anandarup; Hesari, Mahdi; Al-Sharab, Jafar F; Mikmeková, Eliška; Maran, Flavio; Asefa, Tewodros

2014-04-01

341

Magnetic order in two-dimensional nanoparticle assemblies  

NASA Astrophysics Data System (ADS)

This thesis involves a fundamental study of two-dimensional arrays of magnetic nanoparticles using non-contact Atomic Force Microscopy, Magnetic Force Microscopy, and Atomic Force Spectroscopy. The goal is to acquire a better understanding of the interactions between magnetic nanoparticles and the resulting configuration of their magnetic moments. We have studied two systems: 20-nm magnetite (Fe3O4) and 21-nm cobalt ferrite (CoFe2O4) nanoparticles, capped with oleic acid and oleylamine, deposited using drop-casting technique on HOPG (Highly Oriented Pyrolytic Graphite). We present an analytical model to interpret the experimental spectroscopy curves (frequency shift as a function of the tip-sample distance) in terms of force, to enable a quantitative interpretation of the experimental results. In addition, a numerical model based on the Metropolis Monte Carlo method has been developed to calculate the configuration of magnetic moments with minimum energy. The energy consists of dipolar energy and anisotropy energy. The simulations have shown that local energy minima are present that correspond to different configurations of magnetic moments. Because of the thermal energy, the system may jump in between these energy minima. Considering a specific configuration of moments, MFM images were simulated taking the dipolar interactions between the nanoparticles and the tip into account. Spectroscopy curves were calculated for two cases: namely with and without the influence of the tip. The magnetite nanoparticles present a relatively large magnetic moment and exhibit strong dipole-dipole interactions and small, negligible, anisotropy. The observed repulsion between the tip and the nanoparticles at the side of the nanoparticle islands shows that dipolar coupling between the particles causes blocking of their magnetic moments. The experimental observations agree well with the numerical calculations, which show that the magnetic moments arrange themselves in flux-closure structures. However, the magnetite nanoparticle 2D systems can be considered soft-magnetic: their moments are strongly influenced by the field of the tip. This has been observed experimentally and confirmed by simulations for the considered magnetic moment of the tip. The cobalt-ferrite nanoparticles present a similar magnetic moment as the magnetite nanoparticles. The anisotropy, however, increases significantly with decreasing temperature, which leads to blocking of the moments even in the strong field of the tip. As a consequence, attractive and repulsive areas were observed in the MFM image above the islands of nanoparticles at low temperatures. In our simulation we have assumed arbitrary orientations of the easy axes of the particles. Simulation results reveal short-range order of the magnetic moments, consistent with the experimental results.

Georgescu, M.

2008-12-01

342

Structural, electrical, magnetic and dielectric properties of rare-earth substituted cobalt ferrites nanoparticles synthesized by the co-precipitation method  

NASA Astrophysics Data System (ADS)

Pure nanoparticles of the rare-earth substituted cobalt ferrites CoRExFe2-xO4 (where RE=Nd, Sm and Gd and x=0.1 and 0.2) were prepared by the chemical co-precipitation method. X-ray diffraction, Transmission electron microscopy (TEM), d.c. electrical conductivity, Magnetic hysteresis and Thermal analysis are utilized in order to study the effect of variation in the rare-earth substitution and its impact on particle size, magnetic properties like MS, HC and Curie temperature. The phase identification of the materials by X-ray diffraction reveals the single-phase nature of the materials. The lattice parameter increased with rare-earth content for x?0.2. The Transmission electron micrographs of Nd-, Sm- and Gd-substituted CoFe2O4 exhibit the particle size 36.1 to 67.8 nm ranges. The data of temperature variation of the direct current electrical conductivity showed definite breaks, which corresponds to ferrimagnetic to paramagnetic transitions. The thermoelectric power for all compound are positive over the whole range of temperature. The dielectric constant decreases with frequency and rare-earth content for the prepared samples. The magnetic properties of rare-earth substituted cobalt ferrites showed a definite hysteresis loop at room temperature. The reduction of coercive force, saturation magnetization, ratio MR/MS and magnetic moments may be due to dilution of the magnetic interaction.

Nikumbh, A. K.; Pawar, R. A.; Nighot, D. V.; Gugale, G. S.; Sangale, M. D.; Khanvilkar, M. B.; Nagawade, A. V.

2014-04-01

343

Atomic scale dynamics of ultrasmall germanium clusters  

PubMed Central

Starting from the gas phase, small clusters can be produced and deposited with huge flexibility with regard to composition, materials choice and cluster size. Despite many advances in experimental characterization, a detailed morphology of such clusters is still lacking. Here we present an atomic scale observation as well as the dynamical behaviour of ultrasmall germanium clusters. Using quantitative scanning transmission electron microscopy in combination with ab initio calculations, we are able to characterize the transition between different equilibrium geometries of a germanium cluster consisting of less than 25 atoms. Seven-membered rings, trigonal prisms and some smaller subunits are identified as possible building blocks that stabilize the structure.

Bals, S.; Van Aert, S.; Romero, C.P.; Lauwaet, K.; Van Bael, M.J.; Schoeters, B.; Partoens, B.; Yucelen, E.; Lievens, P.; Van Tendeloo, G.

2012-01-01

344

Microfiber-probe-based ultrasmall interferometric sensor.  

PubMed

We report an ultrasmall microfiber-probe-based reflective interferometer for highly sensitive liquid refractive index measurement. It has a 3.5 microm micronotch cavity fabricated by focused ion beam micromachining. A sensitivity of 110 nm/RIU (refractive index unit) in liquid is achieved with over 20 dB extinction ratio. Theoretical analysis shows this kind of device is a hybrid of Fabry-Perot and modal interferometers. In comparison with normal fiber interferometers, this probe sensor is very compact, stable, and cheap, offering great potentials for detecting inside sub-wavelength bubbles, droplets, or biocells. PMID:20596229

Kou, Jun-long; Feng, Jing; Wang, Qian-jin; Xu, Fei; Lu, Yan-qing

2010-07-01

345

Path-Integral Monte Carlo Methods for Ultrasmall Device Modeling  

Microsoft Academic Search

Monte Carlo methods based on the Feynman path -integral (FPI) formulation of quantum mechanics are developed for modeling ultrasmall device structures. A brief introduction to pertinent aspects of the FPI formalism is given. A practical \\

Leonard Franklin Register II

1990-01-01

346

Study of magnetic and structural properties of ferrofluids based on cobalt-zinc ferrite nanoparticles  

NASA Astrophysics Data System (ADS)

Ferrofluids are colloidal systems composed of a single domain of magnetic nanoparticles with a mean diameter around 30 nm, dispersed in a liquid carrier. Magnetic Co (1- x) Zn xFe 2O 4 ( x=0.25, 0.50, 0.75) ferrite nanoparticles were prepared via co-precipitation method from aqueous salt solutions in an alkaline medium. The composition and structure of the samples were characterized through Energy Dispersive X-ray Spectroscopy and X-ray diffraction, respectively. Transmission Electron Microscopy (TEM) studies permitted determining nanoparticle size; grain size of nanoparticle conglomerates was established via Atomic Force Microscopy. The magnetic behavior of ferrofluids was characterized by Vibrating Sample Magnetometer (VSM); and finally, a magnetic force microscope was used to visualize the magnetic domains of Co (1- x) Zn xFe 2O 4 nanoparticles. X-ray diffraction patterns of Co (1- x) Zn xFe 2O 4 show the presence of the most intense peak corresponding to the (311) crystallographic orientation of the spinel phase of CoFe 2O 4. Fourier Transform Infrared Spectroscopy confirmed the presence of the bonds associated to the spinel structures; particularly for ferrites. The mean size of the crystallite of nanoparticles determined from the full-width at half maximum of the strongest reflection of the (311) peak by using the Scherrer approximation diminished from (9.5±0.3) nm to (5.4±0.2) nm when the Zn concentration increases from 0.21 to 0.75. The size of the Co-Zn ferrite nanoparticles obtained by TEM is in good agreement with the crystallite size calculated from X-ray diffraction patterns, using Scherer's formula. The magnetic properties investigated with the aid of a VSM at room temperature presented super-paramagnetic behavior, determined by the shape of the hysteresis loop. In this study, we established that the coercive field of Co (1- x) Zn xFe 2O 4 magnetic nanoparticles, the crystal and nanoparticle sizes determined by X-ray Diffraction and TEM, respectively, decrease with the increase of the Zn at%. Finally, our magnetic nanoparticles are not very hard magnetic materials given that the hysteresis loop is small and for this reason Co (1- x) Zn xFe 2O 4 nanoparticles are considered as soft magnetic material.

López, J.; González-Bahamón, L. F.; Prado, J.; Caicedo, J. C.; Zambrano, G.; Gómez, M. E.; Esteve, J.; Prieto, P.

2012-02-01

347

Influence of cobalt on structural and magnetic properties of nickel ferrite nanoparticles  

NASA Astrophysics Data System (ADS)

Improving the magnetic response of nanocrystalline nickel ferrites is the key issue in high density recording media. A series of cobalt substituted nickel ferrite nanoparticles with composition Ni(1-x)CoxFe2O4, where 0.0 ? x ? 1.0, are synthesized using co-precipitation method. The XRD spectra revealed the single phase spinel structure and the average sizes of nanoparticles are estimated to be 16-19 nm. These sizes are small enough to achieve the suitable signal to noise ratio in the high density recording media. The lattice parameter and coercivity shows monotonic increment with the increase of Co contents ascribed to the larger ionic radii of the cobalt ion. The specific saturation magnetization (Ms), remanent magnetization (Mr) and the coercivity (Hc) of the spinel ferrites are further improved by the substitutions of Co+2 ions. The values of Ms for NiFe2O4 and CoFe2O4 are found to be 43.92 and 78.59 emu/g, respectively and Hc are in the range of 51-778 Oe. The FTIR spectra of the spinel phase calcinated at 600 °C exhibit two prominent fundamental absorption bands in the range of 350-600 cm-1 assigned to the intrinsic stretching vibrations of the metal at the tetrahedral and octahedral sites. The role played by the Co ions in improving the structural and magnetic properties are analyzed and understood. Our simple, economic and environmental friendly preparation method may contribute towards the controlled growth of high quality ferrite nanopowders, potential candidates for recording.

Ati, Ali A.; Othaman, Zulkafli; Samavati, Alireza

2013-11-01

348

Ultrasmall spot size scanning laser ophthalmoscopy  

PubMed Central

An ultrasmall spot size scanning laser ophthalmoscope has been developed that employs an annular aberration-corrected incident beam to increase the effective numerical aperture of the eye thereby reducing the width of the probing light spot. Parafovea and foveal cone photoreceptor visibility determined from small area retinal image scans are discussed from the perspective of mode matching between the focused incident beam and the waveguide modes of individual cones. The cone visibility near the fovea centralis can be increased with the annular illumination scheme whereas the visibility of larger parafovea cones drops significantly as a consequence of poorer mode match. With further improvements of the implemented wavefront correction technology it holds promise for individual cone-photoreceptor imaging at the fovea centralis and for optical targeting of the retina with increased resolution.

Vohnsen, Brian; Rativa, Diego

2011-01-01

349

Brine assemblages of ultrasmall microbial cells within the ice cover of Lake Vida, Antarctica.  

PubMed

The anoxic and freezing brine that permeates Lake Vida's perennial ice below 16 m contains an abundance of very small (?0.2-?m) particles mixed with a less abundant population of microbial cells ranging from >0.2 to 1.5 ?m in length. Fluorescent DNA staining, electron microscopy (EM) observations, elemental analysis, and extraction of high-molecular-weight genomic DNA indicated that a significant portion of these ultrasmall particles are cells. A continuous electron-dense layer surrounding a less electron-dense region was observed by EM, indicating the presence of a biological membrane surrounding a cytoplasm. The ultrasmall cells are 0.192 ± 0.065 ?m, with morphology characteristic of coccoid and diplococcic bacterial cells, often surrounded by iron-rich capsular structures. EM observations also detected the presence of smaller unidentified nanoparticles of 0.020 to 0.140 ?m among the brine cells. A 16S rRNA gene clone library from the brine 0.1- to 0.2-?m-size fraction revealed a relatively low-diversity assemblage of Bacteria sequences distinct from the previously reported >0.2-?m-cell-size Lake Vida brine assemblage. The brine 0.1- to 0.2-?m-size fraction was dominated by the Proteobacteria-affiliated genera Herbaspirillum, Pseudoalteromonas, and Marinobacter. Cultivation efforts of the 0.1- to 0.2-?m-size fraction led to the isolation of Actinobacteria-affiliated genera Microbacterium and Kocuria. Based on phylogenetic relatedness and microscopic observations, we hypothesize that the ultrasmall cells in Lake Vida brine are ultramicrocells that are likely in a reduced size state as a result of environmental stress or life cycle-related conditions. PMID:24727273

Kuhn, Emanuele; Ichimura, Andrew S; Peng, Vivian; Fritsen, Christian H; Trubl, Gareth; Doran, Peter T; Murray, Alison E

2014-06-01

350

Co-ferrite spinel and FeCo alloy core shell nanocomposites and mesoporous systems for multifunctional applications  

NASA Astrophysics Data System (ADS)

We report on the fabrication of condensed and mesoporous silica coated CoFe2O4 and FeCo alloy magnetic nanocomposites. The CoFe2O4 magnetic nanoparticles were encapsulated by well defined silica layer with a uniform thickness of 5 nm. The mesoporous silica shells lead to a larger magnetic coercivity than that of the pure CoFe2O4 magnetic nanoparticles due to decrease of interparticle interactions and magneto-elastic anisotropy. In addition, the FeCo nanoparticles were coated with condensed and mesoporous silica. As a consequence, the condensed silica protects the reactive FeCo alloy from oxidation up to 300 °C, maintaining the high magnetization of the nanoparticles. However, saturation magnetization of silica coated FeCo nanoparticles is dramatically decreased after annealing at 400 °C due to the oxidation of the FeCo core.

Zhang, Kai; Amponsah, O.; Arslan, M.; Holloway, T.; Cao, Wei; Pradhan, A. K.

2012-04-01

351

Ultrasensitive spectroscopy of ultrasmall quantum dots for energy conversion and lighting applications  

NASA Astrophysics Data System (ADS)

Quantum dots typically have narrow spectra with a peak that tunes with their size but ultrasmall semiconductor nanocrystals of diameters less than a few nanometers have size-independent spectra and many other strikingly different properties. One especially interesting feature is that ultrasmall CdSe nanocrystals emit an almost pure white-light spectrum, which has great potential for solid-state lighting that yields excellent color rendering. To gain understanding of the photophysical properties and mechanisms for broadband emission, we have constructed a modular fluorescence microscope for ultrasensitive spectroscopy of individual nanoparticles. Using 400-nm wide-field excitation from a frequency-doubled Ti-Sapphire laser and a high-efficiency electron-multiplying CCD, we observe that single CdSe nanocrystals exhibit blinking and abrupt photobleaching, often after detection of only a few hundred photons. Moreover, spectrally dispersed imaging shows that each particle emits the entire broadband spectrum. We discuss mechanisms for homogeneous broadband emission and ongoing experiments in which the instrument is configured for scanning, confocal, two-channel, time-resolved single photon counting for studies of photon antibunching, emission lifetimes, and correlations between spectral regions.

Davis, Lloyd; Orfield, Noah; Rosenthal, Sandra

2013-03-01

352

Nickel-doped cobalt ferrite nanoparticles: efficient catalysts for the reduction of nitroaromatic compounds and photo-oxidative degradation of toxic dyes.  

PubMed

This study deals with the exploration of NixCo1-xFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ferrite nanoparticles as catalysts for reduction of 4-nitrophenol and photo-oxidative degradation of Rhodamine B. The ferrite samples with uniform size distribution were synthesized using the reverse micelle technique. The structural investigation was performed using powder X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray and scanning tunneling microscopy. The spherical particles with ordered cubic spinel structure were found to have the crystallite size of 4-6 nm. Diffused UV-visible reflectance spectroscopy was employed to investigate the optical properties of the synthesized ferrite nanoparticles. The surface area calculated using BET method was found to be highest for Co0.4Ni0.6Fe2O4 (154.02 m(2) g(-1)). Co0.4Ni0.6Fe2O4 showed the best catalytic activity for reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 as reducing agent, whereas CoFe2O4 was found to be catalytically inactive. The reduction reaction followed pseudo-first order kinetics. The effect of varying the concentration of catalyst and NaBH4 on the reaction rates was also scrutinized. The photo-oxidative degradation of Rhodamine B, enhanced oxidation efficacy was observed with the introduction of Ni(2+) in to the cobalt ferrite lattice due to octahedral site preference of Ni(2+). Almost 99% degradation was achieved in 20 min using NiFe2O4 nanoparticles as catalyst. PMID:24902783

Singh, Charanjit; Goyal, Ankita; Singhal, Sonal

2014-06-26

353

Thermodynamics and Dynamics of Physically Restricted Ultrasmall  

NASA Astrophysics Data System (ADS)

To understand the thermodynamics and dynamics of physically restricted ultrasmall systems and to discern the relative role of the physical restriction of the sample size from that of the surface-fluid interaction on the structural and thermodynamic properties of the confined fluids, we undertook the specific heat and molecular vibrational measurements of cyclohexane physically restricted in well -defined porous silica glasses and of geometrically confined cyclohexane films. Our specific heat results showed that both solid -to-solid (monoclinic-to-cubic) structural transition and solid melting transition temperatures were depressed. The amount of the temperature depression for the both phase transitions, i.e., solid-to-solid and melting, inversely scaled with the pore radius (R_{rm p}). It is argued that the surface heterogeneity, the presence of hydroxyl groups, and the radius of curvature led to the nucleation of crystalline grains of various sizes rather than a single plug. The observation of the lambda-shaped specific heat anomaly also suggested the multigrain formation model. With our developed lithographic techniques, we have measured ultrathin (20 nm) film via a vibrational (FTIR) approach. For the first time, a new metastable phase was manifested when the system was cooled. The results can be explained with the theoretical predictions. Molecular vibrational investigation of cyclohexane physically restricted in filled and partially filled pores of controlled pore glass showed there are indeed two distinct types of cyclohexane in the porous silica, idle and non -idle cyclohexane molecules. In addition, the temperature dependent linewidth of the cyclohexane in the filled silica pores also suggested the existence of a diffuse layer between the idle and the non-idle layers, which exhibited unique temperature dependent characteristics.

Mu, Rixiang

354

High-flux characterization of ultrasmall multijunction concentrator solar cells  

Microsoft Academic Search

A characterization study of ultrasmall ultraefficient multijunction concentrator solar cells is presented, with emphasis on performance sensitivity to light intensity and distribution. Information of this type is essential in the design and optimization of the latest generations of high-flux photovoltaic systems. Cell miniaturization allows increasing the concentration at which efficiency peaks, facilitates passive heat rejection, and permits the use of

Omer Korech; Baruch Hirsch; Eugene A. Katz; Jeffrey M. Gordon

2007-01-01

355

Fabrication and microwave absorption of carbon nanotubes\\/CoFe2O4 spinel nanocomposite  

Microsoft Academic Search

A large-scale carbon nanotube\\/CoFe2O4 (CNTs\\/CoFe2O4) spinel nanocomposite has been fabricated by a chemical vapor deposition method using CoFe2O4 nanoparticles as catalysts. A uniform mixture of CNTs and CoFe2O4 nanoparticles was obtained simultaneously. The structure and chemical composition of the product were investigated using various techniques, such as x-ray diffraction, high-resolution transmission electron microscopy, and electron energy loss spectroscopy. It was

R. C. Che; C. Y. Zhi; C. Y. Liang; X. G. Zhou

2006-01-01

356

Positive homotropic allosteric binding of silver(I) ions in multidentate azacalixpyridine macrocycles: effect on the formation and stabilization of silver nanoparticles.  

PubMed

We report herein the occurrence of a positive homotropic allosteric binding effect of two macrocyclic azacalixpyridines. This effect was firstly found to be crucial in the formation and stabilization of ultra-small silver nanoparticles. PMID:23831935

He, Xin; Xu, Xiao-Bin; Wang, Xun; Zhao, Liang

2013-08-18

357

Dispersive solid-phase extraction based on oleic acid-coated magnetic nanoparticles followed by gas chromatography-mass spectrometry for UV-filter determination in water samples.  

PubMed

A sensitive analytical method to concentrate and determine extensively used UV filters in cosmetic products at (ultra)trace levels in water samples is presented. The method is based on a sample treatment using dispersive solid-phase extraction (dSPE) with laboratory-made chemisorbed oleic acid-coated cobalt ferrite (CoFe(2)O(4)@oleic acid) magnetic nanoparticles (MNPs) as optimized sorbent for the target analytes. The variables involved in dSPE were studied and optimized in terms of sensitivity, and the optimum conditions were: mass of sorbent, 100mg; donor phase volume, 75 mL; pH, 3; and sodium chloride concentration, 30% (w/v). After dSPE, the MNPs were eluted twice with 1.5 mL of hexane, and then the eluates were evaporated to dryness and reconstituted with 50 ?L of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) for the injection into the gas chromatography-mass spectrometry (GC-MS). Under the optimized experimental conditions the method provided good levels of repeatability with relative standard deviations below 16% (n=5, at 100 ng L(-1) level). Limit of detection values ranged between 0.2 and 6.0 ng L(-1), due to the high enrichment factors achieved (i.e., 453-748). Finally, the proposed method was applied to the analysis of water samples of different origin (tap, river and sea). Recovery values showed that the matrices under consideration do not significantly affect the extraction process. PMID:21411104

Román, Iván P; Chisvert, Alberto; Canals, Antonio

2011-05-01

358

Magnetic ionic liquids produced by the dispersion of magnetic nanoparticles in 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf2).  

PubMed

?This paper reports on the advancement of magnetic ionic liquids (MILs) as stable dispersions of surface-modified ?-Fe(2)O(3), Fe(3)O(4), and CoFe(2)O(4) magnetic nanoparticles (MNPs) in a hydrophobic ionic liquid, 1-n-butyl 3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMI.NTf(2)). The MNPs were obtained via coprecipitation and were characterized using powder X-ray diffraction, transmission electron microscopy, Raman spectroscopy and Fourier transform near-infrared (FT-NIR) spectroscopy, and magnetic measurements. The surface-modified MNPs (SM-MNPs) were obtained via the silanization of the MNPs with the aid of 1-butyl-3-[3-(trimethoxysilyl)propyl]imidazolium chloride (BMSPI.Cl). The SM-MNPs were characterized by Raman spectroscopy and Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy and by magnetic measurements. The FTIR-ATR spectra of the SM-MNPs exhibited characteristic absorptions of the imidazolium and those of the Fe-O-Si-C moieties, confirming the presence of BMSPI.Cl on the MNP surface. Thermogravimetric analysis (TGA) showed that the SM-MNPs were modified by at least one BMSPI.Cl monolayer. The MILs were characterized using Raman spectroscopy, differential scanning calorimetry (DSC), and magnetic measurements. The Raman and DSC results indicated an interaction between the SM-MNPs and the IL. This interaction promotes the formation of a supramolecular structure close to the MNP surface that mimics the IL structure and is responsible for the stability of the MIL. Magnetic measurements of the MILs indicated no hysteresis. Superparamagnetic behavior and a saturation magnetization of ~22 emu/g could be inferred from the magnetic measurements of a sample containing 50% w/w ?-Fe(2)O(3) SM-MNP/BMI.NTf(2). PMID:22966984

Medeiros, Anderson M M S; Parize, Alexandre L; Oliveira, Vanda M; Neto, Brenno A D; Bakuzis, Andris F; Sousa, Marcelo H; Rossi, Liane M; Rubim, Joel C

2012-10-24

359

Nanomechanical cantilever active probes for ultrasmall mass detection  

NASA Astrophysics Data System (ADS)

The objective of this study is to employ piezoelectrically driven nanomechanical cantilevers (so-called ``active probes'') for ultrasmall mass detection. The idea originates from utilizing the unique configuration and the embedded piezoelectricity of active probes for high amplitude vibration, the attribute that is essential for precise measurement of ultrasmall mass by cantilever-based vibratory sensors. In this work, using focused ion beam technique, a small mass in the order of picograms is added at the tip of active probes. To detect the added mass, a precise model for modal characterization of the probe with geometrical discontinuities is utilized along with a parameter estimation technique for system identification. Using the shifts in the resonant frequencies of the identified system, the amount of added tip mass is estimated at the most sensitive mode of operation. Through a sensitivity analysis, it is shown that the second mode of the present configuration of the active probe is the most reliable mode for mass detection. Moreover, the effect of parameters' uncertainties on the sensitivity of measurements is studied in more detail. Results indicate that system identification procedure proposed in this work is an inevitable step toward achieving precise measurement of ultrasmall masses through active probes with great potential in bio- and chemomass detection applications.

Salehi-Khojin, Amin; Bashash, Saeid; Jalili, Nader; Müller, Maren; Berger, Rüdiger

2009-01-01

360

Dynamic fluctuations in ultrasmall nanocrystals induce white light emission  

SciTech Connect

Nanocrystals typically emit monochromatically at their size-dependent energy gaps. Recently, it was found that by pushing the size of a nanocrystal to its lower limits, absorption occurs at increasingly larger energies, but the expected blue to ultraviolet emission does not occur. Instead, individual ultrasmall CdSe nanocrystals emit white light1-5. Here we show that following excitation, partial thermalization sets the ultrasmall nanocrystals into a fluxional6 state, with a continuously varying energy gap which results in white light emission. Even the larger, monochromatic nanocrystals have a fluxional surface but a stable crystal core. A degree of fluxionality persists even at room temperature and represents a radical change to the accepted view of nanocrystals, with wide-ranging ramifications for other applications. The results were obtained using a combination of state-of-the-art experiment and theory: dynamic imaging by aberration-corrected scanning transmission electron microscopy and finite-temperature quantum molecular dynamics simulations. The results show that small is different, but ultrasmall is different yet again.

Pennycook, Timothy J [ORNL; Mcbride, J. R. [Vanderbilt University; Rosenthal, Sandra [Vanderbilt University; Pennycook, Stephen J [ORNL; Pantelides, Sokrates T. [Vanderbilt University

2012-01-01

361

Controlling bubbles using bubbles--microfluidic synthesis of ultra-small gold nanocrystals with gas-evolving reducing agents.  

PubMed

Microfluidic wet-chemical synthesis of nanoparticles is a growing area of research in chemical microfluidics, enabling the development of continuous manufacturing processes that overcome the drawbacks of conventional batch-based synthesis methods. The synthesis of ultra-small (<5 nm) metallic nanocrystals is an interesting area with many applications in diverse fields, but is typically very challenging to accomplish in a microfluidics-based system due to the use of a strong gas-evolving reducing agent, aqueous sodium borohydride (NaBH(4)), which causes uncontrolled out-gassing and bubble formation, flow disruption and ultimately reactor failure. Here we present a simple method, rooted in the concepts of multiphase mass transfer that completely overcomes this challenge-we simply inject a stream of inert gas bubbles into our channels that essentially capture the evolving gas from the reactive aqueous solution, thereby preventing aqueous dissolved gas concentration from reaching the solubility threshold for bubble nucleation. We present a simple model for coupled mass transfer and chemical reaction that adequately captures device behaviour. We demonstrate the applicability of our method by synthesizing ultra-small gold nanocrystals (<5 nm); the quality of nanocrystals thus synthesized is further demonstrated by their use in an off-chip synthesis of high-quality gold nanorods. This is a general approach that can be extended to a variety of metallic nanomaterials. PMID:22456754

Khan, Saif A; Duraiswamy, Suhanya

2012-04-24

362

Efficient path-integral Monte Carlo technique for ultrasmall device applications  

Microsoft Academic Search

The ability to model equilibrium electronic properties of ultrasmall devices using a path-integral Monte Carlo (PIMC) method is demonstrated. First, a direct sampling PIMC method and its advantages over Metropolis importance sampling PIMC methods in this application are described. Then two potential structures typical of ultrasmall devices, a single and a coupled double finite square well potential, are analyzed and

L. F. Register; M. A. Stroscio; M. A. Littlejohn

1989-01-01

363

Ultrasmall mixed ferrite colloids as multidimensional magnetic resonance imaging, cell labeling, and cell sorting agents.  

PubMed

One area that has been overlooked in the evolution of magnetic nanoparticle technology is the possibility of introducing informational atoms into the iron oxide core of the coated colloid. Introduction of suitable atoms into the iron oxide core offers an opportunity to produce a quantifiable probe, thereby adding one or more dimensions to the magnetic colloid's informational status. Lanthanide-doped iron oxide nanoparticles have been synthesized to introduce informational atoms through the formation of colloidal mixed ferrites. These colloids are designated ultrasmall mixed ferrite iron oxides (USMIOs). USMIOs containing 5 mol % europium exhibit superparamagnetic behavior with an induced magnetization of 56 emu/g Fe at 1.5 T, a powder X-ray diffraction pattern congruent with magnetite, and R1 and R2 relaxivity values of 15.4 (mM s) (-1) and 33.9 (mM s) (-1), respectively, in aqueous solution at 37 degrees C and 0.47 T. USMIO can be detected by five physical methods, combining the magnetic resonance imaging (MRI) qualities of iron with the sensitive and quantitative detection of lanthanide metals by neutron activation analysis (NA), time-resolved fluorescence (TRF), X-ray fluorescence, along with detection by electron microscopy (EM). In addition to quantitative detection using neutron activation analysis, the presence of lanthanides in the iron oxide matrix confers attractive optical properties for long-term multilabeling studies with europium and terbium. These USMIOs offer high photostability, a narrow emission band, and a broad absorption band combining the high sensitivity of time-resolved fluorescence with the high spatial resolution of MRI. USMIO nanoparticles are prepared through modifications of traditional magnetite-based iron oxide colloid synthetic methods. A 5 mol % substitution of ferric iron with trivalent europium yielded a colloid with nearly identical magnetic, physical, and chemical characteristics to its magnetite colloid parent. PMID:17941682

Groman, Ernest V; Bouchard, Jacqueline C; Reinhardt, Christopher P; Vaccaro, Dennis E

2007-01-01

364

Observation of magnetoelectric coupling and local piezoresponse in modified (Na0.5Bi0.5)TiO3-BaTiO3-CoFe2O4 lead-free composites.  

PubMed

Lead-free particulate multiferroic composites of [0.94(Na0.5Bi0.5)TiO3-0.06 BaTiO3]:(Co0.6Zn0.4)(Fe1.7Mn0.3)O4 were synthesized and magnetoelectric (ME) properties were studied. X-ray diffraction and microstructural studies indicated the formation of a two-phase composite system without any impurities. The shift of Raman modes corresponding to ferroelectric and ferrite phases was assigned to the induced strain amid the formation of a two-phase system, in relation to the fraction of each phase in the samples. A strong local piezoresponse and hysteresis loops observed for composites established the ferroelectric properties at a nanoscale. Magnetostriction measurements revealed values of ?11 = -10.4 and ?12 = 5.3 ppm and piezomagnetic coefficient d?11/dH = -0.0087 ppm Oe(-1) at 0.45 kOe for a composite with a ferrite concentration of 35 mol%. A maximum change of 18.5% in magnetization after electrical poling indicates a strong magnetoelectric response of the present composites followed by a direct ME coefficient of 8.2 mV cm(-1) Oe(-1). Our studies point to the fact that the present multiferroic composites having strong ME coupling are useful for lead-free electronic applications. PMID:24849499

Ramana, E Venkata; Figueiras, F; Graça, M P F; Valente, M A

2014-07-14

365

Finite size effects on the electrical properties of sol-gel synthesized CoFe2O4 powders: deviation from Maxwell-Wagner theory and evidence of surface polarization effects  

Microsoft Academic Search

Fine particles of cobalt ferrite were synthesized by the sol-gel method.\\u000a Subsequent heat treatment at different temperatures yielded cobalt\\u000a ferrites having different grain sizes. X-ray diffraction studies were\\u000a carried out to elucidate the structure of all the samples. Dielectric\\u000a permittivity and ac conductivity of all the samples were evaluated as a\\u000a function of frequency, temperature and grain size. The variation

Mathew George; Swapna S. Nair; K. A. Malini; P. A. Joy; M. R. Anantharaman

2007-01-01

366

THE THICKNESS DEPENDENCE OF OXYGEN PERMEABILITY IN SOL-GEL DERIVED CGO-COFE2O4 THIN FILMS ON POROUS CERAMIC SUBSTRATES: A SPUTTERED BLOCKING LAYER FOR THICKNESS CONTROL  

SciTech Connect

Mixed conductive oxides are a topic of interest for applications in oxygen separation membranes as well as use in producing hydrogen fuel through the partial oxidation of methane. The oxygen flux through the membrane is governed both by the oxygen ionic conductivity as well as the material's electronic conductivity; composite membranes like Ce{sub 0.8}Gd{sub 0.2}O{sub 2-{delta}} (CGO)-CoFe{sub 2}O{sub 4} (CFO) use gadolinium doped ceria oxides as the ionic conducting material combined with cobalt iron spinel which serves as the electronic conductor. In this study we employ {approx} 50 nm sputtered CeO{sub 2} layers on the surface of porous CGO ceramic substrates which serve as solution 'blocking' layers during the thin film fabrication process facilitating the control of film thickness. Films with thickness of {approx} 2 and 4 microns were prepared by depositing 40 and 95 separate sol-gel layers respectively. Oxygen flux measurements indicated that the permeation increased with decreasing membrane thickness; thin film membrane with thickness on the micron level showed flux values an order of magnitude greater (0.03 {micro}mol/cm{sup 2} s) at 800 C as compared to 1mm thick bulk ceramic membranes (0.003 {micro}mol/cm{sup 2}).

Brinkman, K

2009-01-08

367

Capturing Ultrasmall EMT Zeolite from Template-Free Systems  

NASA Astrophysics Data System (ADS)

Small differences between the lattice energies of different zeolites suggest that kinetic factors are of major importance in controlling zeolite nucleation. Thus, it is critical to control the nucleation kinetics in order to obtain a desired microporous material. Here, we demonstrate how careful investigation of the very early stages of zeolite crystallization in colloidal systems can provide access to important nanoscale zeolite phases while avoiding the use of expensive organic templates. We report the effective synthesis of ultrasmall (6- to 15-nanometer) crystals of the large-pore zeolite EMT from template-free colloidal precursors at low temperature (30°C) and very high yield.

Ng, Eng-Poh; Chateigner, Daniel; Bein, Thomas; Valtchev, Valentin; Mintova, Svetlana

2012-01-01

368

Pauli Spin Blockade and the Ultrasmall Magnetic Field Effect  

NASA Astrophysics Data System (ADS)

Based on the spin-blockade model for organic magnetoresistance, we present an analytic expression for the polaron-bipolaron transition rate, taking into account the effective nuclear fields on the two sites. We reveal the physics behind the qualitatively different magnetoconductance line shapes observed in experiment, as well as the ultrasmall magnetic field effect (USFE). Since our findings agree in detail with recent experiments, they also indirectly provide support for the spin-blockade interpretation of organic magnetoresistance. In addition, we predict the existence of a similar USFE in semiconductor double quantum dots tuned to the spin-blockade regime.

Danon, Jeroen; Wang, Xuhui; Manchon, Aurélien

2013-08-01

369

Physicochemical characterization of ultrasmall superparamagnetic iron oxide particles (USPIO) for biomedical application as MRI contrast agents  

PubMed Central

Ultrasmall superparamagnetic iron oxide (USPIO) particles are maghemite or magnetite nanoparticles currently used as contrast agent in magnetic resonance imaging. The coatings surrounding the USPIO inorganic core play a major role in both the in vitro stability and, over all, USPIO’s in vivo fate. Different physicochemical properties such as final size, surface charge and coating density are key factors in this respect. Up to now no precise structure – activity relationship has been described to predict entirely the USPIOs stability, as well as their pharmacokinetics and their safety. This review is focused on both the classical and the latest available techniques allowing a better insight in the magnetic core structure and the organic surface of these particles. Concurrently, this work clearly shows the difficulty to obtain a complete physicochemical characterization of USPIOs particles owing to their small dimensions, reaching the analytical resolution limits of many commercial instruments. An extended characterization is therefore necessary to improve the understanding of the properties of USPIOs when dispersed in an aqueous environment and to set the specifications and limits for their conception.

Di Marco, Mariagrazia; Sadun, Claudia; Port, Marc; Guilbert, Irene; Couvreur, Patrick; Dubernet, Catherine

2007-01-01

370

Magic Family of Discretely Sized Ultrabright Si Nanoparticles.  

National Technical Information Service (NTIS)

We describe a procedure for dispersion bulk Si into a family discretely sized ultrasmall ultrabright nanoparticles. We demonstrate that electrochemically etched, hydrogen capped Si(n)H(x), clusters with n larger than 20 are obtained within a family of dis...

A. Smith G. Belomoin J. Therrien R. Twesten S. Rao

2001-01-01

371

Ultrasmall SnO? nanocrystals: hot-bubbling synthesis, encapsulation in carbon layers and applications in high capacity Li-ion storage.  

PubMed

Ultrasmall SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) have been synthesized by bubbling an oxidizing gas into hot surfactant solutions containing Sn-oleate complexes. Annealing of the particles in N2 carbonifies the densely packed surface capping ligands resulting in carbon encapsulated SnO2 nanoparticles (SnO2/C). Carbon encapsulation can effectively buffer the volume changes during the lithiation/delithiation process. The assembled SnO2/C thus deliver extraordinarily high reversible capacity of 908?mA·h·g(-1) at 0.5 C as well as excellent cycling performance in the LIBs. This method demonstrates the great potential of SnO2/C nanoparticles for the design of high power LIBs. PMID:24732294

Ding, Liping; He, Shulian; Miao, Shiding; Jorgensen, Matthew R; Leubner, Susanne; Yan, Chenglin; Hickey, Stephen G; Eychmüller, Alexander; Xu, Jinzhang; Schmidt, Oliver G

2014-01-01

372

Ultrasmall SnO2 Nanocrystals: Hot-bubbling Synthesis, Encapsulation in Carbon Layers and Applications in High Capacity Li-Ion Storage  

PubMed Central

Ultrasmall SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) have been synthesized by bubbling an oxidizing gas into hot surfactant solutions containing Sn-oleate complexes. Annealing of the particles in N2 carbonifies the densely packed surface capping ligands resulting in carbon encapsulated SnO2 nanoparticles (SnO2/C). Carbon encapsulation can effectively buffer the volume changes during the lithiation/delithiation process. The assembled SnO2/C thus deliver extraordinarily high reversible capacity of 908?mA·h·g?1 at 0.5 C as well as excellent cycling performance in the LIBs. This method demonstrates the great potential of SnO2/C nanoparticles for the design of high power LIBs.

Ding, Liping; He, Shulian; Miao, Shiding; Jorgensen, Matthew R.; Leubner, Susanne; Yan, Chenglin; Hickey, Stephen G.; Eychmuller, Alexander; Xu, Jinzhang; Schmidt, Oliver G.

2014-01-01

373

Ultrasmall SnO2 Nanocrystals: Hot-bubbling Synthesis, Encapsulation in Carbon Layers and Applications in High Capacity Li-Ion Storage  

NASA Astrophysics Data System (ADS)

Ultrasmall SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) have been synthesized by bubbling an oxidizing gas into hot surfactant solutions containing Sn-oleate complexes. Annealing of the particles in N2 carbonifies the densely packed surface capping ligands resulting in carbon encapsulated SnO2 nanoparticles (SnO2/C). Carbon encapsulation can effectively buffer the volume changes during the lithiation/delithiation process. The assembled SnO2/C thus deliver extraordinarily high reversible capacity of 908 mA.h.g-1 at 0.5 C as well as excellent cycling performance in the LIBs. This method demonstrates the great potential of SnO2/C nanoparticles for the design of high power LIBs.

Ding, Liping; He, Shulian; Miao, Shiding; Jorgensen, Matthew R.; Leubner, Susanne; Yan, Chenglin; Hickey, Stephen G.; Eychmüller, Alexander; Xu, Jinzhang; Schmidt, Oliver G.

2014-04-01

374

Ultrasmall NaGdF4 Nanodots for Efficient MR Angiography and Atherosclerotic Plaque Imaging.  

PubMed

Herein, ultrasmall NaGdF4 nanodots (~2 nm) with DTPA conjugation have been synthesized for efficient MR angiography. Impressively, the r1 value in MRI reaches up to 8.93 mM(-1) ·s(-1) . The ultrasmall vessel lumen of a rabbit is lighted up remarkably. After 3 h, atherosclerotic plaques could be discriminated clearly. This is beneficial for the accurate early diagnosis of vascular pathema. PMID:24677351

Xing, Huaiyong; Zhang, Shengjian; Bu, Wenbo; Zheng, Xiangpeng; Wang, Lijun; Xiao, Qingfeng; Ni, Dalong; Zhang, Jiamin; Zhou, Liangping; Peng, Weijun; Zhao, Kuaile; Hua, Yanqing; Shi, Jianlin

2014-06-01

375

Thermal Signatures of Pairing Correlations in Nuclei and Nanoparticles  

NASA Astrophysics Data System (ADS)

The Bardeen-Cooper-Schrieffer (BCS) mean-field theory of the pairing interaction breaks down for nuclei and ultra-small metallic grains (nanoparticles). Finite-temperature pairing correlations in such finite-size systems can be calculated beyond the BCS theory in an auxiliary-field Monte Carlo approach. We identify thermal signatures of pairing correlations in both nuclei and nanoparticles that depend on the particle-number parity.

Alhassid, Y.

2007-05-01

376

Gold Nanoparticles for Neural Prosthetics Devices  

PubMed Central

Treatments of neurological diseases and the realization of brain-computer interfaces require ultrasmall electrodes which are “invisible” to resident immune cells. Functional electrodes smaller than 50?m are impossible to produce with traditional materials due to high interfacial impedance at the characteristic frequency of neural activity and insufficient charge storage capacity. The problem can be resolved by using gold nanoparticle nanocomposites. Careful comparison indicates that layer-by-layer assembled films from Au NPs provide more than threefold improvement in interfacial impedance and one order of magnitude increase in charge storage capacity. Prototypes of microelectrodes could be made using traditional photolithography. Integration of unique nanocomposite materials with microfabrication techniques opens the door for practical realization of the ultrasmall implantable electrodes. Further improvement of electrical properties is expected when using special shapes of gold nanoparticles.

Zhang, Huanan; Shih, Jimmy; Zhu, Jian; Kotov, Nicholas A.

2012-01-01

377

Ultrasmall superparamagnetic iron oxide (USPIO)-based liposomes as magnetic resonance imaging probes  

PubMed Central

Background Magnetic liposomes (MLs) are phospholipid vesicles that encapsulate magnetic and/or paramagnetic nanoparticles. They are applied as contrast agents for magnetic resonance imaging (MRI). MLs have an advantage over free magnetic nanocores, in that various functional groups can be attached to the surface of liposomes for ligand-specific targeting. We have synthesized PEG-coated sterically-stabilized magnetic liposomes (sMLs) containing ultrasmall superparamagnetic iron oxides (USPIOs) with the aim of generating stable liposomal carriers equipped with a high payload of USPIOs for enhanced MRI contrast. Methods Regarding iron oxide nanoparticles, we have applied two different commercially available surface-coated USPIOs; sMLs synthesized and loaded with USPIOs were compared in terms of magnetization and colloidal stability. The average diameter size, morphology, phospholipid membrane fluidity, and the iron content of the sMLs were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), fluorescence polarization, and absorption spectroscopy, respectively. A colorimetric assay using potassium thiocyanate (KSCN) was performed to evaluate the encapsulation efficiency (EE%) to express the amount of iron enclosed into a liposome. Subsequently, MRI measurements were carried out in vitro in agarose gel phantoms to evaluate the signal enhancement on T1- and T2-weighted sequences of sMLs. To monitor the biodistribution and the clearance of the particles over time in vivo, sMLs were injected in wild type mice. Results DLS revealed a mean particle diameter of sMLs in the range between 100 and 200 nm, as confirmed by TEM. An effective iron oxide loading was achieved just for one type of USPIO, with an EE% between 74% and 92%, depending on the initial Fe concentration (being higher for lower amounts of Fe). MRI measurements demonstrated the applicability of these nanostructures as MRI probes. Conclusion Our results show that the development of sMLs is strictly dependent on the physicochemical characteristics of the nanocores. Once established, sMLs can be further modified to enable noninvasive targeted molecular imaging.

Frascione, Daniela; Diwoky, Clemens; Almer, Gunter; Opriessnig, Peter; Vonach, Caroline; Gradauer, Kerstin; Leitinger, Gerd; Mangge, Harald; Stollberger, Rudolf; Prassl, Ruth

2012-01-01

378

Magnetic Polymer Nanocomposites with Tunable Microwave Properties  

Microsoft Academic Search

Due to the multifunctionality, polymer nanocomposites (PNCs) have potential applications for electromagnetic interference shielding, tunable electromagnetic devices and flexible electronics. We report on synthesis, magnetic and RF characterization of polymer films loaded with varying concentrations of Fe3O4 and CoFe2O4 nanoparticles. The nanoparticles (5 ± 1 nm) were synthesized by chemical co-precipitation. Structural properties were characterized by XRD and TEM. Nanoparticles

K. Stojak; S. Pal; H. Srikanth; S. Skidmore; C. Morales; J. Dewdney; J. Wang; T. Weller

2010-01-01

379

Tuning of magnetic properties in cobalt ferrite by varying Fe+2 and Co+2 molar ratios  

NASA Astrophysics Data System (ADS)

Different grades of magnetic cobalt ferrite (CoFe2O4) nanoparticles were synthesized with various molar ratios of Fe+2 to Co+2 ions in the initial salt solutions by the co-precipitation method. The crystal structure and morphology of the nanoparticles are obtained from X-ray diffraction and transmission electron microscopy studies. Fourier transform infrared spectroscopy analysis exhibited the Fe-O stretching vibration ~540 cm-1, confirming the formation of metal oxide. The magnetic studies demonstrate that all of the nanoparticles are superparamagnetic at 300 K. The saturation magnetization and coercivity of the CoFe2O4 nanoparticles are affected by the molar ratios of Fe+2 to Co+2 ions. Among all the synthesized nanoparticles, the system with 75:25 molar ratio of Fe+2 to Co+2 ions with a particle size of 13 nm showed a high magnetization of 90 emu/g.

Biswal, Dipti; Peeples, Brianna N.; Peeples, Caryn; Pradhan, Aswini K.

2013-11-01

380

Nanoparticles for neuroimaging  

NASA Astrophysics Data System (ADS)

The advent of nanotechnology has introduced a variety of novel exciting possibilities into the medical and clinical field. Nanoparticles, ultra-small object sized between 100 and 1 nm, are promising diagnostic tools for various diseases among other devices, thanks to the possibility of their functionalization allowing the selective targeting of organs, tissues and cells and to facilitate their transport to primary target organs. However, brain targeting represents a still unresolved challenge due to the presence of the blood-brain barrier, a tightly packed layer of endothelial cells that prevents unwanted substances entering the central nervous system. We review a range of nanoparticles suitable for in vivo diagnostic imaging of neurodegenerative diseases and brain disorders, highlighting the possibility to potentially increase their efficiency and kinetics of brain-targeting. We also review a range of imaging techniques with an emphasis on most recently introduced molecular imaging modalities, their current status and future potential.

Re, F.; Moresco, R.; Masserini, M.

2012-02-01

381

Hydrogen gas sensing with networks of ultra-small palladium nanowires formed on filtration membranes.  

SciTech Connect

Hydrogen sensors based on single Pd nanowires show promising results in speed, sensitivity, and ultralow power consumption. The utilization of single Pd nanowires, however, face challenges in nanofabrication, manipulation, and achieving ultrasmall transverse dimensions. We report on hydrogen sensors that take advantage of single palladium nanowires in high speed and sensitivity and that can be fabricated conveniently. The sensors are based on networks of ultrasmall (<10 nm) palladium nanowires deposited onto commercially available filtration membranes. We investigated the sensitivities and response times of these sensors as a function of the thickness of the nanowires and also compared them with a continuous reference film. The superior performance of the ultrasmall Pd nanowire network based sensors demonstrates the novelty of our fabrication approach, which can be directly applied to palladium alloy and other hydrogen sensing materials.

Zeng, X. Q.; Latimer, M. L.; Xiao, Z. L.; Panuganti, S.; Welp, U.; Kwok, W. K.; Xu, T. (Materials Science Division); (Northern Illinois Univ.)

2010-11-29

382

Magnetic and spectroscopic properties of Polyacrylamide-CoFe2O4 magnetic hydrogel  

NASA Astrophysics Data System (ADS)

This study investigates synthesis and characterization of polyacrylamide (PAAm) hydrogels containing ferromagnetic CoFe2O4 nanoparticles. Structural, electrical, and magnetic characterization of the gels have been performed with X-ray powder diffractometry, Scanning electron microscopy, DC conductivity, magnetization and fluorescence spectroscopy techniques. Fluorescence and electrical measurements show that nanoparticles have trapped in the gel so they cannot move through the gel even if the gel is swollen and the voltage is applied. Pyranine molecules diffuse easily through the gel due to the presence of ferromagnetic nanoparticles. As number of diffused pyranine molecules increases current densities of the magnetic hydrogel increase. Magnetization measurements reveal that CoFe2O4 nanoparticles do not diffuse out of the gel during swelling. As a result, total magnetization of the gel do not change as volume of the gel increases.

Alvero?lu, E.; Sözeri, H.; Kurtan, U.; ?enel, M.; Baykal, A.

2013-03-01

383

Nanoparticles  

NASA Astrophysics Data System (ADS)

Nanostructured bulk materials are regarded as a means of enhancing the performance of thermoelectric (TE) materials and devices. Powder metallurgy has the distinct advantage over conventional synthesis that it can start directly from nanosized particles. However, further processing, for example extrusion, usually requires elevated temperatures, which lead to grain growth. We have found that introduction of semiconductor nanoparticles of molybdenum disulfide (MoS2), a well-known solid lubricant, suppresses grain growth in bismuth telluride-based alloys, thus improving the extrusion process. Scanning electron microscope images show that adding MoS2 particles at concentrations of 0.2, 0.4, and 0.8 wt% to p-type (Bi0.2Sb0.8)2Te3, under otherwise identical extrusion conditions, reduces average grain size by a factor of four. Scherer's formula applied to x-ray diffraction data indicates that average crystallite sizes (˜17 nm) of powders are not significantly different from those of alloys extruded with MoS2 (˜18 nm), which is in stark contrast with those for conventional alloy (Bi0.2Sb0.8)2Te3 extruded under the same conditions (˜80 nm). Harman measurements of TE properties reveal a decrease of the thermal conductivity accompanied by reduction of the room-temperature figure of merit ( ZT) from 0.9 to 0.7, because of a lower power factor. Above 370 K, however, the performance of alloys containing MoS2 surpasses that of (Bi0.2Sb0.8)2Te3, with reduction of the thermal conductivity which is more significant at temperatures above the cross point of the ZT values.

Keshavarz, Mohsen K.; Vasilevskiy, Dimitri; Masut, Remo A.; Turenne, Sylvain

2014-06-01

384

nanoparticles  

NASA Astrophysics Data System (ADS)

In this work, we present the role of vanadium ions (V+5 and V+3), oxygen vacancies (VO), and interstitial zinc (Zni) to the contribution of specific magnetization for a mixture of ZnO-V2O5 nanoparticles (NPs). Samples were obtained by mechanical milling of dry powders and ethanol-assisted milling for 1 h with a fixed atomic ratio V/Zn?=?5% at. For comparison, pure ZnO samples were also prepared. All samples exhibit a room temperature magnetization ranging from 1.18?×?10-3 to 3.5?×?10-3 emu/gr. Pure ZnO powders (1.34?×?10-3 emu/gr) milled with ethanol exhibit slight increase in magnetization attributed to formation of Zni, while dry milled ZnO powders exhibit a decrease of magnetization due to a reduction of VO concentration. For the ZnO-V2O5 system, dry milled and thermally treated samples under reducing atmosphere exhibit a large paramagnetic component associated to the formation of V2O3 and secondary phases containing V+3 ions; at the same time, an increase of VO is observed with an abrupt fall of magnetization to ??~?0.7?×?10-3 emu/gr due to segregation of V oxides and formation of secondary phases. As mechanical milling is an aggressive synthesis method, high disorder is induced at the surface of the ZnO NPs, including VO and Zni depending on the chemical environment. Thermal treatment restores partially structural order at the surface of the NPs, thus reducing the amount of Zni at the same time that V2O5 NPs segregate reducing the direct contact with the surface of ZnO NPs. Additional samples were milled for longer time up to 24 h to study the effect of milling on the magnetization; 1-h milled samples have the highest magnetizations. Structural characterization was carried out using X-ray diffraction and transmission electron microscopy. Identification of VO and Zni was carried out with Raman spectra, and energy-dispersive X-ray spectroscopy was used to verify that V did not diffuse into ZnO NPs as well to quantify O/Zn ratios.

Olive-Méndez, Sion F.; Santillán-Rodríguez, Carlos R.; González-Valenzuela, Ricardo A.; Espinosa-Magaña, Francisco; Matutes-Aquino, José A.

2014-04-01

385

Synthesis of high-coercivity cobalt ferrite particles using water-in-oil microemulsions  

Microsoft Academic Search

Magnetic nanoparticles of cobalt ferrite (CoFe2O4) have been synthesized using water-in-oil microemulsions consisting of water, cetyl trimethyl ammonium bromide (surfactant), n-butanol (cosurfactant), and n-octane (oil). Precursor hydroxides were precipitated in the aqueous cores of water-in-oil microemulsions and these were then separated and calcined to give the magnetic oxide. X-ray diffraction confirmed the formation of phase pure cobalt ferrite. These nanoparticles

V. Pillai; D. O. Shah

1996-01-01

386

Magnetically Tunable Polymer Nanocomposites for RF and Microwave Device Applications  

Microsoft Academic Search

There has been much interest in polymer nanocomposites (PNC) recently due to potential applications for EMI shielding, tunable electromagnetic devices and flexible electronics. We report synthesis, structural, magnetic and RF characterization on PNCs ranging from 20-80 wt-% loadings of Fe3O4 and CoFe2O4 nanoparticles (˜8nm) in a thermosetting resin from the Rogers Corporation. Nanoparticles were synthesized by thermal decomposition and characterized

K. Stojak; S. Pal; H. Srikanth; C. Morales; J. Dewdney; J. Wang; T. Weller

2011-01-01

387

Ultra-Small Reader/Writer with Multiple Contactless Interfaces on a Flexible Circuit Board  

NASA Astrophysics Data System (ADS)

In order to incorporate the reader/writers (RWs) into mobile electronic devices, miniaturization and flexibility are required. To meet these requirements, we fabricate an ultra-small RW with multiple contactless interfaces by mounting main unit circuits inside the antenna coil and using flexible multi-layer circuit board.

Yamamoto, Hideaki; Ikeda, Minoru; Hosoda, Yasuhiro

388

Networks of ultrasmall Pd\\/Cr bilayer nanowires as high performance hydrogen sensors  

Microsoft Academic Search

The newly developed hydrogen sensor, based on a network of ultrasmall pure palladium nanowires sputter-deposited on a filtration membrane, takes advantage of single palladium nanowires' characteristics of high speed and sensitivity while eliminating their nanofabrication obstacles. However, this new type of sensor, like the single palladium nanowires, cannot distinguish hydrogen concentrations above 3%, thus limiting the potential applications of the

X.-Q. Zeng; Y.-L. Wang; H. Deng; M. L. Latimer; Z.-L. Xiao; J. Pearson; T. Xu; H.-H. Wang; U. Welp; G. W. Crabtree; W.-K. Kwok

2011-01-01

389

Electrochemical Oxidation of 5-Hydroxytryptamine and 5-Hydroxyindoleacetic Acid at Ultrasmall Gold Ring Electrodes.  

National Technical Information Service (NTIS)

Ultrasmall gold ring electrodes have been constructed by electrodeposition of gold onto carbon ring electrodes. Electrodes thus formed show similar adsorption/desorption peaks for oxygen in H2SO4 solution compared to those obtained at conventional-sized e...

Y. Y. Lau D. K. Wong G. Luo A. G. Ewing

1991-01-01

390

The Structure of Carbon Blacks Measured with (Ultra)Small Angle X-Ray Scattering  

Microsoft Academic Search

The particle structure of various carbon blacks was measured using Small Angle X-ray Scattering (SAXS) and Ultra-Small Angle X-ray Scattering (USAXS). The objective of the paper is the characterization of ten new carbon blacks produced in furnace black and in gas black processes by Degussa-Hüls AG and their classification regarding their structure.

Marcus Weth; Johann Mathias; Andreas Emmerling; Joachim Kuhn; Jochen Fricke

2001-01-01

391

Toward Ultrasmall Mass Detection Using Adaptive Self-Sensing Piezoelectrically Driven Microcantilevers  

Microsoft Academic Search

Over the past decade, microcantilever-based mass sensing has grown to become a significant field of research in the engineering community. The ability of microcantilevers to detect extremely small biochemical particles is being investigated for a number of industrial applications. This paper presents an adaptive self-sensing strategy for ultrasmall tip mass estimation using piezoelectrically actuated microcantilevers. A piezoelectric patch actuator deposited

Miheer Gurjar; Nader Jalili

2007-01-01

392

Magnetic nanocomposite spinel and FeCo core-shell and mesoporous systems  

NASA Astrophysics Data System (ADS)

The fabrication of condensed silica and mesoporous silica coated spinel CoFe2O4 and FeCo alloy magnetic nanocomposites are reported. The encapsulation of well-defined 5 nm thick uniform silica layer on CoFe2O4 magnetic nanoparticles was performed. The formation of mesopores in the shell was a consequence of removal of organic group of the precursor through annealing. The NiO nanoparticles were loaded into the mesoporous silica. The mesoporous silica shells leads to a larger coercivity than that of pure CoFe2O4 magnetic nanoparticles due to the decrease of interparticle interactions and magneto-elastic anisotropy. In addition, the FeCo nanoparticles were coated by condensed and mesoporous silica. The condensed silica can protect the reactive FeCo alloy from oxidation up to 300 °C. However, saturation magnetization of FeCo nanoparticles coated by silica after 400 °C annealing is dramatically decreased due to the oxidation of the FeCo core. The mesoporous silica coated magnetic nanostructure loaded with NiO as a final product could be used in the field of biomedical applications.

Zhang, Kai; Amponsah, O.; Arslan, M.; Holloway, T.; Sinclair, David; Cao, Wei; Bahoura, M.; Pradhan, A. K.

2012-06-01

393

Controlling the heterocoagulation process for fabricating PS–CoFe 2O 4 nanocomposite particles  

Microsoft Academic Search

Most ordinary polystyrene (PS) microspheres without any surface modification and hard magnetic cobalt ferrite (CoFe2O4) nanoparticles were, respectively, used as large host particles and small guest particles in a heterocoagulation system. In order to achieve a regular heterocoagulation for fabricating PS–CoFe2O4 composite particles having tailored morphology, chief attention was focused on controlling over the heterocoagulation process instead of the surface

Yunxing Li; Dongping Yin; Zhaoqun Wang; Bing Li; Gi Xue

2009-01-01

394

Thermal, dielectric and microwave absorption properties of polyaniline–CoFe 2O 4 nanocomposites  

Microsoft Academic Search

The present paper deals with the synthesis of conducting ferromagnetic polyaniline–CoFe2O4 (PC) nanocomposites via one-step chemical oxidative polymerization of aniline in the presence of CoFe2O4 nanoparticles (30–40nm). These nanocomposites of PC have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM). Extended thermal analysis has

Namita Gandhi; Kuldeep Singh; Anil Ohlan; D. P. Singh; S. K. Dhawan

2011-01-01

395

Design of an ultrasmall Au nanocluster-CeO2 mesoporous nanocomposite catalyst for nitrobenzene reduction  

NASA Astrophysics Data System (ADS)

In this work we are inspired to explore gold nanoclusters supported on mesoporous CeO2 nanospheres as nanocatalysts for the reduction of nitrobenzene. Ultrasmall Au nanoclusters (NCs) and mesoporous CeO2 nanospheres were readily synthesized and well characterized. Due to their ultrasmall size, the as-prepared Au clusters can be easily absorbed into the mesopores of the mesoporous CeO2 nanospheres. Owing to the unique mesoporous structure of the CeO2 support, Au nanoclusters in the Au@CeO2 may effectively prevent the aggregation which usually results in a rapid decay of the catalytic activity. It is notable that the ultrasmall gold nanoclusters possess uniform size distribution and good dispersibility on the mesoporous CeO2 supports. Compared to other catalyst systems with different oxide supports, the as-prepared Au nanocluster-CeO2 nanocomposite nanocatalysts showed efficient catalytic performance in transforming nitrobenzene into azoxybenzene. In addition, a plausible mechanism was deeply investigated to explain the transforming process. Au@CeO2 exhibited efficient catalytic activity for reduction of nitrobenzene. This strategy may be easily extended to fabricate many other heterogeneous catalysts including ultrasmall metal nanoclusters and mesoporous oxides.In this work we are inspired to explore gold nanoclusters supported on mesoporous CeO2 nanospheres as nanocatalysts for the reduction of nitrobenzene. Ultrasmall Au nanoclusters (NCs) and mesoporous CeO2 nanospheres were readily synthesized and well characterized. Due to their ultrasmall size, the as-prepared Au clusters can be easily absorbed into the mesopores of the mesoporous CeO2 nanospheres. Owing to the unique mesoporous structure of the CeO2 support, Au nanoclusters in the Au@CeO2 may effectively prevent the aggregation which usually results in a rapid decay of the catalytic activity. It is notable that the ultrasmall gold nanoclusters possess uniform size distribution and good dispersibility on the mesoporous CeO2 supports. Compared to other catalyst systems with different oxide supports, the as-prepared Au nanocluster-CeO2 nanocomposite nanocatalysts showed efficient catalytic performance in transforming nitrobenzene into azoxybenzene. In addition, a plausible mechanism was deeply investigated to explain the transforming process. Au@CeO2 exhibited efficient catalytic activity for reduction of nitrobenzene. This strategy may be easily extended to fabricate many other heterogeneous catalysts including ultrasmall metal nanoclusters and mesoporous oxides. Electronic supplementary information (ESI) available: EM images and size distribution of gold NCs, the XRD pattern of the CeO2 mesoporous spheres N2 adsorption-desorption isotherm of Au@CeO2[P], EDS analysis of Au@CeO2[P], the time conversion plot of nitrobenzene reduction, spectroscopic characterization and the NMR spectrum of products. See DOI: 10.1039/c3nr01977b

Chong, Hanbao; Li, Peng; Xiang, Ji; Fu, Fangyu; Zhang, Dandan; Ran, Xiaorong; Zhu, Manzhou

2013-07-01

396

Folate-targeted polymeric micelles loaded with ultrasmall superparamagnetic iron oxide: combined small size and high MRI sensitivity  

PubMed Central

Targeted delivery of contrast agents is a highly desirable strategy for enhancing diagnostic efficiency and reducing side effects and toxicity. Water-soluble and tumor-targeting superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized by loading hydrophobic SPIONs into micelles assembled from an amphiphilic block copolymer poly(ethylene glycol)- poly(?-caprolactone) (PEG-PCL) bearing folate in the distal ends of PEG chains. Compared to the water-soluble SPIONs obtained by small molecular surfactant coating, ultrasmall SPION encapsulation with PEG-PCL micelles (PEG-PCL-SPIONs) simultaneously increases transverse (r2) and decreases longitudinal (r1) magnetic resonance (MR) relaxivities of water proton in micelle solution, leading to a notably high r2/r1 ratio up to 78, which makes the PEG-PCL-SPIONs a highly sensitive MR imaging (MRI) T2 contrast agent. The mean size of folate-attached SPION micelles (Fa-PEG-PCL-SPIONs) is 44 ± 3 nm on average, ideal for in vivo MRI applications in which long circulation is greatly determined by small particle size and is highly desirable. Prussian blue staining of BEL-7402 cells over-expressing folate receptors, after incubation with micelle-containing medium, demonstrated that folate functionalization of the magnetic particles significantly enhanced their cell uptake. The potential of Fa-PEG-PCL-SPIONs as a potent MRI probe for in vivo tumor detection was assessed. At 3 hours after intravenous injection of the Fa-PEG-PCL-SPION solution into mice bearing subcutaneous xenografts of human BEL-7402 hepatoma, a 41.2% signal intensity decrease was detected in the T2-weighted MR images of the tumor, indicating the efficient accumulation of Fa-PEG-PCL-SPIONs in the tumor tissue.

Hong, Guo-bin; Zhou, Jing-xing; Yuan, Ren-xu

2012-01-01

397

Folate-targeted polymeric micelles loaded with ultrasmall superparamagnetic iron oxide: combined small size and high MRI sensitivity.  

PubMed

Targeted delivery of contrast agents is a highly desirable strategy for enhancing diagnostic efficiency and reducing side effects and toxicity. Water-soluble and tumor-targeting superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized by loading hydrophobic SPIONs into micelles assembled from an amphiphilic block copolymer poly(ethylene glycol)- poly(?-caprolactone) (PEG-PCL) bearing folate in the distal ends of PEG chains. Compared to the water-soluble SPIONs obtained by small molecular surfactant coating, ultrasmall SPION encapsulation with PEG-PCL micelles (PEG-PCL-SPIONs) simultaneously increases transverse (r(2)) and decreases longitudinal (r(1)) magnetic resonance (MR) relaxivities of water proton in micelle solution, leading to a notably high r(2)/r(1) ratio up to 78, which makes the PEG-PCL-SPIONs a highly sensitive MR imaging (MRI) T(2) contrast agent. The mean size of folate-attached SPION micelles (Fa-PEG-PCL-SPIONs) is 44 ± 3 nm on average, ideal for in vivo MRI applications in which long circulation is greatly determined by small particle size and is highly desirable. Prussian blue staining of BEL-7402 cells over-expressing folate receptors, after incubation with micelle-containing medium, demonstrated that folate functionalization of the magnetic particles significantly enhanced their cell uptake. The potential of Fa-PEG-PCL-SPIONs as a potent MRI probe for in vivo tumor detection was assessed. At 3 hours after intravenous injection of the Fa-PEG-PCL-SPION solution into mice bearing subcutaneous xenografts of human BEL-7402 hepatoma, a 41.2% signal intensity decrease was detected in the T(2)-weighted MR images of the tumor, indicating the efficient accumulation of Fa-PEG-PCL-SPIONs in the tumor tissue. PMID:22745549

Hong, Guo-bin; Zhou, Jing-xing; Yuan, Ren-xu

2012-01-01

398

Packet communication ultra-small aperture terminal system for the Hokkaido Integrated Telecommunication network  

Microsoft Academic Search

Three aspects of a new minimum cost, high reliability system strategy for the Hokkaido Integrated Telecommunication (HIT) network, in which real time operation is not demanded, are examined. These are: (1) a packet communication ultra-small aperture terminal (PC-USAT) system, which contains a method for overcoming the satellite link's rain attenuation discontinuities; (2) an optimum rain margin technique and the 14\\/12-GHz

Takeshi Hatsuda

1995-01-01

399

Nucleation-promoted L10 ordering in FePt thin films with ultrasmall grain size  

Microsoft Academic Search

FePt thin films with an ultrasmall grain size of ~3.4 nm were successfully prepared by employing a relatively high sputtering pressure of 4 Pa that produces deposited target atoms or clusters with low energy. The L10 ordering in the FePt thin films is dominantly dependent on the nucleation of ordered domains rather than their growth which is usually observed in

X. H. Li; B. T. Liu; H. Y. Sun; W. Li; X. Y. Zhang

2008-01-01

400

Enzymatic and temperature-sensitive controlled release of ultrasmall superparamagnetic iron oxides (USPIOs)  

Microsoft Academic Search

Background  Drug and contrast agent delivery systems that achieve controlled release in the presence of enzymatic activity are becoming\\u000a increasingly important, as enzymatic activity is a hallmark of a wide array of diseases, including cancer and atherosclerosis.\\u000a Here, we have synthesized clusters of ultrasmall superparamagnetic iron oxides (USPIOs) that sense enzymatic activity for\\u000a applications in magnetic resonance imaging (MRI). To achieve

Shann S Yu; Randy L Scherer; Ryan A Ortega; Charleson S Bell; Conlin P O’Neil; Jeffrey A Hubbell; Todd D Giorgio

2011-01-01

401

Magnetic Resonance Imaging of Atherosclerotic Plaque With Ultrasmall Superparamagnetic Particles of Iron Oxide in Hyperlipidemic Rabbits  

Microsoft Academic Search

Background—Based on the observation that ultrasmall superparamagnetic particles of iron oxides (USPIOs) are phagocytosed by cells of the mononuclear phagocytic system, the purpose of this study was to evaluate their use as a marker of atherosclerosis-associated inflammatory changes in the vessel wall before luminal narrowing is present. Methods and Results—Experiments were conducted on 6 heritable hyperlipidemic and 3 New Zealand

Stefan G. Ruehm; Claire Corot; Peter Vogt; Stefan Kolb; Jörg F. Debatin

2009-01-01

402

Ultra-small rare-earth oxide nanocrystals: Development, film assembly, optical and dielectric studies  

Microsoft Academic Search

The oxides of rare-earth elements (rare-earth sesquioxide: RE2O 3) are known for their optical and dielectric properties. Europium oxide is known for characteristic red luminescence and gadolinium oxide has excellent insulating properties (band gap: 5.5 eV). Development of ultra-small nanocrystals (sub-3 nm diameter) of these rare-earth oxides and investigation of their optical and dielectric properties are explored in this dissertation.

Sameer V. Mahajan

2010-01-01

403

Preparation of entangled nanocellulose fibers from APMP and its magnetic functional property as matrix.  

PubMed

Nanocellulose fibers (NCFs) aerogels were prepared from poplar alkaline peroxide mechanical pulp (APMP) using physical ultrasonication method. As raw materials, the unique mechanical effects of APMP cause the fiber folding and loose during the pulping process, which was beneficial to further chemical purification and subsequent treatment for long and entangled NCFs. The obtained NCFs exhibited higher crystallinity (77.8%) compared with that of APMP (72.6%) together with diameters range from 20 to 90 nm and self-assembled to network. The primary thermal degradation of NCFs occurred at 331.5°C. The prepared NCFs network aerogels acted as matrix which can prevent the growth and aggregation of ferromagnetic CoFe2O4 nanoparticles. The ratio of the CoFe2O4 of magnetic composites increased from 34 wt% to 75 wt%, and the magnetic properties were all increased with increasing the reaction concentration of FeSO4/CoCl2 salt. PMID:23544539

Li, Wei; Zhao, Xin; Liu, Shouxin

2013-04-15

404

Ultrasmall particle detection using a submicron Hall sensor  

NASA Astrophysics Data System (ADS)

We demonstrate detection of a single FePt nanoparticle (diameter 150 nm, moment ~107 ?B) using an ultrasensitive InSb Hall sensor with the bar lateral width of 600 nm. The white noise of a typical nanodevice, SV1/2~28 nV/?Hz, is limited only by two-terminal resistance of the voltage leads which results in a minimum field sensitivity of the device Bmin=0.87 ?T/?Hz. To detect a single FePt bead, we employed a phase-sensitive method based on measuring the ac susceptibility change in a bead when exposed to a switched dc magnetic field. Such nano-Hall devices, enabling detection of potentially even smaller moments, are of considerable significance both for nanomagnetic metrology and high sensitivity biological and environmental detectors.

Kazakova, O.; Panchal, V.; Gallop, J.; See, P.; Cox, D. C.; Spasova, M.; Cohen, L. F.

2010-05-01

405

Holographic interferometry of ultrasmall-pressure-induced curvature changes of bilayer lipid membranes  

SciTech Connect

Two-exposure interferometric holograms have been shown to sensitively report ultrasmall-pressure (10 natm)-induced curvature changes in glyceryl monooleate (GMO) bilayer lipid membranes (BLMs). The number of concentric fringes observed, and hence the lateral distance between the plane of the Teflon and the BLM, increased linearly with increasing transmembrane pressure and led to a value of 1.1 {plus minus} 0.05 dyn/cm for the surface tension of the BLM. BLMs with appreciable Plateau-Gibbs borders have been shown to undergo nonuniform deformation; the bilayer portion is distorted less than the surrounding Plateau-Gibbs border upon the application of a transmembrane pressure gradient.

Picard, G.; Schneider-Henriquez, J.E.; Fendler, J.H. (Universite de Montreal, Quebec (Canada))

1990-01-25

406

Nucleation-promoted L10 ordering in FePt thin films with ultrasmall grain size  

NASA Astrophysics Data System (ADS)

FePt thin films with an ultrasmall grain size of ~3.4 nm were successfully prepared by employing a relatively high sputtering pressure of 4 Pa that produces deposited target atoms or clusters with low energy. The L10 ordering in the FePt thin films is dominantly dependent on the nucleation of ordered domains rather than their growth which is usually observed in the films with relatively large grain size. The nucleation-promoted L10 ordering makes a reduction in grain growth and thus yields the L10-FePt thin films with a uniform and small grain size below 10 nm.

Li, X. H.; Liu, B. T.; Sun, H. Y.; Li, W.; Zhang, X. Y.

2008-07-01

407

Fabrication and characterization of well-aligned plasmonic nanopillars with ultrasmall separations  

PubMed Central

We show the fabrication of well-aligned gold and silver nanopillars with various array parameters via interference lithography followed by ion beam milling and compare the etching rates of these two metallic materials. Silver is suitable for fabricating ultrafine arrays with ultrasmall separations due to high milling rates. The optical properties of the fabricated nanopillars are specifically characterized from both normal incidence and oblique incident angles. Tunable surface plasmon resonances are achieved with varying structural parameters. Strong coupling effects are enabled when the separation between adjacent nanopillars is dramatically reduced, leading to useful applications in sensing and waveguiding.

2014-01-01

408

Scanning interferometric microscopy for the detection of ultrasmall phase shifts in condensed matter  

SciTech Connect

We describe a scanning optical microscope based on polarization Sagnac interferometry for measuring ultrasmall phase shifts, and use this method to detect small numbers of absorbing molecules in a solid without the use of fluorescence. The absorption and concomitant optical phase shift of terrylene dopant molecules in a p-terphenyl host crystal are made time dependent by periodic optical saturation of the sample. A detection sensitivity of 8.75x10{sup -8} rad is achieved with a 0.078 Hz bandwidth, and detection of signals from as few as 19{+-}3 terrylene molecules is demonstrated at room temperature.

Hwang, J. [Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Department of Chemistry, Stanford University, Stanford, California 94305 (United States); Fejer, M. M. [Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Moerner, W. E. [Department of Chemistry, Stanford University, Stanford, California 94305 (United States)

2006-02-15

409

Ultrasmall superparamagnetic iron oxides (USPIOs): a future alternative magnetic resonance (MR) contrast agent for patients at risk for nephrogenic systemic fibrosis (NSF)?  

PubMed Central

Gadolinium (Gd) based contrast agents (GBCAs) in magnetic resonance imaging (MRI) are used in daily clinical practice and appear safe in most patients; however, nephrogenic systemic fibrosis (NSF) is a recently recognized severe complication associated with GBCAs. It affects primarily patients with renal disease, such as stage 4 or 5 chronic kidney disease (CKD; glomerular filtration rate <30 ml/min per 1.73 m2), acute kidney injury, or kidney and liver transplant recipients with kidney dysfunction. Contrast-enhanced MRI and computed tomography (CT) scans provide important clinical information and influence patient management. An alternative contrast agent is needed to obtain adequate imaging results while avoiding the risk of NSF in this vulnerable patient group. One potential alternative is ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, which provide enhancement characteristics similar to GBCAs. We review our experience in approximately 150 patients on the potential benefits of the USPIOs ferumoxtran-10 and ferumoxytol. We focus on central nervous system (CNS) MRI but also review imaging of other vascular beds. Safety studies, including USPIO administration (ferumoxytol) as iron supplement therapy in CKD patients on and not on dialysis, suggest that decreased kidney function does not alter the safety profile. We conclude that for both CNS MR imaging and MR angiography, USPIO agents like ferumoxytol are a viable option for patients at risk for NSF.

Neuwelt, Edward A.; Hamilton, Bronwyn E.; Varallyay, Csanad G.; Rooney, William R.; Edelman, Robert D.; Jacobs, Paula M.; Watnick, Suzanne G.

2008-01-01

410

Design and synthesis of ternary cobalt ferrite/graphene/polyaniline hierarchical nanocomposites for high-performance supercapacitors  

NASA Astrophysics Data System (ADS)

A ternary cobalt ferrite/graphene/polyaniline nanocomposite (CGP) is designed and fabricated via a facile two-step approach: cobalt ferrite nanoparticles dispersed on graphene sheets are achieved by a hydrothermal method, followed by coating with polyaniline (PANI) through in situ polymerization process. Electrochemical measurements demonstrate that the specific capacitance of the resulting ternary hybrid (CGP) is up to 1133.3 F g-1 at a scan rate of 1 mV s-1 and 767.7 F g-1 at a current density of 0.1 A g-1 using a three-electrode system, while 716.4 F g-1 at a scan rate of 1 mV s-1 and 392.3 F g-1 at a current density of 0.1 A g-1 using a two-electrode system, which are significantly higher than those of pure CoFe2O4, graphene and PANI, or binary CoFe2O4/graphene, CoFe2O4/PANI and graphene/PANI hybrids. In addition, over 96% of the initial capacitance can be retained after repeating test for 5000 cycles, demonstrating a high cycling stability. The extraordinary electrochemical performance of the ternary CGP nanocomposite can be attributed to its well-designed nanostructure and the synergistic effects of the individual components.

Xiong, Pan; Huang, Huajie; Wang, Xin

411

Sub-2 nm size and density tunable platinum nanoparticles using room temperature tilted-target sputtering  

NASA Astrophysics Data System (ADS)

This paper describes a tilted-target RF magnetron sputter deposition system to grow nanoparticles in a controlled way. With detailed characterization of ultra-high density (up to 1.1 × 1013 cm-2) and ultra-small size Pt nanoparticles (0.5-2 nm), it explains their growth and crystalline properties on amorphous Al2O3 thin films. It is shown that Pt nanoparticle size and number density can be precisely engineered by varying selected experimental parameters such as target angle, sputtering power and time of deposition to control the energy of the metal atoms in the deposition flux. Based on rate equation modelling of nanoparticle growth, three distinct growth regimes, namely nucleation dependent, coalescence dependent and agglomeration dependent regimes, were observed. The correlation between different nanoparticle growth regimes and the consequent crystal structure transformation, non-crystalline clusters ? single crystalline nanoparticles ? polycrystalline islands, is also discussed.

Ramalingam, Balavinayagam; Mukherjee, Somik; Mathai, Cherian J.; Gangopadhyay, Keshab; Gangopadhyay, Shubhra

2013-05-01

412

Networks of ultrasmall Pd/Cr nanowires as high performance hydrogen sensors.  

PubMed

The newly developed hydrogen sensor, based on a network of ultrasmall pure palladium nanowires sputter-deposited on a filtration membrane, takes advantage of single palladium nanowires' characteristics of high speed and sensitivity while eliminating their nanofabrication obstacles. However, this new type of sensor, like the single palladium nanowires, cannot distinguish hydrogen concentrations above 3%, thus limiting the potential applications of the sensor. This study reports hydrogen sensors based on a network of ultrasmall Cr-buffered Pd (Pd/Cr) nanowires on a filtration membrane. These sensors not only are able to outperform their pure Pd counterparts in speed and durability but also allow hydrogen detection at concentrations up to 100%. The new networks consist of a thin layer of palladium deposited on top of a Cr adhesion layer 1-3 nm thick. Although the Cr layer is insensitive to hydrogen, it enables the formation of a network of continuous Pd/Cr nanowires with thicknesses of the Pd layer as thin as 2 nm. The improved performance of the Pd/Cr sensors can be attributed to the increased surface area to volume ratio and to the confinement-induced suppression of the phase transition from Pd/H solid solution (?-phase) to Pd hydride (?-phase). PMID:21854059

Zeng, Xiao-Qiao; Wang, Yong-Lei; Deng, Henry; Latimer, Michael L; Xiao, Zhi-Li; Pearson, John; Xu, Tao; Wang, Hsien-Hau; Welp, Ulrich; Crabtree, George W; Kwok, Wai-Kwong

2011-09-27

413

Post-detection analysis for grating-based ultra-small angle X-ray scattering.  

PubMed

Until recently, the hard X-ray, phase-sensitive imaging technique called grating interferometry was thought to provide information only in real space. However, by utilizing an alternative approach to data analysis we demonstrated that the angular resolved ultra-small angle X-ray scattering distribution can be retrieved from experimental data. Thus, reciprocal space information is accessible by grating interferometry in addition to real space. Naturally, the quality of the retrieved data strongly depends on the performance of the employed analysis procedure, which involves deconvolution of periodic and noisy data in this context. The aim of this article is to compare several deconvolution algorithms to retrieve the ultra-small angle X-ray scattering distribution in grating interferometry. We quantitatively compare the performance of three deconvolution procedures (i.e., Wiener, iterative Wiener and Lucy-Richardson) in case of realistically modeled, noisy and periodic input data. The simulations showed that the algorithm of Lucy-Richardson is the more reliable and more efficient as a function of the characteristics of the signals in the given context. The availability of a reliable data analysis procedure is essential for future developments in grating interferometry. PMID:23375790

Scattarella, F; Tangaro, S; Modregger, P; Stampanoni, M; De Caro, L; Bellotti, R

2013-09-01

414

Networks of ultrasmall Pd/Cr bilayer nanowires as high performance hydrogen sensors.  

SciTech Connect

The newly developed hydrogen sensor, based on a network of ultrasmall pure palladium nanowires sputter-deposited on a filtration membrane, takes advantage of single palladium nanowires' characteristics of high speed and sensitivity while eliminating their nanofabrication obstacles. However, this new type of sensor, like the single palladium nanowires, cannot distinguish hydrogen concentrations above 3%, thus limiting the potential applications of the sensor. This study reports hydrogen sensors based on a network of ultrasmall Cr-buffered Pd (Pd/Cr) nanowires on a filtration membrane. These sensors not only are able to outperform their pure Pd counterparts in speed and durability but also allow hydrogen detection at concentrations up to 100%. The new networks consist of a thin layer of palladium deposited on top of a Cr adhesion layer 1-3 nm thick. Although the Cr layer is insensitive to hydrogen, it enables the formation of a network of continuous Pd/Cr nanowires with thicknesses of the Pd layer as thin as 2 nm. The improved performance of the Pd/Cr sensors can be attributed to the increased surface area to volume ratio and to the confinement-induced suppression of the phase transition from Pd/H solid solution ({alpha}-phase) to Pd hydride ({beta}-phase).

Zeng, X.-Q.; Wang, Y.-L.; Deng, H.; Latimer, M. L.; Xiao, Z.-L.; Pearson, J.; Xu, T.; Wang, H.-H.; Welp, U.; Crabtree, G. W.; Kwok, W.-K. (Center for Nanoscale Materials); ( MSD); (Northern Illinois Univ.); (Illinois Math and Science Academy); (Univ. of Illinois at Chicago)

2011-01-01

415

Ultrasmall Peptides Self-Assemble into Diverse Nanostructures: Morphological Evaluation and Potential Implications  

PubMed Central

In this study, we perform a morphological evaluation of the diverse nanostructures formed by varying concentration and amino acid sequence of a unique class of ultrasmall self-assembling peptides. We modified these peptides by replacing the aliphatic amino acid at the C-aliphatic terminus with different aromatic amino acids. We tracked the effect of introducing aromatic residues on self-assembly and morphology of resulting nanostructures. Whereas aliphatic peptides formed long, helical fibers that entangle into meshes and entrap >99.9% water, the modified peptides contrastingly formed short, straight fibers with a flat morphology. No helical fibers were observed for the modified peptides. For the aliphatic peptides at low concentrations, different supramolecular assemblies such as hollow nanospheres and membrane blebs were found. Since the ultrasmall peptides are made of simple, aliphatic amino acids, considered to have existed in the primordial soup, study of these supramolecular assemblies could be relevant to understanding chemical evolution leading to the origin of life on Earth. In particular, we propose a variety of potential applications in bioengineering and nanotechnology for the diverse self-assembled nanostructures.

Lakshmanan, Anupama; Hauser, Charlotte A.E.

2011-01-01

416

Photon Trapping, Delaying, and Dynamic-Control using Ultra-small High-Q Photonic Crystal Cavities  

Microsoft Academic Search

By employing ultra-small high-Q photonic crystal nanocavities, we demonstrated 1-ns photon trapping and 1.45-ns pulse delaying. The corresponding light speed is 5,800 km\\/s. We also demonstrated dynamic tuning of the Q within the photon lifetime.

Takasumi Tanabe; Masaya Notomi; Eiichi Kuramochi; Akihiko Shinya; Hideaki Taniyama

2007-01-01

417

Thermal Signatures of Pairing Correlations in Nuclei and Metal Nanoparticles  

NASA Astrophysics Data System (ADS)

Atomic nuclei and nano-scale metallic grains are in the crossover regime of pairing correlations between the bulk limit, where the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity is valid, and the fluctuation-dominated regime, where BCS theory breaks down. In this fluctuation-dominated regime, the pairing gap is comparable to or smaller than the single-particle mean level spacing. We discuss thermal signatures of pairing correlations in nuclei and ultra-small metallic grains (metal nanoparticles) that survive despite the large fluctuations of the pairing field.

Alhassid, Y.

2013-01-01

418

Ultrasmall-angle X-ray scattering analysis of photonic crystal structure  

SciTech Connect

The results of an ultrasmall-angle X-ray scattering study of iron(III) oxide inverse opal thin films are presented. The photonic crystals examined are shown to have fcc structure with amount of stacking faults varying among the samples. The method used in this study makes it possible to easily distinguish between samples with predominantly twinned fcc structure and nearly perfect fcc stacking. The difference observed between samples fabricated under identical conditions is attributed to random layer stacking in the self-assembled colloidal crystals used as templates for fabricating the inverse opals. The present method provides a versatile tool for analyzing photonic crystal structure in studies of inverse opals made of various materials, colloidal crystals, and three-dimensional photonic crystals of other types.

Abramova, V. V.; Sinitskii, A. S., E-mail: sinitsky@inorg.chem.msu.r [Moscow State University (Russian Federation); Grigor'eva, N. A. [St. Petersburg State University (Russian Federation); Grigor'ev, S. V. [Russian Academy of Sciences, Konstantinov St. Petersburg Nuclear Physics Institute (Russian Federation); Belov, D. V.; Petukhov, A. V. [Utrecht University, Debye Institute (Netherlands); Mistonov, A. A. [St. Petersburg State University (Russian Federation); Vasil'eva, A. V. [Russian Academy of Sciences, Konstantinov St. Petersburg Nuclear Physics Institute (Russian Federation); Tret'yakov, Yu. D. [Moscow State University (Russian Federation)

2009-07-15

419

Manipulating superconducting fluctuations by the Little-Parks-de Gennes effect in ultrasmall Al loops.  

PubMed

The destruction of superconducting phase coherence by quantum fluctuations and the control of these fluctuations are a problem of long-standing interest, with recent impetus provided by the relevance of these issues to the pursuit of high temperature superconductivity. Building on the work of Little and Parks, de Gennes predicted more than three decades ago that superconductivity could be destroyed near half-integer-flux quanta in ultrasmall loops, resulting in a destructive regime, and restored by adding a superconducting side branch, which does not affect the flux quantization condition. We report the experimental observation of this Little-Parks-de Gennes effect in Al loops prepared by advanced e-beam lithography. We show that the effect can be used to restore the lost phase coherence by employing side branches. PMID:22927386

Staley, Neal E; Liu, Ying

2012-09-11

420

Quantum Tunneling of Magnetization in Ultrasmall Half-Metallic V3O4 Quantum Dots: Displaying Quantum Superparamagnetic State  

PubMed Central

Quantum tunneling of magnetization (QTMs), stemming from their importance for understanding materials with unconventional properties, has continued to attract widespread theoretical and experimental attention. However, the observation of QTMs in the most promising candidates of molecular magnets and few iron-based compounds is limited to very low temperature. Herein, we first highlight a simple system, ultrasmall half-metallic V3O4 quantum dots, as a promising candidate for the investigation of QTMs at high temperature. The quantum superparamagnetic state (QSP) as a high temperature signature of QTMs is observed at 16?K, which is beyond absolute zero temperature and much higher than that of conventional iron-based compounds due to the stronger spin-orbital coupling of V3+ ions bringing high anisotropy energy. It is undoubtedly that this ultrasmall quantum dots, V3O4, offers not only a promising candidate for theoretical understanding of QTMs but also a very exciting possibility for computers using mesoscopic magnets.

Xiao, Chong; Zhang, Jiajia; Xu, Jie; Tong, Wei; Cao, Boxiao; Li, Kun; Pan, Bicai; Su, Haibin; Xie, Yi

2012-01-01

421

From capacitive to tunnelling conduction through annealing in metal-insulating granular films: the role of ultra-small particles  

NASA Astrophysics Data System (ADS)

In situ transmission electron microscopy (TEM) during annealing of metal-insulating granular thin films reveals significant microstructural changes: nucleation of ultra-small particles and growth of those already existing. Radio frequency impedance spectroscopy shows that by subsequent annealing, tunnelling conductance becomes more important at the expense of the decrease of capacitive contributions, giving place to an almost frequency-independent conduction, although being very far from physical percolation. These results are simulated assuming a random resistor-capacitor network, which represents the competing conduction channels between particles through thermally assisted tunnelling and capacitive conductance. The physical parameters derived from this simple model agree well with the microstructural changes observed by TEM through annealing, and evidence the increase of tunnelling conduction paths mediated by segregated ultra-small glue particles in between bigger ones. Those glue particles grow with further annealing and account for the correlation of the microstructural changes to the ac transport properties.

García del Muro, Montserrat; Konstantinovi?, Zorica; Batlle, Xavier; Labarta, Amílcar

2013-12-01

422

Vibrational spectroscopy of CO adsorbed on supported ultra-small transition metal particles and single metal atoms  

Microsoft Academic Search

Ultra-small rhodium, palladium and iridium particles with minimum average sizes of five atoms have been grown on a thin, well-ordered alumina film at temperatures of 90K and below. Scanning tunneling microscopy (STM) served to characterize the morphology of these deposits. In the infrared spectra of adsorbed carbon monoxide, characteristic features were observed by infrared reflection absorption spectroscopy (IRAS). These originate

Martin Frank; Ralf Kühnemuth; Marcus Bäumer; Hans-Joachim Freund

2000-01-01

423

Array antenna characterization technique based on evanescent reactive-near-field probing in an ultra-small anechoic box  

Microsoft Academic Search

This paper presents a new technique in which small array antenna performance is characterized based on reactive-near-field probing in an ultra-small anechoic box and with a multi-probe. Unlike conventional far- or near-field measurement methods, the radiation patterns in the proposed approach are computed from the currents only at discrete points picked up in the evanescent region of an array antenna's

Qing Han; Keizo Inagaki; Takashi Ohira

2003-01-01

424

MR relaxivity measurement of iron oxide nano-particles for MR lymphography applications.  

PubMed

The aim of this study was to assess the T1, T2 and T2* relaxivity of Ultrasmall Super Paramagnetic Iron Oxide (USPIO) nano-particles in vitro and in vivo in rat models with magnetic resonance imaging at 1.5T. First, relaxation properties of USPIO nano-particles at different doses were measured using related SE and GRE MR imaging protocols. The relation between dose and relaxation were observed which is linear; Higher dose of the nano-particles means higher relaxivity. Based on this relation, an optimum protocol can be proposed for obtaining the best image contrast at each situation. Then detection ability of MRI protocols was studied for USPIO nano-particles with injection of the particles in the rat. The optimum MR protocols were used to observe the signal change of lymph nodes in rat. PMID:18817134

Firouznia, K; Amirmohseni, S; Guiti, M; Amanpour, S; Baitollahi, A; Kharadmand, A Arab; Mohagheghi, M A; Oghabian, M A

2008-02-15

425

One-dimensional magnetopolymeric nanostructures with tailored sizes  

Microsoft Academic Search

Ultra-high aspect ratio nanofibers composed of poly(vinyl alcohol) and CoFe2O4 nanoparticles (PVA\\/CoFe2O4) and moderate aspect ratio nanofibers composed of poly(vinyl chloride) and Fe3O4 nanoparticles (PVC\\/Fe3O4) have been prepared. Magnetopolymeric one-dimensional (1D) nanostructures with any diameter and length can be prepared by template synthesis using anodic aluminum oxide (AAO) followed by the replication methods presented in this work. These replication methods

J. Martín; M. Vázquez; M. Hernández-Vélez; C. Mijangos

2008-01-01

426

Influence of calcination temperature on structural and magnetic properties of nanocomposites formed by Co-ferrite dispersed in sol-gel silica matrix using tetrakis(2-hydroxyethyl) orthosilicate as precursor  

PubMed Central

Effects of calcination temperatures varying from 400 to 1000°C on structural and magnetic properties of nanocomposites formed by Co-ferrite dispersed in the sol-gel silica matrix using tetrakis(2-hydroxyethyl) orthosilicate (THEOS) as water-soluble silica precursor have been investigated. Studies carried out using XRD, FT-IR, TEM, STA (TG-DTG-DTA) and VSM techniques. Results indicated that magnetic properties of samples such as superparamagnetism and ferromagnetism showed great dependence on the variation of the crystallinity and particle size caused by the calcination temperature. The crystallization, saturation magnetization Ms and remenant magnetization Mr increased as the calcination temperature increased. But the variation of coercivity Hc was not in accordance with that of Ms and Mr, indicating that Hc is not determined only by the crystallinity and size of CoFe2O4 nanoparticles. TEM images showed spherical nanoparticles dispersed in the silica network with sizes of 10-30 nm. Results showed that the well-established silica network provided nucleation locations for CoFe2O4 nanoparticles to confinement the coarsening and aggregation of nanoparticles. THEOS as silica matrix network provides an ideal nucleation environment to disperse CoFe2O4 nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS as water-soluble silica precursor over the currently used TEOS and TMOS, the organic solvents are not needed owing to the complete solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of Co-ferrite even more versatile.

2011-01-01

427

Influence of calcination temperature on structural and magnetic properties of nanocomposites formed by Co-ferrite dispersed in sol-gel silica matrix using tetrakis(2-hydroxyethyl) orthosilicate as precursor.  

PubMed

Effects of calcination temperatures varying from 400 to 1000°C on structural and magnetic properties of nanocomposites formed by Co-ferrite dispersed in the sol-gel silica matrix using tetrakis(2-hydroxyethyl) orthosilicate (THEOS) as water-soluble silica precursor have been investigated. Studies carried out using XRD, FT-IR, TEM, STA (TG-DTG-DTA) and VSM techniques. Results indicated that magnetic properties of samples such as superparamagnetism and ferromagnetism showed great dependence on the variation of the crystallinity and particle size caused by the calcination temperature. The crystallization, saturation magnetization Ms and remenant magnetization Mr increased as the calcination temperature increased. But the variation of coercivity Hc was not in accordance with that of Ms and Mr, indicating that Hc is not determined only by the crystallinity and size of CoFe2O4 nanoparticles. TEM images showed spherical nanoparticles dispersed in the silica network with sizes of 10-30 nm. Results showed that the well-established silica network provided nucleation locations for CoFe2O4 nanoparticles to confinement the coarsening and aggregation of nanoparticles. THEOS as silica matrix network provides an ideal nucleation environment to disperse CoFe2O4 nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS as water-soluble silica precursor over the currently used TEOS and TMOS, the organic solvents are not needed owing to the complete solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of Co-ferrite even more versatile. PMID:21486494

Gharagozlou, Mehrnaz

2011-01-01

428

Competing mechanisms of catalytic H2 formation and dissociation on ultrasmall silicate nanocluster dust grains  

NASA Astrophysics Data System (ADS)

Silicate dust grains are thought to be essential in catalysing the formation of H2. Ultrasmall silicates (diameter ?1.5 nm) are fundamental intermediates in silicate dust formation in stellar outflows, and are ubiquitous in the interstellar medium. To investigate the catalytic formation and dissociation of H2 on such nanosilicates, we have performed ab initio quantum chemical calculations of hydrogen interacting with a stable 21 atom nanosilicate cluster having the stoichiometry of forsterite, (MgO)6(SiO2)3. Due to its small size and high percentage of surface atoms, our particle inherently does not exhibit the bulk forsterite crystal structure and possesses a range of chemisorption and physisorption sites, presumably similar to those that larger amorphous silicates would offer. We find a number of exothermic H2 formation routes and pathways for H2 catalytic dissociation on the nanosilicate. In particular, we discover some H2 formation routes that are energetically more favourable than that reported for the forsterite (010) surface. Further, we find a linear correlation between the dissociative chemisorption of two H atoms and the dissociation transition state, suggestive of a general Brønsted-Evans-Polanyi relation for H2 dissociation on bare silicates independent of dust grain size and/or crystallinity.

Kerkeni, Boutheïna; Bromley, Stefan T.

2013-10-01

429

Effects of B-N co-doping into the ultra-small diameter zigzag single-walled carbon nanotubes: A density functional theory study  

NASA Astrophysics Data System (ADS)

The boron(B)-nitrogen(N) co-doping ultra-small diameter (5,0) and (4,0) single-walled carbon nanotubes (SWCNTs) have been investigated by using the first-principles pseudopotential plane wave method. The results show that B-N pairs are easy to dope into ultra-small diameter zigzag nanotubes, which have numbers of differences with other large diameter nanotubes, and the B-N co-doping configurations are the energetically stable structures. Furthermore, by introducing B-N pairs, the (5,0) and (4,0) SWCNTs both transform from metal to semiconductor. These ultra-small diameter nanotubes have potential to be applied in semiconductor integrated circuit of extremely small size.

Shao, Cairu; Xia, Jiang; Zhang, Juan; Shao, Qingyi

2014-05-01

430

Nanodots: Ultrasmall NaGdF4 Nanodots for Efficient MR Angiography and Atherosclerotic Plaque Imaging (Adv. Mater. 23/2014).  

PubMed

As shown by J. Shi, W. Bu, and co-workers on page 3867, ultrasmall NaGdF4 nanodots (ca. 2 nm) with diethylenetriaminepenta-acetic acid (DTPA) conjugation are synthesized for efficient magnetic resonance (MR) angiography. Impressively, the r1 value in magnetic resonance imaging (MRI) reaches up to 8.93 mM(-1) s(-1) . The ultrasmall vessel lumen of a rabbit is lit up remarkably. After 3 h, atherosclerotic plaques can be discriminated clearly. This is quite favorable for the accurate early diagnosis of vascular pathema. PMID:24920419

Xing, Huaiyong; Zhang, Shengjian; Bu, Wenbo; Zheng, Xiangpeng; Wang, Lijun; Xiao, Qingfeng; Ni, Dalong; Zhang, Jiamin; Zhou, Liangping; Peng, Weijun; Zhao, Kuaile; Hua, Yanqing; Shi, Jianlin

2014-06-01

431

Detection and Isolation of Ultrasmall Microorganisms from a 120,000-Year-Old Greenland Glacier Ice Core  

PubMed Central

The abundant microbial population in a 3,043-m-deep Greenland glacier ice core was dominated by ultrasmall cells (<0.1 ?m3) that may represent intrinsically small organisms or starved, minute forms of normal-sized microbes. In order to examine their diversity and obtain isolates, we enriched for ultrasmall psychrophiles by filtering melted ice through filters with different pore sizes, inoculating anaerobic low-nutrient liquid media, and performing successive rounds of filtrations and recultivations at 5°C. Melted ice filtrates, cultures, and isolates were analyzed by scanning electron microscopy, flow cytometry, cultivation, and molecular methods. The results confirmed that numerous cells passed through 0.4-?m, 0.2-?m, and even 0.1-?m filters. Interestingly, filtration increased cell culturability from the melted ice, yielding many isolates related to high-G+C gram-positive bacteria. Comparisons between parallel filtered and nonfiltered cultures showed that (i) the proportion of 0.2-?m-filterable cells was higher in the filtered cultures after short incubations but this difference diminished after several months, (ii) more isolates were obtained from filtered (1,290 isolates) than from nonfiltered (447 isolates) cultures, and (iii) the filtration and liquid medium cultivation increased isolate diversity (Proteobacteria; Cytophaga-Flavobacteria-Bacteroides; high-G+C gram-positive; and spore-forming, low-G+C gram-positive bacteria). Many isolates maintained their small cell sizes after recultivation and were phylogenetically novel or related to other ultramicrobacteria. Our filtration-cultivation procedure, combined with long incubations, enriched for novel ultrasmall-cell isolates, which is useful for studies of their metabolic properties and mechanisms for long-term survival under extreme conditions.

Miteva, Vanya I.; Brenchley, Jean E.

2005-01-01

432

Scanning-probe microscope using an ultrasmall coupled-cavity laser distortion sensor based on mechanical negative-feedback stabilization  

NASA Astrophysics Data System (ADS)

A compact scanning-probe microscope (SPM) using an ultrasmall distortion sensor has been developed for versatile implementation. The sensor is based on a coupled-cavity laser (CCL) consisting of a Fabry-Perot laser diode monolithically integrated with a photodiode, an external mirror on a cantilever, and a small ball lens for laser-beam collimation. With the CCL stabilized by a simple mechanically controlled negative-feedback loop, the temporary distortion of the cantilever's sharp tip in response to the surface structure is measured with a vertical accuracy of 0.8 nm. The SPM was verified by imaging tracking grooves of an optical disk.

Katagiri, Yoshitada; Hara, Shigeji

1998-09-01

433

Thermodynamics and dynamics of physically restricted ultrasmall (d < 70 nm) systems  

SciTech Connect

To understand the thermodynamics and dynamics of physically restricted ultrasmall systems and to discern the relative role of the physical restriction of the sample size from that of the surface-fluid interaction on the structural and thermodynamic properties of the confined fluids, the author undertook the specific heat and molecular vibrational measurements of cyclohexane physically restricted in well-defined porous silica glasses and of geometrically confined cyclohexane films. The specific heat results showed that both solid-to-solid (monoclinic-to-cubic) structural transition and solid melting transition temperatures were depressed. The amount of the temperature depression for the both phase transitions, i.e., solid-to-solid and melting, inversely scaled with the pore radius (R[sub P]). It is argued that the surface heterogeneity, the presence of hydroxyl groups, and the radius of curvature led to the nucleation of crystalline grains of various sizes rather than a single plug. The observation of the [lambda]-shaped specific heat anomaly also suggested the multigrain formation model. With the developed lithographic techniques, the author has measured ultrathin (20 nm) film via a vibrational (FTIR) approach. For the first time, a new metastable phase was manifested when the system was cooled. The results can be explained with the theoretical predictions. Molecular vibrational investigation of cyclohexane physically restricted in filled and partially filled pores of controlled pore glass showed there are indeed two distinct types of cyclohexane in the porous silica, idle and non-idle cyclohexane molecules. In addition, the temperature dependent linewidth of the cyclohexane in the filled silica pores also suggested the existence of a diffuse layer between the idle and the non-idle layers, which exhibited unique temperature dependent characteristics.

Mu, R.

1992-01-01

434

How size evaluation of lymph node is protocol dependent in MRI when using ultrasmall superparamagnetic iron oxide nanoparticles  

NASA Astrophysics Data System (ADS)

In this study, the volume of susceptibility artifact was evaluated in T1 and T2-weighted spin echo (SE) and gradient echo (GRE) images at various parameters using registration and subtraction methods. In order to state an important misinterpretation problem in lymphography, it was demonstrated that a lymph node size may be enlarged approximately 10 times when a T2*-weighted GRE protocol is used. To overcome this problem a technical consideration using multisequence (GRE and SE) paradigm was suggested to ensure both lymph node detection and metastasis identification in lymphatic system. The paradigm was also extended by post-processing manipulation of the SE images using a registration and subtraction approach for detection of lymphatic lesions.

Gharehaghaji, Nahideh; Oghabian, Mohammad Ali; Sarkar, Saeed; Darki, Fahimeh; Beitollahi, Ali

2009-05-01

435

Study on the productivity of silicon nanoparticles by picosecond laser ablation in water: towards gram per hour yield.  

PubMed

An investigation on the productivity of silicon nanoparticles by picosecond laser ablation in water is presented. A systematic experimental study is performed as function of the laser wavelength, fluence and ablation time. In case of ablation at 1064 nm silicon nanoparticles with a mean diameter of 40 nm are produced. Instead, ablation at 355 nm results in nanoparticles with a mean diameter of 9 nm for short ablation time while the mean diameter decreases to 3 nm at longer ablation time. An original model based on the in-situ ablation/photo-fragmentation physical process is developed, and it very well explains the experimental productivity findings. The reported phenomenological model has a general validity, and it can be applied to analyze pulsed laser ablation in liquid in order to optimize the process parameters for higher productivity. Finally, an outlook is given towards gram per hour yield of ultra-small silicon nanoparticles. PMID:24663602

Intartaglia, Romuald; Bagga, Komal; Brandi, Fernando

2014-02-10

436

Magnetic and magnetorheological characterization of a polymer liquid crystal ferronematic  

NASA Astrophysics Data System (ADS)

Cobalt ferrite (CoFe2O4) nanoparticles (~12 nm diameter) were suspended in the polymer liquid crystal hydroxypropyl cellulose (HPC)/m-cresol to obtain a new type of ferronematic. Suspension of these particles in 35% wt HPC in m-cresol did not affect the appearance of the liquid crystalline phase as evidenced by small angle x-ray scattering. Magnetic measurements performed on the 35% wt HPC/m-cresol/CoFe2O4 ferronematic showed the appearance of ferromagnetic behavior and magnetic hysteresis. In addition, rheometry of the samples showed magnetorheological effect upon application of a dc magnetic field, with the ferronematic having the largest response.

Santiago-Quiñones, Darlene I.; Acevedo, Aldo; Rinaldi, Carlos

2009-04-01

437

In Vivo Detection of Macrophages in Human Carotid Atheroma Temporal Dependence of Ultrasmall Superparamagnetic Particles of Iron Oxide-Enhanced MRI  

Microsoft Academic Search

Background—It has been suggested that inflammatory cells within vulnerable plaques may be visualized by superpara- magnetic iron oxide particle- enhanced MRI. The purpose of this study was to determine the time course for macrophage visualization with in vivo contrast- enhanced MRI using an ultrasmall superparamagnetic iron oxide (USPIO) agent in symptomatic human carotid disease. Methods—Eight patients scheduled for carotid endarterectomy

Rikin A. Trivedi; Jean-Marie U-King-Im; Martin J. Graves; Justin J. Cross; Jo Horsley; Martin J. Goddard; Jeremy N. Skepper; George Quartey; Elizabeth Warburton; Ilse Joubert; Liqun Wang; Peter J. Kirkpatrick; John Brown; Jonathan H. Gillard

438

Theory of Voltage Oscillations in Ultra-Small Capacitance Josephson Junctions.  

NASA Astrophysics Data System (ADS)

In ultra-small capacitance Josephson junctions, where the junction charging energy E_{Q } = (2e)^2/2C is comparable to or larger than the junction coupling energy E _{J}, the quantum mechanical nature of the phase of the superconducting order parameter becomes important. Such quantum effects lead to novel behavior in the junction dynamics--supplying a constant current I to such a junction produces voltage or "Bloch" oscillations with a frequency omega _{B} = 2pi I/2e, which are the result of the periodic transfer a Cooper pair of charge 2e across the junction. This thesis examines certain theoretical aspects of these Bloch oscillations. Chapters 1 and 2 contain an introduction to the physics of Josephson junctions and Bloch oscillations. Chapter 3 introduces a phenomenological Hamiltonian which models the dissipation due to unpaired electrons in the junction as a resistive shunt R across the junction. Calculations of the junction dynamics using the phenomenological model are in Chapter 4. Using a path integral approach, the translational properties of the phase are treated using a winding number description, and it is shown that for ohmic dissipation the phase may be treated as an extended coordinate. It is then shown that the Bloch oscillations persist in the presence of dissipation, provided that the dissipation satisfies R > 2R_{Q}, where R _{Q} = h/4e^2 = 6.4kOmega. The behavior in the presence of an additional applied AC current of frequency omega is also studied, and it is argued that the DC voltage across the junction should pass through zero whenever the applied DC current is an integer multiple of I = 2eomega/2 pi. Chapter 5 considers the effects of interband or "Zener" transitions by introducing a simple model to study how dissipation affects the rate of interband transitions. Chapter 6 is a synopsis of some experiments which may indirectly provide evidence of Bloch oscillations. Finally, Chapter 7 concludes with some possible extensions of this work to other problems, and lists some open questions which require further theoretical consideration.

Dorsey, Alan Thomas

1987-09-01

439

Targeting of peptide conjugated magnetic nanoparticles to urokinase plasminogen activator receptor (uPAR) expressing cells  

NASA Astrophysics Data System (ADS)

Ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles are currently being used as a magnetic resonance imaging (MRI) contrast agent in vivo, mainly by their passive accumulation in tissues of interest. However, a higher specificity can ideally be achieved when the nanoparticles are targeted towards cell specific receptors and this may also facilitate specific drug delivery by an enhanced target-mediated endocytosis. We report efficient peptide-mediated targeting of magnetic nanoparticles to cells expressing the urokinase plasminogen activator receptor (uPAR), a surface biomarker for poor patient prognosis shared by several cancers including breast, colorectal, and gastric cancers. Conjugation of a uPAR specific targeting peptide onto polyethylene glycol (PEG) coated USPIO nanoparticles by click chemistry resulted in a five times higher uptake in vitro in a uPAR positive cell line compared to nanoparticles carrying a non-binding control peptide. In accordance with specific receptor-mediated recognition, a low uptake was observed in the presence of an excess of ATF, a natural ligand for uPAR. The uPAR specific magnetic nanoparticles can potentially provide a useful supplement for tumor patient management when combined with MRI and drug delivery.Ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles are currently being used as a magnetic resonance imaging (MRI) contrast agent in vivo, mainly by their passive accumulation in tissues of interest. However, a higher specificity can ideally be achieved when the nanoparticles are targeted towards cell specific receptors and this may also facilitate specific drug delivery by an enhanced target-mediated endocytosis. We report efficient peptide-mediated targeting of magnetic nanoparticles to cells expressing the urokinase plasminogen activator receptor (uPAR), a surface biomarker for poor patient prognosis shared by several cancers including breast, colorectal, and gastric cancers. Conjugation of a uPAR specific targeting peptide onto polyethylene glycol (PEG) coated USPIO nanoparticles by click chemistry resulted in a five times higher uptake in vitro in a uPAR positive cell line compared to nanoparticles carrying a non-binding control peptide. In accordance with specific receptor-mediated recognition, a low uptake was observed in the presence of an excess of ATF, a natural ligand for uPAR. The uPAR specific magnetic nanoparticles can potentially provide a useful supplement for tumor patient management when combined with MRI and drug delivery. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr32922d

Hansen, Line; Unmack Larsen, Esben Kjær; Nielsen, Erik Holm; Iversen, Frank; Liu, Zhuo; Thomsen, Karen; Pedersen, Michael; Skrydstrup, Troels; Nielsen, Niels Chr.; Ploug, Michael; Kjems, Jørgen

2013-08-01

440

Electrical detection of surface plasmon resonance phenomena by a photoelectronic device integrated with gold nanoparticle plasmon antenna  

NASA Astrophysics Data System (ADS)

We have proposed a concept of a photoelectronic hybrid device utilizing gold nanoparticles (GNPs), which are supposed to function not only as the plasmon antenna but also as the sensing part. The photocurrent in the fabricated device, consisting of a transparent Nb-doped TiO2 channel and Au electrodes, was enhanced more than eight times at a specific wavelength with GNP arrays located between the electrodes, indicating that surface plasmon resonance was electrically detected with the hybrid device. This result will open new doors for ultra-small biosensor chips integrated with multi-functional solid-state devices.

Hashimoto, Tatsuya; Fukunishi, Yurie; Zheng, Bin; Uraoka, Yukiharu; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

2013-02-01

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