Do Khanh Tung

Facile Synthesis of High Magnetization Air-stable Fe65Co35 Nanoparticles by Mechanical Alloying

Fe65Co35 nanoparticles were prepared by mechanical alloying of the elemental Fe and Co powders in air. The structural, morphology, and magnetic property variations were investigated as a function of milling time (in the 0.25–32 h range) by using xray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The complete formation of bcc Fe65Co35 solid solution was observed after 10 h milling. At this time, the alloy powder with average grain size (crystallite size) of 12 nm and a maximum saturation magnetization (Ms) 200 emu/g was obtained. Intensive milling of Fe-Co powders resulted in a grain refinement down below 10 nm and in reduction of Ms to 170 emu/g. The saturation magnetization of the alloys asmilled for various milling times was almost unchanged, at least after seven days of storing in air, which suggests a formation of certain oxide layer on particles surface to protect them from further oxidation. The annealing of as-milled sample at 800C under gas mixture of hydrogen and argon affected in a strong increase of Ms, from 170 emu/g to 220 emu/g, that supports the above hypothesis on the existence of the oxide layer.

Structural and luminescent properties of (Eu,Tb)PO4·H2O nanorods/nanowires prepared by microwave technique

Abstract Nanowires/nanorods of europium/terbium orthophosphate monohydrate with Eu 3+ concentration of 6, 11, and 20 at.% were prepared by microwave synthesis method. The effects of Eu 3+ doping concentration on structure, morphology and optical properties of nanomaterials were also investigated. The results showed that, for all studied Eu 3+ doping concentrations, a single-crystalline phase of rhabdophane-type (Eu,Tb)PO 4 ·H 2 O nanowires/nanorods was obtained by using microwave heating of an aqueous solution of terbium(III) nitrate, europium(III) nitrate and NH 4 H 2 PO 4 with pH=2. The length and width of these nanowires/nanorods ranged from 150 to 300 nm and from 10 to 50 nm, respectively. The evidence of energy transfer from Tb 3+ to Eu 3+ due to the energy overlap between the donor Tb 3+ and the acceptor Eu 3+ was observed obviously via a significant enhancement in the luminescent intensity of Eu 3+ .

Fabrication of Nd-Fe-B exchange-spring magnets

In this report we present our recent results on fabrication of Nd-Fe-B exchange-spring magnets using melt-spinning method. Additive elements were used to improve useful parameters of this kind of hard magnetic materials. Hot pressing technique was applied to increase mass density of the magnets. The compositions and technology routes for fabricating the Nd-Fe-B exchange-spring magnets with maximum energy product (BH)max above 10 MGOe were shown.

Magnetic Properties of Annealed Powders Prepared By Mechanical Alloying

Fe-Co alloy powders were prepared by mechanical alloying of the elemental Fe and Co powders in air and subsequently annealed at various temperatures. Structural and magnetic characteristics of the annealed powders were studied in detail as a function of annealing temperatures by using an X-ray diffractometer (XRD), a field emission scanning electron microscope, a vibrating sample magnetometer, and a physical property measurement system. The XRD results showed an existence of the nanocrystals with sizes of 15-50 nm. The magnetic studies indicated a strong increase of magnetization and a sharp decrease of coercivity as annealing temperature increased. Both the effect of the oxidation on the magnetic properties as well as magnetization stability of the annealed samples will be discussed.