Microstructures and Magnetic Domain Structures of Sintered Sm(Co<SUB>0.720</SUB>Fe<SUB>0.200</SUB>Cu<SUB>0.055</SUB>Zr<SUB>0.025</SUB>)<SUB>7.5</SUB> Permanent Magnet Studied by Transmission Electron Microscopy

Abstract

Microstructures and magnetic domain structures of precipitation-hardened Sm(Co 0:720 Fe 0:200 Cu 0:055 Zr 0:025 ) 7:5 permanent magnets obtained by various heat treatments are investigated by transmission electron microscopy (TEM). It is found that Cu atoms gradually segregate into SmCo 5 phase with the increase in aging time. The domain walls in the solution-treated, 6-h isothermal-aged magnets are straight, while those in the step-aged magnet are zigzag shaped along the cell boundaries of the SmCo 5 phases (1:5 H phases). In the demagnetized state of the step-aged magnet, it is found that the domain wall is located almost on the 1:5 H cell boundary phase containing Cu atoms, where the distribution of lines of magnetic flux strongly deviates from the axis of easy magnetization, particularly near the zigzag domain wall, and the lines of magnetic flux flow symmetrically along the center of the 1:5 H cell boundary phase. In the remanent state of the step-aged magnet, it is confirmed that domain walls are strongly pinned almost to the 1:5 H cell boundary phase containing Cu atoms, eventually resulting in a high coercivity in a Sm

Unconventional magnetization textures and domain-wall pinning in Sm–Co magnets

“…The domain wall is in fact injected into the hard phase at the location where the three phases meet. These results shed new light on previous observations based on electron mi-croscopy [23], which suggested an out-of-plane tilting of the magnetic flux away from the easy axis around intersections.…”

“…Magnetic imaging experiments, by means of Lorentz transmission electron microscopy (LTEM), magnetic force microscopy, and Kerr microscopy, have revealed that domain walls follow the SmCo 5 cell morphology [17,[19][20][21][22][23][24], thus confirming strong pinning at the cell boundaries. Theory and experiment, however, have yet to converge on the role of the Z phase on the magnetic properties of this material [9][10][11][12].…”

Magnetization reversal process in (Sm, Dy, Gd) (Co, Fe, Cu, Zr)z magnets with different cellular structures

“…1(a). This result is consisted with that reported by Okabe et al 13 It indicates that the domain energy density (γ = √ |AK 1 |, where K 1 is the magnetocrystalline anisotropy constant and A is the exchange constant of the constituent phases) in the CBP is lower than that in the main phase. The CBP exhibits an attractive pinning force to the DWs during applying magnetic field.…”

Electron holography of magnetic materials

“…In order to understand the magnitude of coercivity, it is especially important to clarify the pinning positions of the domain walls. As shown in figure 11 [35], in which Lorentz microscopy is coupled with electron holography, the domain wall is located directly on the cell boundary phase, i.e. SmCo 5 containing Cu.…”