| Summary: | 碩士 === 國立中正大學 === 物理系 === 91 === The effect of cooling rate on the magnetic properties of nanostructured TbMn6Sn6 ribbons of the HfFe6Ge6 type structure (Space Group:P6/mmm), prepared by melt spinning method, were investigated. The coercivity of TbMn6Sn6 ribbons enhances with increasing the wheel speed (Vs) from 25 to 40 m/s. The optimal magnetic properties of σr = 12.3 emu/g, iHc = 4.7 kOe at room temperature, σr = 11 emu/g and iHc = 58.6 kOe at 5K are obtained in TbMn6Sn6 ribbons quenched at Vs = 35 m/s. Based on x-ray diffraction patterns, the TbMn6Sn6 ribbons mainly consist of 1：6：6─type phase. The average grain size of optimized TbMn6Sn6 robbons (Vs = 35 m/s) is about 25 nm according to transmission electron microscopy (TEM) investigation. Exchange coupling effect between TbMn6Sn6 grains is found, as evidenced by Henkel plot, to exist in all the ribbons at room temperature.
It was also tried to substitute Tb with Dy, Mn with transition metals, i.e. Ti, V, Cr, Fe, Co and Ni, in attempts to process nanostructured ribbons. The coercivity, remanence (σr) and Curie temperature of the ribbons under substitution mostly decrease with the increase of substitution volume, except for the Fe substituted alloy ribbons. Its remanence (σr) increases with the increase of Fe contents. Besides, the Curie temperature enhances from 155 ℃ for Fe free alloy ribbons to 170 ℃ for TbMn5.5Fe0.5Sn6.
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