Guo Zhaohui

Magnetic domain structures of precipitation-hardened SmCo 2:17-type sintered magnets: Heat treatment effect

The typical magnetic domains of Sm(CobalFe0.25Cu0.07Zr0.02)7.4 magnets quenched through various heat-treatment steps have been revealed by using magnetic force microscopy (MFM). For the specimens in which the nominal c-axis is perpendicular to the imaging plane, the domain configurations change from plate-like for the as-sintered magnet to corrugation and spike-like for the homogenized one, and then to a coarse and finally to a finer domain structure when isothermally aged at 830°C and then annealed at 400°C. However, only plate-like domains can be detected on the surfaces with the nominal c-axis parallel to the imaging plane. The finer domain (so-called interaction domain) is a characteristic magnetic domain pattern of the Sm–Co 2:17-type magnets with high coercivities. Domain walls in a zigzag shape are revealed by means of MFM in final bulk Sm–Co 2:17-type sintered magnets.

Effect of Sm Volatilization on Magnetic Microstructures of Sintered Sm(Co,Fe,Cu,Zr)z Magnets at High Temperatures

We present a magnetic force microscopy study of surface magnetic microstructure changes at high temperatures in 2:17-type Sm(Co,Fe,Cu,Zr)z (z~7.4) magnets. Surface magnetic microstructures are found to change greatly in parallel and vertical specimens after heat-treatment at 400°C for one hour in vacuum of 10−5 Torr with Ar gas as protecting atmosphere. Changes of microstructures are attributed to the formation of a soft-magnetic surfaces layer in the specimens, resulting from Sm volatilization due to high temperature. This hypothesis is further confirmed by the heat-treatment experiments at 400°C for 0.5 h and 2 h. Finally, the existence of the soft-magnetic layers, which consist primarily of Fe–Co compounds, is verified by the results of both XRD and XPS of the vertical specimens before and after heat-treatment.

Structure and Properties of Sputtered Pt/Co Multilayers

Two series of Pt/Co multilayer films were sputtered under different deposition conditions. The magnetic and magneto-optical properties are found to vary depending on Pt bufferlayer and the number of modulation period. Fine material parameters of Pt/Co multilayers for magneto-optical recording are obtained.