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The Dzyaloshinskii–Moriya interaction (DMI) is well known to favor a chiral rotation of the magnetic moments, which accounts for the emergence of the skyrmions. The DMI is a combined effect of spin–orbit coupling with broken inversion symmetry in magnets. Most of the noncentrosymmetric magnetic materials that bear skyrmions involve nonmagnetic elements. This work shows that strong DMIs exist in elemental cobalt with a β-Mn-type metastable structure. The variation of DMI among different cobalt pairs largely follows the variation of hopping magnitude in which p electrons play an important role. Although the DMIs between different atomic pairs partly cancels with each other, the net interaction is sufficient to result in a left-handed Bloch-type spiral. Spin dynamics simulation shows that a critical magnetic field of 2.9 T stabilizes skyrmions at 0 K.

Herein, for the first time, we report copper-cysteamine (Cu-Cy) nanoparticles having Cu1+ instead of Cu2+ as an efficient heterogeneous Fenton-like catalyst for highly selective cancer treatment. I...

Esophageal cancer (EC) is the sixth leading cause of cancer deaths worldwide with a low 5-year survival rate. More effective chemotherapeutic drugs, either new or repurposing ones, are urgently needed. Disulfiram (DSF) is a safe and public domain drug for alcohol addiction treatment and later shown to have anti-cancer capability, especially when administrated together with copper. The present study is to test the hypothesis that a newly developed copper-cysteamine (Cu-Cy) nanoparticles (NPs) can enhance the anti-tumor effect of DSF on esophageal cancer with reduced risk of copper poisoning. Our results showed that Cu-Cy NPs could greatly facilitate DSF to inhibit cell proliferation in cultured human esophageal cancer cells. Interestingly, the combined inhibitory function could be further enhanced when DSF and Cu-Cy NPs were present at an optimal molar ratio of 1:4. The results of the change in physical color, UV-vis absorption and fluorescence spectra, X-ray diffraction patterns, and FTIR spectra from a mixture of DSF and Cu-Cy NPs suggest a possible reaction between DSF and Cu-Cy NPs and the formation of new materials. Furthermore, cellular mechanistic studies revealed that the combination of DSF and Cu-Cy NPs resulted in reactive oxygen species (ROS) accumulation, and blocked nuclear translocation of NF-ƙB (p65) in esophageal cancer cells. Moreover, in xenograft nude mice, combined administration of DSF and Cu-Cy NPs greatly inhibited tumor growth without noticeable histological toxicity, while any single agent at the same doses presented no inhibitory function. Together, this study demonstrates an effective anti-cancer function of combined treatment of DSF and Cu-Cy NPs in vitro and in vivo, which could be a promising new chemotherapy for esophageal cancer patients.

An efficient heat activating mediator with an enhanced specific absorption rate (SAR) value is attained via control of the iron oxide (Fe3O4) nanoparticle size from 3 to 32 nm. Monodispersed Fe3O4 nanoparticles are synthesized via a seed-less thermolysis technique using oleylamine and oleic acid as the multifunctionalizing agents (surfactant, solvent and reducing agent). The inductive heating properties as a function of particle size reveal a strong increase in the SAR values with increasing particle size up to 28 nm. In particular, the SAR values of ferromagnetic nanoparticles (>16 nm) are strongly enhanced with the increase of ac magnetic field amplitude than that for the superparamagnetic (3–16 nm) nanoparticles. The enhanced SAR values in the ferromagnetic regime are attributed to the synergistic contribution from the hysteresis and susceptibility loss. Specifically, the 28 nm Fe3O4 nanoparticles exhibit an enhanced SAR value of 801 W g−1 which is nearly an order higher than that of the commercially available nanoparticles.

The ternary compound, CuBi2O4, a 1:1 stoichiometric derivative of the two component oxides CuO and Bi2O3, has attracted attention from the solar water splitting and photocatalysis communities as a p-type semiconductor responsive to visible light. This study demonstrates that solution combustion synthesis (SCS) can be used to prepare powders not only of this compound but also nanocomposites with either CuO or Bi2O3 in excess. This was simply done by tuning the SCS precursor mixture composition. The synthesized crystalline samples were characterized by powder X-ray diffraction (with Rietveld refinement for phase purity), diffuse reflectance UV–visible spectroscopy, electron microscopy, and photoelectrochemical (PEC) techniques. The band structure and photoactivity of these oxides were probed by linear sweep voltammetry and by measuring their photoaction spectra (internal photon-to-electron conversion efficiency vs wavelength). The photoactivity (attributed to hydrogen evolution and CO2 photoreduction) was c...

Copper–cysteamine (Cu–Cy) is a novel sensitizer that can be excited by ultraviolet (UV) light, microwave (MW), ultrasound, and X-rays to generate highly toxic reactive oxygen species (ROS) for cancer cell destruction. The purpose of this study is to present a facile method for the synthesis of Cu–Cy nanoparticles. Interestingly, we were able to decrease both the stirring and heating time by about 24 and 6 times, respectively, thus making Cu–Cy nanoparticles more economical than what was reported before. 1,4-Diazabicylo[2.2.2]octane (DABCO), a well-known singlet oxygen quencher, showed that the majority of ROS produced by Cu–Cy nanoparticles upon UV and MW exposure were singlet oxygen. Moreover, ROS generated by Cu–Cy nanoparticles upon UV and MW exposure were confirmed by a known ROS tracking agent, dihydrorhodamine 123, further serving as an additional piece of evidence that Cu–Cy is a promising ROS generating agent to destroy cancer cells as well as bacteria or viruses by a radical therapeutic approach. Additionally, for the first time, the hydroxyl radical (˙OH) produced by Cu–Cy nanoparticles upon MW activation was proved by a photoluminescence (PL) technique using coumarin as a probe molecule. Remarkably, newly synthesized nanoparticles were found to be much more effective for producing ROS and killing cancer cells, suggesting that the new method may have increased the reactivity of the Cu–Cy nanoparticles due to an overall size reduction. Overall, the new method not only reduced the synthesis time but also enhanced the effectiveness of Cu–Cy nanoparticles for photodynamic therapy.

Localized heat induction using magnetic nanoparticles under an alternating magnetic field is an emerging technology applied in areas including, cancer treatment, thermally activated drug release and remote activation of cell functions. To enhance the induction heating efficiency of magnetic nanoparticles, the intrinsic and extrinsic magnetic parameters influencing the heating efficiency of magnetic nanoparticles should be effectively engineered. This review covers the recent progress in the optimization of magnetic properties of spinel ferrite nanoparticles for efficient heat induction. The key materials factors for efficient magnetic heating including size, shape, composition, inter/intra particle interactions are systematically discussed, from the growth mechanism, process control to chemical and magnetic properties manipulation.

Cobalt (Co) is one of the most important 3d transition metal elements used in the development of magnetic materials, especially in hard magnetic materials, from the early Co-based steel magnets to the rare-earth permanent magnets based on the 3d-4f compounds. Like iron (Fe), Co possesses a high saturation magnetization (MS) and a high Curie temperature (TC). Unlike Fe, Co has high magnetocrystalline anisotropy due to its spin-orbit coupling. As a result, it can be used to achieve a high degree of magnetic hardening in its elemental, alloy or compound materials. For instance, Co-based magnetic recording media is based on its elemental material. On the other hand, nano-structuring of Co-based alloys gives important hard magnetic materials including Alnico magnets and Fe–Cr–Co magnets, which are probably the earliest nanostructured hard magnetic materials. Recent progress in the development of Co-containing nanoscale hard magnetic materials has been very encouraging and promising based on the outstanding magnetic properties we have seen in L10 CoPt, tetragonally distorted FeCo and Co-based intermetallics. Particularly, the morphology of the nanoparticles has also been modulated to develop high coercivity via utilizing shape anisotropy, leading to extraordinarily high coercivity in Co nanowire assemblies. This review presents an overview of the development of Co-based hard and semi-hard magnetic materials and their intrinsic and extrinsic magnetic properties in view of fundamental understanding and technological applications.

Fe3O4 nanoparticles (NPs) with different shapes have been prepared by a 'solventless' synthesis approach to probe shape anisotropy effects on the magnetic and inductive heating properties. Various shapes including spheres, octahedrons, cubes, rods, wires, and multipods are obtained through alterations in reaction conditions such as the ratio of precursor to surfactant content and heating rate. Magnetic and Mossbauer measurements reveal better stoichiometry in anisotropic-shaped Fe3O4 NPs than that in the spherical and multipod NPs. As a result, the magnetization value of the anisotropic-shaped NPs approaches the value for bulk material (∼86 emu g-1). More surprisingly, the Verwey transition, which is a characteristic phase transition of bulk magnetite structure, is observed near 120 K in the anisotropic-shaped NPs, which further corroborates the fact that these NPs possess better stoichiometry compared to the spherical and multipod-shaped NPs. Other than the improved magnetic properties, these anisotropic-shaped NPs are more effective for hyperthermia applications. For example, compared to the conventional spherical NPs, the nanowires show much higher SAR value up to 846 W g-1, making them a potential candidate for practical hyperthermia treatment. In particular, the octahedral NPs shows an SAR value higher than the same size spherical NPs, which demonstrates the importance of occurrence of the Verwey transition in Fe3O4 NPs for better stoichiometric and higher heating.

This study reports on the solution combustion synthesis of two different ternary niobium oxides, namely, p-CuNb2O6 and n-ZnNb2O6. Such ternary oxides are attractive candidates in the “Holy Grail” search for efficient and stable semiconductors for solar energy conversion and environmental remediation. We demonstrate how this time- and energy-efficient method is capable of synthesizing high surface area and crystalline nanoparticles of the above compounds with enhanced optoelectronic properties. The synthesized crystalline samples were characterized by powder X-ray diffraction (with Rietveld refinement for phase purity), diffuse reflectance UV–visible and Raman spectroscopy, electron microscopy, and photoelectrochemical (PEC) techniques. The band structure of these oxides was probed by linear sweep voltammetry and by measuring their photoaction spectra (internal photon to electron conversion efficiency vs wavelength). The obtained bandgap energy values (1.9 and 3.2 eV for the Cu- and Zn-containing compounds...

A surfactant- and template-free approach is described for the synthesis of mesoporous α-Fe2O3, Fe3O4 and α-Fe nanowires (NWs). In this approach, α-FeOOH NWs (length 550 nm and diameter 30 nm) were first prepared by hydrolysis of FeCl3. On subsequent thermal treatment in a fluidized bed reactor in the presence of a forming gas (Ar 93% + H2 7%), α-FeOOH transformed to mesoporous NWs of ɑ-Fe2O3, Fe3O4 and ɑ-Fe by controlling the process parameters such as reaction time and temperature. The obtained NWs of α-Fe2O3, Fe3O4 and α-Fe were ferromagnetic at room temperature with a coercive field (Hc) of 412, 583 and 628 Oe respectively. The aligned NWs showed 1.6 to 2 times-enhanced remanence in the parallel direction relative to the perpendicular direction due to magnetic anisotropy. These mesoporous magnetic NWs with a high specific surface area (82 m2 g−1 for α-Fe2O3 NWs) were used in photocatalysis due to the high adsorptivity of three probe dye molecules. The as-prepared α-Fe2O3 NWs exhibited only modest photocatalytic activity; however, the catalytic activity could be further enhanced by decorating the mesoporous ɑ-Fe2O3 NWs with 10 nm sized ZnO nanoparticles. The developed ɑ-Fe2O3/ZnO nanowire nanohybrids could eliminate 100% of the probe dyes: methylene blue, Rhodamine B and methyl orange within 90 min irradiation with solar light, underlining the high photocatalytic degradation efficiency of the nanohybrid. The nanowire nanohybrids could be easily recovered by applying an external magnetic field and reused for at least 4 times without significant loss of their photocatalytic activity.

MnFe 2 O 4 nanoparticles and polyacrylic acid PAA/MnFe 2 O 4 nanocomposites were synthesized by a hydrothermal method and ultrasonic mixing process. The obtained materials were characterized by XRD, FTIR, SEM, TEM, and VSM. XRD patterns indicate that the synthesized MnFe 2 O 4 nanoparticles have a single cubic spinel phase. SEM images confirm the existence of three types of basic morphology of MnFe 2 O 4 nanoparticles: octahedral, flower-like, and plate-like particles. High saturation magnetization M s (up to 74.6 emu/g) of the as-synthesized MnFe 2 O 4 nanoparticles was obtained. Experiments demonstrate that the variation of the hydrothermal reaction time does not remarkably affect the magnetic properties of MnFe 2 O 4 nanoparticles. In PAA/MnFe 2 O 4 nanocomposites, the coating of PAA leads to a slight decrease in magnetization of MnFe 2 O 4 nanoparticles. Additionally, PAA coating greatly enhances the adsorption properties of MnFe 2 O 4 nanoparticles for Methylene Blue (MB) dye. Especially, the removal efficiency reaches 96.3%. This research indicates that the as-synthesized PAA/MnFe 2 O 4 nanocomposites exhibit excellent magnetic properties and can be taken as a promising adsorbent for removal of MB dye in industrial scale.

CoFe 2 O 4 ferrite nanoparticles are synthesized by an ethanol-assisted hydrothermal method, where the ethanol is mixed with water as the solution. In this synthesis, a rapid mixing of reducible metal cations with reducing agent and a simultaneous reduction process take place in a colloid mill. Synthesized ferrite samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and Raman spectroscopy. XRD patterns reveal the formation of CoFe 2 O 4 ferrites with single spinel phase. SEM and TEM images show that the as-synthesized samples are with narrow size distribution. Raman spectroscopy studies clearly indicate the cation distribution in nanosized particles. Here, it is worthy to note that, with increasing ethanol content in ethanol–water mixed solution, an obvious superparamagnetic behavior of as-synthesized nanoparticles at room temperature is observed. The adsorption capability of the as-synthesized ferrite nanoparticles for Congo Red (CR) is examined. Enhancement of adsorption capability for CR with adding ethanol as the mixing solution is shown. The adsorption mechanism is discussed. This investigation reveals that the composition of ethanol/water mixed solution has great effects on the microstructure and magnetic properties as well as adsorption capacity of Congo Red (CR) dye of the as-synthesized CoFe 2 O 4 ferrite samples.

In the search for stable and efficient photocatalysts beyond TiO2 , the tungsten-based oxide semiconductors silver tungstate (Ag2 WO4 ), copper tungstate (CuWO4 ), and zinc tungstate (ZnWO4 ) were prepared using solution combustion synthesis (SCS). The tungsten precursor's influence on the product was of particular relevance to this study, and the most significant effects are highlighted. Each sample's photocatalytic activity towards methyl orange degradation was studied and benchmarked against their respective commercial oxide sample obtained by solid-state ceramic synthesis. Based on the results herein, we conclude that SCS is a time- and energy-efficient method to synthesize crystalline binary tungstate nanomaterials even without additional excessive heat treatment. As many of these photocatalysts possess excellent photocatalytic activity, the discussed synthetic strategy may open sustainable materials chemistry avenues to solar energy conversion and environmental remediation.

A three-sublattice model is applied to study the magnetic properties of scandium substituted ytterbium iron garnet (Sc-YbIG). The magnetic moments in three magnetic sublattices ( a , c and d sites) in Sc-YbIG are analyzed, where the diamagnetic Sc 3+ ions substitute for octahedral Fe 3+ ions. The parameters α i ( i = a , c , d ), associated with the exchange field and the magnetic susceptibility, are introduced. Here, α i show obvious high magnetic field-dependent and temperature-dependent properties. Based on the thought of three magnetic sublattices, the magneto-optical properties in Sc-YbIG, as magnetic field applied along [1 0 0], [1 1 0] and [1 1 1] directions, at low temperatures are studied by an improved magneto-optical four-level model, where the physical mechanism of magneto-optical anisotropy is explored in low magnetic fields. Our theory is in good agreement with the experimental results.

In this report, we present a novel one-step solid-phase reaction method for the synthesis of L10-CoPt@C core-shell nanoparticles (NPs) using organic metal precursors without surfactants. The obtained CoPt@C NPs have a good face-centered tetragonal single crystal structure and regular shape. The mean size of CoPt is 14 nm with a uniform carbon shell. The evolution of the core-shell structure during the synthesizing process is investigated in detail. Firstly organic metal precursors are decomposed, followed by the formation of grains/clusters in a metal-carbon intermediate state. Then the metal-carbon small grains/clusters agglomerate and recrystallize into single crystal metal alloy NPs covered with a carbon layer. The carbon shell is effective in preventing the coalescence of L10-CoPt NPs during high temperature sintering. The prepared L10-FePt nanoparticles have a high coercivity of up to 12.2 kOe at room temperature. This one-step solid-state synthesizing method could also be employed for the preparation of other types of nanostructures with high crystallinity, monodispersity and chemically ordered phase.

The preferential site substitution of Fe by Si, Ge and Sn and its effect on magnetic moments have been studied in Nd 2 Fe 14 B by a first-principles density functional calculation. The substitution energies of Si and Ge are positive at the sites of 4e, 8 j 2 and 16 k 1 while the values are negative at the sites of 4c, 8 j 1 and 16 k 2 . However, the substitution energies of Sn are only negative at the sites of 4c and 8 j 1 in Nd 2 ( Fe,Sn ) 14 B . Based on Maxwell–Boltzmann distribution, Si, Ge and Sn prefer strongly to enter the site of 4c and exhibit a moderate preference at the site of 8 j 1 , in good agreement with the powder neutron diffraction results. Upon doping Si, Ge and Sn, the average Fe magnetic moments remain almost unchanged in addition to the dilute effect of the non-magnetic elements of Si, Ge and Sn. The slight enhancement of Nd magnetic moment results from the reduction of the net Nd 5d spin moment, which is antiparallel to the total Nd 4f moment. The reduction of Nd 5d spin moment is ascribed to the hybrid mixing of the Nd 5d electron states and the p electron states of the Si, Ge, and Sn nearest neighbors.

Nanocrystalline RCo5 (R = Ce, La0.35Ce0.65, and misch-metal noted as MM) ribbons with hexagonal crystal structure and an average grain size of 5 nm have been prepared via a one-step melt-spinning technique. Coercivity as high as 13.0, 13.8, and 10.9 kOe has been obtained at 300 K for the CeCo5, La0.35Ce0.65Co5, and MMCo5 ribbons, respectively. High thermal stability is also achieved as shown by the high coercivity of 9.3 kOe, 10.2 kOe, and 8.8 kOe at 400 K for CeCo5, La0.35Ce0.65Co5, and MMCo5 ribbons, respectively. The coercivity mechanism is studied by magnetization analysis and microstructural observations. The nanocrystalline grains promote a strong exchange interaction, as indicated by the positive δM and the relatively high remanence ratio (∼0.8). In addition, the temperature dependence of coercivity of RCo5 ribbons shows the low coercivity temperature coefficient of −0.2% to −0.25%/K.

Thick permanent magnetic films have potential applications in magnetic microelectromechanical systems. In this paper, we systematically study the effect of deposition parameters including buffer layer, annealing condition and deposition temperature on the structure and magnetic properties of thick Sm-Co-Cu-Fe-Zr films fabricated by magnetron sputtering. It is found that W instead of Cr is more suitable for a buffer layer for preparing the high quality of Sm-Co-Cu-Fe-Zr films. With increasing annealing temperature, the phase in the film was changed from the 2:17 phase to the mixture of 1:5 and 2:17 phases. However, the cellular structure was not formed. The coercivity values of the films were not influenced by the cooling rate. The deposition temperature strongly affects the microstructure, texture and domain structure of the films. The Sm2Co17 phase in high-temperature deposited film prefers a (110) texture, while that in RT deposited film has a (110) and (200) texture. The magnetic domain structure observation indicates that the prepared Sm-Co-Cu-Fe-Zr films exhibit a character of interaction domain. The domain size of the films changes with the deposition temperature.

Partial replacement of Nd by Y and La helps to decrease temperature coefficients of remanent magnetization for Nd 2 Fe 14 B (2:14:1) based magnets. The efficiency of La/Y doping depends on the distribution of La/Y in the multi-phase microstructure of a Nd–Fe–B magnet. To understand and control the La/Y redistribution, the partitioning of La/Y in 2:14:1 and Nd-rich grain boundary phase have been studied by a first-principles density functional calculation. The total energy calculations indicate that La and Y prefer to enter the 4 g and 4 f sites in the 2:14:1 phase, respectively. The substitution energies of La and Y in 2:14:1 are positive (0.41 eV/atom) and negative (−0.38 eV/atom), respectively. The results indicate that Y prefers to enter the 2:14:1 phase while La tends to be expelled from 2:14:1 phase to Nd-rich grain boundary phase. This is the thermodynamic origin for the different partition behavior of La and Y in Nd–Fe–B magnets, which affects the magnetic properties.

The magnetic properties of single crystalline hcp Co nanowire (NW) assemblies with different packing densities are investigated. The compacted assemblies exhibit an unusual increase in coercivity (HC) from 5.5 kOe to 6.1 kOe with the increase of the packing density from 2.1 to 4.5 g/cm3. While Hc decreases with further increase in packing density. A similar trend in Hc value variation with density has also been noticed at different temperatures. The initial increase in HC values is ascribed to magnetostatic interaction between the nanowires, which became stronger with the increased packing density. However, above the density of 4.5 g/cm3, the Hc decreases due to the proximity effect as shown in the δM plot. The δM plot shows a negative peak at high field and it becomes prominent with the increased density. Moreover, it has been found that the variation of HC with the packing density is also related to diameter of Co NWs. A larger diameter of the nanowires gives a negative dependence of the Hc value with the density in the whole investigated region.The magnetic properties of single crystalline hcp Co nanowire (NW) assemblies with different packing densities are investigated. The compacted assemblies exhibit an unusual increase in coercivity (HC) from 5.5 kOe to 6.1 kOe with the increase of the packing density from 2.1 to 4.5 g/cm3. While Hc decreases with further increase in packing density. A similar trend in Hc value variation with density has also been noticed at different temperatures. The initial increase in HC values is ascribed to magnetostatic interaction between the nanowires, which became stronger with the increased packing density. However, above the density of 4.5 g/cm3, the Hc decreases due to the proximity effect as shown in the δM plot. The δM plot shows a negative peak at high field and it becomes prominent with the increased density. Moreover, it has been found that the variation of HC with the packing density is also related to diameter of Co NWs. A larger diameter of the nanowires gives a negative dependence of the Hc value with t...

We report here a simple route for the chemical synthesis of SmCo5 and Sm2Co17 single-phase and SmCo5/Fe composite nanocrystals by polyol reduction of metal precursors and subsequent calcium reductive annealing. Sm2O3 and Co nanoparticles were synthesized first, and nanocrystalline SmCo5 or Sm2Co17, compound with tunable composition was then obtained after the annealing. The composition of the compound was controlled by varying the initial molar ratio of the metal precursors. At room temperature, the obtained SmCo5 and Sm2Co17 show coercivity of 12 kOe and 4 kOe, and saturation magnetization of 70 emu/g and 85 emu/g, respectively. To prepare SmCo5/Fe nanocomposites, Fe, Co and Sm2O3 nanoparticles were synthesized in one-pot by polyol reduction of the metal precursors.

Rhombohedral nickel carbide (Ni3Cx, x=0.7, 1.2 and 1.5) nanoparticles (∼ 110 nm) with enhanced magnetic coercivity (HC up to 1.3 kOe) at temperature below the spin-glass freezing (Tf) have been demonstrated. The presence of spin-glass state, which is seen at ∼17 K, is evident by the field dependence of the freezing temperature following the de Almeida–Thouless (AT) relationship and frequency dependence of Tf. Moreover, the spin-glass state is irreversible to the sweeping applied field and results in high HC at 10 K. With increases of the carbon content, we have found a gradual increasing trend in the saturation magnetization (MS: 6.6 to 9.2 emu/g) and coercivity (350 Oe to 1.3kOe) at 10 K. This is attributed to the increase of spin-glass contribution and the weak ferromagnetic phase.

Fe(x)Pt(y)Au(100-x-y) nanoparticles of size 3.5 nm were prepared by polyol reduction of platinum acetylacetonate and gold acetate and the thermal decomposition of iron pentacarbonyl. The as-synthesized nanoparticles with disordered fcc structure were then heat treated to transform to the L1(0) structure with high magnetocrystalline anisotropy. By tuning the stoichiometry of the Fe(x)Pt(y)Au(100-x-y) nanoparticles, the phase transition temperature was reduced by more than 200 degrees C. After the annealing 500 degrees C, for instance, the highest coercivity of 18 kOe was obtained from the Fe51Pt36Au13 nanoparticles which is substantially higher compared to 2 kOe for Fe51Pt49 nanoparticles annealed at the same temperature. In addition to the high coercivity, the saturation magnetization value obtained from Fe51Pt36Au13 nanoparticles was 47 emu/g which is similar to that for the Fe51Pt49 nanoparticles, indicating that there is no trade-off between the coercivity and the saturation magnetization upon Au doping.

Fe 3 BO 5 nanorods with diameters from 4 nm to 16 nm and length from 43 nm to 60 nm are synthesized by a facile thermal decomposition of iron acetylacetonate and t-butylamine borane (TBAB). TBAB is used to control the 1 D growth and the aspect ratio of the nanorods. These Fe 3 BO 5 nanorods are antiferromagnetic with T N = 174 K, which is higher than that of bulk Fe 3 BO 5 (114 K).

This paper reports an improved synthesis of hard magnetic fct-FePt nanoparticles (NPs) from reductive annealing of fcc-FePt/Fe3O4/MgO NPs followed by MgO removal. The fcc-FePt/Fe3O4 NPs are made by a one-pot reaction of Pt(acac)2 with Fe(CO)5 in the presence of oleic acid and oleylamine and are coated with a layer of MgO via the thermal decomposition of Mg(acac)2. The MgO coating prevents FePt from sintering under high temperature reductive annealing conditions. The fct-FePt NPs obtained from the 650 °C annealing of the fcc-FePt/Fe3O4/MgO NPs show a coercivity value of 2 T at 300 K, suitable for various nanomagnetic applications.

Chemical reduction of ferric acetylacetonate (Fe(acac)3) and platinum acetylacetonate (Pt(acac)2) using polyol as a reducing agent as well as an effective surfactant, has successfully yielded monodisperse FePt nanoparticles with a size of approximately 2 nm. When annealed samples were compared to FePt nanoparticles synthesized using oleic acid and oleylamine as the surfactants under identical conditions, nearly 30% increase in coercivity (Hc) was achieved with the new, simple and economic method.

FePt films were deposited at room temperature on TiN intermediate layer followed by annealing. The effects of TiN layer thickness on the microstructure and magnetic properties of FePt films were investigated. It was found that TiN layer has significant effects on the magnetic anisotropy of the FePt films. The L10 phase transformation of the FePt films with TiN layer was more completely than that without a TiN layer. After annealing at 600 °C, TiN(111) intermediate layer in thickness of 30 nm induced the out-of-plane anisotropy and reached the highest out-of-plane coercivity (4.5 kOe). However, the coercivity was tended to decrease as the thickness of TiN(111) layer increasing to 50 nm. The anisotropy gradually switched from out-of-plane to in-plane when the annealing temperature was increased to 700 °C. The in-plane anisotropy of L10-FePt films may come from the relaxation of internal stress of the TiN layer after annealing at 700 °C, which was not able to provide sufficient in-plane tensile stress to induce the perpendicular growth of L10-FePt grains. Nevertheless, the in-plane coercivity enhanced to 12 kOe when the thickness TiN(111) intermediate layer was 30 nm.

We report here a systematic synthesis and characterization of aligned alpha-Fe2O3 (hematite), epsilon-Fe2O3, and Fe3O4 (magnetite) nanorods, nanobelts, and nanowires on alumina substrates using a pulsed laser deposition (PLD) method. The presence of spherical gold catalyst particles at the tips of the nanostructures indicates selective growth via the vapor-liquid-solid (VLS) mechanism. Through a series of experiments, we have produced a primitive "phase diagram" for growing these structures based on several designed pressure and temperature parameters. Transmission electron microscopy (TEM) analysis has shown that the rods, wires, and belts are single-crystalline and grow along111m or110h directions. X-ray diffraction (XRD) measurements confirm phase and structural analysis. Superconducting quantum interference device (SQUID) measurements show that the iron oxide structures exhibit interesting magnetic behavior, particularly at room temperature. This work is the first known report of magnetite 1D nanostructure growth via the vapor-liquid-solid (VLS) mechanism without using a template, as well as the first known synthesis of long epsilon-Fe2O3 nanobelts and nanowires.

Ferromagnetic metallic Cobalt nanowires are synthesized by the reduction of carboxylate salts of Co in 1, 2-butanediol using a solvothermal chemical process. In this process, the size and shape of the nanocrystals can be controlled via reaction parameters such as surfactant ratio, precursor concentration, and the temperature ramp. Synthesized Co nanocrystals exhibit the hexagonally close-packed phase favored the growth of anisotropic particles and the (002) crystalline direction is along the long axis of the nanowires. By varying the catalyst concentration in proper range, the effect of synthetic parameters on controlling Co nanoparticles with different length of 50 - 700 nm was systematically studied. Magnetic measurements and TEM images of the Cobalt nanowires indicate that the coercivity of the Co nanowires depends substantially on the morphology. The obtained highest coercivity of 8.4 kOe can be attributed to their small mean diameter and high crystallinity of nanowires for 200 - 300 nm.

In this study, controllable morphology evolution of hexagonal strontium ferrite (SrFe12O19) micro/nano-crystals has been demonstrated. Single phase strontium ferrite platelets with hexagonal morphology were successfully prepared by conventional ceramic process. In the hexagonal crystals, it is revealed that the anisotropic growth rate is changed, with the increasing of ball milling time, from relatively high rate along the direction (c-axis) to direction, leading to the morphology evolution. Moreover, the optimal saturation magnetization (MS) is 69.5 emu/g, which is intensely close to the theoretical value (72 emu/g). This study provides the direct evidence of the enhanced reaction activity induced by high energy ball milling in strontium hexaferrite platelets and the obtained SrFe12O19 particles are promising for the hard magnet application and the magnetoelectric electronics.

We report surface cleaning of magnetic nanoparticles (SmCo5 nanochips and CoFe2O4 nanoparticles) by using cold plasma. SmCo5 nanochips and CoFe2O4 nanoparticles, coated with surfactants (oleic acid and oleylamine, respectively) on their surfaces, were treated in cold plasmas generated in argon, hydrogen or oxygen atmospheres. The plasmas were generated using a capacitively coupled pulsed radio frequency discharge. Surface cleaning of nanoparticles was monitored by measurement of the reduction of surface carbon content as functions of plasma processing parameters and treatment times. EDX and XPS analyses of the nanoparticles, obtained after the plasma treatment, revealed significant reduction of carbon content was achieved via plasma treatment. The SmCo5 nanochips and CoFe2O4 nanoparticles treated in an argon plasma revealed reduction of atomic carbon content by more than 54 and 40 in atomic percentage, compared with the untreated nanoparticles while the morphology, crystal structures and magnetic properties are retained upon the treatments.

Cobalt nanowires with high aspect ratio have been synthesized via a solvothermal chemical process. Based on the shape anisotropy and orientation of the nanowire assemblies, a record high room-temperature coercivity of 10.6 kOe has been measured in Co nanowires with a diameter of about 15 nm and a mean length of 200 nm. As a result, energy product of the wires reaches 44 MGOe. It is discovered that the morphology uniformity of the nanowires is the key to achieving the high coercivity and high energy density. Nanowires of this type are ideal building blocks for future bonded, consolidated and thin film magnets with high energy density and high thermal stability.

We report here a novel synthetic method to prepare monodisperse air-stable FeCo nanoparticles with average sizes of 8, 12 and 20 nm. CoFe2O4 nanoparticles of different sizes were first synthesized by a chemical solution method. The as-synthesized CoFe2O4 nanoparticles were then mixed with ball-milled NaCl powders and heated to 400–500 ° C in forming gas (Ar 93%+H2 7%). The salt powder worked as a separating medium that prevents the CoFe2O4 nanoparticles from agglomerating during the heat treatment while the forming gas reduces the CoFe2O4 nanoparticles to FeCo nanoparticles. Monodisperse FeCo nanoparticles were recovered by dissolving the NaCl in water and subsequently washing with ethanol and acetone. Structural analyses confirmed that FeCo nanoparticles retained the same size as their oxide precursors. The size of the FeCo nanoparticles can be well tuned by controlling the size of the CoFe2O4 nanoparticles. The saturation magnetization of FeCo nanoparticles is size dependent and increases with size.

Hard magnetic NdFeB submicron and nanoflakes were successfully prepared by surfactant-assisted ball milling at room temperature (SABMRT) and low temperature (SABMLT) by using oleic acid (OA), oleylamine (OLA) and trioctylamine (TOA) as surfactant, respectively. Among the surfactants used, OA and OLA have similar effects on the morphology of the NdFeB nanoflakes milled at both room and low temperature. In the case of TOA, irregular micron-sized particles and submirco/nanoflakes were obtained for the NdFeB powders prepared by SABMRT and SABMLT, respectively. Samples prepared by SABMLT show better crystallinity and better degree of grain alignment than that prepared by SABMRT with the same surfactant. Comparing with the samples milled at RT, higher coercivity and larger remanence ratio were achieved in the NdFeB samples prepared at LT. The amounts of residual surfactants in final NdFeB powders were also calculated, which reveals that the final NdFeB powders milled at LT possess lower amount of residual surfactants than those milled at RT. It was found that lowering milling temperature of SABM would be a promising way for fabricating permanent magnetic materials with better hard magnetic properties.

By using Fe(CO)x-OAm (oleylamine, x < 5) as the Fe precursor to slow down the formation rate of FePt nanoparticles (NPs), a time dependence of the NPs' nucleation and growth process was observed by transmission electron microscopy (TEM). The complexing temperature of OAm and Fe(CO)5 at which Fe(CO)x-OAm was formed has a strong influence on the nucleation rate and growth process of the NPs. TEM analyses indicated that the NPs with isotropic shape were single crystalline throughout the synthesis and were formed by a diffusion-controlled Ostwald-ripening (OR) growth mechanism. The nanorod particles were first formed via joining of arbitrarily oriented single crystals and the two crystals formed a uniform particle afterwards, as described by the oriented-attachment (OA) mechanism. The ratio of OAm to Fe(CO)5 used in the preparation of Fe(CO)x-OAm has a significant influence on the growth process, and subsequently the shape, size and size distribution of the FePt NPs. By adjusting the ratio and its complexing temperature, single-crystal FePt NPs with controllable size and isotropic shape were obtained. The insight into the exploration of the specific roles of the reaction conditions and the formation mechanisms provided important information for controlling the morphology of the nanoparticles.

Bimagnetic FePt/CoFe2O4 nanoparticles having a bricklike morphology were synthesized by growing a soft magnetic CoFe2O4 phase on FePt cubic nanoparticle seeds. The size of the soft phase could be controlled by tuning the material ratio of the FePt seeds to the CoFe2O4 component. To obtain magnetic hardening, the as-synthesized bricklike nanoparticles were annealed at elevated temperatures under a reductive atmosphere to convert the disordered face-centered cubic FePt phase into the ordered L10 phase having high magnetic anisotropy. When the particles were annealed, a gradual change was observed in morphology from bricklike particles to spherical polycrystalline nanocomposite particles because of diffusion. Meanwhile, the magnetic energy density was enhanced as a result of the exchange coupling between the hard and soft phases. The enhancement was dependent on the ratio of the volumes of the soft phase and the hard phase.

Monodisperse spherical FeCo nanoparticles were synthesized by reduction decomposition of Fe(acac)3 and Co(acac)2 in the presence of surfactants and 1,2-hexadecanediol. The particle size can be controlled by varying the surfactants. The presence of surfactants on the surface of the nanocrystal protects them from surface oxidation. The saturation magnetization of as-synthesized particles is found to be size dependent. The as-synthesized FeCo nanoparticles can be made air-stable by annealing at 500 °C for 30 min without causing particles sintering.

We report a synthesis of FePt nanorods by confining decomposition of Fe(CO)5 and reduction of Pt(caca)2 in surfactant reverse cylindrical micelles. The controlled nucleation and growth kinetics in confined environment allows easy control over Fe/Pt composition, nanorod uniformity, and nanorod aspect ratio. The FePt nanorods tend to self-assemble into ordered arrays along three-dimensions. Directed assembly under external magnetic field leads to two-dimensional ordered arrays, parallel to the substrate magnetic field. We expect that with optimized external magnetic fields, we should be able to assemble these nanorods into orientated one or two-dimensional arrays, providing a uniform anisotropic magnetic platform for varied applications in enhanced data storage, magneto-electron transport, etc.

The preferential site substitution of Fe by Ga and its effect on magnetic moments have been studied in Nd2Fe14B by a first-principles density functional calculation. The calculated substitution energies of Ga are positive values and unfavorable for the Ga substitution at the sites of 8j2, 16k1, and 4e, while those are negative values and favorable for the Ga substitution at the sites of 4c, 8j1, and 16k2, in good agreement with the experimental results. The Ga atom shows a small induced negative moment with a size of about 0.2 μB. The magnetic moments of Fe with the nearest neighbor of Ga reduce by about 0.1–0.2 μB while the moments of Nd with the Ga nearest neighbors are enhanced slightly. These magnetic moment changes originate from the hybrid of the Ga 4p- with the Fe 3d- or the Nd 5d-electron states.

The electronic structure and magnetic properties for GdScGe system have been studied via a first-principles density functional calculation. The energy band structure has been calculated in a generalized gradient approximation, plus Hubbard U approach. For Gd atoms, seven spin-up 4f bands are fully occupied and situated at the bottom of Ge 4s-like states, while the spin-down 4f hole levels are completely unoccupied and well above the Fermi level. The calculated magnetic moment is 7.6 μB per formula unit and is not sensitive to the change of the unit cell volume. The exchange interaction increases with decreasing unit cell volume, which results in a pressure induced enhancement of the Curie temperature (TC). TC increases from about 345 K to 410 K as external pressure increases from 0 to 18 GPa. With the experimental lattice constants, the calculated TC is 353 K, which is in good agreement with the experimental value (TCexp.=349K).

Nd2Fe14B/α-Fe-based hard/soft nanocomposite magnets with Co addition have been prepared by ball-milling and warm compaction. It was found that Co addition into the magnetically hard phase improves magnetic properties significantly, especially the remanence ratio and coercivity. The effect on the magnetic properties of the selective Co addition may be attributed to enhanced interdiffusion across the hard/soft interface that improves the interface conditions for effective interphase exchange coupling. By optimizing the Co content in the Nd15Fe79−xCoxB6 hard phase, an energy product value about 21 MG Oe can be obtained in the isotropic Nd2(FeCo)14B/α-(FeCo) nanocomposite magnets compared with 15 MG Oe of Nd2Fe14B/α-Fe nanocomposite magnets prepared under the same conditions with the same grain size and microstructure, owing to the strengthened intergranular exchange interactions.

Anisotropic bonded magnets are fabricated by surfactant-assisted ball milling in a magnetic field and magnetic field alignment of the milled chip-like nanoparticles of the Sm–Co and Nd–Fe–B materials. It is found that the application of magnetic fields during the ball milling strengthens the anisotropy of the chips and therefore improves the alignment. For SmCo5 phase-based chips, for instance, energy products up to 26.0 MG Oe and 19.1 MG Oe are obtained for the chips and the bonded magnets, respectively. This combined technique opens a new approach to the fabrication of anisotropic bonded magnets for various applications.

We report here the preparation of Fe, Co, and FeCo nanoplates and nanoparticles by ball milling in the presence of surfactants in organic solvents. By controlling the milling and centrifugation conditions, the Fe, Co, and FeCo nanoplates and nanoparticles with different sizes were successfully obtained, from the slurries and from the top part of the solutions, respectively. The thickness of the nanoplates is in the range of 20–200 nm and their diameter is from 5 to 30 μm. The Fe, Co, and FeCo nanoparticles of about 6 nm show superparamagnetic behavior at room temperature and are ferromagnetic at low temperatures with blocking temperatures of 33, 103, and 54 K, respectively. It is found that the surfactants play multifold roles in the process.

We report a facile synthesis of ferromagnetic SmCo nanoparticles (NPs) via a controlled reduction of SmCo–O NPs. The SmCo–O NPs were prepared by co-precipitation of Co(II) and Sm(III) acetates with hexadecyl-trimethylammonium hydroxide and were embedded in a CaO matrix. The 7 nm SmCo3.6–O NPs were reduced by Ca at 960 °C and converted into ferromagnetic 6 nm SmCo5 NPs with their coercivities reaching 7.2 kOe. The synthesis provides a viable route to ferromagnetic SmCo NPs with controlled compositions and magnetism for high performance permanent magnetic applications.