Enhancement of magnetoresistance by inserting thin NiAl layers at the interfaces in Co2FeGa0.5Ge0.5/Ag/Co2FeGa0.5Ge0.5 current-perpendicular-to-plane pseudo spin valves

Abstract

We have investigated the effects of insertion of a thin NiAl layer (≤0.63 nm) into a Co2FeGa0.5Ge0.5 (CFGG)/Ag interface on the magnetoresistive properties in CFGG/Ag/CFGG current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo spin valves (PSVs). First-principles calculations of ballistic transmittance clarified that the interfacial band matching at the (001)-oriented NiAl/CFGG interface is better than that at the (001)-Ag/CFGG interface. The insertion of 0.21-nm-thick NiAl layers at the Co2FeGa0.5Ge0.5/Ag interfaces effectively improved the magnetoresistance (MR) output; the observed average and the highest MR ratio (ΔRA) are 62% (25 mΩ μm2) and 77% (31 mΩ μm2) at room temperature, respectively, which are much higher than those without NiAl insertion. Microstructural analysis using scanning transmission electron microscopy confirmed the existence of thin NiAl layers at the Ag interfaces with only modest interdiffusion even after annealing at 550 °C. The improvement of the interfacial spin-dependent scattering by very thin NiAl insertion can be a predominant reason for the enhancement of the MR output.

Interface Tailoring Effect for Heusler Based CPP-GMR with an L12-Type Ag3Mg Spacer

“…Both $\Delta RA$ and MR ratios monotonically decrease with increasing $t_{\mathrm{Fe}}$. Although the reason for the $RA$ dependence is unclear, a change of band-matching is a possible factor caused by the inserts [23,37]. On the other hand, regarding the junctions with Mg inserts, $RA$, $\Delta RA$ and MR ratios exhibit smaller values than those for junctions with no insert .…”

“…According to literatures [37,38], ultra-thin inserts at Heusler layer/spacer interfaces drastically modified the CPP-GMR properties. For the insert materials, Fe and Mg have been selected.…”

Theoretical Study on Magnetic Tunneling Junctions with Semiconductor Barriers CuInSe₂ and CuGaSe₂ Including a Detailed Analysis of Band-Resolved Transmittances

“…On the other hand, current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) devices have quite low RA because metallic (not insulating) spacers are sandwiched between ferromagnetic electrodes. Although the MR ratio in CPP-GMR devices is increased up to 82% at room temperature (RT) by using Co-based Heusler alloys as electrodes 7) , this value is still insufficient for applications. Recently, Kasai et al used a compound semiconductor CuIn0.8Ga0.2Se2 (CIGS) as a barrier layer of MTJs to achieve high MR ratios and low RA 8) .…”

Systematic investigations of transient response of nuclear spins in the presence of polarized electrons

“…In such a system, a highly efficient spin source is essential for an effective DNP. A Co-based Heusler alloy is an excellent ferromagnetic candidate for spintronic devices, including magnetic tunnel junctions (MTJs) [26][27][28][29][30][31][32][33][34][35], giant magnetoresistance devices [36][37][38][39][40][41][42], and for spin injection into semiconductors [43][44][45][46][47][48], due to its complete spin polarization at the Fermi level [49][50][51]. We recently reported high tunneling magnetoresistance ratios of up to 1995% at 4.2 K and up to 354% at 290 K in MTJs having Mn-rich Co 2 MnSi (CMS) electrodes [32], and found ratios of 2610% at 4.2 K and 429% at 290 K in Mn-rich Co 2 (Mn,Fe)Si MTJs [33,34], demonstrating a high spin polarization of CMS and CMFS.…”