Stable Magnetic Properties Research Articles

Tailored magnetic nanoparticles for optimizing magnetic fluid hyperthermia

Magnetic Fluid Hyperthermia (MFH) is a promising approach towards adjuvant cancer therapy that is based on the localized heating of tumors using the relaxation losses of iron oxide magnetic nanoparticles (MNPs) in alternating magnetic fields (AMF). In this study, we demonstrate optimization of MFH by tailoring MNP size to an applied AMF frequency. Unlike conventional aqueous synthesis routes, we use organic synthesis routes that offer precise control over MNP size (diameter ∼10 to 25 nm), size distribution, and phase purity. Furthermore, the particles are successfully transferred to the aqueous phase using a biocompatible amphiphilic polymer, and demonstrate long-term shelf life. A rigorous characterization protocol ensures that the water-stable MNPs meet all the critical requirements: (1) uniform shape and monodispersity, (2) phase purity, (3) stable magnetic properties approaching that of the bulk, (4) colloidal stability, (5) substantial shelf life, and (6) pose no significant in vitro toxicity. Using a dedicated hyperthermia system, we then identified that 16 nm monodisperse MNPs (σ-0.175) respond optimally to our chosen AMF conditions (f = 373 kHz, H₀ = 14 kA/m); however, with a broader size distribution (σ-0.284) the Specific Loss Power (SLP) decreases by 30%. Finally, we show that these tailored MNPs demonstrate maximum hyperthermia efficiency by reducing viability of Jurkat cells in vitro, suggesting our optimization translates truthfully to cell populations. In summary, we present a way to intrinsically optimize MFH by tailoring the MNPs to any applied AMF, a required precursor to optimize dose and time of treatment.

Stability and Magnetocaloric Properties of Sintered La(Fe, Mn, Si)$_{13}$H$_{z}$ Alloys

Long-term aging treatments of partially hydrogenated ternary La-Fe-Si alloys show that these materials do not have stable magnetic properties. If partially hydrogenated LaFe13- xSixHz is held at its Curie temperature for several days it decomposes into a fraction with an increased Curie temperature and another one with decreased Curie temperature compared to the starting material. Such degrading material cannot be used in applications which require constant properties over a long period of time. By fully hydrogenating manganese containing LaFe13-x-yMnySixHz, stable alloys with adjustable Curie temperatures around room temperature can be produced. These hydrides do not change their magnetic properties if they are operated close to their Curie temperature.

Paleoclimate changes inferred from stable isotopes and magnetic properties of organic-rich lake sediments in Arctic Norway

Stable isotope measures in organic matter are frequently used as indicators of past climate change. Although such analyses can provide valuable information, there is considerable uncertainty associated with studies of organic-rich sediments, especially those from Arctic lakes and bogs. We studied stable isotopes of carbon and nitrogen, and magnetic properties in a sediment core from a small alkaline lake with a high sedimentation rate, Lake Nattmålsvatn, Norway. There is good correspondence among the different sediment variables during the late glacial, and they seemingly reflect major climate variations such as the Allerød Interstade and the Younger Dryas, as well as the transition into the current interglacial. During the early Holocene, however, these relationships are more complex and δ13C and δ15N values do not stabilize until ~7,500 cal year BP. A significant excursion in all variables occurs between 6,850 and 6,500 cal year BP and is interpreted to represent climate deterioration. Holocene δ13C values vary little and indicate that isotopically-depleted dissolved inorganic carbon (DIC) in the lake, possibly influenced by methanotrophy and high pCO2, dominated the lake’s carbon cycle. Holocene δ15N is similarly muted, likely due to the availability of abundant dissolved nitrogen. Bulk organic matter is probably dominated by phytoplankton remains produced beneath the ice cover in late spring and during ice breakup when isotopically-depleted DIC, pCO2 and ammonium availability were maximal. Thus, use of δ13C and δ15N as indicators of Holocene paleoclimate and paleoproductivity variation can be challenging in a lake such as Nattmålsvatn, where ice cover isolates the basin for large parts of the year, allowing dissolved respiratory gases to accumulate in the water column. In contrast, magnetic variables appear to better track climate variations. In particular, runoff-driven influx of minerogenic sediments shows high variability that can be attributed to regional changes in Holocene winter precipitation. The most striking shifts occur between 4,000 and 2,300 cal year BP.

One Step Synthesis of the Smallest Photoluminescent and Paramagnetic PVP-Protected Gold Atomic Clusters

Gold atomic clusters of only two and three atoms were prepared by a simple electrochemical technique based on the anodic dissolution of a gold electrode in the presence of PVP, and subsequent electroreduction of the Au-PVP complexes. These clusters show stable photoluminescent and magnetic properties, which make them the smallest and most elemental gold (0) building blocks in nature (after atoms) bringing new possibilities to construct novel nano/microstructures with large potential interest in biomedicine, catalysis, and so forth.

Adsorption of an Mn atom on a ZnO sheet and nanotube: a density functional theorystudy

First-principles calculations based on density functional theory were performed to studythe stable geometries, electronic structure and magnetic properties of the adsorption of asingle Mn atom on a graphitic ZnO sheet and a (9, 0) single-wall ZnO nanotube. For thegraphitic ZnO sheet, the Mn atom prefers to reside above the center of a hexagon (Hsite), with a relatively large binding energy of 1.24 eV. The H site is also the moststable site for adsorption of an Mn atom inside the ZnO nanotube, with a largebinding energy of 1.47 eV. In both of these cases, the total magnetic moment is5.0 μB per Mn atom, which is the same as that of a free Mn atom. When the Mn atom is adsorbed outsidethe tube, the most energetically favorable site is the atop oxygen site. The magnetic moment is3.19 μB for this configuration. The smaller magnetic moment is mainly due to the strong p–dmixing of O and Mn orbitals. The different adsorption behaviors are related to thecurvatures of the nanostructures.

Polymer-assisted nanoparticulate contrast-enhancing materials

The application of nanotechnology in medicine research has significant potential in modern biomedical research, disease diagnosis and therapy. Organic fluorophore-based detection techniques have been widely used as imaging and signal transduction tools for the detection of trace levels of analytes. The photosensitivity of the fluorophores, however, limits their application in such complex environments as living bio-systems where degradation or photobleaching occurs. Inorganic nanoparticles have unique and stable optical, electrical, magnetic and catalytic properties because of their various shapes, sizes and compositions. The potential of the nanoparticles as novel imaging agents has been studied as a possible solution to this problem. Surface modification of inorganic nanoparticles could enhance their biostability in physiological conditions and ability of targeting bioactive molecules.

Enhanced Ferroelectric and Dielectric Properties of CoFe2O4–Pb(Zr0.53Ti0.47)O3 Multiferroic Composite Thick Films

CoFe2O4–Pb(Zr0.53Ti0.47)O3 (CFO–PZT) multiferroic composite thick films sandwiched by PZT composite films were prepared by sol–gel processing and spin‐coating technique. It is shown that although the deeply buried CoFe2O4 spinel ferrite phase could not be detected in X‐ray diffraction patterns, the stable magnetic properties of films confirm its existence in the films. In addition, EDX results also detected CoFe2O4 composite from the cross section of thick films but was not observed on its surface. The structure of CFO–PZT composite thick films could be made denser by introducing enough PZT sol–gel for infiltration after each coated, composite layer and ferroelectric and dielectric properties of composite thick films were, hence, improved remarkably with stable magnetic properties. All the improvements were attributed to the optimized dense microstructure for CFO–PZT composite films.

Effects of synthetic conditions on particle size and magnetic properties of NiFe 2O 4

Nickel ferrite nanoparticles were prepared by a hydrothermal method. The effects of synthetic conditions on particle sizes and magnetic properties were investigated by TEM, XRD, and VSM. The results show that the concentrations of metal ions were the key factors not only on the particle size of NiFe 2O 4 but also on their magnetic properties. The pH value influenced greatly the magnetic properties through the reacted impurities. Once the reactions were given high enough temperature and long enough time, the particles would reach their ‘mature’ size and relative stable magnetic properties due to more perfect structure and more relaxed structural stress, therefore they showed much lower Hc and higher Ms than that of “immatured” particles. During the growing period of the particles, however, the temperature and the time play predominant roles on the particle size and on the diminishment of impurity. In the growing period of these nanoparticles, the magnetic properties have been demonstrated to follow some size-dependent law.

Stable Amorphous Cobalt Nanoparticles Formed by an in Situ Rapidly Cooling Microfluidic Process

The controlled synthesis of nanoparticles (NPs) with stable crystal structures and stable physical and chemical properties is a key issue for commercial applications. The use of a microfluidic reactor (MR) process has proven to be a flexible approach to control the fine crystal structures and the magnetic properties during the ripening and aging of the NPs. We have developed an in situ rapidly cooling microfluidic process (IRCMP) in which Co NPs with stable crystal structures and magnetic properties are synthesized by using elevated reaction temperatures followed by rapid quenching of the colloids to reduced temperatures. The Co NPs that are obtained by this process demonstrate stable crystal structures and stable magnetic properties for a much longer period of time (at least 3 months) than for Co NPs obtained by performing the reaction and the quenching processes at room temperature or under sonication.

Understanding the bond‐making and bond‐breaking of Fe‐filled SWNT on Ni(111)

AbstractIn the previous studies, the stable structures and magnetic properties of Fe‐filled single‐walled carbon nanotubes (SWNTs) on Ni (111) were investigated based on first principles calculations. The SWNT transformed into arch‐like structure when the Fe atom was placed inside it near the Ni surface.In order to fully understand the formation of nanoarch when placed near the metal surface, we have provided a detailed mechanism of the bond‐breaking of SWNT and the bond‐making of SWNT‐Fe and Ni surface.The electron distributions and the number of electrons in the majority and minority spins per atomic orbital were discussed. Copyright © 2008 John Wiley & Sons, Ltd.

First principles investigation on Fe-filled single-walled carbon nanotubes on Ni (1 1 1) and Cu (1 1 1)

The stable structures and magnetic properties of Fe-filled single-walled carbon nanotubes (SWNTs) on Ni (1 1 1) and Cu (1 1 1) were investigated based on first principles calculations. The SWNT transformed into arch-like structure when the Fe atom was placed inside it near the Ni surface. The same thing happened when the Fe-filled SWNT was placed on the Cu surface. We proposed the possibility that when Fe-filled SWNT (3, 3) was adsorbed on the surface, the C–C bonds of the carbon nanotube were broken by the Fe wire and the metal surface. Hence, the SWNT transformed into an arch-like structure.

Processing and characterization of activated carbon coated magnetic particles for biomedical applications

Synthesis and characterization of Magnetically Targeted Carrier (MTC) powders consisting of activated carbon coated iron particles were carried out. Powders with activated carbon content of 5% by weight (Fe5C) and 35% by weight (Fe35C) were studied. Powders were synthesized via the high energy ball milling route, and the influence of milling time on the morphology, magnetic properties and drug adsorption and desorption characteristics was investigated. Physical and structural characterization included electron microscopy, size analysis, and X-ray diffraction. The magnetic properties, and theophylline adsorption and desorption characteristics were studied. Fe35C milled for 10 h was found to be a suitable candidate for MTC applications with fine size, stable magnetic properties, and superior drug adsorption and desorption behavior.

Interaction of manganese with single-wallB2Onanotubes: Anab initiostudy

Interaction of a manganese atom with a graphitic ${\mathrm{B}}_{2}\mathrm{O}$ sheet and a (3,0) single-wall ${\mathrm{B}}_{2}\mathrm{O}$ nanotube was investigated using first-principles spin-polarized density functional calculations. The stable geometries, electronic and magnetic properties of the Mn-doped planar and tubular systems were analyzed. It was found that the most stable adsorption site is above the hole site for the ${\mathrm{B}}_{2}\mathrm{O}$ sheet. For the (3,0) ${\mathrm{B}}_{2}\mathrm{O}$ nanotube, when the Mn atom is adsorbed outside the tube, the most energetically favorable site is the center of the hexagon with an axial symmetry, followed by the bridge site above the axial $\mathrm{B}\text{\ensuremath{-}}\mathrm{B}$ bond. The magnetic moment of the Mn-doped nanotube is similar to that of the free Mn atom. The atop oxygen site, however, is the most stable site if the Mn atom is inside the tube. In this case, the Mn atom is seven-coordinated and the nanotube is significantly distorted, leading to a larger binding energy and a smaller magnetic moment of $\ensuremath{\sim}1{\ensuremath{\mu}}_{B}$.

Magnetic properties of HITPERM-type alloys at high temperature

(Fe,Co)–Zr,Hf)–Cu–B (HITPERM-type) alloys with variable Hf, Zr and Co content were isothermally crystallised at 500–650 °C for 1 h, and the optimum nanocrystallisation temperature was selected on the basis of the minimum coercive field at room temperature. The quasistatic hysteresis loops were measured at temperature from 20 to 650 °C. Subsequently, the optimally annealed alloys were subjected to long-term annealing at 500, 550 and 600 °C. Working temperature of 600°C is too high for the investigated alloys to maintain stable magnetic properties. Temperature of 550 or 500 °C permits the material to be magnetically stable for a long period. The magnetic hysteresis loops recorded for the nanocrystalline alloys, where Fe:Co ratio is close to 1 and refractory metals content is 7 at.%, prove that coercive field increases slightly with temperature, but remains in the range of 20–40 A/m (depending on the alloy composition) from 20 to 550 °C. This proves that the investigated alloys, after optimisation of chemical composition, may be suitable for high temperature use.

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Stable Structure and Electronic Properties of Carbon Nanoarch Encapsulating Fe Nanowire on Ni(111)

We investigate the stable structures and magnetic properties of Fe-filled single-walled carbon nanotubes (SWNTs) on Ni(111) using first principle calculations. For the two different initial positions of Fe atom inside the nanotube, we find stable geometries and electronic states for the SWNT on Ni(111). When the Fe wire is near the Ni surface, SWNT transforms into arch-like structure. We propose the possibility that the C-C bonds of carbon nanotube are broken by Fe wire and Ni surface. [DOI: 10.1380/ejssnt.2005.266]

The magnetic properties of magnetic nanoparticles produced by microwave flash synthesis of ferrous alcoholic solutions

Microwave heating is an emerging technology that uses the ability of some liquids and solids to transform electromagnetic energy into heat. We present the results of experimental study of magnetic and structural properties of magnetic nanoparticles fabricated by this technique. Compared with similar nanoparticles fabricated by using a conventional heating, we obtained much smaller grain size (up to 10 nm) and very stable magnetic properties. The hysteresis loops for the samples of the nonoriented assemblies of magnetite particles have a coercive force about 100 Oe with a squareness about 0.4. The superparamagnetic fraction was found in the samples. The particles distribution on the anisotropy fields has a maximum at 200 Oe.

Long term stability of dry etched magnetoresistive random access memory elements

The magnetization of Cl2/Ar etched magnetic multilayer (NiFeCo/CoFe/Cu/CoFe/NiFeCo) structures used in magnetoresistive random access memory elements was measured over a period of ∼6 months. Very stable magnetic properties were achieved, with no evidence of corrosion, provided chlorinated etch residues were removed by postetch cleaning. Several different cleaning procedures, including deionized water rinsing or in situ exposure to H2, O2 or SF6 plasmas were investigated. Some slight degradation in magnetization was observed in O2 plasma treated structures, but the other cleaning procedures produced no change in magnetic properties and excellent long-term stability.

Magnetic Properties of Rapidly Quenched (Sm,Zr)(Fe,Co)<SUB>7</SUB>-N+α-Fe

Melt-spun ribbons of Sm-Fe(-Co)-M-N(M=Zr,Nb,B,Si,Al,Ti) system alloys were prepared by the single roller rapid quenching method. The effect of composition, heat-treatment and nitrogenation were studied. A highest (BH) max =126.2 kJ/m 3 with B r =0.95T and H cj =740kA/m were obtained for (Sm 8 Zr 3 Fe 85 Co 4 ) 85 N 15 system isotropic powders. The X-ray diffraction analysis and transmission electron microscopy (TEM) observation showed this powder to consist of a nanoscale mixture with a SmFe7-N phase with the TbCu 7 -type structure and α-Fe in the size range of 20-50nm. Small deterioration of magnetic properties during pulverization and stable magnetic properties for long time aging at elevated temperature for these powders were observed.

Anisotropy of the 3d–4f exchange interaction in R [sbnd]Co intermetallics (R:rare earth)

A comparative study of the pseudo-binary compounds Y(Co 1− x Ni x ) 5 and Gd(Co 1− x Ni x ) 5, rich in cobalt and possessing stable magnetic properties, was carried out in order to characterize the various anisotropies in the R(CO, Ni) 5 intermetallic system. Isothermal magnetization curves have been measured between 5 and 600 K from which the thermal variations of the anisotropy energy are deduced. An excess of anisotropy is shown up in the Gd(Co 1− x Ni x ) 5 compounds which is discussed in terms of an anisotropy of the 3d–4f exchange interactions.