Tunneling magnetoresistance of perpendicular CoFeB-based junctions with exchange bias

Abstract

Recently, magnetic tunnel junctions with perpendicular magnetized electrodes combined with exchange bias films have attracted large interest. In this paper we examine the tunnel magnetoresistance of Ta/Pd/IrMn/Co-Fe/Ta/Co-Fe-B/MgO/Co-Fe-B/capping/Pd magnetic tunnel junctions in dependence on the capping layer, i.e., Hf or Ta. In these stacks perpendicular exchange bias fields of -500 Oe along with perpendicular magnetic anisotropy are combined. A tunnel magnetoresistance of (47.2 ± 1.4)% for the Hf-capped sample was determined compared to the Ta one (42.6 ± 0.7)% at room temperature. Interestingly, this observation is correlated to the higher boron absorption of Hf compared to Ta which prevents the suppression of ∆1 channel and leads to higher tunnel magnetoresistance values. Furthermore, the temperature dependent coercivities of the soft electrodes of both samples are mainly described by the Stoner-Wohlfarth model including thermal fluctuations. Slight deviations at low temperatures can be attributed to a torque on the soft electrode that is generated by the pinned magnetic layer system.

Correlation of tunnel magnetoresistance with the magnetic properties in perpendicular CoFeB-based junctions with exchange bias

“…2(a), the two clear magnetic steps come closer to each other with decreasing t MgO , while for t MgO = 0.6 nm there is the formation of one magnetic step from the two initial. Moreover, the character of the interlayer exchange coupling (IEC) can be extracted by the shift (H s ) of the minor loops with respect to zero field (ferromagnetic for H s < 0 or antiferromagnetic for H s > 0) 11 . As depicted in Figs.…”

“…In addition, the layer stacks Ta(4) / Pd(2) / Mn 83 Ir 17 (8) / Co 50 Fe 50 (1) and Ta(3) / Pd(3) will be symbolized as "sub" and "cap", respectively. Circular devices with D device = (0.14 − 1) µm in diameter were fabricated by electron-beam lithography and Ar-ion milling 11 . The transport properties of the p-MTJs were measured by a conventional two-probe method with a constant dc bias voltage (V bias ).…”

“…The TMR ratio ranging from (120-250) % has been reported in (Co/Pt)based synthetic antiferromagnet pseudo-spin-valve type p-MTJs consisting of CoFeB/MgO/CoFeB [8][9][10] . In our previous work, we utilized MnIr and reported p-MTJs of CoFeB/MgO/CoFeB with EB around 39.8 kA/m and TMR ratio of 47.2 %, at room temperature (RT) 11 .…”

Anisotropy in antiferromagnets

“…Correct selection of materials can result in a hysteresis loop where both values of the pseudo-coercivity (Hc) can lie in (say) a negative field following the system being field cooled in a positive field. Such a structure is shown in Figure 3(b) with the resulting magnetization curve in Figure 3(c) [4]. This type of system is used to pin one F layer in the tunnelling magnetoresistive (TMR) devices that are used in all read heads in hard drives at this time [5].…”

Tailoring sidewall profiles of magnetic tunnel junctions fabricated with various etching conditions

“…interlayer, surface morphology, crystalline structure, properties of magnetic layers with local, site-specific domains. [30][31][32][33][34][35][36] Hence, various factors affect the characteristics of an MTJ stack in which TMR ratio strongly depends on how an electron is penetrated through the FM/MgO interfaces. The barrier height herein plays an important role which determines the electron transmission coefficient at the FM/MgO interfaces.…”