SmCo5 Nanoflakes Research Articles

Removing the surfactant of SmCo5 nanoflakes via ligand-exchange and vacuum heat-treatment

The SmCo5 nanoflakes covered with polyvinylpyrrolidone (PVP) surfactant are obtained via surfactant-assisted ball milling method and were treated by ligand-exchange and vacuum heat-treatment methods. No significant change in the phase structure and surface morphology of as-milled SmCo5 nanoflakes was found upon those as confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, respectively. Moreover, X-ray photoelectron spectroscopy (XPS) analysis revealed that the ligand-exchange and vacuum heat-treatment are effective techniques for removing the polyvinylpyrrolidone (PVP) surfactant from the surface of SmCo5 nanoflakes. Meanwhile, the mechanism of coercivity is studied by the temperature dependence of demagnetization curves, which indicates that the magnetization reversal is controlled by co-existed mechanisms of pinning and nucleation.

A novel strategy for approaching high performance SmCo5/Co nanocomposites

Anisotropic SmCo5/Co magnetic nanocomposites have been fabricated by chemical deposition of Co nanowires based on SmCo5 nanoflakes. The SmCo5 nanoflakes with an average thickness of 200 nm and diameter of 4 μm were first prepared by surfactant-assisted high-energy ball-milling. The Co nanowires with mean diameter of 20 nm and length of 200 nm were then deposited via a solvothermal chemical process. This strategy can effectively control the content of SmCo5 nanoflakes and Co nanowires, and the hard magnetic nanoflakes can be coated with a uniform distribution of Co nanowires. Both of the SmCo5 nanoflakes and Co nanowires are anisotropic, and could be magnetically aligned simultaneously in the nanocomposites, which is confirmed by XRD patterns. Magnetic measurements of the “bi-anisotropic” SmCo5/Co composites show an enhanced remanent magnetization with increasing the content of Co nanowires. The exchange-coupled SmCo5/Co nanocomposites with up to 40 wt % Co content exhibits the highest (BH)max value of 23.8 MGOe, larger than the single phase SmCo5 nanoflakes.

Anisotropic nanostructured SmCo5 bonded magnets fabricated by magnetic-field-assisted liquid phase processing

Abstract In present study, surfactant assisted ball-milling method was applied to prepare SmCo5 nanoflakes, which were then magnetically aligned and warm compacted with a liquid binder to make bulk anisotropic SmCo5 bonded magnets. Warm compaction with magnetic-field-assisted liquid phase processing can decrease the viscosity of the binder to enhance the alignment of the magnetic nanoflakes, and thus can produce high density magnets, providing a novel method to fabricate anisotropic bonded magnets. The magnetic properties, microstructure, and crystal alignment of both nanoflakes and bonded magnets are systematically investigated. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) characterizations suggest that the obtained liquid phase bonded magnets exhibit enhanced magnetic anisotropy compared with those without magnetic field alignment and the solid phase bonded anisotropic magnets. The remanence of anisotropic phenol formaldehyde (PF) bonded magnets (4.43 kG) is higher than isotropic bonded magnets (3.76 kG), and the energy product of bonded magnets increases from 3.4 MGOe to 4.8 MGOe under the effect of the magnetic field.

Cold plasma reduction of surface carbon on SmCo5 nano-flakes prepared by surfactant-assisted ball-milling

Nano-flake SmCo5 powders with typical flake thickness of 200 nm were prepared by high energy ball milling using Oleic Acid (OA) as a surfactant. In order to remove the surfactant, the as-milled powders were exposed to pulse cold plasma of argon. The effects of the plasma parameters on residual surfactant content and magnetic properties of the resulting powder were investigated. Partial (62.5 at. %) surfactant removal was observed by XPS after treatments of 4 h at 150 Watt average power under an argon pressure of 300 mTorr. In addition, the cold plasma cleaning process led to a little bit of increase of oxygen on the surface. Demagnetization measurements revealed a slight decrease of the magnetic performance after plasma treatment. These results indicate that pulse cold plasma is an effective way for surfactant removal without morphological change and magnetic property degradation of the SmCo5 nano-flakes.

Phase transformation in anisotropic nanocrystalline SmCo5 magnets

SmCo5 nanoflakes with excellent texture have great potential applications in high performance nanocomposite magnets, in which the phase structure of the hard magnetic phase is crucial for obtaining large coercivity. Phase transformation from 1:5H phase to 2:17 R phase is observed in anisotropic nanocrystalline SmCo5 magnets when sintering the nanoflakes at 600–650 °C. The phase transformation is interesting because the 1:5H phase is relatively stable according to the thermodynamic and kinetic analysis. The phase transformation results in much lower coercivity of the wet-milled anisotropic magnets when compared with dry-milled isotropic magnets with 1:5H single phase. Analyses of differential scanning calorimetry, thermogravity and energy dispersive X-ray validate that the phase transformation originates from the oxidation of the nanoflakes with large specific surface area during sintering. The results suggest that controlling oxygen content strictly during sintering is necessary for maintaining 1:5H single phase in anisotropic nanocrystalline SmCo5 magnets prepared by sintering the nanoflakes.

Ultrathin SmCo5 nanoflakes with high-coercivity prepared by solid particle (NaCl) and surfactant co-assisted ball milling.

The ultrathin SmCo5 nanoflakes with average thickness smaller than 50 nm are prepared by a novel method of solid particle (NaCl) and surfactant co-assisted ball milling. The as-prepared nanoflakes exhibit a narrower thickness distribution of 10–50 nm and high coercivity of 23 kOe. The possible formation mechanism of nanoflakes are proposed. Temperature dependence of demagnetization curves indicate that the magnetization reversal may be controlled by both nucleation and pinning. The results of X-ray powder diffraction and magnetic measurement for aligned SmCo5 nanoflakes resin composite indicate that the nanoflakes have a high texture degree. The ultrathin thickness and high coercivity are beneficial for preparing the high performance soft/hard coupling magnets and nanocomposite magnets.

Effect of flake thickness on coercivity of nanocrystalline SmCo5 bulk prepared from anisotropic nanoflake powder

In this study, nanocrystalline SmCo5 bulk magnets were prepared by hot-pressing of nanoflake powders fabricated via surfactant-assisted high energy ball milling. Effect of the flake thickness on magnetic coercivity of the SmCo5 bulk was investigated. Anisotropic SmCo5 nanoflakes with thickness between 100 and 1000 nm were prepared by varying the milling parameter of ball-to-powder weight ratio. XRD analysis revealed that as-milled flake powders possessed nanocrystalline grains with no observable oxide peaks. The coercivity of the flake powders varied between 19.9 and 21.3 kOe for 1000 nm to 100 nm thick flakes, which indicated that the flake thickness in this range had no obvious effect on the coercivity of the powders. However, the coercivity of the bulks showed a strong dependence on the flake thickness. The bulk coercivity value of 10.97 kOe corresponding to the flake thickness of 100 nm, was 80% higher compared to the bulk prepared with the flakes of 1000 nm. XRD results on compacted samples did not show any grain growth, however, Sm2O3 and free Co were detected in SmCo5 bulks and their content increased with reduced flake thickness. Interestingly enough the bulk coercivity was not deteriorated with the presence of Sm oxide and Co.

Strong textured SmCo5 nanoflakes with ultrahigh coercivity prepared by multistep (three steps) surfactant-assisted ball milling.

The high coercivity of 26.2 kOe for SmCo5 nanoflakes are obtained by multistep (three steps) surfactant-assisted ball milling. The magnetic properties, phase structure and morphology are studied by VSM, XRD and SEM, respectively. The results demonstrate that the three step ball-milling can keep more complete crystallinity (relatively less defects) during the process of milling compared with one step high energy ball-milling, which enhances the texture degree and coercivity. In addition, the mechanism of coercivity are also studied by the temperature dependence of demagnetization curves for aligned SmCo5 nanoflakes/resin composite, the result indicates that the magnetization reversal could be controlled by co-existed mechanisms of pinning and nucleation.

Highly anisotropic SmCo5 nanoflakes by surfactant-assisted ball milling at low temperature

Surfactant-assisted ball milling (SABM) has been shown to be a promising method for preparing rare earth-transition metal (RE-TM) nanoflakes and nanoparticles. In this work, we prepared SmCo5 nanoflakes by SABM at low temperature, and 2-methyl pentane and trioctylamine were specially selected as solvent and surfactant, respectively, due to their low melting points. The effects of milling temperature on the morphology, microstructure and magnetic performance of SmCo5 nanoflakes were investigated systematically. Comparing with the samples milled at room temperature, the SmCo5 nanoflakes prepared at low temperature displayed more homogeneous morphology and lower oxygen content. Remarkably, better crystallinity, better grain alignment and larger remanence ratio were shown in the samples milled at low temperature, which resulted from the distinct microstructure caused by low milling temperature. The differences in structural evolution between the SmCo5 nanoflakes milled at room temperature and low temperature, including the formation of nanocrystalline, grain boundary sliding, grain rotation, et al., were discussed. It was found that lowering the temperature of SABM was a powerful method for the fabrication of RE-TM nanoflakes, which showed better hard magnetic properties and lower oxygen content. This was important for the preparation of high-performance sintered magnets, bonded magnets and nanocomposite magnets.

Structure and magnetism of SmCo5 nanoflakes prepared by surfactant-assisted ball milling with different ball sizes

Anisotropic magnetic SmCo5 nanoflakes have been fabricated by surfactant-assisted ball milling (SABM) using hardened steel balls of one of the following sizes: 4, 6.5, 9.5 and 12.7mm in diameters. The magnetic properties of SmCo5 particles prepared by SABM with different milling ball sizes in diameters were investigated systematically. It was showed that the nanoflakes milled by amount of small size balls had a higher coercivity and lower anisotropy, i.e., worse grain orientation although in a short milling time while the nanoflakes prepared with same weight of big balls tend to have a lower coercivity, better grain orientation. The coercivity mechanism of the nanoflake was studied and it was mainly dominated with the domain-wall pinning. The SEM analysis shows that the morphology of nanoflakes prepared with different ball sizes are almost the same when the balls to powder weight ratio is fixed. The different magnetic properties caused by different ball sizes are mainly due to the different microstructure changes, i.e, grain refinement and c-axis orientation, which are demonstrated by X-ray diffraction (XRD) analysis and transmission electron microscope (TEM). Based on the experiments above, a combined milling process was suggested and done to improve magnetic properties as your need.

PREPARATION, STRUCTURE AND MAGNETIC PROPERTIES OF SmCo<SUB>5</SUB> NANOPARTICLES AND NANOFLAKES

Surfactant-assisted high energy ball milling technique is a new method of producing magnetic nanoparticles. In this study, permanent magnetic SmCo5 nanoparticles and nanoflakes with high room-temperature coercivity values and narrow particle size distributions were produced by this technology and a subsequent size-selection process. The SmCo5 nanoparticles with average particle sizes of 9.8 and 47.5 nm, exhibited room-temperature coercivity values of 6.8 x 10(4) and 7.3 x 10(5) A/m, respectively, while the SmCo5 nanoflakes, with the mean particle size of about 1.4 mu m and average thickness of 75 nm, showed excellent permanent magnetic properties with an obvious c-axis crystal texture, a strong magnetic anisotropy and high coercivity values of 5.5 x 10(5) and 1.6 x 10(6) A/m in their easy-axis and hard-axis directions, respectively. The coercivity values of SmCo5 nanoparticles and nanoflakes exhibited a significant particle size dependance effect.

Effect of milling parameters on SmCo5 nanoflakes prepared by surfactant-assisted high energy ball milling

In this study, we discuss the effect of different milling parameters, such as the type and concentration of surfactants, milling energy, and milling time on the structural, morphological and magnetic properties of hard magnetic SmCo5 nanoflakes prepared by surfactant assisted high energy ball milling. Two kinds of surfactants, polyvinylpyrolidone (PVP) with ethanol and oleic acid (OA) with n-heptane, were used as milling media. Increase in surfactants concentration and decrease in milling energy result in the decrease of degree of amorphization and reduction in grain size with milling time. Milling at 200 rpm results in more homogeneous and thicker flakes with fewer fractions of nanoparticles as compared to milling at 800 rpm. Increase in surfactants concentration results in the increase of the aspect ratio of flakes. Due to better capping ability of OA, the degree of flaking is higher when milling in OA than that in case of PVP. A maximum coercivity of 2.3 T was obtained after milling for 1.0 and 2.0 h for 10 and 50 wt. % of OA, respectively, at 800 rpm. A maximum (BH)max of 23.8 MGOe (188.9 kJ m−3) and degree of texture of 93% were obtained for 10 wt. % OA after 10 h of milling at 200 rpm. The pronounced anisotropy and high coercivity of the nanoflakes should prove advantageous for the preparation of textured exchange spring magnets.

Effect of ball-milling surfactants on the interface chemistry in hot-compacted SmCo5 magnets

Anisotropic SmCo5 nanoflakes prepared by high-energy ball-milling with surfactants have great potential in applications for high-performance nanocomposite magnets. For such “nanocomposite” applications, the surface structure and chemistry of nanoflakes are crucial for achieving high coercivity. In this study, hot-pressed samples from anisotropic SmCo5 nanoflakes, ball-milled with different surfactants, oleic acid (OA) and oleylamine (OY), were investigated. Interface layers between the SmCo5 nanoflakes were found to consist of samarium oxides and a soft magnetic Co phase. These surface layers contribute to the degradation of hard magnetic performance, which is confirmed by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy analysis of the cross-section of a single flake ball-milled with OA. Samples milled with OY show a much thinner interface layer in compacted samples, which means that the surface degradation during ball-milling with OY is much less than that with OA. The results show clearly that the choice of proper surfactant and the control of processing parameters are the key factors for improving the surface condition of the nanoflakes and the resulting hard magnetic properties.

The effect of particle size on coercivity and crystallinity of SmCo5

It is observed a turning point in the particle size for which the coercivity Hci of a Sm-Co alloy reaches a peak. Using a broad size range from 20 nm to 5 mm, the turning point of the flake thickness for SmCo5 nanoflakes is determined in the range of 100–180 nm with Hci peak at ∼20 kOe. A lower coercivity at a particle size well below the turning point is likely related to a more detailed nanoscale morphology that controls coercivity. The effect of particle size on crystallinity for high energy milled powder is also discussed with four observations.

Influence of the type of surfactant and hot compaction on the magnetic properties of SmCo5 nanoflakes

In this study, we discuss the effects of a type of surfactant (oleylamine, oleic acid, and trioctylamine) and hot pressing on the hard magnetic properties of crystallographically anisotropic SmCo5 nanoflakes prepared by surfactant-assisted high energy ball milling. The phase, microstructure, and magnetic properties of the hot-pressed SmCo5 were investigated by using x-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The coercivities of the precursor flakes prepared using oleylamine, oleic acid, and trioctylamine were 14.9, 15.8, and 15 kOe, respectively. Hot-compacted SmCo5 magnets prepared from the nanoflakes milled with oleic acid had the lowest coercivity of 8.1 kOe. It is believed that even after repeated washing in an ultrasonic bath with different solvents, the remaining oleic acid in the SmCo5 nanoflakes led to oxidation of SmCo5 at the surface/interface of nanoflakes during the hot-pressing process. The compacted SmCo5 magnets prepared from the nanoflakes milled with trioctylamine and oleylamine had higher coercivity values of 14.8 and 12.8 kOe, respectively. Unlike oleic acid, oleylamine and trioctylamine contain no oxygen atoms, and therefore there was less oxidation during the process. The compaction temperature also influences the coercivity. The SmCo5 magnets hot pressed at 550 °C had the highest coercivity, whereas those hot pressed at 650 °C had the lowest coercivity; this is attributed to the change of phases and composition of SmCo5 alloys during the hot-pressing process.

Anisotropic SmCo5 nanoflakes by surfactant-assisted high energy ball milling

Crystallographically anisotropic SmCo5 nanoflakes were fabricated directly by one-step surfactant-assisted high energy ball milling (HEBM) of Sm17Co83 ingot powders for 5 h in heptane and oleic acid (OA) without preprocessing or further annealing. The SmCo5 nanoflakes have a strong [001] out-of-plane texture. The thickness of nanoflakes is in the range of 8–80 nm while their length is 0.5–8 μm. The surfactant OA plays an important role in the formation of SmCo5 nanoflakes. HEBM of SmCo5 ingots in heptane without OA resulted in the formation of magnetically isotropic more or less equiaxed SmCo5 particles with a size of 2–30 μm. Closely packed “kebablike” SmCo5 nanoflakes were formed by HEBM in heptane with 15 wt % OA. HEBM in 150 wt % OA led to well-separated nanoflakes instead of the closely packed kebablike nanostructure. This resulted in the enhanced [001] out-of-plane texture. In-plane transmission electron microscope examination showed that the SmCo5 nanoflakes were composed of grains with sizes in the range of 4–8 nm. Coercivities of about 18.0 kOe were obtained for the anisotropic SmCo5 nanoflakes.