All-metallic nonlocal spin valves using polycrystalline Co₂(FeMn)Si Heusler alloy with large output

Abstract

A large output voltage of 0.7 mV at 1 mA charge current is demonstrated for all-metallic nonlocal spin valves using Co 2 (FeMn)Si Heusler alloy and Cu with a junction area of about 50 nm 2 . The output is attributed to the junction size reduction as well as to the high spin polarization in the Heusler alloy. An analysis using a one-dimensional model reveals that the spin diffusion length in the Cu layer shows no clear degradation even in the case of a 50 nm 2 junction. When the junction is reduced further to 10 nm 2 , an output voltage of about 10 mV is expected.© 2015 The Japan Society of Applied Physics F or high-density magnetic recording over 2 Tbit/in. 2 , the total thickness of a read sensor should be reduced to less than 20 nm. However, conventional spin valve sensors cannot meet this specification because of their thick stack of pinned magnetic and antiferromagnetic layers. Nonlocal spin valves (NLSVs), which have a lateral structure and use spin-accumulation effects, 1,2) are promising for solving this problem. The pinned/antiferromagnetic layer stack is placed outside the read gap area. The output voltage generated by a pure spin current is also preferable from the standpoints of electric circuit noise and reliability.One of the challenges for NLSV sensors is the small output voltage. It has been reported that the output (measured by the resistance change) of all-metallic NLSVs using NiFe wire ranges from a value below 1 m³ (submicrometer junction) to 9 m³ (50 nm junction). 3-9) All-metallic NLSVs using Heusler alloys, which have a higher spin polarization than NiFe, show an output of up to 17 m³. [10][11][12] From these results, it is effective to use the Heusler alloys with a reduced junction size for obtaining a high output. However, the reported outputs are still too low for application in read head sensors. NLSVs with a thin MgO layer between ferromagnetic (FM) and nonmagnetic (NM) wires are reported to have a large output of 400 m³ 13) However, a large junction resistance is not suitable for high-density high-speed hard disk drive applications.In this paper, attempts to increase the output of all-metallic NLSVs are reported. The junction size is reduced to 50 nm. Co 2 (FeMn)Si (CFMS) polycrystalline Heusler alloys 14,15) are used to increase spin polarization. Results are analyzed using a one-dimensional analytical model. The extensibility of this system to recording densities of over 2 Tbit/in. 2 is also discussed.Figure 1(a) shows a layout of a test chip. The widths of the NM wire (W N ), FM wires (W F ), and gap between the two FM wires (W gap ) were set to the same value. They were changed from 50 to 150 nm. The film stack at the FM/NM junction was Ta (2 nm)/Cu (10 nm)/Co 2 Fe 0.4 Mn 0.6 Si (6-20 nm)/ Cu (20 nm). The area around the junction was filled with a SiO 2 insulating layer.First, the FM wires were deposited by conventional magnetron sputtering at room temperature on a thermally oxidized Si substrate. The film stack was Ta (2 nm)/Cu (10 nm)/ Co 2 Fe 0.4 Mn 0.6 Si (6-20 nm)/Cu (20 nm)/...

Equiatomic quaternary Heusler alloys: A material perspective for spintronic applications

“…High magnetoresistance (MR) ratios and large spin accumulation signals in spintronic devices using Co-based Heusler alloys clearly reflect the half-metallic nature of these alloys [17][18][19][20][21][22][23][24]. Recently, a very high value of spin polarization was observed for Co-based alloys at low temperatures, but a strong degradation in the transport properties was seen at room temperature [15,17,19,20].…”

“…HMF materials have potential applications as spin polarized current sources for current perpendicular to plane giant magnetoresistance (CPP-GMR) [17][18][19], magnetic tunnel junctions (MTJ) [20,21], non-local spin-valve (NLSV) devices [22,23] and spin injectors to semiconductors [24]. High magnetoresistance (MR) ratios and large spin accumulation signals in spintronic devices using Co-based Heusler alloys clearly reflect the half-metallic nature of these alloys [17][18][19][20][21][22][23][24].…”

Enhancement of L2 1 order and spin-polarization of Heusler alloy Co 2 MnSi thin film by Ag alloying

“…Heusler alloys [2] are the most promising material because of their high Curie temperatures well above room temperature (RT). High magnetoresistance (MR) ratios and large spin accumulation signals reflecting the half-metallicity of Co-based Heusler alloys have been clearly demonstrated in current perpendicular to plane giant magnetoresistance (CPP-GMR) [3][4][5][6][7][8][9], tunneling magnetoresistance (TMR) [10][11][12][13] and non-local spin-valve (NLSV) devices [14][15][16] using Co 2 MnSi (CMS), Co 2 Fe (Al 0.5 Si 0.5 ), Co 2 (Fe 0.4 Mn 0.6 )Si (CFMS), Co 2 Fe(Ga 0.5 Ge 0.5 ) (CFGG), and Co 2 FeSi as FM electrodes. Especially in the CPP-GMR devices using CFMS and CFGG, MR ratios over 50% at room temperature were reported, which are one order of magnitude higher than those using conventional FMs such as CoFe or NiFe.…”

Ab initio study of electronic structure and magnetic properties of CoMnTaZ (Z = Si, Ge) quaternary Heusler compounds

“…1 Introduction Numerous investigations have been extensively done regarding the Heusler compounds structure with different compositions and structures, motivated by their possible applications in spintronics [1][2][3][4][5]. They have shown a wide range of attractive properties such as magnetoresistance [6][7][8], non-local spin-valve devices [9,10], spin injectors to semiconductors [11], and magnetic tunnel junctions [12,13].…”