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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Magnetic properties of patterned tunnel junctions

Benedicte Warot, Amanda K. Petford-Long, and Thomas C. Anthony

J. Appl. Phys. 93, 7287 (2003); http://dx.doi.org/10.1063/1.1557391 (3 pages) | Cited 9 times

Online Publication Date: 9 May 2003

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Patterned magnetic tunnel junctions are being actively studied for their application in magnetic random access memory (MRAM) and read-heads. For MRAM application purposes, a clean magnetization reversal is one of the required properties. Various parameters such as junction size, shape or layer sequence are being investigated to optimize element properties. In this article, we report the results of Lorentz transmission electron microscopy used to study the magnetization reversal mechanism of (Ta/NiFe/MnFe/NiFe/Al2O3/NiFeCo) tunnel junction elements. Single layer NiFeCo element properties have also been investigated for comparison with the tunnel junctions. The results on tunnel junctions show the influence of size and aspect ratio of the patterned elements on magnetic properties. For the wider elements, domain formation and propagation is the dominant reversal mechanism and no asymmetry is observed between the antiparallel (AP) to parallel (P) and P–AP reversal measured as a function of aspect ratio. Single-domain reversal is the main process for narrower elements and there is an asymmetry in reversal field between the AP–P and P–AP reversals as a function of aspect ratio. Many energy terms (such as Néel coupling, stray field coupling, and the internal demagnetizing field) need to be taken into account to explain this behavior. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.47.Np Metals and alloys
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.60.Ch Domain walls and domain structure
68.37.Lp Transmission electron microscopy (TEM)
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Precessional switching of the magnetization in microscopic magnetic tunnel junctions (invited)

H. W. Schumacher, C. Chappert, R. C. Sousa, P. P. Freitas, J. Miltat, and J. Ferré

J. Appl. Phys. 93, 7290 (2003); http://dx.doi.org/10.1063/1.1557376 (5 pages) | Cited 11 times

Online Publication Date: 9 May 2003

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We study the precessional switching of the magnetization in a microscopic magnetic tunnel junction cell as used in magnetic random access memories. By measuring the tunneling magnetoresistance versus time we follow the dynamical response of the cell’s free layer magnetization to ultrashort field pulses applied along the in-plane magnetic hard axis. In the presence of a strong easy axis bias field a pronounced precession of the magnetization with damping times of the order of 2 ns is observed. At lower bias fields the large angle precession induced by pulses as short as 170 ps can switch large domains of the free layer magnetization. Multiple application of identical pulses reversibly toggles the magnetization between the two easy directions. For longer pulses coherent higher order switching is observed in full agreement with theory. © 2003 American Institute of Physics.
Show PACS
75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Size dependence of switching current and energy barrier in the magnetization reversal of rectangular magnetic random access memory cell

Y. Nozaki and K. Matsuyama

J. Appl. Phys. 93, 7295 (2003); http://dx.doi.org/10.1063/1.1557375 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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Write operation in magnetic random access memory (MRAM) with bit density of Gbit/cm2 order has been numerically simulated for low submicron scale magnetic cells. The amplitude of both the switching current Iw and the energy barrier ΔE of the magnetic cell show strong dependence on the width w and the thickness t of the cell. The calculated results show that the amplitude of Iw is proportional to t/w, while that of ΔE is proportional to wt2. To obtain the sufficient energy barrier against a thermal stability (ΔE>80kBT, at 300 K), the thicker magnetic cell is required as the cell is downsized for high-density memory applications, although the thinner one is preferred to lower the switching current. From the calculated results, it appears that the margin of the switching current for selective write operation is decreased with decreasing the lateral aspect ratio of the cell. The addressability for the write operation is also degraded by the formation of structural defect in the cell. In this article, optimum configurations of the magnetic cell applicable for Gbit MRAM are discussed. © 2003 American Institute of Physics.
Show PACS
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.60.Jk Magnetization reversal mechanisms
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Performance of current-in-plane pseudo-spin-valve devices on CMOS silicon-on-insulator underlayers

R. R. Katti, D. Zou, D. Reed, D. Schipper, O. Hynes, G. Shaw, and H. Kaakani

J. Appl. Phys. 93, 7298 (2003); http://dx.doi.org/10.1063/1.1557374 (3 pages)

Online Publication Date: 9 May 2003

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Prior work has shown that current-in-plane (CIP) giant magnetoresistive (GMR) pseudo-spin-valve (PSV) devices grown on bulk Si wafers and bulk complementary metal-oxide semiconductor (CMOS) underlayers exhibit write and read characteristics that are suitable for application as nonvolatile memory devices. In this work, CIP GMR PSV devices fabricated on silicon-on-insulator CMOS underlayers are shown to support write and read performance. Reading and writing fields for selected devices are shown to be approximately 25%–50% that of unselected devices, which provides a margin for reading and writing specific bits in a memory without overwriting bits and without disturbing other bits. The switching characteristics of experimental devices were compared to and found to be similar with Landau–Lifschitz–Gilbert micromagnetic modeling results, which allowed inferring regions of reversible and irreversible rotations in magnetic reversal processes. © 2003 American Institute of Physics.
Show PACS
85.75.Bb Magnetic memory using giant magnetoresistance
75.47.De Giant magnetoresistance
85.30.Tv Field effect devices
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
84.30.Sk Pulse and digital circuits
75.60.Jk Magnetization reversal mechanisms

Effects of swift heavy ion bombardment on magnetic tunnel junction functional properties

Y. Conraux, J. P. Nozières, V. Da Costa, M. Toulemonde, and K. Ounadjela

J. Appl. Phys. 93, 7301 (2003); http://dx.doi.org/10.1063/1.1558659 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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In this article, we report on recent irradiation experiments on magnetic tunnel junctions (MTJ) using either light (C, O) or heavy (Ni) ion beams with energies in the range of 10 MeV/A. For all ions, albeit with different fluence thresholds, the tunnel magnetoresistance decreases irreversibly with increasing ion fluence, with conversely little or no impact on overall resistance. This can only be explained by a modification of the alumina barrier stoechiometry, rather than by interdiffusion. Measurements on irradiated so-called “spin-mirrors” sheet films show that AlOx/metal interface is altered by radiations. Finally, it is shown that MTJs are not a fortiori insensible to swift heavy ion bombardment. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
75.47.Np Metals and alloys
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
61.80.Jh Ion radiation effects
72.25.Ba Spin polarized transport in metals
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.82.Bg Metals and alloys
61.66.Bi Elemental solids
61.66.Dk Alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Design of Curie point written magnetoresistance random access memory cells

J. M. Daughton and A. V. Pohm

J. Appl. Phys. 93, 7304 (2003); http://dx.doi.org/10.1063/1.1557373 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2003

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Very high density magnetoresistance random access memory (MRAM) cells may be subject to thermal upset. This article describes designs that enhance thermal stability and increase ultimate density by using the combination of heat and magnetic field for writing data. The basic storage mechanism can be shape anisotropy, the coupling between an antiferromagnetic layer and a ferromagnetic layer, or a combination of the two. Two designs are described in this article. The first uses a low Curie point material with high shape anisotropy at room temperature. These cells use active semiconductor devices to restrict heating current to only one cell in an array. The second approach employs the interface coupling between a ferromagnetic film and an antiferromagnetic film as the storage mechansism. A cell may be written by heating above the Néel temperature and cooling the interface in a magnetic field by using orthogonal lines for heating and magnetic field. Heating and cooling times are a few nanoseconds. These design approaches could lead to stable MRAM cells with diameters less than 0.1 μm and requiring lower drive currents. © 2003 American Institute of Physics.
Show PACS
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.
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions

Low switching current flux-closed magnetoresistive random access memory

Y. K. Zheng, Y. H. Wu, K. B. Li, J. J. Qiu, Y. T. Shen, L. H. An, Z. B. Guo, G. C. Han, P. Luo, D. You, and Z. Y. Liu

J. Appl. Phys. 93, 7307 (2003); http://dx.doi.org/10.1063/1.1557372 (3 pages) | Cited 5 times

Online Publication Date: 9 May 2003

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A spin valve magnetoresistive random access memory with a flux-closed structure is presented. The flux-closed structure prevents the disruption to magnetization of the recording layer and increases the thermal stability. Simulation results show that the switching field increases under the uniform external field, however, the switching field has no change under the bit current field. Only the bit current that flows mostly at the center is used to switch the cell. Experimental results show that the bit current of 10 mA is sufficient to switch the 1 μm×4 μm cell. © 2003 American Institute of Physics.
Show PACS
85.75.Bb Magnetic memory using giant magnetoresistance
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
84.30.Sk Pulse and digital circuits
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