Structural, Microstructural and Magnetic Properties of Ball Milled Boron-Substituted Sm(Co,Fe,Cu,Zr)<sub>7.5</sub> Compounds

Abstract

The powders in the micrometer scale of Sm(Co0.86Fe0.1B0.04)7.5, Sm(Co0.82Fe0.1Zr0.04B0.04)7.5, Sm(Co0.715Fe0.1Cu0.12Zr0.04B0.025)7.5, Sm(Co0.69Fe0.1Cu0.12Zr0.04B0.05)7.5 compounds have been prepared by using a high-energy planetary ball miller. The X-ray diffraction patterns have an amorphous state after 42 hours milling while the average grain size is in the range of 0.5-10 μm, as measured by using a scanning electron microscope. Amorphization has been achieved at shorter milling times for samples with higher boron content. Depending on the annealing temperature, the major phases are 1:7, 2:17 hexagonal or fcc-Co as revealed from the Xray patterns. The annealing at temperature over 900 oC for 1h helps the formation of the fcc-Co which becomes the dominant phase, mostly on the higher boron doped samples. From the hysteresis curve of Sm(Co0.715Fe0.1Cu0.12Zr0.04B0.025)7.5, a coercive field of ~9 kOe has been determined. For this sample there is difference between the two coercive fields, Ηc(χirr=max) and Ηc(M=0). The zirconium doped sample has higher coercive field than the Sm(Co0.86Fe0.1B0.04)7.5 one. The coercive field is significant increases to the copper doped samples. In the thermomagnetic curves of the asmilled powders, it has been evidenced that there is crystallization, connected to the increase of the magnetization under the constant applied field. The initial and demagnetization curves exhibit slope variations that are connected to the soft fcc-Co phase. Almost zero hydrogen absorption was found for the Cu-doped samples at room temperature.