強磁性ナノ粒子層を介した二重トンネル接合のTMR

概要

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Tunnel magnetoresistance (TMR) in double tunnel junctions with layered ferromagnetic nanoparticles was investigated. The sample comprised two ferromagnetic electrodes (CoFe/Fe) separated by an Al_2O_3 insulating layer in which a layer of Co_<80>Pt_<20> nanoparticles was embedded. The nanoparticles were ellipsoidal with an average diameter of 3. 7 nm, and composed a well-defined layer. The TMR and the tunnel resistance of the sample showed steep increases around 100 K, and weak temperature dependence below 50 K. The zero-bias TMR rose from 1% at room temperature to 18% at 20 K. Below 20 K, we observed magnetoresistance oscillation with respect to the bias voltage. The observed TMR oscillations, with periods of 1.6 and 15 mV, accompanied oscillations of the conductance. We consider that the conductance oscillations may originate from the coexistence of the discrete energy level of the nanoparticles and the discrete electrostatic potential due to the single-electron charging effect.
社団法人日本磁気学会の論文
2000-04-15