H Bruckl

AIT Austrian Institute of Technology, Wien, Vienna, Austria

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Publications (66)107.19 Total impact

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    ABSTRACT: A method is presented for measuring weak magnetic fields by applying a measurement principle known from fluxgate magnetometers to a magnetic tunnel junction. The fluxgate measurement principle based on second harmonic detection is transferred to magnetic tunnel junctions embedded in current lines. Based on Fourier analysis, we developed an analytical model to describe the response of a magnetic tunnel junction fluxgate sensor. The analytical result is compared to MATLAB simulations using Fast Fourier Transformation. Experimental results are obtained with a sensor prototype using lock-in amplification to detect the second harmonic component of the signal generated by the resistance change of the junction. A linear sensor characteristic with a sensitivity in the order of mV/mT is detected in an unshielded setup. Design improvements of the sensor layout as well as a low RA product of the magnetic tunnel junctions should make it possible in the future to detect pT-fields. A cheap sensing technology using magnetic tunnel junctions with the ability of measuring fields in the order of pT could promote novel diagnostic methods such as magnetocardiography into daily clinical routine.
    IEEE Transactions on Magnetics 07/2011; 47(6-47):1549 - 1553. DOI:10.1109/TMAG.2011.2106114 · 1.21 Impact Factor
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    ABSTRACT: This work investigates the spin-torque-related dynamics of nonuniform magnetic vortexlike states in spin-valve nanocontacts, employing an unpinned artificial antiferromagnet as polarizer and amorphous Co Fe B as free layer. Subgigahertz spectra are obtained for contacts of 150–200 nm in diameter. Low critical current density and reversibility of the dynamic spectra with respect to the current are obtained. The spectral power and linewidth depend on the in-plane magnetic field, assuming maximum, respectively minimum, values within the free layer’s magnetization switching. For certain field and current windows metastable dynamic states are clearly demonstrated.
    Applied Physics Letters 02/2011; 98(4-98):042504 - 042504-3. DOI:10.1063/1.3537953 · 3.52 Impact Factor
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    ABSTRACT: Analytical electron microscopy is employed to study the structural properties of NiFe Schottky diodes and NiFe/MgO tunneling diodes after annealing up to 400° C. Electrical characterization revealed a drop of the barrier height for the Schottky diodes, while the tunneling diodes are thermally stable. From the cross-sectional TEM images of the Schottky diodes, metal diffusion into Si substrate was found. Investigations of the diffusion using energy dispersive spectroscopy and energy filtered transmission electron microscopy revealed that Ni diffused into the Si substrate to form nickel silicide. Moreover, in some cases, the gold capping layer also diffused into the substrate even deeper than Ni. In the case of the tunneling diodes, metal diffusion was inhibited by the presence of MgO.
    IEEE Transactions on Magnetics 06/2010; 46(6):2067-2069. DOI:10.1109/TMAG.2010.2040594 · 1.21 Impact Factor
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    ABSTRACT: We report a structural and electrical study of sputter-deposited SiO <sub>2</sub>/ MgO barriers for developing magnetic Si-based transistors. We propose that SiO <sub>2</sub>/ MgO tunneling barriers may utilize spin-filtering by achieving crystalline MgO (001) while reducing spin-scattering due to the Si / SiO <sub>2</sub> interface. We find that MgO ( ≪3 nm thick) crystallizes with (001) preferred orientation on thermally oxidized Si (≪2 nm ) . Typical processing temperatures do not cause significant intermixing with SiO <sub>2</sub> or ferromagnetic electrode. Conversely, MgO on Si is amorphous up to 2 nm thick. Capacitance-voltage characteristics of MgO capacitors are influenced significantly by the density of interface-states, as high as 5×10<sup>13</sup> cm <sup>-2</sup>  eV <sup>-1</sup> while Si / SiO <sub>2</sub>/ MgO structures are electrically beneficial by reducing to 6×10<sup>12</sup> cm <sup>-2</sup>  eV <sup>-1</sup> .
    Applied Physics Letters 08/2009; 95(4-95):042506 - 042506-3. DOI:10.1063/1.3182732 · 3.52 Impact Factor
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    ABSTRACT: Zinc metal nanowires have been oxidized at temperatures of 200–500 ° C in ambient air in order to obtain ZnO nanowires. X-ray diffraction investigations reveal a complete transformation from Zn to ZnO at a temperature of ≥300 ° C within 30 min. Temperature-induced grain growth attains saturation at about 350 ° C . Scanning electron microscopy studies show a pronounced morphology change from smooth, unidirectional to rough, bursted nanorods at a temperature of ≫250 ° C . The corresponding transformation mechanism is discussed.
    Journal of Applied Physics 06/2009; 105(10-105):104307 - 104307-5. DOI:10.1063/1.3126519 · 2.19 Impact Factor
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    ABSTRACT: In this work we present the structural and electrical characterization of sputter-deposited CoFe(B)/MgO/Si metal-insulator-semiconductor tunneling junctions for injection and detection of spin polarized current in silicon. The multilayers have been deposited in 700 nm deep trenches, patterned in thick SiO <sub>2</sub> dielectric, on n - and p -doped wafers. The films inside the trenches are continuous with a correlated and low roughness. The MgO barrier grows amorphous without indication of pinholes. The dc and ac transport properties of the junctions were studied as a function of temperature and frequency. A relatively high interface trap density at the MgO/Si-interface is extracted from admittance spectra measurements. Transport is dominated by majority carriers in the case of n -doped and by minority carriers for the p -doped wafers. This leads to distinct rectification characteristics for the two wafer types, which would significantly influence the spin injection efficiency of the tunneling junctions.
    Journal of Applied Physics 04/2008; 103(6-103):063709 - 063709-5. DOI:10.1063/1.2891503 · 2.19 Impact Factor
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    ABSTRACT: Spin-valve magnetic tunnel junctions (SV-MTJs) with the structure: substrate Si(100)/SiO2 47 nm/ buffer layers /IrMn 12 nm/CoFe 15 nm/Al-O 1.4 nm/NiFe 3 nm/Ta 5 nm were prepared with four different buffers: (a) Cu 25 nm, (b) Ta 5 nm/Cu 25 nm, (c) Ta 5 nm/Cu 25 nm/Ta 5 nm/Cu 5 nm and (d) Ta 5 nm/Cu 25 nm/Ta 5 nm/NiFe 2 nm/Cu 5 nm in order to investigate crystal texture of the MTJs. The junctions were characterized by XRD theta-2 theta scans and rocking curve (omega scans). The multilayer stack is textured in columnar-like fashion, which produces roughness. The texture and the roughness modified strongly the tunnel magnetoresistance (TMR), interlayer Neel and the exchange bias coupling fields in the SV-MTJs. The design of buffer layers allows to optimize the exchange coupling and tunneling parameters for magnetoelectronics devices. (c) 2007 Elsevier B.V. All rights reserved.
    Journal of Magnetism and Magnetic Materials 09/2007; 316(2):E998-E1001. DOI:10.1016/j.jmmm.2007.03.168 · 2.00 Impact Factor
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    ABSTRACT: (c) 2006 American Institute of Physics. Spin valve magnetic tunnel junctions (SV-MTJs) with the structure Si(100)/SiOx/buffer(A,B)/IrMn/CoFe/AlOx/NiFe/Ta have been deposited on two buffers: Cu (group A) and Ta/Cu (group B). The A junctions were characterized by a low degree of texture and a small amplitude of roughness, and B junctions by a high degree of texture and a high amplitude of roughness. The strongly textured buffer Ta/Cu (group B) grew in a columnarlike fashion and induced interfacial roughness. The texture and the roughness modified strongly the interlayer and the exchange bias coupling fields in the SV-MTJs. A substantial influence of the roughness, due to barrier thickness fluctuation, on the resistance area product (RxA) of junctions was also observed. The influence on the temperature dependence of conductance and tunnel magnetoresistance (TMR) was, however, small and only observable at low temperature for the two groups of junctions. A significantly larger increase of the conductance and decrease of the TMR with increasing bias voltage was found for the A junctions. The obtained results imply that composition of buffer layers and their sequence can be used as one of the ways to improve the magnetic and tunneling properties of SV-MTJs. (c) 2006 American Institute of Physics.
    Journal of Applied Physics 07/2006; 100(1). DOI:10.1063/1.2209180 · 2.19 Impact Factor
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    ABSTRACT: 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.
    Physica B Condensed Matter 02/2006; 372(1-2):337-340. DOI:10.1016/j.physb.2005.10.080 · 1.28 Impact Factor
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    ABSTRACT: We report on the development and first experimental results of a “at wavelength” full-field imaging technique for defect inspection of multilayer mask blanks for extreme ultraviolet (EUV) lithography. According to the International Semiconductor Roadmap by Sematech, less than 5×10<sup>-3</sup> defects per cm <sup>2</sup> should be present on such multilayer mask blank to enable mass production of microelectronics using EUV lithography, thus fast high-resolution methods for mask defect inspection and localization are needed. Our approach uses a photoemission electron microscope in a normal incidence illumination mode at 13 nm to image the photoelectron emission induced by the EUV wave field on the multilayer mask blank surface. We show that by these means, buried defects in the multilayer stack can be probed down to a lateral size of 50 nm.
    Applied Physics Letters 02/2006; 88(5-88):053113 - 053113-3. DOI:10.1063/1.2168263 · 3.52 Impact Factor
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    ABSTRACT: We experimentally demonstrate the feasibility of reprogrammable logic gate arrays with lateral dimensions down to 10x10 mu m(2). The gates are based on magnetic tunnel junctions which are elliptically patterned by e-beam lithography with sizes down to 200x100 nm(2). The junctions are realized with different tunneling systems and are investigated magnetically and electrically, where the magnetization reversal of the junctions' soft magnetic layer is done via currents in conducting lines. The switching currents could be reduced by a factor of about 2 by introducing an additional NiFe layer on top of the lines. Thus it is possible to use these gate arrays within a highly integrated environment. (c) 2006 American Institute of Physics.
    Journal of Applied Physics 01/2006; 99(2). DOI:10.1063/1.2164540 · 2.19 Impact Factor
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    ABSTRACT: In this study, we report the relationship between interface roughness, texture and the exchange bias and the interlayer-Neel coupling fields of the spin-valve magnetic tunnel junction (SV-MTJ). SV-MTJs with the structure: Si(100)/SiO2/buffer/IrMn/CoFeB/AlOx/NiFe/Ta were deposited on two buffers: Cu and Ta/Cu/Ta/Cu, and next the samples were annealed in vacuum and in a magnetic field. XRD analysis reveals that the texture degree of MTJ with Cu buffer is significantly lower than that of the sample with Ta/Cu/Ta/Cu buffer. The enhancement of IrMn and CoFeB texture leads to a higher amplitude of roughness and an increase of exchange bias and Neel coupling fields. The comparison of junctions with CoFe and CoFeB bottom electrodes shows that addition of 5% B in a CoFe layer makes the surface of the pinned layer smoother. This leads to a lower Neel coupling field, which is desirable for application of MTJ in MRAM technology. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    physica status solidi (b) 01/2006; 243(1):197-201. DOI:10.1002/pssb.200562456 · 1.61 Impact Factor
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    ABSTRACT: This work reports on the magnetic interlayer coupling between two amorphous CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic coupling which oscillates as a function of the Ru thickness x, with the second antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found that the coercivity depends on the net magnetic moment, i.e. the thickness difference of the two CoFeB layers. The antiferromagnetic coupling is almost independent on the annealing temperatures up to 300 degree C while an annealing at 350 degree C reduces the coupling and increases the coercivity, indicating the onset of crystallization. Used as a soft electrode in a magnetic tunnel junction, a high tunneling magnetoresistance of about 50%, a well defined plateau and a rectangular switching behavior is achieved.
    Applied Physics Letters 10/2005; 85(11). DOI:10.1063/1.1792375 · 3.52 Impact Factor
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    ABSTRACT: This work reports on the thermal stability of two amorphous CoFeB layers coupled antiferromagnetically via a thin Ru interlayer. The saturation field of the artificial ferrimagnet which is determined by the coupling, J, is almost independent on the annealing temperature up to more than 300 degree C. An annealing at more than 325 degree C significantly increases the coercivity, Hc, indicating the onset of crystallization.
    Journal of Magnetism and Magnetic Materials 10/2005; DOI:10.1016/j.jmmm.2004.11.539 · 2.00 Impact Factor
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    ABSTRACT: The magnetic and chemical interface properties of Mn-Ir/Co-Fe/Al+oxidation/Ni-Fe magnetic tunnel junctions are investigated for different barrier thickness, oxidation times, and annealing conditions by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. For underoxidized samples the formation of Co-Fe-Al alloy at the lower barrier interface during optimal annealing is observed. For optimally oxidized and overoxidized samples FeOx is formed during oxidation, which is reduced by Mn diffusing to the barrier during annealing. The reduction of FeOx is accompanied by an increase of the interfacial magnetic Fe moment, whereas the Co moments hardly change with the postannealing. Comparison of these results with transport properties of the junctions shows that their polycrystalline structure has to be taken into account to understand the annealing temperature and oxidation state dependence of the tunneling magnetoresistance effect. (c) 2005 American Institute of Physics.
    Journal of Applied Physics 06/2005; 97(12). DOI:10.1063/1.1939086 · 2.19 Impact Factor
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    ABSTRACT: Exchange-biased IrMn/CoFe full films are magnetically structured with He-ion bombardment into stripes with antiparallel-aligned loop shift. The patterning results in a two-step magnetization loop corresponding to two regions of oppositely aligned exchange bias. The longitudinal magnetization reversal through head-on domain-wall motion and partial penetration of magnetization from neighboring strips is highly asymmetric involving ripplelike domain structures and incoherent rotation of magnetization. In addition, Neel-wall-like structures with a preferred sense of rotation are formed at the edges of the strips. Along the transverse direction the reversal is dominated by the switching of the magnetic border structures between the strips. Complicated domain patterns are generated under other external field angles. (c) 2005 American Institute of Physics.
    Journal of Applied Physics 05/2005; 97(10, Part 3). DOI:10.1063/1.1847213 · 2.19 Impact Factor
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    ABSTRACT: The magnetization reversal in a periodic magnetic stripe array has been studied with a combination of direct and reciprocal space methods: Kerr microscopy and polarized neutron scattering. Kerr images show that during magnetization reversal over a considerable magnetic-field range a ripple domain state occurs in the stripes with magnetization components perpendicular to the stripes. Quantitative analysis of polarized neutron specular reflection, Bragg diffraction, and off-specular diffuse scattering provides a detailed picture of the mean magnetization direction in the ripple domains as well as longitudinal and transverse fluctuations, and reveals a strong correlation of those components over a number of stripes.
    Physical Review B 01/2005; 71(2-2). DOI:10.1103/PhysRevB.71.020403 · 3.66 Impact Factor
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    ABSTRACT: A new scheme of combined movement by on-chip currents and detection of magnetically labeled biomolecules has been introduced. This was the first step on the way to an on-chip laboratory. A conductor pair has been placed to this end on both sides of the sensor with the possibility of parallel or series connection. This connector setup made it possible to magnetize the beads and move them over the sensor area. This bead motion caused the detection signal. Magnetoresistance curves were measured and micromagnetic calculations have been done for the sensor types: giant magnetoresistance and tunneling magnetoresistance. The results showed an increase in sensitivity and also a corresponding change in the GMR curve. This therefore established an ideal sensor for the bead detection up to large values of bead surface concentration
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    ABSTRACT: Magnetic tunnelling junctions (MTJ) were prepared by magnetron sputtering on thermally oxidized Si (100) wafers at room temperature. Two different half MTJ were grown: V/Co2MnSi/Al with plasma oxidation and in situ annealing and the same stack with natural oxidation only. Transport properties like tunnelling magnetoresistance, and X-ray absorption spectra of the two samples were obtained. In the investigated samples, the measured shape of the Mn-L2,3 edges of plasma oxidized sample resulted from the superposition of a signal from MnOx and a signal from unoxidized Mn in Heusler alloy.

Publication Stats

591 Citations
107.19 Total Impact Points

Institutions

  • 2011
    • AIT Austrian Institute of Technology
      • Department of Health & Environment
      Wien, Vienna, Austria
  • 1998–2006
    • Bielefeld University
      • Faculty of Physics
      Bielefeld, North Rhine-Westphalia, Germany
  • 1997
    • Leibniz Institute for Solid State and Materials Research Dresden
      • Institute for Solid State Research
      Dresden, Saxony, Germany