Room Temperature Magnetization Curves Research Articles

Getting saturation magnetization of superparamagnetic nanoparticles more accurately from room-temperature magnetization curve

Getting saturation magnetization of superparamagnetic nanoparticles more accurately from room-temperature magnetization curve

Morphologic, structural, and magnetic characterization of cobalt ferrite nanoparticles synthesized at different temperatures

In this study we report on the synthesis and characterization of cobalt ferrite (CoFe2O4) nanoparticles (NPs), synthesized by chemical co-precipitation in alkaline medium. Two samples were synthesized at two different temperatures, 35 and 90 oC. Both samples were characterized by Transmission Electron Microscopy (TEM), x-ray diffraction (XRD), and room-temperature (RT) magnetization. Two samples showed superparamagnetic behavior (SPM) at RT. TEM reveals morphological mean diameter increasing 5.8 nm to 10.4 nm, with the increase of the co-precipitation temperature. XRD confirm the inverse cubic spinel structure. The RT magnetization curves were analyzed by the first-order Langevin function averaged out by a lognormal distribution function of magnetic moments. This analysis showed saturation magnetization and magnetic moment increases from 60.2 to 74.8 emu/g and from 3.9 x 103 to 8.2 x 103 mB, respectively.

Bimodal Approach for the Use of Co Doped Magnetite as MRI Contrast Agent and Potential Antitumor

Cobalt doped magnetite CoSUP2+/SUP SUB0.1/SUBFeSUP2+/SUP SUB0.9/SUBFeSUP3+/SUP ₂O₄ nanocrystals were synthesized chemically using simple one step coprecipitation in the absence and presence of the magnetic field. The nanocrystals were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetization studies by vibrational spectroscopy magnetometer (VSM). The signal intensity of the prepared nanoparticles was measured by magnetic resonance imaging (MRI). The cytotoxicity of the two samples versus W138 normal lung cells and AS49 lung cancer cells was investigated by MTT assay, in vitro. The TEM images showed non-spherical and aggregated nanoparticles, heterogeneously dispersed with 100 nm average size. The XRD and selected area electron diffraction of the two samples revealed good crystallinity for both samples. The room temperature magnetization curves demonstrate the general ferrimagnetic trend with a clear difference in the coercivity and the remanence keeping the saturation magnetization nearly stable. The measured MR signal intensity was well-matched with the result of the M-H loops where the sample prepared in the absence of the field was a promising T2 contrast agent. Both samples have low cytotoxicity compared to Doxorubicin.

Sol-gel derived cobalt containing Ni–Zn ferrite nanoparticles: Dielectric relaxation and enhanced magnetic property study

A systematic study of transitional metal ion doped nickel-zinc ferrite (NZF) nanoparticles with its magnetic properties and conductivity relaxation mechanism are the objectives of this research. We have prepared cobalt doped NZF nanoparticles (NZCo) via a facile chemical route. X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) analyses suggest the formation of single phase nearly spherical nanoparticles around 60 nm in size. UV–Vis study reveals the redshift of the optical band gap for doped samples. Estimation of particle size using the effective mass model agrees well with TEM/XRD results. The electrical modulus spectra have been analyzed using Harvilliak-Negami model function. Migration energy has been found to be the minimum for 10 mol % doped sample. Frequency-dependent modulus spectra have been converted to time domain data and the relaxation process shows Kohlrausch–Williams–Watts (KWW) type behavior. Carrier motion inside the lattice has been found to be strongly correlated. Room temperature magnetization curve shows that very weak AFM/PM contribution and strong FM interaction inside the system as well as non-collinear spin arrangements between interstitial sites. Law of Approach (L.A.) analysis of the AFM/PM part subtracted hysteresis curve delineates the enhanced magnetic properties such as saturation magnetization, anisotropy constant and coercivity. Multi-functional materials of such kind with optimum behavior at specific doping percentages can be fruitful for electronic industries.

Magnetic Property of Thin Film of Co-Tb Alloys Deposited on the Barrier Layer of Ordered Anodic Alumina Templates

Recently, search for novel materials for bit patterned media (BPM) has been very intense due to their potential application in ultra-high-density hard disk drive. In a quest of finding new materials for BPM, we have taken up to study ordered array of nanostructured Co-Tb alloy. Thin films of Ta (1 nm)/Co1−xTbx (24 nm)/Ta (4 nm) (x = 0.10, 0.15, 0.18 and 0.33) alloys were deposited on the barrier layer of auto-assembled anodic alumina template using dc magnetron sputtering to form a nanostructured array, the so-called nanobump. Similar array of compounds on a flat Si substrate was also deposited for comparison (reference sample). The measurement of room temperature magnetization (M) versus field (H) curve indicates that the coercivity and the squareness [Mr/Ms] of nanobumps as well as reference samples were found to increase with increase of Tb content. However, the values of HC and Mr/MS for nanobumps were found to be higher than those of reference samples. The measurements of in-plane and out-plane M-H curves reveal that Co1−xTbx (x = 0.15, 0.20 and 0.33) nanobumps exhibit magnetic isotropy behaviour. The measurements of temperature variation of magnetization demonstrate that these films exhibit ferrimagnetism with a compensation temperature much above the room temperature.

Magnetic and transport properties in 57Fe/Co/Al multilayers

In this work,the transport properties of as deposited Fe/Co/Al multilayer’s system and post annealing effect on magnetic propertieshave beenstudied.Average chemical composition of the as deposited multilayer structure (MLS) has been verified by energy dispersive X-ray spectroscopy (EDX). Room temperature VSM measurement performed at different orientations to see the anisotropic behavior of both samples. The quantitative analysis of atomic percentages Fe, Co and Al elements conclude that both as-deposited samples were stoichiometric and the average composition of as-deposited 20 TLs and 40 TLs to be close to XRR fitted thickness which was the intended thicknesses. Room temperature magnetization curve for 773K annealed sample suggest that uniaxial anisotropy present in both samples upto 773K. Very small anisotropic magneto resistance is observed in both samples. On annealing multilayer structure destroyed that leads to increase in coercivity and decrease in saturation magnetization. The obtained Curie temperature is more than 800K for both samples

Synthesis, characterization and influence of fuel to oxidizer ratio on the properties of spinel ferrite (MFe2O4, M = Co and Ni) prepared by solution combustion method

Abstract The effect of fuel to oxidizer ratio on the crystallite size and the physical properties of cobalt and nickel ferrite samples synthesized by solution combustion method using glycine as fuel are reported. Powder X-ray diffraction studies indicate that pure nanocrystalline ferrite phase is formed when the fuel to oxidizer ratio is less than one. The crystallite size can also be controlled by controlling the fuel to oxidizer ratio. The Mossbauer and Raman studies on the sample prepared at F/O 0.6 indicate that high quality samples having inverse or mixed spinel structure can be prepared by solution combustion method. Room temperature magnetization curves of the samples prepared under fuel lean condition have a systematic trend of coercivity with increasing crystallite size.

Structural, optical and magnetic modulation in Mn and Mg co-doped BiFeO3 films grown on Si substrates

Slightly Mn and Mg co-doped BiFeO3 films (BiFeO3, BiFe0.95Mg0.01Mn0.04O3, BiFe0.94Mg0.02Mn0.04O3 and BiFe0.93Mg0.03Mn0.04O3, xBFMMO, x=0, 0.01, 0.02 and 0.03) have been grown on Si (100) substrates by sol-gel technique. Rhombohedral lattice structure and phase transition is confirmed by X-ray diffraction and Raman spectroscopy. The improved surface morphology and decreased grain size of films can be observed in SEM micrographs due to the influence of Mn and Mg co-doping. Blue emissions of xBFMMO films can be found in Photoluminescence spectra, meanwhile the nonlinear shift of emission peaks imply the variation of bandgap. Room-temperature magnetization versus magnetic field (M-H) curves exhibit enhanced saturation magnetization compared with parental BiFeO3, which can attribute to destroyed spin cycloid and released locked magnetization. These properties offer a great potential on the multiferroic information storage application.

Magneto-optical investigation and hyperfine interactions of copper substituted Fe3O4 nanoparticles

Copper substituted Fe3O4 nanoparticles (NPs) (CuxFe1−xFe2O4 (0.0≤x≤1.0)) were synthesized by polyol method and the effect of Cu2+ substitution on structural, magnetic and optical properties of Fe3O4 was investigated. X-ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), UV–Visible spectroscopy and Vibrating sample magnetometer (VSM) were used to study the physical properties of the products. The room temperature (RT) magnetization (σ–H) curves revealed the superparamagnetic nature of the products. The extrapolated specific saturation magnetization (σs) decreases from 42.69emu/g to 14.14emu/g with increasing Cu content (x). The particle size dependent Langevin fit studies were applied to determine the magnetic particle dimensions (Dmag). The average magnetic particle diameter is about 9.89nm. The observed magnetic moments of NPs are in range of (0.61–1.77) µB and rather less than 4µB of bulk Fe3O4 and 1µB of bulk CuFe2O4. Magnetic anisotropy was assigned as uniaxial and calculated effective anisotropy constants (Keff) are between 10.89×104Erg/g and 26.95×104Erg/g. The average value of magnetically inactive layer for CuxFe1−xFe2O4 NPs was calculated as 1.23nm. The percent diffuse reflectance spectroscopy (DR%) and Kubelka–Munk theory were applied to determine the energy band gap (Eg) of NPs. The extrapolated optical Eg values from Tauc plots are between minimum 1.98eV to 2.31eV. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer splitting, quadrupole splitting and hyperfine magnetic field values on Cu+2 ion substitution have been determined. Although, the Mössbauer spectra for the sample x=0.2 and 0.8 are composed of paramagnetic doublets, ferromagnetic sextets were also formed for other products.

Unraveling structural and magnetic information during growth of nanocrystalline SrFe12O19

Hydrothermal synthesis of SrFe12O19is followedin situusing PXRD, and successfully reproducedex situusing a custom-designed batch-type reactor.

Facile approach to suppress γ-Fe2O3 to α-Fe2O3 phase transition beyond 600 °C in Fe3O4 nanoparticles

Magnetic iron oxide nanoparticles on a zeolite template have been synthesized using wet chemical approach. The average particle size initially decreases from 8.5 to 6 nm (increasing zeolite concentration from 0 to 75 mg) but increases to 11 nm for higher zeolite concentration (100 mg). Room temperature magnetization curves show an initial decrease in saturation magnetization from 62 to 42 emu per gram due to decrease in particle size as well as increase in contribution from nonmagnetic zeolite template. Further increase in zeolite concentration to 100 mg results in a significant increase in saturation magnetization from 42 to 51 emu per gram. Calorimetric studies show a continuous enhancement in γ-Fe2O3 to α-Fe2O3 phase transition temperature from 590 to 715 °C by increasing the zeolite concentration from 0 to 75 gm. The exothermic peak corresponding to the γ-Fe2O3 to α-Fe2O3 phase transition has been completely suppressed for nanoparticles prepared in presence of 100 mg of zeolite. Mössbauer spectra of as-synthesized nanoparticles show an increase of superparamagnetic components from 7 to 36% corresponding to increase in zeolite concentration from 0 to 100 mg. Mössbauer spectra of pure Fe3O4 nanoparticles annealed at 500 °C shows formation of pure α-Fe2O3 phase and Mössbauer spectra of particles prepared in presence of 25 mg shows only 18% of α-Fe2O3 phase after annealing at 550 °C. Further increase in zeolite concentration to 50 and 75 mg (annealed at 550 °C) leads to pure γ-Fe2O3. Annealing of Fe3O4 nanoparticles prepared in the presence of 100 mg of zeolite at 650 °C shows formation of only 8% α-Fe2O3 phase. Our results show an easy and effective method to enhance the thermal stability of magnetic iron oxide nanoparticles making it suitable for high temperature applications.

Thickness Dependent Structure and Magnetic Properties in <sup>57</sup>Fe/Ti/Co Multilayers

Structural and magnetic properties of57Fe/Ti/Co multilayers (MLs), prepared by Ion beam sputtering on Si substrate have been studied as a function of trilayers (TLs) thickness and modulation periods. X-ray reflectivity (XRR) shows the successful growth of high-quality layered structures along with up to 3rdorder Bragg peaks with distinct Kiessig oscillation. X-ray diffraction (XRD) and Mössbauer studies evidence the formation of different phases mainly at the interfaces. Soft magnetic properties with high saturation values (~800emu/cm3) and high anisotropy field (~20kOe) are observed in the room temperature magnetization curve. The in plane value of coercivities are 18Oe and 60Oe for the 12 and 24 TLs respectively while in the out-of plane direction it increases to nearly 8 and 12 times respectively. The 12 TLs sample shows the presence of two fold anisotropy whereas the 24 TLs sample shows an isotropic behaviour. Low temperature DC magnetization studies evidence the presence of weak antiferromagnetic coupling while the Kelly Henkel plots for these samples show that the dominant exchange interactions between the grains are ferromagnetic.

Nano-particle magnetism with a dispersion of particle sizes

In this paper, different definitions of the distribution functions that can be used to account for the magnetization of dispersed nano-particle systems are discussed. The volume and number weighted distributions are both found to be equally valid for the representation of distribution functions in nanoparticle magnetic systems. This study also shows that the room temperature magnetization curve M(H) of a superparamagnetic system is sensitive to the particle size distribution parameters and, that for a non-interacting system, these parameters can be unambiguously determined. Furthermore, the temperature variation of the initial susceptibility χ(T) for a dispersion of particle sizes is also examined using both the exact and the critical approaches. The critical approach is found to be a reasonable and valid approximation, since the discrepancy in the calculated χ(T) curves between the exact and the approximated form of the function exp(−tm/τ) was found to be very small. For a dispersion of anisotropy energies, both approaches adequately describe the unblocking process of the particle magnetic moments within the system when the temperature is increased. In this study, the distribution of the critical transition temperatures that can be obtained from the temperature variation of the initial susceptibility is also examined. For different definitions of the distribution functions, the retrieved distributions from the experimental data are bound to be different. Furthermore, the calculated temperature variation of the initial susceptibility is found to be sensitive to the constant value of the frequency factor f0 used in the calculations. The discrepancy in calculating the χ(T) curve using an improper value of f0 is larger than that discrepancy arising from the step-like approximation of exp(−tm/τ). Thus, the f0 value has to be calculated using the physical parameters of the system and not just taken as a constant value between 109 and 1011 Hz.

Distributions of dipolar interaction fields in nano-granular magnetic systems

In this work, the effect of a distribution of dipolar interaction fields on the magnetization of superparamagnetic nano-granular system is examined using a general Monte-Carlo model. The model consists of a cubic cell in which the particles’ locations and directions of easy axes are generated randomly. The particle sizes are generated according to a lognormal distribution with a median diameter Dm = 6 nm. The room temperature magnetization curves at different particle packing densities are simulated. The calculations show that the magnetization curves are always depressed with increasing packing density. Usually, this effect would be taken as denoting predominantly demagnetizing interaction effects (i.e., negative dipolar fields). We have investigated the distribution of dipolar interaction fields along the x, y, and z directions and found them to be symmetric and Gaussian in form with a mean very close to zero. The net effect of the transverse field components is to reduce the magnetization. The same is true for the component in the direction of applied field, Hiz, despite the fact that positive and negative dipolar fields are found to be equally probable. According to this picture, it is not correct to say that dipolar interaction fields are negative. Thus, we ascribe the reduction in magnetization to the non-linear response of the magnetization to the applied field, which weighs the negative interaction fields more strongly than the positive fields. It is concluded that the non-linear response of the magnetization is equally important as the sign of the interaction field.

Ferromagnetism of polythiophene-capped Au nanoparticles

The magnetic and electrical transport properties of regioregular poly(3-hexylthiophene)-capped Au nanoparticles (NPs) doped with iodine have been investigated to clarify the effectiveness of conductive polymer capping on the induction of ferromagnetism in Au. The room-temperature magnetization curve of the undoped polythiophene-capped Au NPs exhibits a clear hysteresis behavior with a coercive force of 160 Oe. The spontaneous magnetization normalized by the mass of Au is 2.0 × 10−2 emu/g. The spontaneous magnetization was found virtually unaffected by iodine doping, whereas the electrical conductivity is enhanced dramatically to ∼10 S/cm. Our results show that polythiophene capping could lead to spontaneous magnetic polarization in Au NPs, and the conductivity of the polymer capping does not affect the ferromagnetism of the Au nanoparticles, opening a possibility for further investigation into the magnetotransport behavior of ferromagnetic Au NPs.

Hydrothermal Synthesis and Characterization of PEG-Mn3O4 Nanocomposite

Abstract Here, we report on the synthesis of PEG-Mn3O4 nanocomposite (NP’s) via a hydrothermal route by using Mn(acac)2, ethanol, NH3 and PEG-400. The crystalline phase was identified as Mn3O4. The crystallite size of the PEG-Mn3O4 nanocomposite was calculated as 12±5 nm from X-ray line profile fitting and the average particle size from TEM was obtained as 200 nm. This reveals polycrystalline character of Mn3O4 NP’s. The interaction between PEG-400 and the Mn3O4 NP’s was investigated by FTIR. Temperature independent AC conductivity of PEG-Mn3O4 nanocomposite beyond 20 kHz provides a strong evidence of ionic conduction through the structure. The conductivity and permittivity measurements strongly depend on the secondary thermal transition of nanocomposite beyond 100°C. Above that temperature, Mn3O4 particles may interact with each other yielding a percolated path that will facilitate the conduction. On the other hand, the relatively lower activation energy (Ea=0.172 eV) for relaxation process suggests that polymer segmental motions of PEG and electrons hopping between Mn2+ and Mn3+ may be coupled in the sample below 100°C. Room temperature magnetization curve of the sample does not reach to a saturation, which indicates the superparamagnetic character of the particles. As the temperature increases, the frequency at which (ε″) reaches a maximum shifted towards higher frequencies. The maximum peak was observed at 1.4 kHz for 20°C while the maximum was detected at 23.2 kHz for 90°C.

Preparation and characterization of polyaniline (PANI)–Mn 3O 4 nanocomposite

Polyaniline (PANI)–Mn 3O 4 nanocomposite was synthesized by a combination of sonochemical synthesis of Mn 3O 4 NP's and in-situ polymerization of aniline. Structural characteristics were evaluated by XRD, FT-IR, TGA, VSM, TEM and SEM analysis, and conduction characteristics were evaluated by total conductivity measurements in the temperature range of 20–100 °C and frequency range of 0.1 Hz–1 MHz. Our findings show that PANI is successfully coated on nanoparticles surface and overall conductivity of nanocomposite is approximately 50–1000 times higher than that of uncapped Mn 3O 4 or PANI base with increase in temperature. Morphology of the synthesized powder was observed to be thin nanosheets with a thickness of 2–3 nm based on SEM analysis. Room temperature magnetization curves for nanocomposite show no hysteresis, indicating the super-paramagnetic character of the sample in the region of measured field strength. σ AC increased after polyaniline coating.

Size controlled and morphology tuned fabrication of Fe 3O 4 nanocrystals and their magnetic properties

Size controlled and morphology tuned fabrication of Fe 3O 4 nanocrystals were achieved by a simple hydrothermal method using (NH 4) 2Fe(SO 4) 2·6H 2O, hexamethylenetetramine, and sodium sulfate as original reaction materials. Fe 3O 4 particles with controlled size ranging from 160 nm to 2 μm were obtained by adding an appropriate amount of NH 4Ac to the reaction system. Fe 3O 4 quadrangular nanoplates with side length of about 500 nm were fabricated by adding optimum amount of urea. Box-like Fe 3O 4 nanocrystals were synthesized by adjusting the mol ratio between (NH 4) 2Fe(SO 4) 2·6H 2O and hexamethylenetetramine. The as-synthesized products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Room-temperature magnetization curves that measured by vibrating sample magnetometer show morphology and size dependent magnetism.

Effect of Organic Capping on the Magnetic Properties of Au Nanoparticles

The magnetic and optical properties of regioregular poly(3-hexylthiophene)-capped Au nanoparticles (NPs) have been investigated in order to clarify the effectiveness of polythiophene capping on the induction of ferromagnetism in Au. The room-temperature magnetization curve of the polythiophene-capped Au NPs exhibits a clear hysteresis behavior with a spontaneous magnetization of 8.5 x 10-3 emu/g. The average magnetic moment of the surface Au atoms is estimated to be 2.6 x 10-3 B. The ultraviolet-visible spectrum shows a clear sign of the surface plasmon absorbance of metallic Au which reflects the week character of the chemical bond between the Au and S atoms on capping surface. Our results show clearly that Au NPs capped with polythiophene can be ferromagnetic.

Magnetization behavior of ordered and high density Co nanowire arrays with varying aspect ratio

Densely packed and ordered cobalt nanowire (NW) arrays with aspect ratios (wire length/diameter) varying between 5 and 250 have been fabricated via electrodeposition into alumina templates. The wire length and diameter were controlled by monitoring the total deposited charge or by adjusting the template pore size, respectively. It is observed from room temperature magnetization curves that the magnetic properties of a given array is largely dependent on the aspect ratio and packing factor. It is shown that behavior of magnetic NW arrays are governed to a large extent by the magnetostatic interactions between NWs and that magnitude of the interaction field increases not only with NW diameter (or packing factor) but also with NW length.