22 research outputs found
Template-Assisted Synthesis and Characterization of Passivated Nickel Nanoparticles
Potential applications of nickel nanoparticles demand the synthesis of self-protected nickel nanoparticles by different synthesis techniques. A novel and simple technique for the synthesis of self-protected nickel nanoparticles is realized by the inter-matrix synthesis of nickel nanoparticles by cation exchange reduction in two types of resins. Two different polymer templates namely strongly acidic cation exchange resins and weakly acidic cation exchange resins provided with cation exchange sites which can anchor metal cations by the ion exchange process are used. The nickel ions which are held at the cation exchange sites by ion fixation can be subsequently reduced to metal nanoparticles by using sodium borohydride as the reducing agent. The composites are cycled repeating the loading reduction cycle involved in the synthesis procedure. X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron microscopy, Energy Dispersive Spectrum, and Inductively Coupled Plasma Analysis are effectively utilized to investigate the different structural characteristics of the nanocomposites. The hysteresis loop parameters namely saturation magnetization and coercivity are measured using Vibrating Sample Magnetometer. The thermomagnetization study is also conducted to evaluate the Curie temperature values of the composites. The effect of cycling on the structural and magnetic characteristics of the two composites are dealt in detail. A comparison between the different characteristics of the two nanocomposites is also provided
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
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
Aqueous Solution Preparation, Structure, and Magnetic Properties of Nano-Granular ZnxFe3−xO4 Ferrite Films
This paper reports a simple and novel process for preparing nano-granular ZnxFe3−xO4 ferrite films (0 ≤ x ≤ 0.99) on Ag-coated glass substrates in DMAB-Fe(NO3)3-Zn(NO3)2 solutions. The deposition process may be applied in preparing other cations-doped spinel ferrite films. The Zn content x in the ZnxFe3−xO4 films depends linearly on the Zn2+ ion concentration ranging from 0.0 to 1.0 mM in the aqueous solutions. With x increasing from 0 to 0.99, the lattice constant increases from 0.8399 to 0.8464 nm; and the microstructure of the films changes from the non-uniform nano-granules to the fine and uniform nano-granules of 50–60 nm in size. The saturation magnetization of the films first increases from 75 emu/g to the maximum 108 emu/g with x increasing from 0 to 0.33 and then decreases monotonously to 5 emu/g with x increasing from 0.33 to 0.99. Meanwhile, the coercive force decreases monotonously from 116 to 13 Oe
On the Synthesis and Multifunctional Properties of some Nanocrystalline Spinel Ferrites and Magnetic Nanocomposites
This thesis lays importance in the preparation and characterization of a
few selected representatives of the ferrite family in the nanoregime. The candidates being manganese zinc ferrite and cobalt ferrite prepared by coprecipitation
and sol-gel combustion techniques respectively. The thesis not only
stresses importance on the preparation techniques and optimization of the reaction
conditions, but emphasizes in investigating the various properties namely
structural, magnetic and electrical. Passivated nickel nanocomposites are
synthesized using polystyrene beads and adopting a novel route of ion exchange
reduction. The structural and magnetic properties of these magnetic
nanocomposites are correlated. The magnetocaloric effect (MCE) exhibited by
these materials are also investigated with a view to finding out the potential of
these materials as magnetic refrigerants. Calculations using numerical methods
are employed to evaluate the entropy change on selected samples.Department of Physics,
Cochin University of Science & Technolog
Evidence for polaron conduction in nanostructured manganese ferrite
Nanoparticles of manganese ferrite were prepared by the chemical co-precipitation technique.
The dielectric parameters, namely, real and imaginary dielectric permittivity (ε and ε ),
ac conductivity (σac) and dielectric loss tangent (tan δ), were measured in the frequency range
of 100 kHz–8MHz at different temperatures. The variations of dielectric dispersion (ε ) and
dielectric absorption (ε ) with frequency and temperature were also investigated. The variation
of dielectric permittivity with frequency and temperature followed the Maxwell–Wagner
model based on interfacial polarization in consonance with Koops phenomenological theory.
The dielectric loss tangent and hence ε exhibited a relaxation at certain frequencies and at
relatively higher temperatures. The dispersion of dielectric permittivity and broadening of the
dielectric absorption suggest the possibility of a distribution of relaxation time and the
existence of multiple equilibrium states in manganese ferrite. The activation energy estimated
from the dielectric relaxation is found to be high and is characteristic of polaron conduction in
the nanosized manganese ferrite. The ac conductivity followed a power law dependence
σac = Bωn typical of charge transport assisted by a hopping or tunnelling process. The
observed minimum in the temperature dependence of the frequency exponent n strongly
suggests that tunnelling of the large polarons is the dominant transport processCochin University of Science and TechnologyJ. Phys. D: Appl. Phys. 41 (2008) 185005 (9pp
Inverse magnetocaloric effect in sol–gel derived nanosized cobalt ferrite
The magnetocaloric properties of cobalt ferrite
nanoparticles were investigated to evaluate the potential of
these materials as magnetic refrigerants. Nanosized cobalt
ferrites were synthesized by the method of sol–gel combustion.
The nanoparticles were found to be spherical with
an average crystallite size of 14 nm. The magnetic entropy
change ( Sm) calculated indirectly from magnetization
isotherms in the temperature region 170–320 K was
found to be negative, signifying an inverse magnetocaloric
effect in the nanoparticles. The magnitudes of the Sm values
were found to be larger when compared to the reported
values in the literature for the corresponding ferrite materials
in the nanoregime.Cochin University of Science and
TechnologyAppl Phys A (2010) 99: 497–50
On the dielectric dispersion and absorption in nanosized manganese zinc mixed ferrites
The temperature and frequency dependence of dielectric permittivity and dielectric loss of nanosized Mn1-xZnxFe2O4 (for x = 0, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The impact of zinc substitution on the dielectric properties of the mixed ferrite is elucidated. Strong dielectric dispersion and broad relaxation were exhibited by Mn1-xZnxFe2O4. The variation of dielectric relaxation time with temperature suggests the involvement of multiple relaxation processes. Cole-Cole plots were employed as an effective tool for studying the observed phenomenon. The activation energies were calculated from relaxation peaks and Cole-Cole plots and found to be consistent with each other and indicative of a polaron conduction
Mechanism of ac conduction in nanostructured manganese zinc mixed ferrites
Mn1−xZnxFe2O4 nanoparticles (x = 0 to 1) were synthesized by the wet chemical
co-precipitation technique. X-ray diffraction and transmission electron microscopy and high
resolution transmission electron microscopy were effectively utilized to investigate the
different structural parameters. The ac conductivity of nanosized Mn1−xZnxFe2O4 were
investigated as a function of frequency, temperature and composition. The frequency
dependence of ac conductivity is analysed by the power law σ(ω)ac = Bωn which is typical
for charge transport by hopping or tunnelling processes. The temperature dependence of
frequency exponent n was investigated to understand the conduction mechanism in different
compositions. The conduction mechanisms are mainly based on polaron hopping conductionCochin University of Science and TechnologyJ. Phys. D: Appl. Phys. 42 (2009) 165005 (8pp
Impact of zinc substitution on the structural and magnetic properties of chemically derived nanosized manganese zinc mixed ferrites
Mn1-xZnxFe2O4 nanoparticles (x=0-1) were synthesized by wet chemical co-precipitation techniques. X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy were effectively utilized to investigate the different structural parameters. The elemental analysis was conducted using energy-dispersive spectrum and inductively coupled plasma analysis. The magnetic properties such as magnetization and coercivity were measured using vibrating sample magnetometer. The observed magnetization values of the nanoparticles were found to be lower compared to the bulk counterpart. The magnetization showed a gradual decrease with zinc substitution except for a small increase from x=0.2 to 0.3. The Curie temperature was found to be enhanced in the case of ferrites in the nanoregime. The variation in lattice constant, reduced magnetization values, variation of magnetization with zinc substitution, the presence of a net magnetic moment for the zinc ferrite and the enhancement in Curie temperature in Mn1-xZnxFe2O4 all provide evidence to the existence of a metastable cation distribution together with possible surface effects at the nanoregime