Atomic and magnetic structures of Fe<Subscript>70</Subscript>Al<Subscript>5</Subscript>B<Subscript>25</Subscript> amorphous alloys

The short-range order around boron, aluminum, and iron atoms in Fe₇₅B₂₅ and Fe₇₀Al₅B₂₅ amorphous alloys has been studied by ¹¹B and ²⁷Al nuclear magnetic resonance at 4.2 K and ⁵⁷Fe Mössbauer spectroscopy at 87 and 295 K. The average magnetic moment of iron atoms μ(Fe) in these alloys has been measured by a vibrating sample magnetometer. It has been revealed that the substitution of aluminum atoms for iron atoms does not disturb μ(Fe) in the Fe₇₀Al₅B₂₅ alloy, gives rise to an additional contribution to the ¹¹B NMR spectrum in the low-frequency range, and shifts maxima of the distribution of hyperfine fields at the ⁵⁷Fe nuclei. In the Fe₇₀Al₅B₂₅ amorphous alloy, the aluminum atoms substitute for iron atoms in the nearest coordination shells of boron and iron atoms. This alloy consists of nanoclusters in which boron and iron atoms have a short-range order of the tetragonal Fe₃B phase type.     

P2-type Na<Subscript>0.67</Subscript>Mn<Subscript>0.6</Subscript>Fe<Subscript>0.4-x-y</Subscript>Zn<Subscript>x</Subscript>Ni<Subscript>y</Subscript>O<Subscript>2</Subscript> cathode material with high-capacity for sodium-ion battery

The P2-type Na_0.67Mn_0.6Fe_0.4O₂ (NaMnFe), Na_0.67Mn_0.6Fe_0.3Zn_0.1O₂ (NaMnFeZn), and Na_0.67Mn_0.6Fe_0.2Zn_0.1Ni_0.1O₂ (NaMnFeZnNi) are prepared using an acetate decomposition reaction and developed as promising cathode materials for high-capacity sodium-ion batteries. The XRD patterns show that Zn²⁺ and Ni²⁺ ions are successfully incorporated into the lattice of the Na-Mn-Fe-O system, and the P2-type structure remains unchanged after substitution. The charging/discharging tests exhibit that the Na_0.67Mn_0.6Fe_0.4O₂, Na_0.67Mn_0.6Fe_0.3Zn_0.1O₂, and Na_0.67Mn_0.6Fe_0.2Zn_0.1Ni_0.1O₂ electrodes have the capacities of 200.4, 182.0, and 202.2 mAhg^?1, respectively. The Na_0.67Mn_0.6Fe_0.4O₂ electrode has a higher initial capacity but faster capacity decay. When partially substituting Zn and Ni for Fe, the Na_0.67Mn_0.6Fe_0.3Zn_0.1O₂ and Na_0.67Mn_0.6Fe_0.2Zn_0.1Ni_0.1O₂ electrodes exhibit lower reversible capacity but improved cycling stability (88.3 and 93.4% capacity retention over 100 cycles). The greatly improved electrochemical performance of the Na_0.67Mn_0.6Fe_0.2Zn_0.1Ni_0.1O₂ electrode apparently belongs to the contribution of the Zn²⁺ and Ni²⁺ substitution, which facilitates to alleviate the Jahn-Teller distortion of Mn and suppresses the polarization.     

Pressure-Induced Decrease in the Curie Temperature of Gd<Subscript>2</Subscript>Fe<Subscript>17</Subscript>: LSDA+U Calculations

To explain the magnetic properties of advanced ferromagnetic intermetallic compounds of the R₂Fe₁₇ (R is a rare-earth element) class, experimentalists often use the hypothesis of competition between ferromagnetic exchange and antiferromagnetic exchange between four types of the nearest iron atoms in nonequivalent lattice sites. For the rhombohedral Gd₂Fe₁₇ ferromagnet, we calculate the magnetic moments of iron and gadolinium ions, the parameters of exchange between Fe atoms, and Curie temperature T_C at a zero pressure and during hydrostatic lattice compression. The magnetic moment of the unit cell of Gd₂Fe₁₇ is shown to decrease under pressure, and this decrease is almost completely associated with a decrease in the magnetic moments of Fe rather than Gd ions, the pressure dependence of the magnetic moments of which is weaker by an order of magnitude. In contrast to the hypothesis regarding the competition of exchange interactions between different kinds of Fe atoms, the parameters of exchange between the nearest iron atoms in different crystallographic sites are found to be positive ferromagnetic (at a zero pressure and during compression), and a ferromagnetic character of interaction is shown to remain unchanged under pressure even for Fe atoms in the so-called dumbbell sites with the nearest interatomic distances. The Curie temperature T_C of Gd₂Fe₁₇ is shown to decrease with increasing pressure. The changes in the exchange parameters and the magnetic moments of Gd₂Fe₁₇ during compression are found to be mainly related to a change in the position of energy spectrum branches with respect to each other and the Fermi level ?_F rather than to a change in the overlapping of wavefunctions, which play a minor role.     

Improving the electrochemical performance of Li-rich Li<Subscript>1.2</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>Mn<Subscript>0.54</Subscript>O<Subscript>2</Subscript> cathode material by LiF coating

To suppress the capacity fade of Li-rich Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ material as cathode materials for lithium-ion battery, we introduce a LiF coating layer on the surface to improve the cycling performance of Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ material. The modified sample shows a capacity of 163.2 mAh g^?1 with a capacity retention of 95% after 100 cycles at a current density of 250 mA g^?1, while the pristine sample only delivers a capacity of 129.9 mAh g^?1 with a capacity retention of 82%. Compared with the pristine material, the LiF-modified sample exhibits an obvious enhancement in the electrochemical performance, which will be very beneficial for this material to be commercialized on the new energy vehicles and other related areas.     

Fe<Subscript>3</Subscript>P impurity phase in high-quality LiFePO<Subscript>4</Subscript>: X-ray diffraction and neutron-graphical studies

High discharge capacity and long life cycles of electrodes fabricated from various LiFePO₄ powders have been used to select samples for detailed structural studies. In some samples, the presence of ferromagnetic Fe₃P crystallites was revealed by the synchrotron X-ray diffraction analysis, with the integral intensity ratio of the peaks Fe₃P (231) and LiFePO₄ (112) equal to ～1/12. Small-angle polarized neutron scattering (SAPNS) detected the presence of magnetic nuclear contrasting regions with size of 17 ± 1 nm. The average diameter of LiFePO₄ crystallites is 230 nm, and Fe₃P crystallites were found as 17 × 54 nm² plates. The high quality of these samples was provided by their manufacturer via synthesis of the Fe₃P impurity phase. It can be stated that the set of studies, developed in the study, is helpful in a search for new effective impurity phases and in optimization of their parameters.     

Electronic and magnetic properties of Fe<Subscript>2</Subscript>SiC

The electronic structure and magnetic properties of Fe₂SiC compound have been studiedusing the framework of an all-electron full-potential linearized augmented-plane wave(FP-LAPW) method within the local density (LSDA) and + U corrected(LSDA + U)approximations. An antiferromagnetic spin ordering of Fe atoms is shown to be the groundstate for this compound. From the electronic band structures and density of states (DOS),Fe₂SiC has ametallic character and from the analysis of the site and momentum projected densities, itis deduced that the bonding is achieved through hybridization of Fe-3d with C-2p states andFe-3d withSi-3pstates. It is also pointed out that the Fe-C bonding is more covalent than Fe-Si. In theFM phase, the spin polarized calculations indicate that the total magnetic moment ofFe₂SiC increasesfrom 0.41 to 4.33μ _B when the Hubbard U parameter for iron isconsidered.     

Synthesis of Ni<Subscript>80</Subscript>Fe<Subscript>20</Subscript> and Co nanodot arrays by self-assembling of polystyrene nanospheres: magnetic and microstructural properties

Array of dots have been designed by assembling a monolayer of polystyrene nanospheres (PN) on sputtered thin films having Ni₈₀Fe₂₀ and Co composition with different thickness, ranging in the interval 20 ÷ 80 nm. Subsequently the films are nanopatterned using the nanospheres as a mask during sputter etching with Ar⁺ ions. A Reactive Ion Etching (RIE) process before sputter etching is used to control the final diameter of the magnetic dots that thus can be tailored as desired (typically ranging in the interval 250 ÷ 400 nm depending on the PN starting diameter). In addition, electron beam lithography has been exploited to obtain arrays of dots in Ni₈₀Fe₂₀ thin films having approximately the same mean size and dot distance as in self-assembled samples. All films have been routinely characterized by SEM and AFM microscopy to evaluate the microstructure. Magnetic domain patterns at magnetic remanence and in the demagnetised state have been imaged by MFM microscopy technique. Room-temperature hysteresis properties have been measured by an alternating gradient force magnetometer. In general, the magnetization process in all patterned films has been observed to have features typical of a vortex whose nucleation field depends on sample thickness and mean dot dimension. A comparison between magnetic arrays of Ni₈₀Fe₂₀ dots prepared by self-assembling of polystyrene nanospheres and electron beam lithography is presented to rule out the role of microstructure (i.e., order, size, and mutual distance of the magnetic dots) on magnetic properties.     

Long-wavelength magnetic excitations in the Fe<Subscript>65</Subscript>Ni<Subscript>35</Subscript> alloy

A theoretical analysis of small-angle neutron scattering is performed for the Fe₆₅Ni₃₅ alloy at a temperature T=0.9T _C =450 K. The results obtained indicate the existence of long-wavelength magnetic excitations that do not correspond to spin waves of the Holstein-Primakoff type. The possible nature of these excitations is discussed.     

Valence and magnetic states of impurity iron ions in the La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>Co<Subscript>0.98</Subscript>Fe<Subscript>0.02</Subscript>O<Subscript>3</Subscript> perovskite

The local magnetic and valence states of impurity iron ions in the rhombohedral La_0.75Sr_0.25Co_0.98 ⁵⁷Fe_0.02O₃ perovskite were studied using Mössbauer spectroscopy in the temperature range 87–293 K. The Mössbauer spectra are described by a single doublet at 215–293 K. The spectra contained a paramagnetic and a ferromagnetic component at 180–212 K and only a broad ferromagnetic sextet at T < 180 K. The results of the studies showed that, over the temperature range 87–295 K, the iron ions are in a single (tetrahedral) state with a valence of +3. In the temperature range 180–212 K, two magnetic states of Fe³⁺ ions were observed, one of which is in magnetically ordered microregions and the other, in paramagnetic microregions; these states are due to atomic heterogeneity. In the magnetically ordered microregions in the temperature range 87–212 K, the magnetic state of the iron ions is described well by a single state with an average spin S = 1.4 ± 0.2 and a magnetic moment μ(Fe) = 2.6 ± 0.4μ _B .     

Surface modification of permalloy (Ni<Subscript>80</Subscript>Fe<Subscript>20</Subscript>) nanoparticles for biomedical applications

We report a simple and novel method for surface biofunctionalization onto recently reported Ni₈₀Fe₂₀ permalloy nanoparticles (~71 nm) and the immobilization of a model protein, IgG from human serum. The strategy of protein immobilization involved attachment of histidine-tagged streptavidin to the Ni₈₀Fe₂₀ nanoparticles via a non-covalent ligand binding followed by biotinylated human IgG binding on the nanoparticle surface using the specific high affinity avidin–biotin interaction. The biofunctionalization of Ni₈₀Fe₂₀ permalloy nanoparticles was confirmed by Fourier Transform InfraRed (FTIR) spectroscopy and protein denaturing gel electrophoresis (lithium dodecyl sulfate-polyacrylamide gel electrophoresis, LDS-PAGE). This protocol for surface functionalization of the novel nanometer-sized Ni₈₀Fe₂₀ permalloy particles with biological molecules could open diverse applications in disease diagnostics and drug delivery.     

Site occupancy of Fe in ternary Ni<Subscript>75−</Subscript><Emphasis Type="Italic">x</Emphasis>Fe<Subscript>x+y</Subscript>Al<Subscript>25−</Subscript><Emphasis Type="Italic">y</Emphasis>alloys

The results of a detailed structural and magnetic study clearly indicate that regardless of the thermal history of the samples, Fe has a strong preference for the Ni sites in Ni-poor (nonstoichiometric) Ni₇₅Al₂₅ alloys. Fe substitution has a profound effect on the nature of magnetism in Ni₂₅Al₂₅ Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India.     

Magnetic properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> surface

The magnetic properties of the magnetite Fe₃O₄(110) surface have been studied by spin resolved Auger electron spectroscopy (SRAES). Experimental spin resolved Auger spectra are presented. The results of calculation of Auger lines polarization carried out on the basis of electronic state density are presented. Problems related to magnetic moments of bivalent (Fe²⁺) and trivalent (Fe³⁺) ions on the Fe₃O₄(110) surface are discussed. It is established that the deposition of a thin bismuth film on the surface results in significant growth of polarization of iron Auger peaks, which is due to additional spin-orbit scattering of electrons by bismuth atoms.     

The properties research of ferrum additive on Li [Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>] O<Subscript>2</Subscript> cathode material for lithium ion batteries

Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3] O₂(x?=?0.0, 0.1, 0.3, 0.5, 0.7, and 0.9) cathode materials have been synthesized via hydroxide co-precipitation method followed by a solid state reaction. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were utilized to determine the calcination temperature of precursor sample. The crystal structure features were characterized by X-ray diffraction (XRD). The electrochemical properties of Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3]O₂ were compared by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy(EIS), and galvanostatic charge/discharge test. Electrochemical test results indicate that Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ decrease charge transfer resistance and enhance Li⁺ ion diffusion velocity and thus improve cycling and high-rate capability compared with Li[Ni_1/3Co_1/3Mn_1/3]O₂. The initial discharge specific capacity of Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ was 178.5 mAh/g and capacity retention was 87.11 % after 30 cycles at 0.1C, with the battery showing good cycle performance.     

Magnetic properties of Pb<Subscript>2</Subscript>Fe<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>9</Subscript> single crystals

Single crystals of Pb₂Fe₂Ge₂O₉ have been grown. They were subjected to X-ray diffraction, magnetic, neutron diffraction, Mössbauer and spin resonance studies. It has been established that Pb₂Fe₂Ge₂O₉ is a weak ferromagnet with a Néel temperature T _N = 46 K, and the exchange and spin-flop transition fields have been estimated. It has been demonstrated that the weak ferromagnetic moment is actually the result of the single-ion anisotropy axes for the magnetic moments of different magnetic sublattices being not collinear.     

Understanding the thermal stability and bonding characteristic of Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> as cathode materials for lithium-ion battery from first principles

The thermodynamic stability is a very important quantity for the electrode materials, because it is not only related to the electrochemical performances of the materials but also the safety issue of the cells. To evaluate the thermodynamic stability of Li _x Ni_0.5Mn_1.5O₄ (x = 0, 1), the formation enthalpies from elemental phases and oxides were obtained. The values for LiNi_0.5Mn_1.5O₄ were calculated to be ?1341.10 and ?141.84 kJ mol^?1, while those for Ni_0.5Mn_1.5O₄ were ?949.11 and ?49.21 kJ mol^?1. These values are much more negative than those of LiCoO₂ and LiNiO₂ compounds, indicating that the thermodynamic stability of Li _x Ni_0.5Mn_1.5O₄ is better than the two classic compounds. To clarify the microscopic origin, the density of states, magnetic moments, and bond orders were systematically investigated. The results showed that the excellent thermodynamic stability of LiNi_0.5Mn_1.5O₄ is attributed to the absence of Jahn-Teller distortions, strong electrostatic interactions of Li–O ionic bond, and strong Ni–O/Mn–O ionic-covalent mixing bonds. After lithium extraction, the disappearance of the pure Li–O bonds leads to an increase of formation enthalpy, indicating a decreasing thermodynamic stability for Ni_0.5Mn_1.5O₄ with respect to LiNi_0.5Mn_1.5O₄.     

Magnetic ordering in Fe<Subscript>1.087</Subscript>Te under pressure

The crystal and magnetic structures of Fe_1.087Te have been studied by neutron powder diffraction in the temperature range from 1.7 to 80 K at pressures of  ≈0.4 and ≈1.2 GPa. No symmetry change of the tetragonal paramagnetic ambient pressure phase (space group P4/nmm) was observed for temperatures above 60 K and pressures up to  ≈1.2 GPa. A novel pressure-induced phase of Fe_1.087Te having orthorhombic symmetry (space group Pmmn) and incommensurate antiferromagneticbicollinear order was observed in the temperature range from 50 to 60 K at  ≈1.2 GPa. The known monoclinic ambient pressure phase of Fe_1.087Te (space group P2 ₁/n) with commensurate antiferromagnetic order was found to be stable up to at least  ≈1.2 GPa at low temperature.     

Modification of the “Transcritical” state in Ni<Subscript>75</Subscript>Fe<Subscript>16</Subscript>Cu<Subscript>5</Subscript>Mo<Subscript>4</Subscript> films produced by RF sputtering

The saturation magnetization, the perpendicular and rotational anisotropy constants, and the coercitivity of Ni₇₅Fe₁₆Cu₅Mo₄ thin magnetic films produced by rf sputtering are measured in the initial state and after annealing. A relation between the presence of perpendicular anisotropy and the “transcritical” state in the films is established. It is shown that, after additional thermal treatment, the magnetic softness of the films can be improved.     

Synthesis and characterization of mesoporous and hollow-mesoporous M<Subscript>x</Subscript>Fe<Subscript>3-x</Subscript>O<Subscript>4</Subscript> (M=Mg,Mn, Fe,Co, Ni,Cu, Zn) microspheres for microwave-triggered controllable drug delivery

Spinel ferrites can be used in magnetic targeting and microwave heating and can therefore be used for targeted and controllable drug delivery. We used the cetyltrimethylammonium bromide-assisted solvothermal method to synthesize a series of spinel ferrites (M_xFe_3-xO₄, M=Mg, Mn, Fe, Co, Ni, Cu, Zn) with a mesoporous or hollow-mesoporous structure suitable for direct drug loading and the particle diameters ranging from 200 to 350 nm. We investigated the effects of M²⁺ cation on the morphology and properties of these products by analyzing their transmission electron microscopy images, mesoporous properties, magnetic properties, and microwave responses. We chose hollow-mesoporous M_xFe_3-xO₄ (M=Fe, Co, Zn) nanoparticles, which had better overall properties, for the drug VP16 (etoposide) loading and microwave-controlled release. The Co_xFe_3-xO₄ and Fe₃O₄ particles trapped 61.5 and 64.8%, respectively, of the VP16, which were higher than that (60.4%) of Zn_xFe_3-xO₄. Controllable drug release by these simple magnetic nanocarriers can be achieved by microwave irradiation, and VP16-loaded Co_xFe_3-xO₄ released the most VP16 molecules (more than 50% after 1 h and 69.1% after 6 h) under microwave irradiation. Our results confirm the favorable drug loading and microwave-controlled delivery by these ferrites, and lay a theoretical foundation to promote clinical application of the targeted controllable drug delivery system.

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Graphical abstract In the present study, we prepared mesoporous or hollow-mesoporous spinel ferrites (M_xFe_3-xO₄, M=Mg, Mn, Fe, Co, Ni, Cu, Zn) by CTAB-assisted solvothermal method and solved the problem of Cu and Ni impurities in Cu_xFe_3-xO₄ and Ni_xFe_3-xO₄ products by means of magnetic separation and additional redox reactions, respectively. We investigated the effects of the M²⁺ cation on the morphology, mesoporous properties, magnetic properties, and microwave responses of these ferrites. Then, the drug loading and microwave-controlled drug release of hollow-mesoporous M_xFe_3-xO₄ (M?=?Fe, Co, Zn) nanoparticles with better overall properties were also studied. Co_xFe_3-xO₄ has the best overall performances for microwave-controlled drug release.

     

Magnetic and Mössbauer Studies of Fe<Subscript>76</Subscript>Mo<Subscript>8</Subscript>Cu<Subscript>1</Subscript>B<Subscript>15</Subscript> Amorphous Alloy

“Zero field”-Mössbauer and magnetization measurements have been performed on an amorphous Fe₇₆Mo₈Cu₁B₁₅ alloy in the temperature range of (10-340) K. The room-temperature Mössbauer spectrum exhibits magnetic dipole and electric quadrupole interactions. At approximately 306 K, the magnetic interactions vanish and the alloy shows fully paramagnetic behavior. On the other hand, the relative representation of paramagnetic component becomes weak with decreasing temperature and below 220 K the magnetic dipole interactions prevail. Below this temperature an anomaly in the low-temperature dependencies of ac susceptibility and of magnetization, measured during cooling the specimen from 340 K down to 20 K is observed. The anomaly on the magnetization curve vanishes in the field of 200 Oe.     

Optical spectroscopic analysis of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> doped CuO containing phosphate glass

The effect of Fe₂O₃ in sodium zinc phosphate glass system containing CuO with the chemical composition 40P₂O₅:38ZnO:1CuO:(21 ? x)Na₂O:xFe₂O₃ (where x = 1, 2, 3, 4, 5 and 6 mol%) has been studied. The glass formability of the prepared samples was examined by means of XRD which proved that there are no natural crystal contents. Archimedes method has been employed to measure the density of the prepared glass samples hence, the molar volume was calculated. The density and the molar volume were found to be increased by increasing Fe₂O₃ content. The optical spectroscopic analysis for the obtained glass samples has been carried out over the whole range (190–1000 nm) for studying the effect of bandpass absorption glass filter, its color peak center and UV cut-off. The center for bandpass filter is found to exhibit a red shift by increasing Fe₂O₃ content. Moreover, all glass samples showed a bandstop in UV-range which was increased by increasing Fe₂O₃ content. The results reveal the practicality of this glass composition in optical color glass bandpass filter for UV preventing applications such as UV-Laser protection.