[19p-P06-1~50] 10 Spintronics and Magnetics (Poster)

English Presentation

[19p-P06-45] Dielectric constant and VCMA effect of epitaxial MgO tunnel barrier

〇Tomohiro Nozaki¹, Hiroshige Onoda¹, Shingo Tamaru¹, Hiroyasu Nakayama¹, Makoto Konoto¹, Takayuki Nozaki¹, Shinji Yuasa¹ (1.AIST)

Keywords:

Dilectric constant,VCMA effect,MgO tunnel barrier

Voltage controlled magnetic anisotropy (VCMA) effect has received much attentions as a magnetization control technique with ultra-low power consumption. Toward practical applications, further enhancement of VCMA coefficient has been desired. One approach to further enhance VCMA coefficient is to use high-k dielectrics for the tunnel barrier. Thus far, incorporation of high-k dielectrics such as HfO₂, ZrO₂, Pb(Zr_xTi_1-x)O₃, and SrTiO₃ has been attempted. However, achieving both a large dielectric constant and a large tunnel magnetoresistance (TMR) ratio is challenging. On the other hand, MgO tunnel barrier itself has the potential for a larger dielectric constant: strain induced enhancement of dielectric constant has demonstrated for rocksalt-type dielectrics in the past. In this study, we investigated the dielectric constant of MgO tunnel barrier in epitaxial stacks (MgO sub./MgO (5 nm)/Cr (50 nm)/Fe (0.9 nm)/Ir (0.06 nm)/Co (0.1 nm)/MgO (t_MgO nm)/cap structure) and demonstrated large dielectric constatn > 15, which is more than 50 % larger than that of bulk MgO (~10). We found that the dielectric constant increases with decreasing t_MgO. From in-plane XRD measurements, we clarified that lattice parameter a of epitaxial MgO tunnel barrier decreases with decreasing t_MgO. We interpreted the large dielectric constant of epitaxial MgO tunnel barrier in terms of the compressive strain induced enhancement of dielectric constant. We also investigated the VCMA coefficient of the epitaxial stacks and confirmed that the VCMA coefficient increases as the dielectric constant increases. This study provides a new perspective to the large VCMA effect of the epitaxial stacks and also demonstrates the importance of the strain engineering.