Magnetic properties of Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub x/)/sub z/ alloys and their melt-spun materials (x=0.02--0.04,z=7.5--12)
Cast alloys and melt-spun ribbons with nominal compositions of Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub x/)/sub z/ (x=0.02-0.04,z=7.5-12) have been synthesized and characterized in a temperature range of 10-1273 K and at fields up to 5T. The main phase in the as-cast alloys exhibited a Th/sub 2/Ni/sub 17/ type structure, with a strong uniaxial anisotropy. Minor phases with a TbCu/sub 7/ and/or CaCu/sub 5/ structure emerged as z (3d/R) decreased. As a result, the anisotropy field (H/sub A/) increased from 67 to 120 kOe, while 4/spl pi/M/sub s/ fell from 12.8 to 10.5 kG at 300 K when z was decreased from 12 to 7.5. For melt-spun ribbons, they are nano-structured in nature and magnetically hard, even in the as-spun state. By lowering the value of z(3d/R) and raising the B content, a finer microstructure and a higher H/sub ci/ were obtained. Hard magnetic properties of H/sub ci/=4.9-12 kOe, 4/spl pi/M/sub s/=9.0-12.0 kG at 300 K have been obtained from ribbon samples. Among them, Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub 0.02/)/sub 10/ ribbon showed the highest (BH)/sub max/ of 10.8 MGOe at 300 K. A Henkel plot analysis suggested the existence of exchange-coupling interaction between the magnetically hard and soft phases in the ribbon materials.
Magnetic properties and microstructure of melt-spun Sm(Co,Fe,Cu,Zr) 8 magnets
Abstract We report on the microstructural and magnetic properties of rapidly quenched Sm(Co bal Fe 0.1 Cu x Zr 0.04 ) 8 ribbons. Samples spun at velocities above 40 m/s are nanocrystalline and magnetically hard, even in the as-spun state. The coercivity and its temperature coefficient can be improved by annealing at 750°C. Samples spun at low speeds have low coercivity in the as-spun state and are characterized by larger grain sizes. By annealing a cellular precipitation structure within the grains, similar to that of bulk Sm(Co,Fe,Cu,Zr) z magnets, can be obtained in Cu-containing samples, resulting in an increase of the coercivity, since the precipitates act as pinning centers. Some precipitation occurs even in as-spun Cu-free samples, indicating that their formation is not directly related to the existence of Cu, in contrast to the cellular structure. Compared to the bulk materials, lower annealing temperatures and shorter heat treatment times are required and the slow cooling process is not needed. The activation volumes for the magnetic reversal process are estimated by magnetic relaxation measurements.
Temperature dependence of coercivity in Sm/sub 2/TM/sub 17/ magnets and domain wall motion in magnetic materials
It was observed in Sm/sub 2/TM/sub 17/ magnets that decreasing Fe content did not strongly affect room temperature coercivity but led to a significantly higher coercivity at high temperatures; increasing Sm content resulted in much lower room temperature coercivity but substantially higher coercivity at high temperatures; increasing Cu content led to higher coercivity at all temperatures. In this paper, the effects of Fe, Sm, and Cu on coercivity are explained by using the temperature dependence of magnetocrystalline anisotropy of the 2:17 cell phase and 1:5 cell boundary phase. In order to explain complex temperature dependence of coercivity, thermal activation of domain walls must be taken into account. It is believed that the energy necessary for domain walls to overcome the energy barrier between the 1:5 cell boundary phase and 2:17 cell phase can be acquired not only from the magnetic field, but also from thermal energy k/sub B/T. This concept may apply to all magnetic materials in which domain wall motion is involved during magnetization and demagnetization processes.