Thermal Stability, Blocking Regime and Superparamagnetic Behavior in Mn-Al-C Melt Spun Ribbons

Alloys possessing nominal compositions Mn53Al45C2 and Mn52Al46C2 were prepared by the melt spinning method and were subjected to complex structural, morphological and magnetic investigations. As these alloys can exhibit tetragonal L10-type and τ phase, they have good potential as rare earth (RE)—free magnets. It is, therefore, important to monitor the ε–τ phase transformation and the stability and the magnetic features of the tetragonal phase in an entire temperature interval. By using synchrotron X-ray diffraction, it has been proven that the ε–τ phase transformation occurs gradually, with the τ phase becoming predominant only after 450 °C. Moreover, this phase has been proven to be quite stable without any grain growth even at the highest temperature investigated at 800 °C. Low temperature behavior was thoroughly investigated by using a complex combination of major and minor hysteresis loops combined with the zero field cooled-field cooled magnetization protocols (ZFC-FC). Two different regimes, blocking and superparamagnetic, were documented. A spin reorientation transition was proven to occur at 55 K while a maximum magnetization observed in ZFC-FC curves proved that at about 75 K, a transition from ferro to superparamagnetic state occurs. The existence of a blocking regime below 55 K that is characteristic to nanogranular systems with superparamagnetic behavior has shown further development towards obtaining RE-free magnets.

Zn2+ substituted superparamagnetic MgFe2O4 spinel-ferrites: Investigations on structural and spin-interactions

Nano-magnetic ferrites with composition Mg1−xZnxFe2O4 (x = 0.3, 0.4, 0.5, 0.6, and 0.7) have been prepared by coprecipitation method. X-ray diffraction (XRD) studies showed that the lattice parameter was found to increase from 8.402 to 8.424 Å with Zn2+ ion content from 0.3 to 0.7. Fourier transform infrared (FTIR) spectra revealed two prominent peaks corresponding to tetrahedral and octahedral at around 560 and 430 cm−1 respectively that confirmed the spinel phase of the samples. Transmission electron microscopy (TEM) images showed that the particle size was noted to increase from 18 to 24 nm with an increase in Zn content from x = 0.3 to 0.7. The magnetic properties were studied by vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR) which ascertained the superparamagnetic behavior of the samples and contribution of superexchange interactions. The maximum magnetization was found to vary from 23.80 to 32.78 emu/g that increased till x = 0.5 and decreased thereafter. Further, X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical composition and substantiate their oxidation states.

Effect of Sm and Mn Co-Doping on the Crystal Structure and Magnetic Properties of \(\text{BiFeO}_{3}\) Polycrystalline Ceramics

The crystal structure, phonon vibration, microstructure, and magnetic properties have been investigated in multiferroics Bi0.9Sm0.1Fe1-xMnxO3 for x = 0.02 – 0.1. The structural analysis by XRD and Rietveld refinement suggest that Mn doping compounds crystallize in the polar R3c rhombohedral symmetry (isostructural with BiFeO3). Raman analysis confirms no structural transformation but the change of line widths and peak intensities reveal the lattice distortion in Mn-substitution samples. The study of microstructure shows no obvious change of grain size and shape. The magnetic properties of the as-prepared samples show the linear magnetic field dependence of magnetization, suggesting the antiferromagnetic feature of polycrystalline ceramics. The field dependence of magnetization measured after two-years synthesis and after applying an electric field reveal a decrease of maximum magnetization but the hysteresis loops retain the antiferromagnetic behavior. The implication of these results is that the magnetic properties of single structural phase compound, including coercivity and remanent magnetization, do not show the aging behavior as observed in the morphotropic phase boundary systems.

Structural transition and magnetic properties of high Cr-doped BiFeO3 ceramic

Magnetic properties of BiFe1-xCrxO3 perovskite-type solids reaction synthesized at high pressure were investigated and a magnetic phase diagram was established. X-ray diffraction data revealed a crystal structure transformation from rhombohedral to monoclinic as Cr3+ ions substituted Fe ions in the samples. Néel temperature TN and spin-reorientation temperature TSR were determined from dM/dT by measuring the temperature dependence of magnetization (M-T). The magnetization results indicated that TN and TSR were strongly dependent on Cr3+ ion doping; both TN and TSR decreased with the increase of Cr3+ doping. The magnetic hysteresis loops investigated at room temperature reflected an antiferromagnetic behavior from x= 0.4 to 0.6 and weak ferromagnetic at x=1.0. Besides, the remnant magnetization Mr and maximum magnetization Mmax increased with increasing x from 0.4 up to 1.0. The Cr doping was found to be helpful in reducing coercivity Hc for the magnetic samples from x= 0.4 to 0.8 and their applications as magnetic sensors are possible.

Crystal Structures and Magnetic Properties of Polyethylene Glycol (PEG-4000) Encapsulated Co0.5Ni0.5Fe2O4 Magnetic Nanoparticles

Nanocrystalline mixed spinel ferrite of Co0.5Ni0.5Fe2O4 magnetic nanoparticles (MNPs) has been successfully synthesized by coprecipitation method and encapsulated by PEG-4000 with various concentrations. X-Ray Diffraction (XRD) patterns showed that nanoparticles contained Co0.5Ni0.5Fe2O4 spinel ferrite with crystallite size of 14.9 nm. After PEG-4000 encapsulation particles size decreased became 7.7 nm. Interaction Co0.5Ni0.5Fe2O4 nanoparticles with long chain PEG-4000 caused the crystal growth trap. Lattice parameter and X-Ray density have no significant difference after encapsulated PEG-4000. The coercivity (𝐻𝑐) of Co0.5Ni0.5Fe2O4 was 214 Oe. The 𝐻𝑐 decreased after PEG-4000 encapsulation became 127 Oe, which is due to the decrease of crystallite size. The maximum magnetization (Mmax) of Co0.5Ni0.5Fe2O4 was 12.0 emu/g, and decreased after PEG-4000 encapsulation to 11.7 emu/g, because PEG-4000 is paramagnetic. After the concentration of PEG-4000 increased, then the amount of paramagnetic material increase which lead maximum magnetization decrease.

Magnetoliposomes containing magnesium ferrite nanoparticles as nanocarriers for the model drug curcumin

Magnesium ferrite nanoparticles, with diameters around 25 nm, were synthesized by coprecipitation method. The magnetic properties indicate a superparamagnetic behaviour, with a maximum magnetization of 16.2 emu g −1 , a coercive field of 22.1 Oe and a blocking temperature of 183.2 K. These MgFe 2 O 4 nanoparticles were used to produce aqueous and solid magnetoliposomes, with sizes below 130 nm. The potential drug curcumin was successfully incorporated in these nanosystems, with high encapsulation efficiencies (above 89%). Interaction by fusion between both types of drug-loaded magnetoliposomes (with or without PEGylation) and models of biological membranes was demonstrated, using FRET or fluorescence quenching assays. These results point to future applications of magnetoliposomes containing MgFe 2 O 4 nanoparticles in cancer therapy, allowing combined magnetic hyperthermia and chemotherapy.

Structural and Magnetic Properties of Pure and Mn-Doped Bismuth Ferrite Powders

ABSTRACTMultiferroic materials are of great interest from the scientific and technological viewpoints based on their multifunctional behavior involving ferroelectricity, ferromagnetism, ferroelasticity and strong electromagnetic coupling properties. Among these materials, BiFeO3 (BFO), is a well-known multiferroic with simultaneous ferroelectricity (TC=1103K) and G-type antiferromagnetism (TN=643K). In this work, we doped BiFeO3 with Mn species and studied the doping effect on the corresponding magnetic properties, expected from the substitution of Bi3+ by Mn2+. Additionally, the optimum processing conditions to minimize the formation of any impurity phase were also identified. X-Ray Diffraction (XRD) characterization confirmed the formation of powdered impurity-free BFO in pure and 7 at.% Mn-BFO only after annealing of the precursor compounds at suitable temperatures and time (700°C, 15 minutes). Scanning Electron Microscopy (SEM) analyses were used to determine the size and morphology of synthetized powders. Vibrating sample magnetometry (VSM) measurements showed that maximum magnetization values increased with doping and reached a maximum value in the 7 at.% Mn-doped BFO annealed at 700°C for 15min; the corresponding magnetization in the non-saturated MH loops reached 0.68 emu/g. This behavior can be attributed to the actual incorporation of Mn species into the BFO lattice and the substitution of non-magnetic Bi species.

Magnetism of N-doped graphene nanoribbons with zigzag edges from bottom-up fabrication

Two graphene nanoribbons with atomically precise N-doping zigzag edges from bottom-up fabrication by a condensation reaction exhibited intrinsically magnetic properties with a maximum magnetization of 0.303 emu g−1.

The influence of mechanochemical activation and thermal treatment on magnetic properties of the BaTiO3-FexOy powder mixture

Powder mixture of 50 mass % of barium titanate (BaTiO3) and 50 mass % of iron (Fe) was prepared by solid-state reaction technique, i.e. ball milled in air for 60 min, 80 min, 100 min, 120 min and 150 min. During mechanochemical activation it was observed the iron powder transitsion to iron oxides. Depending on the activation time the content of iron oxides FeO, Fe2O3 and Fe3O4 varies. Simultaneously, with the content change of the activated system, magnetic properties change as well. The XRD analysis of milled samples shown that as the activation time increase, the iron oxide percentage increases to, whereby the percentage of BaTiO3 in a total sample mass decreases. The percentage of iron oxides and BaTiO3 in annealed samples changes depending on annealing temperature. The thermomagnetic measurements performed by Faraday method shown that the powder mixture milled for 100 minutes exhibit maximum magnetization prior to annealing. The increase of magnetization maximum was observed after annealing at 540?C with all milled samples, and at room temperature it has enhancement from 10 % to 22 % depending on the activation time. The samples milled for 100 min and 150 min and then sintered at 1200w?C exhibit magnetoelectric properties.

Synthesis of water dispersed Fe3O4@ZnO Composite Nanoparticles by the Polyol Method

ABSTRACTWater-soluble Fe3O4@ZnO composite nanoparticles (NPs) were synthesized using a polyol route. The effects of the addition of the ZnO phase were evaluated by varying the Zn/Fe molar ratio in the 0.25-1.00 range as a function of the reaction time. X-ray diffractometry confirmed the formation of the magnetite and ZnO phases and suggested the possible formation of a composite structure. Also, using this method, pure magnetite and ZnO NPs were synthesized. The average crystallite sizes were estimated to 6.3 ± 0.3 nm and 8.6 ± 0.6 nm for magnetite and ZnO NPs, respectively. The samples were examined using transmission electron microscopy. Fourier transform infrared spectra indicated the presence of adsorbed species onto the solids surface, which may explain the good stability of the materials in water. Photoluminescence measurements at room temperature for pure ZnO nanoparticles exhibited the characteristic excitonic emission around 395 nm. Vibrating Sample Magnetometer measurements at room temperature evidenced the superparamagnetic behavior of magnetite nanocrystals, with a saturation magnetization of 60emu/g. The maximum magnetization ranged from 28 to 54emu/g for the composite NPs. Mössbauer spectroscopy measurements at room temperature showed evidence of evolving Fe-sites associated to superparamagnetic particles, as reflected on the coexistence of prominent doublet peaks and very weak sextet peaks.