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Magnetite (Fe3O4) nanoparticle (MNP)-substituted glass-ceramic (MSGC) powders with compositions of (45 − x)SiO2–24.5CaO–24.5Na2O–6P2O5–xFe3O4 (x = 5, 8, and 10 wt%) have been prepared by a sol–gel route by introducing Fe3O4 nanoparticles during the synthesis. The X-ray diffraction patterns of the as-prepared MSGC nanopowders revealed the presence of combeite (Na2Ca2Si3O9), magnetite, and sodium nitrate (NaNO3) crystalline phases. Heat-treatment up to 700 °C for 1 h resulted in the complete dissolution of NaNO3 along with partial conversion of magnetite into hematite (α-Fe2O3). Optimal heat-treatment of the MSGC powders at 550 °C for 1 h yielded the highest relative percentage of magnetite (without hematite) with some residual NaNO3. The saturation magnetization and heat generation capacity of the MSGC fluids increased with an increase in the MNP content. The in vitro bioactivity of the MSGC pellets was evaluated by monitoring the pH and the formation of a hydroxyapatite surface layer upon immersion in modified simulated body fluid. Proliferation of MG-63 osteoblast cells indicated that all of the MSGC compositions were non-toxic and MSGC with 10 wt% MNPs exhibited extraordinarily high cell viability. The MSGC with 10 wt% MNPs demonstrated optimal characteristics in terms of cell viability, magnetic properties, and induction heating capacity, which surpass those of the commercial magnetic fluid FluidMag-CT employed in hyperthermia treatment. [ABSTRACT FROM AUTHOR]

Fine quaternary single-domain Heusler alloy nanoparticles with a composition of Fe2CoGa0.5Al0.5 have been synthesized using a simple template-less chemical route for the first time. Ab initio calculations and standard models have been used to analyze and interpret the experimental findings. The synthesized nanoparticles with an average crystallite size of 42 nm exhibited high saturation magnetization (>5 μB f.u.−1), high effective anisotropy constant (≈8 × 106 erg cc−1), high Curie temperature (>1200 K), low magnetic remanence (<0.2 μB f.u.−1) and low coercive field (<90 Oe), declaring their suitability for fabricating various nanomagnetic devices. [ABSTRACT FROM AUTHOR]

Magnetic interactions in sol–gel‐derived bioactive magnetic glass–ceramics (MGCs) with compositions of (45 − x)SiO2·24.5CaO·24.5Na2O·6P2O5xFe2O3 (2 ≤ x ≥ 15 wt.%) have been investigated using electron paramagnetic resonance (EPR), and temperature‐dependent magnetic susceptibility and magnetization (M–T) techniques. EPR spectra of the MGC samples revealed strong composition dependence in the intensity and linewidth of resonance absorptions at g ≈ 2.0 and g ≈ 4.3. EPR linewidth analysis showed the dominance of dipole–dipole interaction in MGC samples with iron oxide content ≤4 wt.% and a crossover to super‐exchange type interaction in samples with higher iron oxide content. Composition‐dependent magnetic interaction in these MGC could be related to Fe2+ and Fe3+ ion concentrations using high‐temperature magnetic susceptibility studies. Zero‐field cooled and field cooled M–T curves indicate different magnetic behavior for MGC samples with x ≤ 6 and x ≥ 8 wt.% iron oxide. Although the former show weak magnetic behavior, the latter exhibit superparamagnetic behavior which could be correlated with the percentage of magnetic phases present in each sample. These studies reveal composition‐dependent variation in dipolar and super‐exchange type interaction in the samples which could help in assessing these MGC for biomedical applications. [ABSTRACT FROM AUTHOR]

Magnetic bioactive glass-ceramic (MGC) powders with nominal compositions of (45 − x)SiO224.5CaO24.5Na2O6P2O5xFe2O3 (x = 2, 4, 6, 8, 10, and 15 wt%) have been synthesized by a sol–gel route by systematically substituting silicon dioxide with iron oxide in Hench's 45S5 glass composition. Powder X-ray diffraction studies revealed a variation in the percentage of combeite (Ca2Na2Si3O9), magnetite (Fe3O4), and hematite (Fe2O3) nanocrystalline phases in MGC powders as a function of composition. Zeta potential measurements showed that MGC containing up to 10 wt% iron oxide formed stable suspensions. The saturation magnetization and heat generation capacity of MGC fluids increased with an increase in iron oxide content. Degradation of MGC powders was investigated in phosphate buffered saline (PBS). The in vitro bioactivity of the MGC powders taken in pellet form was confirmed by observing the pH variation as well as hydroxyapatite layer (HAp) formation upon soaking in modified simulated body fluid. These studies showed a decrement in the overall bioactivity in samples with high iron oxide content due to the proportional decrease in the silanol group. Monitoring the proliferation of MG-63 osteoblast cells in Dulbecco's Modified Eagle Medium (DMEM) revealed that MGC with up to 10 wt% iron oxide exhibited acceptable viability. The systematic study revealed that the MGC with 10 wt% iron oxide exhibited optimal cell viability, magnetic properties and induction heating capacity, which were better than those of FluidMag-CT, which is used for hyperthermia treatment. [ABSTRACT FROM AUTHOR]

The influence of small amounts of replacement of Mn with Co/Fe on the structural, magnetic, and magneto-caloric properties of polycrystalline off-stoichiometric Ni-Mn-In Heusler alloy films has been investigated. An enhancement in Curie temperature (TC) up to 317 K was observed upon Fe substitution. The change in magnetic entropy (ΔSM) and refrigeration capacity (RC) across the second order ferromagnetic to paramagnetic phase transition increased significantly upon substituting Fe/Co in Mn sites. ΔSM (RC) estimated for a magnetic field change of 18 kOe near TC increased from −7.93 × 104 erg/cc K (1.98 × 106 erg/cc) to −12.79 × 104 erg/cc K (2.82 × 106 erg/cc) and −9.99 × 104 erg/cc K (2.60 × 106 erg/cc) in ∼3 at. % Fe and Co substituted Ni-Mn-In films, respectively. [ABSTRACT FROM AUTHOR]

Single phase X type Fe2CoGa Heusler alloy nanoparticles with average crystallite sizes of 56 nm, 26 nm, and 21 nm have been synthesized using a refined template-less chemical route. Size-dependent structural and magnetic properties of the Fe2CoGa alloy nanoparticles are compared with the bulk counterpart prepared by arc melting. Fe2CoGa nanoparticles show soft ferromagnetic behavior with high magnetic moment and Curie temperature. Ab initio calculations have been carried out to interpret the experimental results. The estimated critical size and measured magnetic properties of the nanoparticles reveal that the synthesized nanoparticles are in a single domain superparamagnetic regime. [ABSTRACT FROM AUTHOR]

Large magnetoresistance (MR) with a linear response to the magnetic field is an important feature in MR devices for magnetic sensor applications. Following the largest MR ratio realized in a current-in-plane (CIP) giant magnetoresistance (GMR) device using a metastable body-centered cubic (bcc)-Cu spacer, we developed a new CIP-GMR device with a combination of two spacer materials, i.e. CoFe/Rh/CoFe (sensing layer)/bcc-Cu/CoFe asymmetric structure and realized a large linear sensitivity due to large MR ratio (21%) and linear response through a biquadratic coupling, high sensitivity of 0.047% mT−1, reduced nonlinearity of 0.98% full scale along with a substantially wider operation field range of 220 mT. Our numerical simulation analyses of magnetization curves clearly establish that the middle CoFe sensing layer is well-controlled by interlayer exchange coupling through the Rh spacer, giving rise to a linear response without losing the high MR ratio through the bcc-Cu spacer. These findings demonstrate that CIP-GMR devices are promising for wide dynamic range magnetic sensors. [ABSTRACT FROM AUTHOR]

The authors report thickness dependent magneto-static and magneto-dynamic properties of amorphous Co40Fe40B20 films with thickness, t = 10–200 nm deposited on thermally oxidized Si substrates using magnetron sputtering technique at ambient temperature. Magnetic hysteresis loops of films with t ≤ 20 nm transformed from rectangular or flat type shape to transcritical nature for t ≥ 50 nm. This is attributed to a change in the magnetic domain structure from in-plane magnetization with uniaxial anisotropy in thinner films to stripe domains with effective magnetic anisotropy in thicker films. Magnetization dynamics in the films has been investigated using ferromagnetic resonance spectra. Out-of-plane angular dependent resonance field (Hr) and linewidth (ΔH) data have been interpreted using the Smit–Beljers formula. It is found that ΔH contains large extrinsic contribution with the major one being two-magnon scattering. An inverse scaling of Gilbert damping constant (α) with the film thickness over the entire thickness range of 10–200 nm is observed with the lowest α value of 0.004. The results reveal a cost effective strategy for developing films for spintronics based microwave devices and spin-transfer-torque based magnetic devices. [ABSTRACT FROM AUTHOR]

The effects of the partial substitution of Mn by Co/Fe on the structural, magnetostatic, and magnetodynamic properties of Ni–Mn–In Heusler alloy films were studied using X-ray diffraction, field-dependent magnetization, and ferromagnetic resonance studies. It was observed that the substitution of up to 3 at.% Co or Fe atoms in Mn sites does not alter the crystal structure much. However, an increase in grain size and surface roughness was noticed upon substitution of the fourth element. The magnetic moment of the films could be increased up to 120 kA/m by introducing Co/Fe in Mn sites. For the first time, low Gilbert damping constant ($\alpha$) of 0.008 is observed in Co substituted Ni–Mn–In film together with high saturation magnetization, high perpendicular anisotropy, and an easy axis along film plane, which are the promising factors for application in high-density random-access memory devices. [ABSTRACT FROM AUTHOR]

Melt-quenched 15(ZnO,Fe2O3) 50SiO2·20(CaO,P2O5) 15Na2O bioactive glass was heat treated at temperatures ( TA) ranging from 550°C to 850°C for different time periods ( tA=1, 2 and 3 hours) to understand its devitrification characteristics. Crystallization of calcium sodium phosphate, zinc ferrite, magnetite, and hematite phases depended on heat treatment conditions. Decrease in saturation magnetizations ( Ms) with increase in tA of glass heat treated at TA≥750°C is attributed to the formation of hematite which is a weak magnetic material. Magnetic properties as functions of TA and tA are interpreted on the basis of clustering of Fe ions, super-exchange interaction between Fe2+ and Fe3+ ions and formation of ferrimagnetic and weakly magnetic iron oxide phases with different heat treatment conditions. Electron paramagnetic resonance parameters reveal the variations in site distortions and randomness in Fe ion environment in the matrix upon heat treatment. In vitro mineralization ability of the glass-ceramics was evaluated by immersion in simulated body fluid ( SBF) and monitoring both the pH variation of SBF and formation of hydroxyapatite surface layer as a function of immersion time. These studies help in assessing these glass-ceramics for hyperthermia treatment and in optimizing the processing conditions for this application. [ABSTRACT FROM AUTHOR]

Aqueous solution containing polyvinyl alcohol and zinc acetate was electrospun into composite nanofibers. Upon heat treatment between T A =500 and 600 °C under ambient as well as nitrogen atmospheres, the as-spun composite nanofibers transformed into ZnO nanowires and exhibited room temperature ferromagnetism (RTFM). Powder X-ray diffraction and high resolution transmission electron microscopy confirmed that the heat treated nanowires consisted of single phase ZnO in hexagonal wurtzite structure. Photoluminescence spectra showed green emission at ~505 nm implying the presence of oxygen vacancy defects in ZnO lattice. Micro-Raman spectra revealed a defect related band at ~579 cm −1 as well as the wurtzite band at ~438 cm −1 . Presence of singly ionized oxygen ( V o + ) vacancy in the nanowires was confirmed by resonance absorption at g ≈1.99 in electron paramagnetic resonance spectra of the samples. Magnetization measurements showed ferromagnetic behavior in the samples with high Curie temperature. Strong dependency of the properties on T A provides insights on the mechanism behind RTFM and the way to enhance it in undoped ZnO nanowires. [ABSTRACT FROM AUTHOR]

Calcium ferrite nanoparticles with average crystallite size of ∼11 nm have been synthesized by sol-gel method by mixing calcium and ferric nitrates in stoichiometric ratio in the presence of ethylene glycol. As-synthesized nanoparticles were annealed at different temperatures and their structural and magnetic properties have been evaluated. X-ray diffraction studies showed that unlike most ferrites, as-synthesized cubic calcium ferrite showed a slow transformation to orthorhombic structure when annealed above 400 °C. Single phase orthorhombic CaFe 2 O 4 was obtained upon annealing at 1100 °C. Divergence of zero field cooled and field cooled magnetization curves at low temperatures indicated superparamagnetic behavior in cubic calcium ferrite particles. Superparamagnetism persisted in cubic samples annealed up to 500 °C. As-synthesized nanoparticles heat treated at 1100 °C exhibited mixed characteristics of antiferromagnetic and paramagnetic grains with saturation magnetization of 0.4 emu/g whereas nanoparticles calcined at 400 °C exhibited superparamagnetic characteristics with saturation magnetization of 22.92 emu/g. An antiferromagnetic to paramagnetic transition was observed between 170 and 190 K in the sample annealed at 1100 °C, which was further confirmed by Mössbauer studies carried out at different temperatures across the transition. [ABSTRACT FROM AUTHOR]

Magnetic and crystallographic properties of bulk Co2Fe(Ga1-xSix) alloys with 0≤x≤1 are reported in this work. The alloys with x=0.75 and 1.00 exhibit L21 structure whereas the alloys with x=0, 0.25 and 0.50 crystallized in the disordered A2 phase. Unit cell volume of this series of alloys decreased from 189.1 to 178.5ų as x was increased from 0 to 1.00. All alloy compositions exhibit ferromagnetic behavior with a high Curie temperature (TC) which showed a systematic variation with x (1089K, 1075K, 1059K, 1019K and 1015K for x=0, 0.25, 0.5, 0.75 and 1.00, respectively). The saturation magnetization moment Ms for the alloys with x=0, 0.25 and 0.50 are 5.05μB, 5.23μB, 5.49μB, respectively, in accordance with the Slater-Pauling rule, but alloys with x=0.75 and 1.00 deviated from this rule. The effective moment per magnetic atom (pc) of the alloys was estimated from the inverse DC magnetic susceptibility data above TC. A comparison of Ms with pc reveals the half-metallic character of the alloys. [ABSTRACT FROM AUTHOR]

Sol-gel-based mesoporous 45SiO 2 -16.5CaO-24.5Na 2 O-6P 2 O 5 -8Fe 3 O 4 bioglass-ceramics were obtained by substituting magnetite nanoparticles for CaO in a 45SiO 2 -24.5CaO-24.5Na 2 O-6P 2 O 5 bioglass composition. To enhance the dissolution of the precursors and to vary the crystalline phases, the as-synthesized ceramic powders were processed for 1 h each at temperatures ( T A ) between 550 and 700 °C. A gradual decline in the saturation magnetization with an increase in T A was observed, which is linked to the gradual conversion of magnetite into hematite at different T A > 550 °C. All of the processed samples indicated a hydroxyapatite surface layer formation in in vitro tests. Aqueous solutions of the ceramic processed at 600 °C exhibited superior magnetic induction capacity. Thus, the substitution of magnetite nanoparticles for CaO in the base composition, coupled with appropriate heat treatment, results in a promising bioactive glass-ceramic for magnetic hyperthermia treatment of deep-rooted cancer cells.

Magnetite (Fe 3 O 4 ) nanoparticle (MNP)-substituted glass-ceramic (MSGC) powders with compositions of (45 - x )SiO 2 -24.5CaO-24.5Na 2 O-6P 2 O 5 - x Fe 3 O 4 ( x = 5, 8, and 10 wt%) have been prepared by a sol-gel route by introducing Fe 3 O 4 nanoparticles during the synthesis. The X-ray diffraction patterns of the as-prepared MSGC nanopowders revealed the presence of combeite (Na 2 Ca 2 Si 3 O 9 ), magnetite, and sodium nitrate (NaNO 3 ) crystalline phases. Heat-treatment up to 700 °C for 1 h resulted in the complete dissolution of NaNO 3 along with partial conversion of magnetite into hematite (α-Fe 2 O 3 ). Optimal heat-treatment of the MSGC powders at 550 °C for 1 h yielded the highest relative percentage of magnetite (without hematite) with some residual NaNO 3 . The saturation magnetization and heat generation capacity of the MSGC fluids increased with an increase in the MNP content. The in vitro bioactivity of the MSGC pellets was evaluated by monitoring the pH and the formation of a hydroxyapatite surface layer upon immersion in modified simulated body fluid. Proliferation of MG-63 osteoblast cells indicated that all of the MSGC compositions were non-toxic and MSGC with 10 wt% MNPs exhibited extraordinarily high cell viability. The MSGC with 10 wt% MNPs demonstrated optimal characteristics in terms of cell viability, magnetic properties, and induction heating capacity, which surpass those of the commercial magnetic fluid FluidMag-CT employed in hyperthermia treatment.

Fine quaternary single-domain Heusler alloy nanoparticles with a composition of Fe 2 CoGa 0.5 Al 0.5 have been synthesized using a simple template-less chemical route for the first time. Ab initio calculations and standard models have been used to analyze and interpret the experimental findings. The synthesized nanoparticles with an average crystallite size of 42 nm exhibited high saturation magnetization (>5 μ B f.u. -1 ), high effective anisotropy constant (≈8 × 10 6 erg cc -1 ), high Curie temperature (>1200 K), low magnetic remanence (<0.2 μ B f.u. -1 ) and low coercive field (<90 Oe), declaring their suitability for fabricating various nanomagnetic devices.