Large magnetoresistance in Heusler alloy-based current perpendicular to plane giant magnetoresistance sensors

Abstract

Increasing the data storage in next-generation hard disk drives requires a reduction in the physical dimensions of read sensors. Tunneling magnetoresistance (TMR) heads yield high magnetoresistance (MR) ratio but with a high resistance-area product (RA) that is suboptimal for devices. Giant magnetoresistance (GMR) head with different materials is an alternative way to improve reader performance with high MR ratio and low RA. In this paper, we theoretically study the effect of material properties and the layer thickness on RA and MR ratio in a trilayer system via an atomistic model combined with the spin transport model. The GMR stack can be constructed by the atomistic model and the RA and MR ratio can be directly calculated by considering the spin accumulation and spin current from the spin transport model. It is found that the spin valve using the Co 2 FeAl Heusler alloy electrode with high spin polarization exhibits a high MR ratio and RA of 64 mΩ • µm 2 which is better than the spin valves using conventional ferromagnets (FM) such as Co, NiFe and CoFe. Moreover, we consider the thickness dependence of the change of RA (∆RA). Increasing the free layer thickness yields the increase in ∆RA and MR ratio because of the enhancement of the bulk spin scattering. Additionally, the results show that the △RA depends on the spin diffusion length of the nonmagnetic materials (λ sdl,NM ). The ∆RA increases from 3 up to 10 mΩ • µm 2 when λ sdl,NM increases from 35 to 1200 nm. This investigation shows the possibility for read head design of HDDs with areal density beyond 2 Tb/in 2 .

Heusler-alloy-based magnetoresistive sensor with synthetic antiferromagnet

“…The Heusler-alloy-based read sensor gives a low RA of less than RA < 100 mΩ • µm 2 and a high MR ratio of up to 120%, as shown in figure 4, which is consistent with the experimental results in [42]. The results demonstrate a better performance of the read sensor with Heusler alloy than that with conventional FMs, such as CoFe and NiFe [23,43,44]. Previously, Heusler alloy material has been utilized as the FL in the read element, giving a low RA of less than 100 mΩ • µm 2 and a high MR ratio [45,46].…”

“…Interestingly, it is seen as a promising candidate because of its high spin polarization, high saturation magnetization, and high Curie temperature. It serves more roles in the read element than only the sensing layer, leading to a high MR ratio [21,23,24]. Recently, CFS has been proposed as the pinned Heusler alloy layer in the EB system [25][26][27].…”

“…In this work, we focus on the investigation of Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) sensors providing a high signal-to-noise ratio and low resistance-area product (RA) for the application of next-generation HDDs. In the general reader model, the effect of the diffuse interface is not taken into account, and the PL is not explicitly considered [23,[31][32][33][34]. Therefore, the atomistic model coupled with the spin accumulation model is employed here.…”

Dimensional scaling effects on critical current density and magnetization switching in CoFeB-based magnetic tunnel junction

“…Therefore, the stationary solution of the spin accumulation can be solved by applying equations ( 7) and ( 8) through the use of the transfer matrix approach within a rotated coordinate system b1 , b2 and b3 which is parallel and perpendicular to the local spin moment. The solution can be decomposed into two parts: longitudinal (⃗ m ∥ ) and transverse components (⃗ m ⊥ ), taking the following form [26][27][28][29]:…”

Effect of off-stoichiometric composition on half-metallic character of Co2Fe(Ga,Ge) investigated using saturation magnetization and giant magnetoresistance effect

“…Magneto-resistive (MR) devices with low device resistance and a high output signal are indispensable for use as read sensors in next-generation hard disk drives [1]. A currentperpendicular-to-plane (CPP) giant magnetoresistance (GMR) device using Co-based Heusler alloy (Co 2 YZ, where Y is usually a transition metal and Z is a main group element) is a promising candidate for such devices [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. This is because many Co-based Heusler alloys, such as Co 2 MnSi (CMS) and Co 2 MnGe (CMG), have theoretically 100% spin polarization at Fermi level (E F ) due to their half-metallic nature, which is characterized by an energy gap for one spin direction at E F [18][19][20][21][22].…”