The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors.

/pdf/giant-magnetoresistance-basic-concepts-microstructure-38jkcne8io.pdf

Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications

Interlayer exchange coupling (IEC) in fully epitaxial Fe∕MgO∕Fe(001) tunnel junctions with wedge-shaped MgO layers is measured at room temperature from the unidirectional shift of the Kerr hysteresis loop. It is found that the IEC is antiferromagnetic for small MgO thickness but changes sign at 0.8nm. Ab initio calculations of IEC show that this behavior can be explained by the presence of O vacancies in the MgO barrier which makes IEC antiferromagnetic for thin barriers. With increasing MgO thickness the resonance contribution to IEC from localized defect states is reduced resulting in the ferromagnetic coupling typical for perfect MgO barriers.

/pdf/interlayer-exchange-coupling-in-fe-mgo-fe-magnetic-tunnel-4iny3vfcjc.pdf

Interlayer exchange coupling in Fe/MgO/Fe magnetic tunnel junctions

Tunneling magnetoresistive (TMR) reading heads at an areal density of 80-100 Gbit/in/sup 2/ in a longitudinal magnetic recording mode have for the first time been commercialized for both laptop and desktop Seagate hard disk drive products. The first generation TMR products utilized a bottom TMR stack and an abutted hard bias design. These TMR heads have demonstrated three times the amplitude of comparable giant magnetoresistive (GMR) devices, resulting in a 0.6 decade bit error rate gain over GMR. This has enabled high component and drive yields. Due to the improved thermal dissipation of current-perpendicular-to-plane geometry, TMR runs cooler and has better lifetime performance, and has demonstrated the similar electrical static discharge robustness as GMR. TMR has demonstrated equivalent or better process and wafer yields compared to GMR. The TMR heads is proven to be a mature and capable reader technology. Using the same TMR head design in conjunction with perpendicular recording, 274 Gbit/in/sup 2/ has been demonstrated. Advanced design can reach 311 Gbit/in/sup 2/.

Commercial TMR heads for hard disk drives: characterization and extendibility at 300 gbit/in/sup 2/

Magnetoas well as flexible electronics have emerged as two of themost rapidly developing technologies of the 21st century. Low processing costs and mechanical stretchability render flexible electronic devices highly attractive for a variety of applications such as flexible circuit boards, solar cells, paper-like displays, and sensitive skin. The giant magnetoresistance (GMR) effect, discovered in 1988, is broadly applied in read heads in hard disk drives or in nonvolatile memory devices, and has helped to initiate the development of magnetoelectronics (also known as spintronics). Magnetoelectronics on flexible substrates allows the direct integration of GMR devices onto bendable supports, which can be shaped into almost any arbitrary geometry. However, only limited progress has been made over the last years towards flexible magnetoelectronics due to the relatively small GMR effect achievable on plastics. The establishment of highperformance flexible magnetoelectronics would open straightforward access to practical magnetic field sensors, as well as promising perspectives towards accurate fine-tuning of the GMR by substrate stretching or bending. In this study, we show that the GMR effect of Co/Cu multilayers (MLs) on a flexible plastic substrate can be enhanced up to 200% by introducing an appropriate buffer layer. GMR values of Co/Cu MLs on buffered flexible substrates are even larger than those on thermally oxidized Si substrates due to an increased antiferromagnetic coupling fraction. Furthermore, we experimentally demonstrate to tune (increase or decrease) the GMR effect, by applying external tensile stress through substrate stretching. The sample structure is schematically shown in Figure 1a. Following a 1nmCo bottom layer directly deposited on oxidized Si substrates or on flexible plastic substrates, N periods of Co/Cu bilayers were deposited. Except where stated differently, the plastic substrate in this study is made out of polyester, and the

Towards Flexible Magnetoelectronics: Buffer‐Enhanced and Mechanically Tunable GMR of Co/Cu Multilayers on Plastic Substrates

Currently, there is great interest in using solid electrolytes to develop resistive switching based nonvolatile memories (RRAM) and logic devices. Despite recent progress, our understanding of the microscopic origin of the switching process and its stochastic behavior is still limited. In order to understand this behavior, we present a statistical “breakdown” analysis performed on Cu doped Ge0.3Se0.7 based memory devices under elevated temperature and constant voltage stress conditions. Following the approach of electrochemical phase formation, the precursor of the “ON resistance switching” is considered to be nucleation — the emergence of small clusters of atoms carrying the basic properties of the new phase which forms the conducting filament. Within the framework of nucleation theory, the observed fluctuations in the time required for “ON resistance switching” are found to be consistent with the stochastic nature of critical nucleus formation.

/pdf/on-the-stochastic-nature-of-resistive-switching-in-cu-doped-12ji6n5lm9.pdf

On the stochastic nature of resistive switching in Cu doped Ge0.3Se0.7 based memory devices

Magnetic multilayer structures of Co/Cu prepared by dc magnetron sputtering are studied with respect to changing number of bilayers (N) for different thicknesses of the Cu spacer layer corresponding to different coupling conditions according to the oscillatory interlayer exchange coupling. X-ray reflectivity and diffuse scattering show that the multilayers become smoother with increasing N. The growth exponent of the roughness is found to be lower for a multilayer than for a single-layer film of similar thickness. The roughness of subsequent interfaces along the stack is conformal, and the lateral correlation does not change with the period number, but depends on the thickness of the spacer layers. The improved layer structure for larger N increases the antiferromagnetic coupling fraction as inferred from magneto-optic Kerr effect measurements and thereby increases the giant magnetoresistance (GMR) ratio up to 35% for N = 10. Thus, the first few bilayers do not contribute to the GMR but act as a buffer to improve the growth conditions for the following bilayers. The first about five bilayers can be replaced by a bottom Co layer of equivalent thickness which also improves the layer structure for a subsequently deposited lower number of bilayers without much loss in the GMR ratio. This smoothening effect due to the increasing of the thickness of the bottom-most layer is related to the simultaneously decreasing grain size.

Correlation of magnetotransport and structure in sputtered Co/Cu multilayers

Magneto-tunneling injection device (MAGTID)

To obtain reliable magnetic tunnel junctions (MTJs) for sensor and memory applications, the quality of the Al2O3 tunnel barrier is extremely important. Here, we studied the reliability of MTJs with a 1.6 nm Al2O3 tunnel barrier formed by ultraviolet light assisted oxidation. In the stress measurements, prebreakdown current jumps and, finally, breakdown are observed. We show, by using statistics, that both the current jumps and the final breakdown can be attributed to single trap generation. Moreover, we can relate the current jump height to the trap location. In this way, we reveal the breakdown mechanism in MTJs and illustrate the importance of reliability studies.

/pdf/statistical-model-for-prebreakdown-current-jumps-and-48sgbzvw93.pdf

Statistical model for prebreakdown current jumps and breakdown caused by single traps in magnetic tunnel junctions

Spin-dependent tunnel junctions with Co75Fe25 electrodes and a Fe50Mn50 pinning layer were fabricated with tunneling magnetoresistance of about 20% at room temperature. The Al2O3 barriers were formed by ultra-violet light assisted oxidation. The resistance × area (R×A) product was about 375 kΩ μm2 in the parallel alignment of the magnetizations. The effect of barrier impurities has been investigated via tunneling conductance as a function of temperature and bias voltage for as-deposited and annealed samples. The spin wave parameter α was determined to be 3.06×10−5 and 2.03×10−5 K−3/2 before and after annealing, respectively. The improved barrier properties after annealing are explained by inelastic hopping via several localized states and reduced magnon scattering. We propose a qualitative model of the barrier homogenization during annealing which supports former Rutherford backscattering and x-ray photoelectron spectroscopy studies.

/pdf/magnon-scattering-and-tunneling-through-localized-states-in-2eup0uczo3.pdf

Magnon scattering and tunneling through localized states in magnetic tunnel junctions

Die Erfindung beschreibt ein Dreitorbauelement mit einem Emitter (1), einem Kollektor (2) und einer Basis (3), worin der Kollektor (2) und die Basis (3) ferromagnetische Schichten sind, zwischen welchen eine Tunnel-Isolationsschicht (4) angeordnet ist, welches dadurch gekennzeichnet ist, das der Emitter (1) von einer ferromagnetischen oder nichtmagnetischen Schicht gebildet wird, die von dem Kollektor (2) durch eine dazwischenliegende Tunnel-Isolationsschicht (5) getrennt ist.

Dreitorbauelement, insbesondere Spininjektionstransistor

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