Current-perpendicular-to-plane Giant Magnetoresistance Research Articles

Improvement in CPP-GMR read head sensor performance using [001]-oriented polycrystalline half-metallic Heusler alloy Co2FeGa0.5Ge0.5 and CoFe bilayer electrode

ABSTRACT A current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) device with a half-metallic electrode is one of the most promising candidates of next-generation read head for hard disk drive. In this study, we fabricate [001]-oriented polycrystalline CPP-GMR devices with the normal ferromagnet (NFM) CoFe/half-metallic ferromagnet (HMFM) Co2FeGa0.5Ge0.5 (CFGG) bilayer electrodes to enhance the magnetoresistance (MR) ratio by large interfacial spin-dependent scattering at the NFM/HMFM interface. The CoFe/CFGG bilayer electrode provides the additional large interfacial spin-dependent scattering and achieves high MR ratio of 22.7% with the CoFe(4.5 nm)/CFGG(2.5 nm) bilayer electrodes, which is almost three(two) times larger than the MR ratio with the single CoFe(CFGG) (7 nm) electrodes. The bias voltage dependent study revealed an additional advantage of increasing the output voltage |ΔV| by using the CoFe/CFGG bilayer due to the improvement of the endurance against spin-transfer torque under high bias current. A maximum output voltage Δ V max of 6.5 mV was obtained with the CoFe(5.5 nm)/CFGG(1.5 nm) electrodes, which is the highest ever reported in the CPP-GMR devices with a uniform metallic spacer including high-quality epitaxial devices.

First-Principles Studies on Spin-Dependent Transport of Magnetic Junctions with Half-Metallic Heusler Compounds

Two types of magnetoresistance (MR), i.e., tunnel magnetoresistance (TMR) and current perpendicular to plane giant magnetoresistance (CPP-GMR), are theoretically discussed for systems with half-metallic (HFM) Co-based full Heusler compounds. In TMR, the non-collinear spin structure at the Co2MnSi(CMS)/MgO(001) interface that results from thermal spin fluctuations significantly reduced the TMR ratio at room temperature (RT). Enhancement of the exchange stiffness of CMS/MgO was essential to suppress the reduction in TMR at RT. Furthermore, it is proposed that inserting of a B2-CoFe layer between CMS and MgO is a promising way to enhance the interface exchange stiffness constant. In CPP-GMR, the interface spin asymmetry γ in the Valet-Fert model was essential to enhance GMR at RT, because the temperature dependence of γ in experiments was much larger than that of the bulk spin asymmetry β. I showed that the experimental CPP-GMR ratio increases with the decrease in the theoretical resistance-area product RPA, which is roughly consistent with the RP dependence of γ. This means that matching of the conductive channel between HMF and a non-magnetic metallic spacer is a key parameter to enhance γ. These findings will be very important for room temperature spintronics devices applied in future artificial intelligence hardware.

Effect of Ni addition on CPP-GMR response in electrodeposited Co-Ni/Cu multilayered nanocylinders with an ultra-large aspect ratio

Effect of Co–Ni alloy composition on the current perpendicular-to-plane giant magnetoresistance (CPP-GMR) response of electrochemically synthesized Co–Ni/Cu multilayered nanocylinders was studied using anodized aluminum oxide membranes (AAOM) with nanochannel diameter D ∼67 nm and length L ∼70 μm. Co–Ni/Cu multilayered nanocylinders, which have an aspect ratio L/D of ∼1,045, were fabricated in the AAOM nanochannel templates by utilizing a pulse-current electrochemical growth process in an electrolytic bath with Co2+, Ni2+ and Cu2+ ions. Co–Ni/Cu alternating structure with Co84Ni16 alloy layer-thickness of 9.6 nm and Cu layer-thickness of 3.8 nm was clearly observed in a nanocylinder with a diameter of 63 nm. The alternating structure was composed from crystalline layers with preferential orientations in hcp-CoNi (002) and fcc-Cu (111). The Co–Ni/Cu multilayered nanocylinders were easily magnetized in the long axis direction because of the extremely large aspect ratio L/D. In Co84Ni16/Cu multilayered nanocylinders, the coercivity and squareness were ∼0.46 kOe and ∼0.5, respectively. The CPP-GMR value was achieved up to 22.5% (at room temperature) in Co84Ni16/Cu multilayered nanocylinders.

Spin-scattering asymmetry at half-metallic-ferromagnet|ferromagnet interface

We study spin-scattering asymmetry at the interface of two ferromagnets (FMs) based on a half-metallic ${\mathrm{Co}}_{2}{\mathrm{Fe}}_{0.4}{\mathrm{Mn}}_{0.6}\mathrm{Si}$ (CFMS)/CoFe interface. First-principles ballistic transport calculations based on Landauer formula for (001)-CoFe/CFMS/CoFe indicate strong spin-dependent conductance at the CFMS/CoFe interface, suggesting a large interface spin-scattering asymmetry coefficient ($\ensuremath{\gamma}$). Fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valve (PSV) devices involving CoFe/CFMS/Ag/CFMS/CoFe structures exhibit an enhancement in MR output owing to the formation of the CFMS/CoFe interface at room temperature (RT). This is well reproduced qualitatively by a simulation based on a generalized two-current series-resistor model with considering the presence of $\ensuremath{\gamma}$ at the CFMS/CoFe interface, half-metallicity of CFMS, and combinations of terminated atoms at the interfaces in the CPP-GMR PSV structure. We show direct evidence for a large $\ensuremath{\gamma}$ at a half-metallic FM/FM interface and its impact on the CPP-GMR effect even at RT.

Current-Perpendicular-to-Plane Giant Magnetoresistance Effect in van der Waals Heterostructures

Spin-dependent transport in a full van der Waals (vdW) giant magnetoresistance (GMR) junctions with the structure of Fe3GeTe2/XTe2/Fe3GeTe2 (X = Pt, Pd) has been investigated by using first-principles calculations. The ballistic conductance, magnetoresistance (MR) and resistance-area product (RA) have been calculated in a current-perpendicular-to-plane (CPP) geometry. A giant magnetoresistance of around 2000% and RA less than 0.3 {\Omega} {\mu}m2 have been found in the proposed vdW CPP GMR. In addition, the spin-orbit coupling effect on transport and anisotropy magnetoresistance (AMR) has also been investigated. The calculated AMR is found to be around 20% in Fe3GeTe2/trilayer-PdTe2/Fe3GeTe2 CPP GMR. Both GMR and AMR in the proposed vdW CPP GMR mainly originate from the bulk electronic structure properties of Fe3GeTe2. This work demonstrates a vdW CPP GMR with superior advantages including perpendicular magnetic anisotropy, large GMR, low RA as well as sizable AMR may stimulate future experimental explorations and should be appealing for their applications in spintronic devices including magnetic sensor and memory.

Current-perpendicular-to-plane giant magnetoresistance in Co/Cu multilayered nanocylinders electrodeposited into anodized aluminum oxide nanochannels with ultra-large aspect ratio

An anodized aluminum oxide (AAO) thick film with numerous nanochannels was synthesized by a cathodic exfoliation technique from a metallic aluminum rod. The nanochannel diameter D and length L were about 60 nm and 60 µm, respectively. The aspect ratio L/D reached ~ 1000. A rectangular pulsed potential deposition technique was applied to electrochemically grow the multilayered nanocylinders with alternating Cu and Co thin layers in the AAO nanochannels. The Co/Cu bilayer thickness was decreased to around 7 nm at the minimum by controlling the pulsed potential and duty cycle during the electrodeposition process. An electrochemical in situ single contact process was demonstrated by monitoring the observed current until a Co/Cu multilayered nanocylinder reached the nanoporous Au film on the AAO thick film. The resistance of the Co/Cu multilayered nanocylinder was determined to range from 1 to 2 kΩ, which corresponded well with a theoretical estimation. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of a Co/Cu multilayered nanocylinder with ~ 6000 bilayers (Cu = 2.4 nm, Co = 7.1 nm) reached up to 31.5% at room temperature. Valet–Fert model agreed well with the present study concerning the effect of Cu-layer thickness on CPP-GMR.

Determination of Cobalt Spin-Diffusion Length in Co/Cu Multilayered Heterojunction Nanocylinders Based on Valet-Fert Model.

Anodized aluminum oxide (AAO) nanochannels of diameter, D, of ~50 nm and length, L, of ~60 µm (L/D: approx. 1200 in the aspect ratio), were synthesized and applied as an electrode for the electrochemical growth of Co/Cu multilayered heterojunction nanocylinders. We synthesized numerous Co/Cu multilayered nanocylinders by applying a rectangular pulsed potential deposition method. The Co layer thickness, tCo, ranged from ~8 to 27 nm, and it strongly depended on the pulsed-potential condition for Co layers, ECo. The Cu layer thickness, tCu, was kept at less than 4 nm regardless of ECo. We applied an electrochemical in situ contact technique to connect a Co/Cu multilayered nanocylinder with a sputter-deposited Au thin layer. Current perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect reached up to ~23% in a Co/Cu multilayered nanocylinder with ~4760 Co/Cu bilayers (tCu: 4 nm and tCo: 8.6 nm). With a decrease in tCo, (ΔR/Rp)−1 was linearly reduced based on the Valet–Fert equation under the condition of tF > lFsf and tN < lNsf. The cobalt spin-diffusion length, lCosf, was estimated to be ~12.5 nm.

Thickness dependence of degree of B2 order of polycrystalline Co2(Mn0.6Fe0.4)Ge Heusler alloy films measured by anomalous X-ray diffraction and its impacts on current-perpendicular-to-plane giant magnetoresistance properties

We investigated the degree of B2 order (SB2) of 4-10 nm-thick polycrystalline Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy films using anomalous X-ray diffraction (AXRD) and its correlation to the magnitude of current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) effect. We found that SB2 of the CMFG films is degraded for the film thickness below 6 nm, which is an issue for practical applications of CPP-GMR devices such as read head sensors of hard disk drives. Since SB2 has a thickness-dependence, the bulk spin polarization (β) of the CMFG layers is also expected to vary depending on the thickness; thus, the deduction of β using the Valet-Fert model, where β is assumed to be thickness-independent, is not valid for these CPP-GMR devices.

Fully epitaxial giant magnetoresistive devices with half-metallic Heusler alloy fabricated on poly-crystalline electrode using three-dimensional integration technology

Fully-epitaxial magnetoresistance (MR) devices with half-metallic Heusler alloys has attracted considerable attention for years due to their excellent spin-dependent transport properties such as high MR ratio and ultra-low resistance-area product. However, their poor manufacturability due to the necessity of epitaxial growth on a special single crystalline substrate such as MgO(001) hinders their practical applications. To overcome this issue, in this study, we fabricated Heusler-based epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) film grown on Si substrate and directly bonded it to poly-crystalline electrode wafer by using three-dimensional (3D) integration processes such as direct wafer bonding and removal of backside Si substrate. First we explored suitable seed/buffer layers for the (001)-oriented epitaxial growth of Heusler CPP-GMR on Si(001) substrate. Si-subs/NiAl/CoFe seed/buffer structure was found to induce (001)-oriented epitaxial growth and to suppress an Al diffusion from NiAl to the Heusler electrode even after annealing at 500 °C, resulting in large MR ratio comparable to that with MgO substrate. After direct wafer bonding process, the microstructure analysis revealed clean damage-free bonded interface between the epitaxial Heusler GMR and poly-crystalline electrode films with Au capping layers. After the 3D integration processes, high MR performance has been successfully reproduced. This unique processing method enables the integration of high performance Heusler-based epitaxial spintronic devices for various practical applications.

Thickness Dependence of Degree of B2 Order of Polycrystalline Co &lt;sub&gt;2&lt;/sub&gt;(Mn &lt;sub&gt;0.6&lt;/sub&gt;Fe &lt;sub&gt;0.4&lt;/sub&gt;)Ge Heusler Alloy Films Measured by Anomalous X-Ray Diffraction and its Impacts on Current-Perpendicular-To-Plane Giant Magnetoresistance Properties

We investigated the degree of B2 order (SB2) of 4-10 nm-thick polycrystalline Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy films using anomalous X-ray diffraction (AXRD) and its correlation to the magnitude of current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) effect. We found that SB2 of the CMFG films is degraded for the film thickness below 6 nm, which is an issue for practical applications of CPP-GMR devices such as read head sensors. Since SB2 has a thickness-dependence, the bulk spin polarization (β) of the CMFG layers is also expected to vary depending on the thickness; thus, the deduction of β using the Valet-Fert model, where β is assumed to be thickness-independent, is not valid for the CPP-GMR devices with polycrystalline CMFG layers.

CPP-GMR Performance of Electrochemically Synthesized Co/Cu Multilayered Nanowire Arrays with Extremely Large Aspect Ratio.

Anodized aluminum oxide (AAO) films, which have numerous nanochannels ca. 75 nm in diameter, D and ca. 70 µm in length, L (ca. 933 in aspect ratio, L/D), were used as a template material for growing Co/Cu multilayered nanowire arrays. The multilayered nanowires with alternating Cu layer and Co layers were synthesized by using an electrochemical pulsed-potential deposition technique. The thickness of the Cu layer was adjusted from ca. 2 to 4 nm while that of the Co layer was regulated from ca. 13 to 51 nm by controlling the pulsed potential parameters. To get a Co/Cu multilayered nanowire in an electrochemical in-situ contact with a sputter-deposited Au thin layer, the pulsed potential deposition was continued up to ca. 5000 cycles until the nanowire reached out toward the surface of AAO template. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect reached up to ca. 23.5% at room temperature in Co/Cu multilayered nanowires with ca. 3500 Co/Cu bilayers (Cu: 1.4 nm and Co: 18.8 nm). When decreasing the thickness of Co layer, the CPP-GMR value increased due to the Valet–Fert model in the long spin diffusion limit.

Heavy‐Metal‐Free, Low‐Damping, and Non‐Interface Perpendicular Fe16N2 Thin Film and Magnetoresistance Device

Realization of sub‐10 nm spin‐based logic and memory devices relies on the development of magnetic materials with perpendicular magnetic anisotropy that can provide low switching current and large thermal stability simultaneously. In this work, the authors report on one promising candidate, Fe16N2, a heavy‐metal‐free, non‐interface perpendicular magnetic material and demonstrate a perpendicularly magnetized current‐perpendicular‐to‐plane (CPP) giant magnetoresistance (GMR) device based on Fe16N2. The crystalline‐based perpendicular anisotropy of Fe16N2 in the CPP GMR device is measured to be about 1.9 × 106 J m−3 (1.9 × 107 erg cm−3), which is sufficient to maintain the thermal stability of sub‐10 nm devices. A first principle calculation is performed to support this large magnitude of the perpendicular anisotropy. Moreover, the Gilbert damping constant of the Fe16N2 thin film (α ≈0.01) measured by ferromagnetic resonance (FMR) is lower than for most existing materials with crystalline perpendicular magnetic anisotropy. The non‐interface perpendicular anisotropy and low damping properties of Fe16N2 may offer a pathway for future spintronics logic and memory devices.

High magnetic field sensitivity in anti-ferromagnetically coupled 001-epitaxial [Co2Fe(Al0.5Si0.5)/Ag]N multilayers

We have investigated the effects of the number of repetition (N) of ferromagnetic/nonmagnetic bilayers on the magnetic property and current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) in [Co2Fe(Al0.5Si0.5) (CFAS)/Ag]N multilayer for a potential magnetic field sensor application. The antiferromagnetic interlayer exchange coupling (AFM-IEC) between CFAS layers through the Ag(2.1 nm) spacer realized an anti-parallel magnetization configuration between the adjacent CFAS layers with N up to 6, which led to the stable linear response of magnetoresistance (MR) against a magnetic field in the range of 60-70 mT. The resistance change-area product (ΔRA) and the MR ratio were monotonically increased with N from 6.6 mΩ μm2 and 16% for N = 1 (CFAS/Ag/CFAS trilayer) to 23 mΩ μm2 and 43% for N = 6, respectively, giving an enhancement of field sensitivity with N up to 4.5%/mT. We also found nearly 3 times smaller non-linearity (1.2% Full Scale) in the device with N = 6 compared to that with N = 1. This study suggests a potential of Heusler-alloy based multilayer CPP-GMR device having AFM-IEC for magnetic field sensor applications.

Optimization of half-Heusler PtMnSb alloy films for spintronic device applications

Half-Heusler PtMnSb alloy films were optimized with varying deposition temperatures on Cr/Ag-buffered MgO(0 0 1) substrates by investigating structural and magnetic properties. Epitaxial growth was achieved in PtMnSb films grown at 200 °C while high magnetization of 530 emu cm−3 was observed at 500 °C. Compared to other Heusler alloys, the PtMnSb films show relatively large anisotropic magnetoresistance ratios with negative sign, which could be attributed to high spin–orbit interaction in the PtMnSb films owing to Pt. Furthermore, current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices as a kind of representative spintronic devices were fabricated with the structure of PtMnSb/Ag/PtMnSb. Room-temperature CPP-GMR effect was first observed in the PtMnSb-based CPP-GMR devices.

Size dependence of vortex-type spin torque oscillation in a Co2Fe0.4Mn0.6Si Heusler alloy disk

This paper reports the systematic investigation of vortex-type spin torque oscillation in circular disks of highly spin-polarized Co2Fe0.4Mn0.6Si (CFMS) Heusler alloys. We fabricated the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with various disk diameters (D) using the layer stack of CFMS/Ag3Mg/CFMS. The gyrotropic motion of the vortex core was successfully excited for the CFMS circular disks with 0.2 µm ⩽ D ⩽ 0.3 µm. The CPP-GMR device with D = 0.2 µm exhibited the Q factor of more than 5000 and the large output power of 0.4 nW owing to the high coherency of vortex dynamics and the high spin-polarization of CFMS. However, the Q factor was remarkably decreased as D was reduced from 0.2 µm to 0.14 µm. The comparison with the calculated resonance frequencies suggested that this degradation of the Q factor was due to the transition of the oscillation mode from the vortex mode to other modes such as the low-coherent out-of-plane precession mode. The present experimental results also suggest that there exists an adequate disk size for the enhanced Q factor of the vortex-type spin torque oscillation.

Damping constant measurement and inverse giant magnetoresistance in spintronic devices with Fe4N

Fe4N is one of the attractive materials for spintronic devices due to its large spin asymmetric conductance and negative spin polarization at the Fermi level. We have successfully deposited Fe4N thin film with (001) out-of-plane orientation using a DC facing-target-sputtering system. A Fe(001)/Ag(001) composite buffer layer is selected to improve the (001) orientation of the Fe4N thin film. The N2 partial pressure during sputtering is optimized to promote the formation of Fe4N phase. Moreover, we have measured the ferromagnetic resonance (FMR) of the (001) oriented Fe4N thin film using coplanar waveguides and microwave excitation. The resonant fields are tested under different microwave excitation frequencies, and the experimental results match well with the Kittel formula. The Gilbert damping constant of Fe4N is determined to be α = 0.021±0.02. We have also fabricated and characterized the current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) device with Fe4N/Ag/Fe sandwich. Inverse giant magnetoresistance is observed in the CPP GMR device, which suggests that the spin polarization of Fe4N and Fe4N/Ag interface is negative.

Investigation of spin-dependent transports and microstructure in NiMnSb-based magnetoresistive devices

We have fabricated fully epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices using C1b-half Heusler compound NiMnSb, the first candidate of the half-metallic material, as the electrode with a Ag spacer. The device shows magnetoresistance ratios of 25% at 4.2 K and 9.6% at 290 K, which are one of the highest values for the CPP-GMR with half-Heusler compounds. However, these values are much lower compared to those reported for CPP-GMR devices with L21-full Heusler compounds. Careful analysis of the microstructure using scanning transmission electron microscopy and energy dispersive spectroscopy through the upper NiMnSb/Ag interface indicates the heterogeneous formation of Ag-rich solid solution or the island growth of Ag on top of NiMnSb, which clarified a difficulty in evaluating an intrinsic spin-polarization in NiMnSb from CPP-GMR devices. Thus, to evaluate a spin-polarization of a NiMnSb thin film, we fabricated non-local spin valve (NLSV) devices using NiMnSb with Cu channel wires, which is free from the diffusion of Cu to NiMnSb because of no annealing proccess after deposition of Cu. Finally, intrinsic spin polarization of the NiMnSb single layer was extrapolated to be around 50% from NLSV, suggesting a difficulty in obtaining half-metallic nature in the NiMnSb epitaxial thin film.

Enhancement of current-perpendicular-to-plane giant magnetoresistive outputs by improving B2-order in polycrystalline Co2(Mn0.6Fe0.4)Ge Heusler alloy films with the insertion of amorphous CoFeBTa underlayer

We studied the origin of the enhancement of current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect by inserting a thin amorphous CoFeBTa (CFBT) underlayer below a Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy ferromagnetic (FM) layer. Large magnetoresistance ratio of ∼25% and resistance change-area product of ∼7.5 mΩ μm2 were obtained at room temperature by inserting a CFBT (1.2 nm) underlayer. X-ray diffraction (XRD) and transmission electron microscope analyses confirmed that the CMFG FM layer deposited on the CFBT underlayer was amorphous in the as-deposited state and crystallized to a B2-ordered polycrystalline film by annealing at 300 °C. The degree of B2 order (SB2) of the CMFG films was estimated by anomalous XRD using x-ray energies around the Co K-absorption edge. SB2 of the CMFG film deposited on the amorphous CFBT (1.2 nm) underlayer was ∼0.76, much larger than that of the CMFG film deposited on a crystalline CoFe underlayer (SB2 ∼0.47). First-principles calculations indicated that the spin polarization of the sp-conduction electrons in CMFG increases with increasing SB2, which accounts for the enhanced CPP-GMR effect in the pseudo spin-valve by inserting an amorphous CFBT underlayer.

Dual-spacer nanojunctions exhibiting large current-perpendicular-to-plane giant magnetoresistance for ultrahigh density magnetic recording

Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) heterostructures were fabricated using half-metallic Co2Fe0.4Mn0.6Si (CFMS) ferromagnetic electrodes and dual Ag-Mg spacers. The magnetic properties and (001)-epitaxial growth of the CFMS films were investigated in the whole CPP-GMR stacks. A large intrinsic CPP-GMR ratio of 73% (observed CPP-GMR value: 63%) at room temperature was achieved in the nanopatterned CPP-GMR junctions. The change in resistance-area product (ΔRA) value of the junctions was enhanced to 27 mΩ·μm2. The large CPP-GMR effect in the dual-type CPP-GMR heterostructures could be attributed to their enhanced interfacial spin asymmetry scattering owing to the increased CFMS/Ag-Mg interfaces. The temperature dependence of the CPP-GMR effect was also studied, and a local maximum CPP-GMR ratio of 175% with a ΔRA value of 47 mΩ·μm2 was observed at low temperatures. This work indicates that the dual-type CPP-GMR devices made up of CFMS electrodes and Ag-Mg spacers could be promising for future spintronic applications.

Current perpendicular-to-plane giant magnetoresistance devices using half-metallic Co2Fe0.4Mn0.6Si electrodes and a Ag–Mg spacer

Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effects in devices including Co2Fe0.4Mn0.6Si (CFMS)/Ag100−xMgx/CFMS structures were investigated theoretically and experimentally.First-principles transport calculation revealed that the Fermi surface matching between CFMS and L12 Ag3Mg is better than that between CFMS and fcc-Ag. In the experiments the Mg composition, x was changed from 0 to 26 at.%, in which both face centered cubic phase and L12 phase of Ag–Mg alloys are included depending on the Mg composition. It was confirmed by a cross-sectional high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image that the Ag–Mg spacer layer with L12 ordered phase was successfully fabricated for x = 22 at.%. The maximum CPP–GMR ratio and the change of the areal resistance () were 56% and 20 mm2, respectively, for x = 22 at.% at room temperature, which is much higher than that of the conventionally used pure Ag spacer devices. It was suggested from the HAADF-STEM images and the results of the temperature dependence of CPP–GMR effects that the diffusion of Mn atoms occurred less at the CFMS/Ag–Mg interfaces for the L12 ordered Ag–Mg spacer devices than the Ag spacer devices, which might be a key factor for the enhancement of the value. The newly developed L12 Ag–Mg spacer is a promising material for realizing large of the CPP–GMR devices.