Hiromasa Takeuchi

Electrical and Magnetic Properties and Colossal Magnetoresistance Effect of La1-xBixMnO3

Perovskite-type La1-xBixMnO3 (LBMO) crystals, which were prepared by doping a Bi atom for a La atom in LaMnO3, were shown to exhibit the colossal magnetoresistance (CMR) effect. Samples were produced by sintering in an air atmosphere that depended on the Bi composition ratio x. X-ray diffraction measurements showed that the LBMO crystal structure can be orthorhombic (or rhombohedral) with γ (=c/a)=1.02 for 0.0<x<0.3, cubic with γ=1.005 for 0.3<x<0.5 or monoclinic with γ=1.014 for 0.5<x. The CMR effect of LBMO for x=0.2 was approximately 400% at 88 K. In addition, the magnetoresistance of LBMO was found to be proportional to the square of magnetization. On the basis of these results, the CMR occurrence mechanics of LBMO were shown to significantly contribute to a Mn3+–Mn4+ double exchange interaction, which is closely associated with the cooperative phenomenon in the Jahn–Teller effect.

Damping capacity of Mg-Al and Mg-Li-Al alloy castings

The cast structure, damping capacity and mechanical properties of Mg-Al and Mg-Li-Al alloy castings were investigated. It was found that the structures of Mg-Al and Mg-Li-Al alloys became finer wit...

Magnetoresistance Effect in a La0.8Bi0.2MnO3/MgO/Co Trilayer Device

The device composed of La_0.8Bi_0.2MnO₃/MgO/Co trilayer (with a tunnnel barrier made of MgO film) as an L_1-xBi_xMnO₃ substrate are prepared, and the magnetoresistance effect of the device is examined. Fundamental temperature properties of electrical conduction of the La_0.8Bi_0.2MnO₃/MgO/Co trilayer device as a function of MgO thickness is determined. It was found that the magnetoresistance was about 33% of the maximum value when the MgO film thickness was 2.0 nm and the device shows damped oscillation with increasing MgO film thickness.

Magnetoresistance Effect of La0.8Bi0.2MnO3/MgO/Co Heterojunction Device

The La0.8Bi0.2MnO3/MgO/Co heterojunction device was fabricated by vacuum evaporation with an electron gun on a well-polished perovskite-type oxide La0.8Bi0.2MnO3 substrate. The magnetoresistance through MgO (thickness: 2.0nm) tunnel junction of these devices was 33% of the maximum value. At this point, a spin polarization value of LBMO was about 0.42. The experiments showed that the devices have a transition temperature at around 240K, namely, between that of the ferromagnetic phase (for low temperature) and that of a semiconductor-like phase (for high temperature).