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Porous silicon (PS) with different porosity was obtained by anode electrochemical etching of boron-doped Si (100); the as-etched samples were then covered with Fe films by magnetron sputter technique. Analysis of surface profile and structural investigation were done by scanning tunneling microscopy and X-ray diffraction. Magneto-optical Kerr effect was employed to measure the hysteresis loops of the iron films sputtered onto PS and the reference sample on the Si substrate. The coercivity of the PS-based Fe films is larger than that of the Si-based ones, and increases with the porosity of the PS substrate. As for the PS-based samples with the same porosity, the coercivity of Fe films decreases with their thicknesses in a certain range. We found that the spongelike structure of PS can be effectively used to control the coercivity of iron films on the PS substrates.

The magnetism of Co1-xMnx alloys strongly depends on their structure and the Mn content.An ab initio linearized augmented plane wave (LAPW)method has been carried out to provide the electronic and magnetic structures for the fcc and bcc Co1-xMnx alloys with x=0.00,0.25,0.50,0.75 and 1.00. By increasing the Mn content,the magnetism of fcc Co1-xMnx alloys changes from ferromagnetism to ferrimagnetism,finally to antiferromagnetism;on the other hand, the magnetism of bcc Co1-xMnx alloys changes from ferromagnetism to ferrimagnetism.A good agreement is reached between out calculations and the previous experimental results.

The epitaxial growth crystal structure and magnetism of Co100-xMnx alloys grown on GaAs(001) substrate have been studied by using reflection high energy electron diffraction,X-ray diffraction and surface magneto-optic Kerr effect. For 0100-xMnx alloys.They show strong ferromagnetism.For 42100-xMnx alloy exists in bodycentered cubic(bcc)and face-centered cubic(fcc)phases respectively,and the coexistence of the bcc and fcc structures is observed in the middle stage.It is proved by using wedge samples that only the bcc phase contributes to the ferromagnetism.For x>78,the epitaxial alloys have fcc structure and show no Ferromagnetism.

By using in-situ reflection high energy electron diffraction, the epitaxial growth of Co films on GaAs(001) surface is studied. When the growth temperature was 150℃, the growth process of Co films can be divided into three stages. The crystal structure of the first 3nm of the Co film is body-center-cubic(bcc) metastable phase. Then the next 4nm film is a complicated polycrystalline phase. After the thickness exceeds 7nm, the Co film is a single-crystalline hexagonal-close-packed(hcp) stable phase. This new result clears up the controversy in former experiments about the structure of the Co epilayer, and establishes, for the first time to our knowledge, a clear physical picture of the epitaxial growth of Co films on GaAs(001).