Synthesis of Samarium-Cobalt Sub-micron Fibers and Their Excellent Hard Magnetic Properties

Abstract

High-throughput synthesis of Samarium-Cobalt sub-micron fibers with controlled composition and dimension was demonstrated by combining electrospinning and reduction-diffusion processes. The composition of fibers was readily varied (8 < Sm < 20 at.%) by adjusting precursor composition whereas the diameter of fibers was precisely controlled by varying electrospinning parameters (e.g., applied voltage, solution feed rate, temperature, and humidity) to reach single-domain size. X-ray diffraction patterns confirmed that single phase Sm2Co17 fibers were synthesized when the metal precursor ratio (Sm3+/(Sm3++Co2+)) was precisely controlled at 10.6%, whereas mixed phases (i.e., Co-Sm2Co17 or Sm2Co17-Sm2Co7) were observed when the ratio is deviated from the stoichiometric. Magnetic saturation (Ms) of the synthesized fibers monotonically decreased with an increased in Sm content. In contrast, coercivity (Hci) monotonically increased with an increase in Sm content.

Near theoretical ultra-high magnetic performance of rare-earth nanomagnets via the synergetic combination of calcium-reduction and chemoselective dissolution

“…As a hard magnetic material, Sm 2 Co 17 was comparatively easier to prepare than three-element systems such as Nd-Fe-B. Sm 2 Co 17 nanofibre synthesis was performed through a procedure modified from our previous work that involved electrospinning and several annealing processes 12 . The precursor fibres consisting of Sm 2 O 3 and fcc-Co were mixed with CaH 2 granules (CaH 2 /as-prepared nanofibre = 2 ( vol .))…”

“…As hard nanomagnets, rare earth element based metallic phases, including neodymium-iron-boron (Nd-Fe-B), samarium-cobalt (Sm-Co), and samarium-iron-nitride (Sm-Fe-N), are expected to experimentally exhibit the strongest exchange-coupling behavior due to their exceptionally high coercivity and energy product 9 . Among magnetic hard materials, Sm-Co ( e.g ., Sm 2 Co 17 , SmCo 5 ) nanostructures have been prepared through a variety of chemical methods such as sol-gel 10 , co-precipitation 11 , electrospinning 12 , and electrodeposition 13 , followed by a subsequent reduction-diffusion (R-D) process. Recently, studies with regard to control over the microstructures of single-phased nanomagnets with either a near single-domain size or a high-anisotropic feature are being developed in order to achieve further enhanced magnetic properties 14 , 15 .…”

“…The reduction process is an indispensable step in all the chemical approaches to prepare rare earth magnets from oxides. Because rare earth elements possess a highly negative reduction potential ( e.g ., Sm 3+ /Sm = −2.41 eV; while transition metal, Co 2+ /Co = −0.28 eV) and a low free energy for oxidation ( e.g ., Sm = −5.73 × 10 5 J at 25 °C), rare earth oxides are extremely stable and are difficult to reduce to their metallic phase under H 2 conditions 12 , 17 , 18 . Calcium (Ca) granule or calcium hydride (CaH 2 ) powder with an oxidation energy ( e.g ., Ca = −6.04 × 10 5 J at 25 °C) lower than all other rare earth metals has enabled the reduction, leading to a production of metallic rare earth magnets and oxidized Ca (CaO) 19 .…”

Synthesis of mesoscopic particles of multi-component rare earth permanent magnet compounds

“…Besides these, the Sm(Co or Fe)–O NPs with tunable sizes in the range of 60–220 nm and different morphologies were synthesized directly from thermal decomposition of Sm(acac) 3 and Co/Fe(acac) 2 ( Figure 6(b–j) ) [ 74 ] or SmCo–oleate complex ( Figure 6(k–s) ) [ 75 ]. The SmCo–O NPs with various morphologies, such as Sm(OH) 3 –Co nanorods [ 76 ] or urchin-like [ 77 ], Sm(OH) 3 –Co(OH) 2 nanoflakes [ 78 , 79 ], and SmCo–O nanofibers [ 80 , 81 ], could be successfully obtained by sonification [ 76 ], hydro/solvothermal reaction [ 77–79 ], and electrospinning [ 80 , 81 ]. Once the R amounts in these encapsulated nanostructures are under the critical concentration for the solid-solution formation, the R-doped T–O nanostructures can be synthesized by using procedures which are similar to the above [ 81–85 ].…”

“…intermetallics, leading to the successful synthesis of some binary R-T MMPs (e.g., [69]; their sizes were tuned from 20 to 200 nm by varying the OA concentration, as shown in Figure 3 as Sm(OH) 3 -Co nanorods [76] or urchin-like [77], Sm(OH) 3 -Co(OH) 2 nanoflakes [78,79], and SmCo-O nanofibers [80,81], could be successfully obtained by sonification [76], hydro/solvothermal reaction [77][78][79], and electrospinning [80,81].…”