MBE Growth of MnBi-based Single Crystal and Superlattice Films and Its Characterization by Nonlinear Magneto-Optical Effect

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In this project we have finished following three major topics (1) Epitaxial growth of good quality thin films of manganese pnictides including MnBi by MBE technique (2) Establishment of nano-fabrication technology for magnetic materials (3) Observation of surface magnetic properties by nonlinear magneto-optical effectDetails of these topics are described as follows : (1) Epitaxial growth of manganese pnictides : MBE growth of MnAs on nano-structured GaAs substrate and MBE growth of GaAlAs doped with 7% Mn. MBE growth of MnBi on MgO (001) substrate was carried out using Cu or Au layers as a buffer. Eiptaxial growth was unsuccessful by this method. On the other hand, simultaneous evaporation of Mn and Bi fluxes on a seed layer prepared by sequential deposition of Mn and Bi lead to successful epitaxial growth with a streaky RHEED pattern. The obtained film showed a perpendicular anisotropy with a magnetic hysteresis loop of a good squareness. Magneto-optical studies were also carried out … More in this film. (2) Nano-fabrication of magnetic material Embedded arrays of submicron magnetic dots were fabricated by electron-beam lithography technique : Si substrate was patterned to make a dot-array of less than 0. 1μm in diameter by electron beam exposure and was etched by reactive ion etching (RIE) technique. Co metal was evaporated to fill the hole prepared by RIE process and polished to make a flat surface by CMP (chemical mechanical polishing) technique. Next, magnetic films (Co) were etched directly by focused ion beam (FIB) method to fabricate 0.1μm pattern. MFM observation showed snake pattern, the same as that of un-structured Co film, suggesting that the nano-structure made no significant effect on the anisotropy. (3) Nonlinear magneto-optical effect was observed in a few magnetic films. In Fe/Au magnetic superlattices, azimuthal angle dependence of nonlinear Kerr effect showed a well defined four-fold symmetry pattern similar to that observed in the azimuthal dependence of MSHG in the same superlattice. The result was successfully analyzed considering the symmetry properties of nonlinear susceptibility tensor.During the term of this project, these three experiments were carried out independently using the different materials. Fabrication of nano-structures as described in (2) using the epitaxial MnBi film prepared by the process (1) and observation of nonlinear magneto-optical effect by means of (3) on the same sample is a future problem. Less