G. S. Dong

Abnormal magnetic transport in Co/Mn/Co sandwiches

A series of Co/Mn/Co sandwiches was prepared on GaAs(001) surfaces at room temperature via a molecular beam epitaxy (MBE) technique. Reflection high-energy electron diffraction (RHEED) and x-ray-diffraction (XRD) analysis indicated a polycrystalline structure. By standard magnetoresistance measurements, it was found that with a Mn spacer thickness of 8 A, a seldom-seen positive magnetoresistance (PMR) as high as 16% was exhibited at room temperature. The measurement under different geometries of H and I indicated that it was not an anisotropic magnetoresistance (AMR) effect. The MR–H curve displayed no hysteresis in contrast to the magnetometry measurement. An interface effect is proposed as a possible origin of this phenomenon.

Structure and magnetism of Co1−xMnx alloys epitaxially grown on GaAs(001)

The structure and magnetism of Co1−xMnx films grown on GaAs(001) substrates were characterized by reflection high energy electron diffraction and magneto-optical Kerr effect measurements. It is found that the Co-rich and Mn-rich films exist in body-centered-cubic and face-centered-cubic structures, respectively. Meanwhile, the Co1−xMnx films show ferromagnetism whenever the structure is bcc, but they show antiferromagnetism or paramagnetism whenever the structure is fcc. This strong correlation established between the structure and magnetism was further studied and confirmed by an ab initio electron linearized augmented-plane-wave calculation with the local-spin-density approximation.

Epitaxial structure and magnetic anisotropies of metastable single crystal Co0.70Mn0.30 film

Alloy films of Co0.70Mn0.30 were grown on GaAs (001) substrates by molecular beam epitaxy at room temperature. The metastable tetragonally distorted single crystal structure was confirmed by reflection high energy electron diffraction and x-ray diffraction measurement, which exhibited a 2.87 A in-plane lattice parameter. Ferromagnetic resonance measurements and theoretical fitting were performed and showed that, with a Mn capping layer, a uni-directional anisotropy existed. In addition, a fourfold tetragonal magnetocrystalline anisotropy as well as a uniaxial term in the film plane was also confirmed. The hysteresis loops recorded by longitudinal magneto-optical Kerr-effect also demonstrated the existence of different kinds of in-plane magnetic anisotropy. The origins of the anisotropy are explained tentatively.

XPS Study of Mn Thin Films Grown on GaAs(001) Surfaces

The composition depth profiles of the Mn thin films grown on GaAs(00l) surface using MBE technique are studied with X-ray photoelectron spectroscopy(XPS) . The experimental results show that the fcc-Mn/GaAs(001) system grown on a 400 K substrate has a sandwich structure with a Mn-Ga-As buffer layer located between the fcc-Mn layer and the GaAs substrate; the α-Mn/GaAs (001) system grown on a 300 K substrate also has a similar buffer layer which is much thinner than that of the fcc-Mn/GaAs(001) system;and the system grown on a 450 K substrate is a Mn-Ga-As alloy beyond the GaAs substrate and it has no Mn-dominated area. It is concluded that to keep the substrate at a proper temperature(400 K) during growth to obtain a suitable thickness of buffer layer is an essential requirement to grow fcc-Mn on GaAs(00l) surface.

Morphology of monolayer CuxAu1 ? x on Cu(001)

Protruding nanostructure is produced in the single layer of Cu(x)Au(1 - x) surface alloy grown on Cu(001) due to the mismatch strain which has been utilized as a template to tune the magnetic anisotropy of overlays recently. The protrusion network was investigated by in situ scanning tunneling microscopy (STM) combined with low energy electron diffraction (LEED) as a function of the stoichiometry. The measurement revealed the structure of the protrusion and its correlation with the composition. Interestingly, we observed a twin-domain phase of the protrusion when the film approaches the fully hetero-epitaxial range.

Correlation between spin reorientation transition and Curie temperature of NixPd1-x alloy on Cu(001)

The correlation between spin reorientation transition SRT and Curie temperature of NixPd1−x alloy on Cu 001 was investigated by ac susceptibility and magneto-optic Kerr-effect measurements. The result shows that NixPd1−x alloy exhibits a SRT at Ni concentration of 87% for 9 ML and of 96% for 7 ML. No reduction in Curie temperature was observed in the region of SRT as declared by F. Matthes et al. J. Appl. Phys 91, 8144 2002 . In addition it was found that Curie temperature increased with Ni concentration in different trends before and after SRT, which are attributed to the anisotropy variation.