Baozhi Cui

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 th...

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 wi...

Anisotropic SmCo5 flakes and nanocrystalline particles by high energy ball milling

This work is focused on the evolution of structure, texture and magnetic properties in SmCo5 powders during high energy ball milling (HEBM) in heptane with and without oleic acid (OA). Single-crystal micron SmCo5 flakes were formed in the early stage of HEBM (0–0.5 h). However, HEBM of 1–2 h without OA led to the formation of a mixture of single-crystal microflakes and loosely agglomerated polycrystalline microparticles with the highest coercivity of 15.7 kOe. HEBM of 3–5 h without OA led to the formation of isotropic, more or less equiaxed SmCo5 particles with a size of 2–30 μm and a polycrystalline nanostructure due to the coalescence of flakes and particles. In the case of HEBM in heptane with 15 wt. % OA, prolonged milling (from 1 to 5 h) led first to the formation of SmCo5 single-crystal submicron flakes and later to submicron- and nanosize-nanocrystalline flakes with a [001]-out-of-plane texture. OA plays an essential role in the formation of anisotropic SmCo5 flakes via the impediment of cold weldi...

High magnetization Fe-Co and Fe-Ni submicron and nanosize particles by thermal decomposition and hydrogen reduction

This paper reports morphology, structure, and magnetic properties of air-stable soft magnetic FexCo100−x (x = 65, 50, and 34) and Fe50Ni50 (at. %) submicron and nanosize particles fabricated by template-free thermal decomposition of nitrates of Fe, Co, and Ni and subsequent hydrogen reduction. The particle compositions were tuned by modification of the precursor solution concentrations. The as-synthesized Fe-Co and Fe50Ni50 particles have body centered cubic and face centered cubic poly-nanocrystalline structures, respectively. The Fe-Co and Fe50Ni50 particles have particle sizes in the range of 28–200 nm and 70–480 nm, and average grain sizes of 16–29 nm and 20–24 nm, respectively. The particle and grain sizes were controlled by tuning particle composition, and the temperature and time of hydrogen reduction. Saturation magnetization Ms as high as 207–224 emu/g and intrinsic coercivity Hci of 59–228 Oe were obtained in the Fe-Co particles reduced at 550 °C for 90 min. Of special note, the Ms of 224 emu/g ...

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 Sm2...

Crystallographically anisotropic Sm2Fe17Nδ and Nd(Fe,Mo)12Nx hard magnetic flakes

This paper reports the morphology, structure, and magnetic properties of Sm2Fe17Nδ and Nd(Fe,Mo)12Nx anisotropic flakes prepared by surfactant–assisted high energy ball milling (HEBM). Sm14Fe86Nδ jet milled microparticles with a size of 1–2.5 μm and NdFe10.5Mo1.5Nx nitride crushed microparticles with a size of 1–80 μm were subjected to HEBM in heptane with 10 or 20 wt. % oleic acid. As the milling time increased, first, single-crystal, and then [001] textured poly-nanocrystalline nitride flakes with micron, submicron, or nanosized thicknesses were synthesized. The intrinsic coercivity, Hci, of Sm14Fe86Nδ flakes initially increases and reaches a maximum value of 12.3 kOe upon milling for 3 h, at which point the thickness becomes less than 250 nm and the length is 1–4 μm. A maximum Hci value of 8.7 kOe for NdFe10.5Mo1.5Nx flakes was obtained after milling for 12 h, with the thickness less than 100 nm and the length 1–16 μm. Anisotropic magnetic behavior was observed for all of the nitride flakes.

L10-FePd nanocluster wires by template-directed thermal decomposition and subsequent hydrogen reduction

This paper reports the nanostructure, formation mechanism, and magnetic properties of tetragonal L10-type Fe55Pd45 (at. %) nanocluster wires (NCWs) fabricated by thermal decomposition of metal nitrates and subsequent hydrogen reduction in nanoporous anodized aluminum oxide templates. The as-synthesized NCWs have diameters in the range of 80–300 nm, and lengths in the range of 0.5–10 μm. The NCWs are composed of roughly round-shaped nanoclusters in the range of 3–30 nm in size and a weighted average size of 10 nm with a mixture of single-crystal and poly-crystalline structures. The obtained intrinsic coercivity iHc of 3.32 kOe at room temperature for the tetragonal Fe55Pd45 NCWs is higher than those of electrodeposited Fe-Pd solid nanowires while among the highest values reported so far for L10-type FePd nanoparticles.