強磁性ナノ粒子を介したスピン依存トンネル  [in Japanese] Spin-Dependent Tunneling through layered Hard-Magnetic Nano-Particles  [in Japanese]

Spin-dependent tunneling was investigated in double tunnel junctions through Co_<80>Pt_<20> hard-magnetic nano-particles with double Al_2O_x barriers prepared by direct sputtering using an Al_2O_3 target. The junction magnetoresistances were 15.6% and 20.5% with low resistance in a low field at room temperature, when Co-based alloy electrodes (Co_<80>Pt_<20> bottom and Co_9Fe top electrodes) and Co_1Fe_1 top and bottom electrodes were used, respectively. It was revealed that the bias and temperature dependencies of the tunneling magnetoresistance are weak for the present junction structure. This indicates that the bias and tepmerature dependencies of the resistance and resistance change between antiparallel and parallel alignments between electrodes and nano-particles are not mainly attributable to magnon excitations. The main contributions to the tempearture and bias dependencies are shown to be the particle size effect and the broadening effect of Fermi distributions of electrons in the ferromagnetic electrodes and the layered Co_<80>Pt_<20> hard magnetic nano-particles, due to the low barrier height.