Giant tunneling magnetoresistance effect in low-resistance CoFeB∕MgO(001)∕CoFeB magnetic tunnel junctions for read-head applications

TLDR

The giant tunneling magnetoresistance effect has been achieved in low‑resistance CoFeB/MgO(001)/CoFeB magnetic tunnel junctions at room temperature. These MTJs will accelerate the realization of highly sensitive read heads for ultrahigh‑density hard‑disk drives. The high MR ratio at low resistance is achieved by inserting a 4 Å Mg layer between the CoFeB bottom electrode and the MgO(001) barrier, which improves the crystalline orientation of the thin MgO(001) layer. The MTJs exhibit a 138 % MR ratio—seven times higher than state‑of‑the‑art devices—at a low RA of 2.4 Ω μm², with the Mg layer’s partial oxidation reducing MR for thick barriers while enhancing it for thin barriers.

Abstract

The giant tunneling magnetoresistance effect has been achieved in low-resistance CoFeB∕MgO(001)∕CoFeB magnetic tunnel junctions (MTJs) at room temperature. A magnetoresistance (MR) ratio as high as 138%, seven times that of state-of-the-art MTJs for magnetic sensor application, was obtained at room temperature in MTJs with a resistance-area product (RA) as low as 2.4Ωμm2. Such a high MR ratio at such a low resistance was made possible by introducing an ultrathin Mg metal layer with a thickness of 4 Å between the CoFeB bottom electrode layer and the MgO(001) tunnel barrier layer. The Mg layer was slightly but not fully oxidized, which resulted in a reduction in MR for a thicker MgO barrier (high RA) region and in an increase in MR for a thinner barrier (low RA) region. The Mg layer improves the crystalline orientation of the MgO(001) layer when the MgO(001) layer is thin. These MTJs will accelerate the realization of highly sensitive read heads for ultrahigh-density hard-disk drives.