2002 年 26 巻 4 号 p. 405-409
Ferromagnetic tunnel junctions (MTJs) in which a thin MgO seed layer was inserted between Fe bottom electrode and MgF2 insulating barrier were fabricated through the use of molecular beam epitaxy. The structure and tunnel magnetoresistance (TMR) were investigated for Fe (200Å)/MgO (5Å)/MgF2 (20Å)/Co (200Å) junctions. RHEED observation suggested that an MgF2 layer deposited at room temperature was in amorphous or nanocrystalline state. The TMR ratio observed for a typical MTJ with barrier height of 1.6 eV was 1.8 % at 4.2 K and decreased with increasing temperature, down to 0.7 % at 293 K. It was found that the bias dependence of TMR shows a strong asymmetric feature, in contrast to conventional MTJs with amorphous alumina barriers.