3D-simulations of magnetic structures in af-coupled multilayers with pinholes

Schepper W, Diplas K, Reiss G. 3D-simulations of magnetic structures in af-coupled multilayers with pinholes. In: Journal of Applied Physics. JOURNAL OF APPLIED PHYSICS. Vol 87. AMER INST PHYSICS; 2000: 6597-6599.For antiferromagnetically (af) coupled Py (Ni81Fe19\Cu)-multilayers lattice calculations have been used already for the investigation of pinholes in GMR elements. The very thin spacer layer (< 10 Angstrom) is sensitive against pinholes as a link between the magnetic layers. Additional coupling through the pinhole modifies drastically the af-coupling between the magnetic layers and leads to strong changes in the M(H) and Delta R/R(H) curves. Improved lattice calculations with large grids offer the opportunity, to study effects of geometry in layers structured laterally. (C) 2000 American Institute of Physics. [S0021-8979(00)86608-6]

Optimization processes of giant magnetoresistance characteristic for mixed magnetic multilayers

Schepper W, Hütten A, Reiss G. Optimization processes of giant magnetoresistance characteristic for mixed magnetic multilayers. JOURNAL OF APPLIED PHYSICS. 2000;88(2):993-998.Up to now, giant magnetoresistance (GMR) multilayers usually consist of only one type of double layer (e.g., permalloy/copper). In this work, we report on results obtained on mixed systems, i.e., multilayers containing simultaneously the first and second maximum of the antiferromagnetic coupling. Both a phenomenological numerical approach as well as experimental results demonstrate, that such systems can be used for tailoring new shapes of GMR curves. (C) 2000 American Institute of Physics. [S0021-8979(00)04314-0]

Analysis of the Disturbing Influence of Stray Fields in Very Small MRAM Cells by Computer Simulation

Schepper W, Kubota H, Reiss G. Analysis of the Disturbing Influence of Stray Fields in Very Small MRAM Cells by Computer Simulation. In: Nanostructured Magnetic Materials and Their Applications. Lecture Notes in Physics, 593. 2002: 75-90

Single molecule detection with magnetic beads - computer simulation

Schepper W, Schotter J, Brueckl H, Reiss G. Single molecule detection with magnetic beads - computer simulation. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS. 2004;272-276:E1695-E1696.The detection of single molecules, e. g. in biology is possible by marking the interesting molecules with magnetic beads and detect the influence of the beads on a GMR/TMR/SV multilayer. The development of suitable sensors has been studied experimentally as well as theoretically in order to optimize the sensor parameters. A FD method including the usually used contributions to the total energy ( exchange, af coupling, anisotropy and magnetostatic) is used for the simulation with additional contributions to the local field according to the stray fields of the beads. In this work, we present the results of micromagnetic calculations of the magnetization behavior of GMR/TMR sensors considering also the dipole fields of the beads as additional contributions to the local field. (C) 2003 Elsevier B. V. All rights reserved

Analysing a magnetic molecule detection system - computer simulation

Schepper W, Schotter J, Brückl H, Reiss G. Analysing a magnetic molecule detection system - computer simulation. JOURNAL OF BIOTECHNOLOGY. 2004;112(1-2):35-46.The detection of single molecules, e.g. in biology is possible by marking the interesting molecules with magnetic beads and detect the influence of the beads on giant magnetoresistance (GMR)/tunnel magnetoresistance (TMR)/spin valve (SV) sensors. The development of suitable multilayers has been studied experimentally as well as theoretically in order to optimize the sensor parameters. A finite difference (FD) method including the usually used contributions to the total energy [exchange, antiferromagnetically (af) coupling, anisotropy and magnetostatic] is used for the simulation with additional contributions to the local field according to the stray fields of the beads. In this work, we will show the results of micromagnetic calculations of the magnetization behavior of GMR/TMR sensors considering also the interaction between the domains in the magnetic layers of the sensor and the bead area. We can present first calculations where the bead particles (signal source) and the magnetic layers (sensor device) are considered as a whole magnetic ensemble. (C) 2004 Elsevier B.V. All rights reserved

A magnetic molecule detection system - A comparison of different setups by computer simulation

Schepper W, Schotter J, Brückl H, Reiss G. A magnetic molecule detection system - A comparison of different setups by computer simulation. In: Physica B: Condensed Matter. Physica B: Condensed Matter. Vol 372. Elsevier Science; 2006: 337-340.The results of micromagnetic calculations of GMR sensors are shown under the influence of the stray fields of magnetic beads (microspheres), aligned out of plane or in plane of the sensor layers. These detection cases show very different characteristics and sensitivities. An analytical formula can be presented showing the GMR signal dependence on the bead height and the bead and sensor dimensions. (c) 2005 Elsevier B.V. All rights reserved

Enhanced GMR amplitude and temperature stability of copper/permalloy combination multilayers

Heitmann S, Hütten A, Hempel T, Schepper W, Reiss G. Enhanced GMR amplitude and temperature stability of copper/permalloy combination multilayers. In: Journal of Magnetism and Magnetic Materials. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS. Vol 226. ELSEVIER SCIENCE BV; 2001: 1752-1754.The high effect amplitude of {Cu/Py} multilayers at first antiferromagnetic coupling maximum (AFCM) can be combined with the temperature stability of multilayers at second AFCM by using both corresponding copper layer thicknesses in one multilayer stack. Multilayers that consist of alternating blocks of 1st and 2nd AFCM with at least two double layers each reveal the same temperature stability as multilayers at 2nd AFCM but retain higher GMR amplitude. Knowing the GMR characteristics of the multilayers at 1st and 2nd AFCM as well as of the multilayer with directly alternating copper layer thicknesses (1st, 2nd) the GMR characteristics of combination multilayers with enhanced temperature stability can be predicted. (C) 2001 Elsevier Science B.V. All rights reserved

Giant magnetoresistance of hysteresis-free Cu/Co-based multilayers

Hütten A, Hempel T, Schepper W, Kleineberg U, Reiss G. Giant magnetoresistance of hysteresis-free Cu/Co-based multilayers. In: Journal of Magnetism and Magnetic Materials. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS. Vol 226. ELSEVIER SCIENCE BV; 2001: 1758-1760.It has been demonstrated that hysteresis-free multilayers based on {Cu/Co} and {Cu/Ni57Co43} can be experimentally realized obtaining room temperature GMR effect amplitudes from 6.5% up to 20%. A critical window for the layer thickness for hysteresis-free GMR curves can be achieved for both systems, ranging from 0.38 to 0.45 nm and 0.59 to 0.7 nm, respectively. The corresponding sensitivities range from 0.075 up to 0.114%/Oe, but are still below that of normal {Cu/Co} multilayers. Hysteresis-free multilayers based on these systems are stable up to 180 degreesC upon isochronal annealing. It is shown that hysteresis-free. {Cu/Co or Ni57Co43}-multilayers are neither a solution to achieve good temperature stability nor a higher sensitivity compared with normal ones and hence are not candidates for application. (C) 2001 Elsevier Science B.V. All rights reserved

Magnetoresistance and dipole shift of ultrasmall magnetic tunnel junctions characterized by conducting atomic force microscopy

Kubota H, Reiss G, Brückl H, Schepper W, Wecker J, Gieres G. Magnetoresistance and dipole shift of ultrasmall magnetic tunnel junctions characterized by conducting atomic force microscopy. JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS. 2002;41(Part 2, No. 2B):L180-L182.Conducting atomic force microscopy was used for the characterization of magnetic tunnel junctions with various areas down to a minimum of 0.0025 mum(2) and a tunnel magnetoresistance (TMR) value up to 20%. Minor loops of large junctions show jumps, of the resistance, which can be related to magnetic domains formation in the ferromagnetic electrodes. For the smallest junctions, a TMR signal between 10% and 17% was obtained. The range of TMR values increased with decreasing junction,sizes. The minor loops of such small junctions did not show hints of domains. We observed, however, a shift of the minor loop in the opposite direction as obtained for larger junctions, which can be related to dipolar antiferromagnetic coupling of the ferromagnetic electrodes