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1 May 2007

Volume 101, Issue 9, Articles (09xxxx)

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back to top Magnetic Tunnel Junctions

80% tunneling magnetoresistance at room temperature for thin Al–O barrier magnetic tunnel junction with CoFeB as free and reference layers

H. X. Wei, Q. H. Qin, M. Ma, R. Sharif, and X. F. Han

J. Appl. Phys. 101, 09B501 (2007); http://dx.doi.org/10.1063/1.2696590 (3 pages) | Cited 28 times

Online Publication Date: 11 April 2007

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Magnetic tunnel junctions (MTJs) with structures of Ta(5)/Cu(10)/Ta(5)/Ir21Mn79(10)/Co75Fe25(2)/Ru(0.75)/Co40Fe40B20(3)/Al(0.6)–O/Co40Fe40B20(2.5)/Ta(3)/Ru(7) (units in nanometers) were deposited via ultrahigh vacuum magnetron sputtering (ULVAC). Microscale ring-type magnetic tunnel junctions (RMTJs) with an outer radius of 2 μm and an inner radius of 1 μm were patterned using standard UV lithography combined with ion milling. Both reference and free layers were Co40Fe40B20 and a very thin Al–O (0.6 nm) barrier layer was used. Tunneling magnetoresistances (TMRs) of up to 81% at room temperature and 107% at 4.2 K were observed. These RMTJs with high TMR and low coercivity, of about 26 Oe, combined with the ring-type geometry, which greatly reduces stray magnetic field, are ideal for certain magnetic field sensor applications.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Thermal stability, sensitivity, and noise characteristics of MgO-based magnetic tunnel junctions (invited)

Dipanjan Mazumdar, Xiaoyong Liu, B. D. Schrag, Weifeng Shen, Matthew Carter, and Gang Xiao

J. Appl. Phys. 101, 09B502 (2007); http://dx.doi.org/10.1063/1.2710953 (6 pages) | Cited 9 times

Online Publication Date: 27 April 2007

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Thermal stability, sensitivity, and noise of micron-scale magnetic tunnel junctions based on MgO tunnel barriers have been studied for both the memory and sensing configurations. Junctions show solid high-temperature performance with substantial magnetoresistance observed even at 500 °C. At temperatures above 375 °C, the junctions begin to experience irreversible degradation due to interlayer diffusion. The thermal stability of these devices depends strongly on the exchange bias of the device and hence on the properties of the antiferromagnetic layer. Sensitivities as high as 3.3%/Oe have been obtained at room temperature for junctions configured as low-field sensors. Sensitivity values are constant up to temperatures of 300 °C, above which performance decays due to a loss of exchange bias and overall magnetoresistance. Noise spectra are 1/f at frequencies up to 51 kHz, and sensors have a resultant field noise better than 1 nT/Hz0.5 at 100 kHz. A comparison is made with devices fabricated with alumina tunnel barriers.
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75.50.Ss Magnetic recording materials
75.47.Lx Magnetic oxides
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Brief rapid thermal treatment effect on patterned CoFeB-based magnetic tunneling junctions

Kuo-Ming Wu, Chao-Hsien Huang, Yung-Hung Wang, Ming-Jer Kao, Ming-Jinn Tsai, Jong-Ching Wu, and Lance Horng

J. Appl. Phys. 101, 09B503 (2007); http://dx.doi.org/10.1063/1.2712317 (3 pages)

Online Publication Date: 3 May 2007

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The brief thermal treatment effects on the magnetoresistance of microstructured Co60Fe20B20-based magnetic tunneling junctions have been studied. The elliptical shape of devices with long/short axis of 4/2 μm was patterned out of film stack of seed layer (20)/PtMn(15)/Co60Fe20B20(3)/Al(0.7)oxide/C60Fe20B20(20)/capping layer (48) (thickness unit in nanometers) combining conventional lithography and inductively coupled plasma reactive ion beam etching technologies. The thermal annealing was carried out with device loading into a furnace with preset temperatures ranging from 100 to 400 °C for only 5 min in the absence of any external magnetic field. The magnetoresistance was found to increase with increasing annealing temperatures up to 250 °C and then decrease at higher annealing temperatures. In addition, the magnetoresistance ratio of around 35%, similar to that of as-fabricated devices, sustains up to annealing temperature of 350 °C. This survival of magnetoresistance at higher annealing temperature is due to boron conservation in the amorphous CoFeB ferromagnetic layer at higher annealing temperature for only a short time, which is manifested using x-ray diffractometer technique.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Temperature dependence of tunnel resistance for CoFeB/MgO/CoFeB magnetoresistive tunneling junctions: The role of magnon

Sumio Ikegawa, Hisanori Aikawa, Tomomasa Ueda, Makoto Nagamine, Naoharu Shimomura, Masatoshi Yoshikawa, Keiji Hosotani, and Hiroaki Yoda

J. Appl. Phys. 101, 09B504 (2007); http://dx.doi.org/10.1063/1.2712322 (3 pages) | Cited 5 times

Online Publication Date: 4 May 2007

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Tunnel resistance for CoFeB/MgO/CoFeB junctions with a wide variety of resistance has been investigated as a function of bias voltage Vb and temperature to elucidate bias voltage dependence of the magnetoresistance ratio. Comparison with a conventional NiFe/AlOx/CoFe junction is also discussed. In the case of a parallel alignment of the magnetic moments with a MgO barrier, the Vb dependence was much smaller than that of the antiparallel (AP) alignment with a MgO barrier and of both alignment with an AlOx barrier. This probably originates from the unique tunnel mechanism with a MgO barrier: coherent tunneling of Δ1 electron states. In the case of AP alignment with a MgO barrier, distinctive features were observed: temperature coefficient of tunnel resistance steeply decreased with increasing absolute value of Vb at −0.2 V<Vb<0.2 V. This suggests that inelastic tunneling with excitation of magnon modes plays a crucial role.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Ds Spin waves

Structural analysis of the CoFeB thin film in Ru/CoFeB and MgO/CoFeB layers

Dong Joon Kim, Ji Young Bae, Woo Chang Lim, Kee Won Kim, and Taek Dong Lee

J. Appl. Phys. 101, 09B505 (2007); http://dx.doi.org/10.1063/1.2713431 (3 pages) | Cited 6 times

Online Publication Date: 4 May 2007

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In the last few years, magnetic tunnel junctions with MgO barrier have attracted attention due to the theoretically predicted and experimentally verified huge TMR. In the present work, crystallization behavior of CoFeB layer adjacent to the MgO or Ru layer was studied by annealing at various temperatures for 1 h. The crystallization started at MgO/CoFeB interface but crystallization temperature changed with materials and thickness of adjacent layer. When the thickness of MgO layer increased in MgO/CoFeB bilayer, crystallization temperature decreased. This strongly suggests that B from CoFeB layer diffused into adjacent layer to crystallize at lower temperature and MgO can serve as a sink of B. Details will be discussed.
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68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
68.65.Ac Multilayers
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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