Low resistance and high thermal stability of spin-dependent tunnel junctions with synthetic antiferromagnetic CoFe/Ru/CoFe pinned layers

Sun, J. J.; Shimazawa, K.; Kasahara, N.; Sato, Kazuki; Saruki, S.; Kagami, T.; Redon, O.; Araki, S.; Morita, H.; Matsuzaki, M.

doi:10.1063/1.126364

Cited by 63 publications

(23 citation statements)

References 11 publications

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“…However, in most of the cases theories were limited to specific problems where intricate structures at the interfaces were simplified. Until now, EB effects have been exploited in several technological applications such as read head of recording devices [39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54], magnetoresistive random access memories (MRRAM) [55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76] and it has been proposed for the technological applications in stabilizing magnetization of superparamagnetic nanoparticles [77,78,79,80] or to improve coercivity and energy product of the permanent magnets [81,82,83,84].…”

Section: Introductionmentioning

confidence: 99%

Exchange bias effect in alloys and compounds

Giri

Patra

Majumdar

2011

J. Phys.: Condens. Matter

321

225

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Abstract. The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, clusterglass, disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.

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Section: Introductionmentioning

confidence: 99%

Exchange bias effect in alloys and compounds

Giri

Patra

Majumdar

2011

J. Phys.: Condens. Matter

321

225

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“…Recently there are reports wherein MTJs having lower RA values were obtained, using ultrathin Al 2 O 3 barriers. [6][7][8] Also, from the fundamental physics viewpoint, there are theoretical predictions and some experimental interpretations of barrier dependence of spin polarized tunneling. 9 The motivation and necessity to study alternative tunnel barrier materials that show good spin tunneling properties is thus apparent.…”

mentioning

confidence: 99%

“…The increase of JMR and R J values shows that during annealing the barrier quality has improved, similar to the case of Al 2 O 3 barrier junctions. 7,8,[14][15][16] However, the annealing conditions were not optimized, whereas further studies can be expected to show better results.…”

mentioning

confidence: 99%

Gallium oxide as an insulating barrier for spin-dependent tunneling junctions

Groot

Moodera

2000

Applied Physics Letters

115

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Spin-dependent tunneling has been shown to occur through Ga 2 O 3 as the insulating tunnel barrier. Magnetic tunnel junctions of the type Co/Ga 2 O 3 /Ni 80 Fe 20 were prepared by oxidizing thin metal layer of Ga in oxygen plasma and characterized. The highest junction magnetoresistance observed was 18.2% at room temperature, increasing to 27.6% at 77 K. The average barrier height was estimated to be about 2 eV, as opposed to over 3 eV for junctions with Al 2 O 3 barrier of comparable quality. Otherwise these junctions behave similar to those with Al 2 O 3 . This shows the feasibility of obtaining lower resistance junctions with Ga 2 O 3 as the barrier for magnetic storage applications. © 2000 American Institute of Physics. ͓S0003-6951͑00͒04348-5͔Tunneling studies in magnetic tunnel junctions ͑MTJs͒ are being actively pursued in the last few years for their fundamental complexity as well as their application potential in data storage industry.1-3 It has been shown that the quality of the tunnel barriers plays a critical role in the success of spin tunneling in MTJs.1 Aluminum oxide is widely used as the insulating barrier since Al metal film can be reproducibly grown as ultrathin layer. [4][5][6][7] The excellent insulating properties of ultrathin Al 2 O 3 as well as its large forbidden gap, in general, lead to high resistance-area ͑RA͒ product, which is unfavorable from the application point of view. Recently there are reports wherein MTJs having lower RA values were obtained, using ultrathin Al 2 O 3 barriers.6-8 Also, from the fundamental physics viewpoint, there are theoretical predictions and some experimental interpretations of barrier dependence of spin polarized tunneling. 9 The motivation and necessity to study alternative tunnel barrier materials that show good spin tunneling properties is thus apparent. In this letter, our successful study of spin tunneling with Ga 2 O 3 as tunnel barrier, in MTJs, is described. Ga 2 O 3 is an insulator with a forbidden gap of 4.8 eV and is the only reported stable phase.10-12 However, there have been studies about the nonstoichiometric compound formation. Ga 2 O 3Ϫx becomes n-type semiconductor due to oxygen vacancies, which act as shallow donors with activation energy of 30-40 meV.11 Ga metal can be readily oxidized, relatively slower than Al 2 O 3 , having a heat of formation energy ͑kJ/mol͒ of 1080.2 compared to 1675.6 for Al 2 O 3 . 10MTJs were prepared in a high vacuum system ͑base pressure of 10 Ϫ8 Torr͒ thermal evaporation system. 1 Initially the LN 2 cooled glass substrate was covered with a 1 nm thick Si seed layer, followed by an 8-nm-thick Co electrode of long strips. Shadow metal masks were used to define the film and the junction pattern. A gallium film with the thickness ranging from 0.4 to 1.8 nm was deposited to cover the entire Co layer. After the substrate was warmed to room temperature ͑RT͒ the Ga layer was oxidized in oxygen glow discharge plasma at a pressure of 80 mTorr and a dc voltage of 1.6-1.8 kV for varying time ͑5-110 s͒. After pumping dow...

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“…The increased interfacial area should, in turn, increase the average potential barrier height, hence, enhancing the TMR ratio. Increased bottom electrode roughness prior to the insulator deposition normally leads to the junction deterioration [20]; however, the 7.7 A junction had a uniform insulator in the as-deposited state as evidenced by the TEM micrograph and the large MR ratio of > 30% prior to annealing. It is only after annealing during which the insulator interfaces were altered.…”

Section: Resultsmentioning

confidence: 99%

Transmission Electron Microscopy Study of Thermally Annealed Low Resistance Magnetic Tunnel Junction

Kyung

Lee

Yoon

et al. 2002

phys. stat. sol. (a)

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Low-resistance magnetic tunneling junctions consisting of Ta/NiFe/Cu/NiFe/IrMn/CoFe/Al (6.6 and 7.7 A)-oxide/CoFe/NiFe/Ta were fabricated with the plasma-oxidized insulation layer. Electrical properties and microstructure of the junctions are characterized before and after annealing the junction at temperatures up to 300 C. While the Al (7.7 A)-oxide junction showed a continuous increase in the magnetoresistance (MR) ratio, reaching the maximum of 48% at 300 C, the Al (6.6 A)-oxide junction showed a moderate enhancement at 250 C and then a sharp drop in the MR ratio at 275 C. Transmission electron microscopy revealed, prior to the heat treatment, rough interfaces at the insulation layer. The annealing process made the oxide interfaces sharper, but also caused microstructural alteration of the bottom electrode. While the smoother oxide interface appears to be beneficial to the TMR effect, the Al (6.6 A)-oxide junction was susceptible to the localized short-circuiting of the electrodes and the thermal treatment would promote such shortcircuiting leading to the marked drop in the MR ratio. We have shown that the thermal treatment of the multi-layer tunnel junctions can either enhance or degrade the electrical properties depending on the insulator thickness due to changes in the oxide interface and electrode microstructure; hence, it would be critical to control the oxide thickness and roughness as well as the electrode microstructure during the deposition process.

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Low resistance and high thermal stability of spin-dependent tunnel junctions with synthetic antiferromagnetic CoFe/Ru/CoFe pinned layers

Cited by 63 publications

References 11 publications

Exchange bias effect in alloys and compounds

Exchange bias effect in alloys and compounds

Gallium oxide as an insulating barrier for spin-dependent tunneling junctions

Transmission Electron Microscopy Study of Thermally Annealed Low Resistance Magnetic Tunnel Junction

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