Co ∕ Pt multilayer based magnetic tunnel junctions using perpendicular magnetic anisotropy

Abstract

Magnetic tunnel junctions that utilize perpendicular magnetic anisotropy have attracted growing attention due to their potential for higher storage densities in future high capacity magnetic memory applications. In this study, we present an experimental demonstration of magnetic tunnel junctions composed of perpendicularly magnetized Co∕Pt multilayer electrodes and an AlOx tunnel barrier. The emphasis has been on how to maximize the thickness of the Co layers adjacent to the tunnel barrier while still magnetized perpendicularly for possible spin torque utilization in future applications. It is found that the thickness ratio between the Co and Pt layers and the number of bilayers were significant parameters to customize the magnetic properties. The difference between the switching fields of the soft and the hard layers can be adjusted by the number of repeats of the Co∕Pt bilayers. The measured hysteresis shows virtually zero exchange coupling between the two layers through the tunnel barrier. Measured tunneling magnetoresistance ratio of the fabricated submicron-size tunnel junctions ranges from 10% to 15% at room temperature.

Large enhanced perpendicular magnetic anisotropy in CoFeB/MgO system with the typical Ta buffer replaced by an Hf layer

“…[1][2][3][4][5][6][7][8][9][10] Such MTJs combine several important advantages over the MTJs with in-plane anisotropy, i.e., higher energy barrier against thermal agitation at reduced dimensions due to larger anisotropy energy; and smaller critical current density and faster reversal speed for current induced magnetization switching (CIMS) due to the absence of the demagnetization term. [11][12][13] So far most of the available PMA materials have been explored as MTJ electrodes, including the rare-earth/ transition-metal alloys, [3][4][5] L1 0 -ordered (Co, Fe)-(Pt, Pd) alloys, 6,7 and Co/(Pt, Pd, Ni) multilayers.…”

“…[11][12][13] So far most of the available PMA materials have been explored as MTJ electrodes, including the rare-earth/ transition-metal alloys, [3][4][5] L1 0 -ordered (Co, Fe)-(Pt, Pd) alloys, 6,7 and Co/(Pt, Pd, Ni) multilayers. [8][9][10] Attempts have also been made to search for strong PMA in Co or CoFeB layers sandwiched by Pd (Pt) and MgO (or other oxides) layers. 14,15 However, all these material systems suffer from either difficulties in integrating them into MTJs with high magnetoresistance ratio, or insufficient chemical/thermal stability, or large critical current needed for CIMS due to their large Gilbert damping constant.…”

Tunnel Junction with Perpendicular Magnetic Anisotropy: Status and Challenges

“…For the multilayer based on transition and noble metal such as Co/Pd (Pt), PMA, saturation magnetization, anisotropy field, and other parameters can be easily modulated by adjusting the number of bilayer periods, as well as the thickness of each layer [10][11][12]. However, the face-centered cubic fcc Co/Pd (Pt) (111) multilayers possess low spin polarization compared to CoFeB or CoFe, and cannot favor the formation of MgO (001) tunnel barriers, thereby impeding the improvement of TMR ratio [13,14]; Moreover, the free layer thickness should be reduced for lower threshold current to manipulate magnetization direction reversal. Thus, Yakushiji et al [15,16] developed the ultra-thin Co/Pd (Pt) multilayers configured with 0.14-0.2 nm films, which present not only large PMA, but also a relatively high TMR ratio of 62% and an ultra-low resistance area product (RA) with adherent CoFeB film.…”

Static and dynamic magnetic properties of FeMn/Pt multilayers

“…Some of these multilayer films have already been applied in magneto-optic recording 2 and more recently also in magnetic tunnel junctions as part of the reference layer. 3,4 Stimulated by earlier work on proximity effect at the FeMn and Pt interface, 5 we have recently carried out a systematic study of FeMn/Pt multilayers. 6,7 Despite the fact that FeMn is an antiferromagnet (AFM), FeMn/Pt multilayers with ultrathin FeMn and Pt layers (< 1 nm) were found to exhibit global FM ordering with in-plane magnetic anisotropy.…”