Title Page
Contents
ABSTRACT 13
Ⅰ. Introduction 14
1. Fundamentals of soft magnets 14
1.1. Magnetic hysteresis curve 14
1.2. Curie temperature 18
1.3. Energy losses 18
2. Fe-based Amorphous/nanocrystalline alloys 21
2.1. Historical perspective 21
2.2. Properties of amorphous/nanocrystalline materials 23
Ⅱ. Experimental Procedure 31
1. Alloy design strategy 31
2. Synthesis of master alloys 33
3. Production of as-quenched ribbons 33
4. Nano-crystallization of amorphous precursors 36
5. Characterization of Fe-Co-B-P-Cu alloy ribbons 36
5.1. Density measurements 36
5.2. Thermal analysis 37
5.3. Structural analysis 37
5.4. Magnetic measurements 37
Ⅲ. Results and Discussion 39
1. Effect of Co content of Fe-Co-B-P-Cu 39
1.1. Structural characteristics 39
1.2. Magnetic properties 43
2. Effect of nanocrystallization on amorphous precursor 49
2.1. Structural transformation 49
2.2. Magnetic properties 62
Ⅳ. Conclusions 71
REFERENCES 72
ABSTRACT IN KOREAN 79
Table 1. Chemical composition of the test alloys. 48
Table 2. Saturation magnetization µ₀Ms of as-spun and annealed Fe-Co-B-P- Cu alloys according to annealing temperature. 48
Table 3. Best fitted hyperfine parameters for the as-quenched and annealed Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ ribbons. (Hhf. hyperfine field, IS: isomer shift)[이미지참조] 56
Table 4. Calculated chemical compositions of the residual amorphous phase. 58
Table 5. Best fitted hyperfine parameters for the as-quenched and annealed Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ ribbons. (Hhf: hyperfine field, QS: quadrupole...[이미지참조] 61
Table 6. Saturation magnetization (Ms), coercivity (Hc), and core loss (Pcv) of Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ ribbons with different annealing temperature (Ta).[이미지참조] 68
Figure 1. B-H hysteresis loop of a soft magnetic material. 16
Figure 2. Herzer Diagram illustrating dependence of the coercivity with grain size in magnetic alloys. 17
Figure 3. Relation between effective permeability (at 1 kHz) and saturation polarization for soft magnetic materials. 22
Figure 4. Schematic illustration of microstructural evolution in typical Fe- based nanocrystalline 26
Figure 5. The composition design of the Fe-Co-B-P-Cu high Ms nanocrystalline alloys[이미지참조] 32
Figure 6. Schematic diagram of melt spinning 35
Figure 7. XRD patterns of (a) as-quenched and (b) optimally annealed Fe-Co-B-P-Cu ribbons corresponding to Co content. 40
Figure 8. (a) DSC curves of Fe-Co-B-P-Cu as-quenched ribbon and (b) corresponding Tx₁, Tx₂ and ΔT.[이미지참조] 42
Figure 9. Temperature dependence of the magnetization-temperature (M-T) curves and the dM/dT curves (inset figure) taken from the M-T curve of an... 44
Figure 10. M-H magnetic hysteresis curve and B-H magnetic hysteresis curve (inset) of as-quenched and annealed ribbons when Co=3.6 at.%. 45
Figure 11. (a) The variation of Ms with annealing temperature for the five compositions after 10 minutes of annealing and (b) the Hc of as-quenched...[이미지참조] 47
Figure 12. (a) XRD patterns and (b) DSC curves of the Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ ribbons in the as-quenched state and Ta=360-520℃...[이미지참조] 51
Figure 13. Room temperature transmission Mössbauer spectrum of the as- quenched Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ alloy. 53
Figure 14. Room temperature transmission Mössbauer spectrum of the Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ alloy annealed at (a) 360℃, (b) 400℃, (c) 440℃,... 55
Figure 15. Dependence of Fe concentration in nanocrystalline and fraction of nanocrystalline phase on annealing temperature of Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ alloy. 58
Figure 16. Room temperature transmission Mössbauer spectrum of the Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ alloy annealed at 520℃ for 10 min. 60
Figure 17. The trigonal prism of bct-Fe₃B phase. 61
Figure 18. Magnetic Domain images of Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ ribbons observed with MOKE microscopy (a) in the as-quenched state and annealed... 64
Figure 19. Dependence of saturation magnetization (Ms) and coercivity (Hc) on annealing temperature (Ta) of Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ alloy ribbon.[이미지참조] 66
Figure 20. Dependence of core loss on annealing temperatures (Ta) and operating frequencies of the Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ ribbons.[이미지참조] 68
Figure 21. (a) Iinitial B-H curve and (b) dependence of Pcv on operating frequencies of Fe₈₃.₃Co₃.₆B₈.₇P₃.₆Cu₀.₇ alloy and commercial Si steel. [이미지참조] 70