Liya Lü

The structure, morphology and magnetic properties of Sr-ferrite powder prepared by the molten-salt method

Sub-micrometre high-performance Sr-ferrite powder was prepared by a molten-salt method using Na2SO4 as the fluxing agent. In the reaction process, a mixture of superfine powder was pre-sintered at 1150 °C for 3 h and then annealed at 850 °C for 2 h. The as-obtained Sr-ferrite powder is SrFe12O19 with a hexagonal magnetoplumbite structure. We observe that with raising the pre-sintering temperature as well as increasing the annealing temperature and time, there is an enlargement of particle size. We regulated the reaction parameters to optimize the magnetic properties of the Sr-ferrite powder. The structure with the best magnetic properties is quasi-cubic in shape and relatively uniform in size, showing a coercivity of 471.89 kA m−1, a saturation magnetization of 91.51 µWb m kg−1, a remanence ratio of 0.50 and a maximum magnetic energy product of 7.89 kJ m−3. We then studied the effects of particle size, demagnetization factor and magnetocrystalline anisotropy on coercivity. Compared with the conventional ceramic process, the one presented here is more convenient and economical for the production of homogeneous hexagonal ferrite powders of high magnetic performance.

Ferromagnetic CrSb thicker films epitaxially grown on NaCl (1 0 0) substrates

A series of relatively thicker CrSb films were deposited on NaCl (1 0 0) substrates by magnetron sputtering. Strong ferromagnetism was observed in the CrSb films with a zinc-blende CrSb (ZB-CrSb) phase epitaxially grown on the NaCl sustrate. The critical thickness of the ZB-CrSb film was close to 4 nm, which is sufficiently thick to investigate the half-metallicity nature of ZB-CrSb and to be practically applied in spintronics devices.

Ferromagnetic chaoite macrotubes prepared at low temperature and pressure

Chaoite, a rare allotrope of carbon, is considered as a high-temperature phase abundant in circumstellar shells and is difficult to be synthesized at low temperature. However, in this study, chaoite phase was synthesized by quenching the pyrolysate of acetylene gas at low temperature and pressure. The typical morphology is a tube with 20–60μm in diameter and more than 8mm in length. Another interesting feature of these carbon macrotubes (CMTs) is the unexpected but clear intrinsic ferromagnetism. The ferromagnetism of sp-hybridized CMTs indicates that the sp-hybridized structure may be an origin of ferromagnetism.

Microstructure and magnetic properties of rapidly quenched Sm2(Fe,Al,Zr)17C1.5 ribbons with Zr additions

The effect of Zr additions on the microstructure and magnetic properties of melt-spun Sm2Fe(15.5−x)ZrxAl1.5C1.5 alloys has been systematically studied. The additions of Zr to Sm2(Fe,Al,Zr)17C1.5 alloys result in the precipitation of a ZrC compound within intergranular regions. It is found that the Zr addition is helpful in eliminating free iron dendrites, and effective on inhibiting grain growth during annealing. The x-ray diffraction analysis and transmission electron microscopy observation show that annealed ribbons with the Zr addition consist of a multiphase of the 2:17-type carbide, α-Fe and ZrC compound with an average grain size of about 25–35 nm. A remanence of up to 55 emu/g along with a coercivity of up to 11.6 kOe is obtained for Sm2Fe15.3Zr0.2Al1.5C1.5 ribbons annealed at 750 °C for 30 min. It is suggested that the high coercivity and remanence may be attributed to the Zr addition.