SmCo5 Nanoparticles Research Articles

Investigation on crystallographic alignment of Sm-Co alloy nanoparticles by external magnetic field

In order to improve the magnetic properties of Sm-Co nanopowder prepared using the low oxygen-induction thermal plasma (LO-ITP) process, the effect of heat treatment on the phase transformation and magnetic properties of Sm-Co nanopowder was investigated. Sm-Co nanopowder was annealed at 873, 973, 1073, and 1173 K. The X-ray diffraction results indicate that uniform Sm-Co nanopowder with a dominant SmCo5 phase can be prepared at annealing temperatures higher than 1073 K. The coercivity of the Sm-Co nanopowder annealed at 1173 K was measured to be 1.5 MA/m. The Sm-Co nanoparticles can be sufficiently oriented using an external magnetic field. Although perfect crystal orientation could not be achieved in the annealed nanopowder owing to necking, short-duration heat treatment promoted the formation of the hard magnetic phase and suppressed necking. The results of this study demonstrate the importance of the rapid heat treatment effect during particle formation in the ITP process for preparing dispersible Sm-Co nanoparticles with high coercivity and improved anisotropic magnetic behavior.

Exchange Coupled SmCo5/FeCo Core/Shell Nanocomposites Fabricated By Ultrasound Assisted Electroless Deposition

Owing to high Saturation Magnetization (Ms) and high Remanence Magnetization (Mr), Rare Earth (RE) based Permanent Magnet (PM) has been widely used in various applications such as motor in Electric Vehicle (EV) and generator. With increasing concerns about climate change, EV is considered as a next generation vehicle because EV did not emit pollutants such as CO2, NOx and SOx. Over the past years, Nd2Fe14B is mainly used as PM in EV due to excellent maximum energy product (BHmax) around room temperature. However, The Nd2Fe14B has relatively low operating temperature (<200℃), which limits high speed operation. On the other hand, SmCo5 possesses high thermal, chemical stability and coercivity (Hc), making it a suitable magnetic material for high speed operation in harsh environment. However, unfortunately SmCo5 PM was only used in limited areas due to the lower Ms, Mr, BHmax than Nd2Fe14B. Therefore, interest in research to improve magnetic properties of SmCo5 is increasing. In particular, exchange coupling in core/shell structure between hard magnetic core and soft magnetic shell has attracted much attention because it can increase Ms, Mr, BHmax simultaneously while reducing high price RE element. In our work, we utilized electroless deposition on SmCo5 Nanoparticles (NPs) to fabricate exchange coupled SmCo5/FeCo hard/soft nanocomposites because of low cost and easy to control the soft phase thickness by modulating electrolyte bath parameters such as pH, temperature and additives. However, prior research clarified that the exchange coupling in 0-Dimensional NPs via electroless deposition was difficult because of inevitable particle aggregation caused by magnetic dipoles. Thus, inhibition of particle aggregation would be significant breakthrough. Accordingly, we prevented particle aggregation through ultrasound during the electroless deposition process.The SmCo5 NPs were fabricated through Sn-sensitization, Pd-activation, and ultrasound assisted FeCo-electroless deposition, successively. Figure 1 shows that the schematic illustration of the effects of ultrasound. The magnetic properties of SmCo5/FeCo NPs were measured by Vibrating-Sample Magnetometer (VSM). When ultrasound was not applied, the hard magnetic properties reduced due to agglomerated NPs. On the other hand, in case ultrasound was applied exhibits exchange coupled hysteresis loop. Figure 2 shows that minor hysteresis loops of exchange coupled SmCo5/FeCo NPs fabricated by ultrasound assisted electroless deposition. We successfully fabricated exchange coupled SmCo5/FeCo NPs and the Ms, Mr, theoretical BHmax increased about 11%, 10.7%, 24.3%, respectively.As a result, SmCo5/FeCo which fabricated by ultrasound assisted electroless deposition showed the increase in magnetic properties while maintaining Mr/Ms, which might broaden the future application fields. Figure 1

Morphology evolution of SmCox permanent magnetic nanoparticles

Sm-Co nanoparticles (NPs) are promising candidates for preparing superstable magnets and exchange-coupled nanocomposite magnets with unprecedented magnetic properties. However, the morphology evolution of the NPs remains unclear. Here, single crystalline SmCox (x = 4.07, 4.79, 6.94, and 8.61) NPs with dimensions below the critical size of a single magnetic domain were synthesized. These NPs consist of Sm2Co7, SmCo5, and Sm2Co17 phases with divergent typical morphologies. An evolution model for the different morphological characteristics was proposed based on phase-structure changes and surface-energy calculations using the density functional theory. The results show that these SmCo4.79 NPs can be well aligned along the easy magnetization axis and exhibit an ultrahigh coercivity of 5.7 T, thus enabling to advance the control of NP morphology and to facilitate their use in superstable or nanocomposite magnets.

Impact of magnetic field on the thermal properties of chemically synthesized Sm-Co nanoparticles based silicone oil nanofluid

This work aims to study the enhanced thermal conductivity of silicone oil on increasing mass % of hard magnetic Sm-Co based nanoparticles (NPs) in the presence of external magnetic fields. Sm-Co NPs were synthesized using the low temperature 'Pechini-type sol–gel' process. The presence of mixed phases is evident through XRD, FESEM, and TEM. The average hydrodynamic size of Sm-Co NPs was measured 51 nm by DLS. The study of magnetization vs. magnetic field reveals the weak ferromagnetic ordering along with the paramagnetic behaviour of the Sm-Co NPs. Thermal conductivity enhancement of Sm-Co nanofluids showed an increasing trend with the rising particle concentration and magnetic flux density. A high thermal conductivity enhancement of ~ 373% is reported at 15 mass % concentration of Sm-Co nanofluids and at a magnetic flux density of 0.5 T. The mechanism behind this thermal conductivity enhancement in the presence of an externally applied magnetic field has been discussed on the basis of near field magneto-static interactions of the magnetic nanoparticles. Microstructural, magnetic, and heat transport studies of Sm-Co based MNFs are very useful for device applications.

Stabilizing Hard Magnetic SmCo5 Nanoparticles by N-Doped Graphitic Carbon Layer.

We report a chemical method to synthesize size-controllable SmCo5 nanoparticles (NPs) and to stabilize the NPs against air oxidation by coating a layer of N-doped graphitic carbon (NGC). First 10 nm CoO and 5 nm Sm2O3 NPs were synthesized and aggregated in reverse micelles of oleylamine to form SmCo-oxide NPs with a controlled size (110, 150, or 200 nm). The SmCo-O NPs were then coated with polydopamine and thermally annealed to form SmCo-O/NGC NPs, which were further embedded in CaO matrix and reduced with Ca at 850 °C to give SmCo5/NGC NPs of 80, 120, or 180 nm, respectively. The 10 nm NGC coating efficiently stabilized the SmCo5 NPs against air oxidation at room temperature or at 100 °C. The magnetization value of the 180 nm SmCo5/NGC NPs was stabilized at 86.1 emu/g 5 days after air exposure at room temperature and dropped only 1.7% 48 h after air exposure at 100 °C. The stable SmCo5/NGC NPs were aligned magnetically in an epoxy resin, showing a square-like hysteresis behavior with their Hc reaching 51.1 kOe at 150 K and 21.9 kOe at 330 K and their Mr stabilized at around 84.8 emu/g. Our study demonstrates a new strategy for synthesizing and stabilizing SmCo5 NPs for high-performance nanomagnet applications in a broad temperature range.

Dispersible SmCo5 nanoparticles with huge coercivity.

It is difficult to obtain dispersed particles of SmCo5 by calciothermic reduction because of sintering during the high-temperature reaction. This study presents a new strategy to synthesize dispersible SmCo5 particles by co-precipitating a precursor containing amorphous Sm(OH)3 and coherent nanoscale Co(OH)2 and Ca(OH)2 crystallites. The Ca(OH)2 dehydrates into CaO which forms an isolation shell around the SmCo5 particles that prevents them sintering during the reaction at 860 °C. A magnetization of 90 Am2 kg-1, a remanence ratio of 0.96 and a huge coercivity of 6.6-7.2 T were achieved at room temperature after dissolving the CaO and orienting a dispersion of the particles in epoxy in a 0.8 T external field. Based on its scan-rate dependence in high quasi-static and pulsed magnetic fields, the coercivity mechanism is identified as nucleation and growth of 88 nm3 nucleation volumes in a low-anisotropy surface region about 15 nm thick. The coercivity is the highest yet reported for nanoparticles of any permanent magnet and it opens the prospect of new high-temperature magnet composites.

Chemical Synthesis of Magnetically Hard and Strong Rare Earth Metal Based Nanomagnets

AbstractWe report a general chemical approach to synthesize strongly ferromagnetic rare‐earth metal (REM) based SmCo and SmFeN nanoparticles (NPs) with ultra‐large coercivity. The synthesis started with the preparation of hexagonal CoO+Sm2O3 (denoted as SmCo‐O) multipods via decomposition of Sm(acac)3 and Co(acac)3 in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo5 NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo5 NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG‐SmCo5 NP composite with the room temperature coercivity (Hc) of 49.2 kOe, the largest Hc among all ferromagnetic NPs ever reported, and saturated magnetic moment (Ms) of 88.7 emu g−1, the highest value reported for SmCo5 NPs. The method was extended to synthesize other ferromagnetic NPs of Sm2Co17, and, for the first time, of Sm2Fe17N3 NPs with Hc over 15 kOe and Ms reaching 127.9 emu g−1. These REM based NPs are important magnetic building blocks for fabrication of high‐performance permanent magnets, flexible magnets, and printable magnetic inks for energy and sensing applications.

Chemical Synthesis of Magnetically Hard and Strong Rare Earth Metal Based Nanomagnets.

We report a general chemical approach to synthesize strongly ferromagnetic rare-earth metal (REM) based SmCo and SmFeN nanoparticles (NPs) with ultra-large coercivity. The synthesis started with the preparation of hexagonal CoO+Sm2 O3 (denoted as SmCo-O) multipods via decomposition of Sm(acac)3 and Co(acac)3 in oleylamine. These multipods were further reduced with Ca at 850 °C to form SmCo5 NPs with sizes tunable from 50 to 200 nm. The 200 nm SmCo5 NPs were dispersed in ethanol, and magnetically aligned in polyethylene glycol (PEG) matrix, yielding a PEG-SmCo5 NP composite with the room temperature coercivity (Hc ) of 49.2 kOe, the largest Hc among all ferromagnetic NPs ever reported, and saturated magnetic moment (Ms ) of 88.7 emu g-1 , the highest value reported for SmCo5 NPs. The method was extended to synthesize other ferromagnetic NPs of Sm2 Co17 , and, for the first time, of Sm2 Fe17 N3 NPs with Hc over 15 kOe and Ms reaching 127.9 emu g-1 . These REM based NPs are important magnetic building blocks for fabrication of high-performance permanent magnets, flexible magnets, and printable magnetic inks for energy and sensing applications.

Synthesis of SmCo5 nanoparticles with small size and high performance by hydrogenation technique

SmCo5 nanoparticles (NPs) have promising applications in high-density magnetic storage and magnetic nanocomposites. In this work, A novel method to yield SmCo5 particles with small size and high coercivity was reported. Firstly, Sm2O3–Co NPs with size of 6–15 nm were fabricated by a solvothermal route. Then the agglomerated SmCo5 particles were obtained by thermal reduction of the precursor, which show high coercivity of 2.0 T at room temperature. At last, the as-synthesized SmCo5 particles were further hydrogenated under high hydrogen pressure of 4 MPa at room temperature, where hydrogen absorption process could form small-sized SmCo5Hx particles due to their lattice expansion and hydrogen desorption process could convert SmCo5Hx NPs into SmCo5 NPs. The prepared SmCo5 NPs after hydrogenation, showing well distribution, have a small size of 5–20 nm and room temperature coercivity of 1.22 T.

The chemical synthesis of SmCo5 single-crystal particles with small size and high performance

SmCo5 nanoparticles have promising applications in high-density magnetic storage and magnetic nanocomposites. However, conventional calciothermic reduction process yields agglomerated SmCo5 magnets for high temperature annealing, limiting the application and development of SmCo5 nanoparticles. In this work, we exploited a novel strategy to fabricate SmCo5 single-crystal nanoparticles by an assistance of graphite oxide sheets. Sm2O3-Co particles coated with graphite oxide sheets were synthesized by solvothermal route, and the following reductive annealing generated SmCo5 particles. The size and magnetic performance of SmCo5 particles can be tuned by manipulating surfactants. The high coercivity of 24.4kOe and ideal size of 20–100nm can be achieved in SmCo5 single-crystal nanoparticles. In this technology, graphite oxide sheets can prevent the particles from sintering effectively and sustain the generation of single crystal.

Application of Mechanochemical Synthesis to Manufacturing of Permanent Magnets

Synthesis of permanent magnet powders through mechanically and thermally activated reduction of metal oxides with calcium, which allows for the production of fine single crystal particles, may contribute to the ongoing search for alternatives to the Nd-Fe-B magnets. The reviewed efforts demonstrate the possibilities to prepare (1) high-coercivity SmCo5 nanoparticles for anisotropic exchange-coupled nanocomposites, (2) YCo5/LaCo5 powders with the magnetic properties superior to those obtained through other manufacturing methods and (3) submicron Mn-Bi powders with large concentration of the MnBi phase. Also discussed are less successful attempts to prepare Mn-Al, Zr-Co and Hf-Co hard magnetic alloys in which the principal phases are known or likely to be metastable.

Exchange-coupled SmCo5/Co nanocomposites synthesized by a novel strategy

SmCo5/Co nanocomposites with exchange-coupling are synthesized by a reverse design where Co is decomposed from SmCo5 nanoparticles by hydrogen disproportionation process to fabricate two-phase nanocomposites.

A facile synthesis of high performance SmCo5 nanoparticles

SmCo5 nanoparticles have promising applications in high-density magnetic storage and magnetic nanocomposites. A combination of solution-phase synthesis and calciothermic reduction shows obvious advantage for preparing rare-earth hard magnetic nanoparticles. In this process, the Sm2O3 precursor was previously prepared in organic solvent, leading to a low coercivity due to the presence of CoC in SmCo5 nanoparticles. In this paper, a facile procedure for fabricating high performance ferromagnetic, crystalline SmCo5 nanoparticles in inorganic system is approached. 10–40nm SmCo5 nanoparticles have been prepared with the coercivity of 20.0kOe by reductive annealing of amorphous Sm(OH)3 and Co(OH)2 precursor at 900°C. Thereinto, the addition of CaO can effectively prevent the particles growth. While, polycrystalline Sm2Co17 particles with stackable sheet morphology have been obtained by reduction of crystalline Sm(OH)3 and Co(OH)2 at 1100°C. This environmentally friendly method avoids the presence of CoC successfully and improves the coercivity up to 20.0kOe.

Effect of Additives on the Formation of SmCo Magnetic Nanoparticles by Chemical Synthesis

Monodispersed magnetic SmCo nanoparticles have been prepared by polyol synthesis using non-toxic inorganic precursors (nitrates). The effect of the additives of NaOH, HNO3, CH3COOH and poly vinyl pyrrolidone (PVP) on the formation of SmCo nanoparticles is studied in this paper. The results indicate that base solution can boost the reduction of Co while acid solution is helpful for the formation of SmCo due to decreasing the reduction velocity of Co. CH3COOH is appropriate additive for the synthesis of SmCo nanoparticles, but more addition of CH3COOH will result in the emergence of CoC2 phase and decrease the coercivity of the resultants. The additive of PVP not only is a dispersing agent, but can prevent them from oxidating during preparation process. The SmCo nanoparticles with a size of 5-8 nm have the ferromagnetic properties of high coercivity (&gt;1000 Oe).

The microwave absorbing properties of SmCo attached single wall carbon nanotube/epoxy composites

The SmCo nanoparticles attached single wall carbon nanotubes (SmCo attached SWCNTs) were prepared by hydrogen dc arc discharge method using 2:17 type SmCo permanent powder as catalyst. The SmCo attached SWCNT/epoxy composites with different doping ratios were investigated in the frequency region of 2–18GHz. The complex permittivity and permeability of the SmCo attached SWCNT/epoxy composites were calculated. The reflection loss properties were simulated by transmission line theory and the microwave absorptive mechanisms were discussed. The results indicate that, due to the better interfacial polarization absorption mechanism of SmCo attached SWCNTs and the electromagnetic (EM) matching of magnetic loss and dielectric loss, the microwave absorption properties of SmCo attached SWCNT/epoxy are evidently improved. When the SmCo attached SWCNTs is doped by 1wt%, the composite display a larger and wider absorption peak, and the bandwidth of the reflection loss below −20dB is larger than 6GHz with the thickness of 3.3mm. It is expected that the new SmCo attached SWCNT/epoxy composites will be a good microwave absorbing material for the applications in X band, Ku band, or even K band.

Direct synthesis of large size ferromagnetic SmCo5 nanoparticles by a gas-phase condensation method

Ferromagnetic SmCo5 nanoparticles with large size have been directly synthesized by a magnetron-sputtering-based gas-phase condensation method. Based on this method, we studied the effect of thermodynamic environment for the growth of SmCo5 nanoparticles. It was found that the well-crystallized SmCo5 nanoparticle tends to form a hexagonal disk shape with its easy axis perpendicular to the disk plane. More importantly, under the condition of high sputtering current, well-crystallized nanoparticles were found to be formed through a three-stage growth process: aggregation, coalescence, and second crystallization.

PREPARATION, STRUCTURE AND MAGNETIC PROPERTIES OF SmCo&lt;SUB&gt;5&lt;/SUB&gt; 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 Exchange Interactions on the Coercivity of SmCo5 Nanoparticles Made by Cluster Beam Deposition

AbstractSingle crystal SmCo5 nanoparticles with an average size of 3.5 nm are produced by cluster‐beam deposition. When deposited without matrix, the nanoparticles showed a super‐paramagnetic behavior with a blocking temperature of 145 K. Dispersion of the SmCo5 nanoparticles in a carbon matrix results in an increase in both the coercivity and the blocking temperature. Room temperature coercivities as high as 12 kOe are obtained for the first time in mono‐layers of SmCo5 nanoparticles dispersed in C matrix. δM plots show that the interactions in the samples are of exchange type, which can decrease the overall effective anisotropy and coercivity according to the random‐anisotropy model. Coercivity is found to be inversely proportional to the packing density of the particles. SmCo5 nanoparticles with high coercivity are potential candidates for the next generation ultra high‐density magnetic recording media.

Separated Sm-Co hard nanoparticles by an optimization of mechanochemical processes

Sm-Co hard nanoparticles have been synthesized by a modified mechanochemical processing. The phases, microstructure, particle sizes and magnetic properties of the synthesized Sm-Co nanoparticles have been investigated. The results showed that the precursors and milling times had great effects on the structure and magnetic properties of the synthesized Sm-Co nanoparticles. It is interesting to find that either Sm2Co7, SmCo5 or Sm2Co17 hard single phases can be obtained by manipulating the amount and ratio of starting materials of Sm2O3 and Co. After the mixture of Sm2O3, Co, Ca, and CaO powders were milled for 2–12 h, no Sm-Co based hard phases was formed, whereas the Sm-Co hard nanocrystallites were formed by a subsequent annealing at 650 °C for 1 h. The maximum coercivities of the synthesized Sm2Co7, SmCo5, and Sm2Co17 were 37.1, 35.5, and 10.8 kOe, respectively. Separated Sm2Co17 nanoparticles were obtained after washing the annealed powder with a solution of acetic acid aqueous solution. The washed Sm2Co17 particles were single crystals and had an average particle size of 81 nm.

Magnetism of directly ordered Sm-Co clusters

Sm-Co bulk alloys have shown superior permanent-magnet properties, but research on Sm-Co nanoparticles is challenging because of the need to control particle size, size-distribution, crystalline ordering, and phase purity. In the present study, a cluster-deposition method was used to produce Sm-Co nanoparticles having desired crystal structures without the requirement of subsequent high-temperature thermal annealing. Poorly crystallized SmCo5 nanoparticles exhibit a low room-temperature coercivity of only 100 Oe, whereas crystalline SmCo5 and Sm2Co17 nanoparticles show room-temperature coercivities of 2000 and 750 Oe, respectively. The direct synthesis of Sm-Co nanoparticles having sizes of less than 10 nm and a high degree of atomic ordering is an important step toward creating nanoparticle building blocks for permanent-magnets and other significant applications.