| Budget Amount *help |
¥15,000,000 (Direct Cost: ¥15,000,000)
Fiscal Year 2003: ¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2002: ¥11,900,000 (Direct Cost: ¥11,900,000)
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| Research Abstract |
Mn_4N is perovskite-derived structure described as the chemical form of ABX_3 with A=Mn(I) at the corner positions, B=N at the body center and X=Mn(II) at the face centers of the cubic cell. The magnetic moments of Mn(I) and Mn(II) cant and the net magnetic moment is not cancelled. The ferrimagnetic transition temperature is around 500C. Our first-principles band-structure calculation of the Mn_4N shows that the Mn d states are metallic and well hybridize with p states of N. The up and down spin states coexist at, the Fermi level. On the other hand, the band-structure calculation of (Ga, Mn)N showed that the Mn d states are well localized and show the half metallic states giving the perfect spin-polarized electronic states at the Fermi level.
In this work, we have succeeded in the MBE growth of the ferrimagnetic Mn_4N and the heterostructure with (Ga, Mn)N. In the MBE work, we used NH_3 as N source instead of N_2-radical cell with RF-plasma excitation. The serious NH_3 adsorption on the
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internal wall of MBE chamber was avoided by heating up the whole chamber at about 150C by baking heater. Hence, the MBE method is called here "hot-wall MBE". Then, NH_3 pressure was stably set around 1.0×10^<-2> Pa during the growth. Firstly, Mn_4N/GaN/Al_2O_3(0001) and Mn_4N/(Ga, Mn)N/Al_2O_3(0001) heterostructures have been grown. The X-ray diffraction analysis showed that the polycrystalline Mn_4N layer was formed on the epitaxial GaN and (Ga, Mn)N. The hysteresis curves of the magneto-optical Kerr rotation were observed at room temperature. The saturated Kerr-rotation angles were around 0.01 degree at the magnetic field of 0.5T parallel to the growth planes for both structures. Mn_4N/GaN/(Ga, Mn)N tunneling magneto-resistance (TMR) structure has been also grown on ITO-coated quartz substrates. The nonlinear current-voltage characteristic has been observed as due to the TMR structure. An anisotropy in the magneto-resistance depending on the current direction through the TMR structure has been observed under the magnetic field perpendicular to the Mn_4N/GaN/(Ga, Mn)N growth plane at 70K. This suggests the spin-dependent carrier rectification through the Mn_4N/GaN/(Ga, Mn)N TMR structure. Less
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