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Jordan A. Katine - One of the best experts on this subject based on the ideXlab platform.

  • nanoscale magnetic tunnel junction sensors with Perpendicular Anisotropy sensing layer
    Applied Physics Letters, 2012
    Co-Authors: Jordan A. Katine, Khalili P Amiri, Zhongming Zeng, J Langer, Kang L Wang, H Jiang
    Abstract:

    A nano-scale linear magnetoresistance sensor is demonstrated using magnetic tunnel junctions with an in-plane magnetized reference layer and a sensing layer with interfacial Perpendicular Anisotropy. We show that the sensor response depends critically on the thickness of the sensing layer since its Perpendicular Anisotropy is significantly associated with thickness. The optimized sensors exhibit a large field sensitivity of up to 0.02% MR/Oe and a high linear field range of up to 600 Oe. These findings imply that this sensing scheme is a promising method for developing nano-scale magnetic sensors with simple design, high sensitivity, and low power consumption.

  • high power coherent microwave emission from magnetic tunnel junction nano oscillators with Perpendicular Anisotropy
    ACS Nano, 2012
    Co-Authors: Jordan A. Katine, Jian Ping Wang, I N Krivorotov, Zhongming Zeng, Hui Zhao, Pedram Khalili Amiri, G Finocchio, Yiming Huai, Juergen Langer
    Abstract:

    The excitation of the steady-state precessions of magnetization opens a new way for nanoscale microwave oscillators by exploiting the transfer of spin angular momentum from a spin-polarized current to a ferromagnet, referred to as spin-transfer nano-oscillators (STNOs). For STNOs to be practical, however, their relatively low output power and their relatively large line width must be improved. Here we demonstrate that microwave signals with maximum measured power of 0.28 μW and simultaneously narrow line width of 25 MHz can be generated from CoFeB–MgO–based magnetic tunnel junctions having an in-plane magnetized reference layer and a free layer with strong Perpendicular Anisotropy. Moreover, the generation efficiency is substantially higher than previously reported STNOs. The results will be of importance for the design of nanoscale alternatives to traditional silicon oscillators used in radio frequency integrated circuits.

  • sub 200 ps spin transfer torque switching in in plane magnetic tunnel junctions with interface Perpendicular Anisotropy
    Journal of Physics D, 2012
    Co-Authors: Hui Zhao, Graham Rowlands, Zhongming Zeng, Yujin Chen, Pedram Khalili Amiri, B Glass, Andrew Lyle, Yisong Zhang, Pramey Upadhyaya, Jordan A. Katine
    Abstract:

    Ultrafast spin transfer torque (STT) switching in an in-plane MgO magnetic tunnel junction with 50 nm×150 nm elliptical shape was demonstrated in this paper. Switching speeds as short as 165 ps and 190 ps at 50% and 98% switching probabilities, respectively, were observed without external field assistance in a thermally stable junction with a 101% tunnelling magnetoresistance ratio. The minimum writing energy of P-AP switching for 50% and 98% switching probability are 0.16 pJ and 0.21 pJ, respectively. The observed ultrafast switching is believed to occur because of partially cancelled out-of-plane demagnetizing field in the free layer from interface Perpendicular Anisotropy between the MgO layer and the Co20Fe60B20 layer. High J/Jc0 ratio and magnetization nucleation at the edge of free layer, which result from the reduced Perpendicular demagnetizing field, are possibly two major factors that contribute to the ultrafast STT switching.

  • switching current reduction using Perpendicular Anisotropy in cofeb mgo magnetic tunnel junctions
    Applied Physics Letters, 2011
    Co-Authors: Khalili P Amiri, Graham Rowlands, Jian Ping Wang, I N Krivorotov, Zhongming Zeng, J Langer, Hui Zhao, Yujin Chen, Hongwen Jiang, Jordan A. Katine
    Abstract:

    We present in-plane CoFeB–MgO magnetic tunnel junctions with Perpendicular magnetic Anisotropy in the free layer to reduce the spin transfer induced switching current. The tunneling magnetoresistance ratio, resistance-area product, and switching current densities are compared in magnetic tunnel junctions with different CoFeB compositions. The effects of CoFeB free layer thickness on its magnetic Anisotropy and current-induced switching characteristics are studied by vibrating sample magnetometry and electrical transport measurements on patterned elliptical nanopillar devices. Switching current densities ∼4 MA/cm2 are obtained at 10 ns write times.

  • reducing the critical current for spin transfer switching of Perpendicularly magnetized nanomagnets
    Applied Physics Letters, 2009
    Co-Authors: Stephane Mangin, Jordan A. Katine, Dafine Ravelosona, Y Henry, Eric E Fullerton
    Abstract:

    We describe nanopillar spin valves with Perpendicular Anisotropy designed to reduce the critical current needed for spin transfer magnetization reversal while maintaining thermal stability. By adjusting the Perpendicular Anisotropy and volume of the free element consisting of a [Co/Ni] multilayer, we observe that the critical current scales with the height of the Anisotropy energy barrier and we achieve critical currents as low as 120 μA in quasistatic room-temperature measurements of a 45 nm diameter device. The field-current phase diagram of such a device is presented.

Eric E Fullerton - One of the best experts on this subject based on the ideXlab platform.

  • Torque magnetometry of Perpendicular Anisotropy exchange-spring heterostructures
    Journal of Applied Physics, 2016
    Co-Authors: P Vallobra, Thomas Hauet, Eric E Fullerton, F Montaigne, E Shipton, S Mangin
    Abstract:

    The field-induced magnetic configurations in a [Co/Pd]15 /TbFeCo exchange-spring system with Perpendicular magnetic Anisotropy are studied using torque magnetometry. The experimental results are compared to a 1D micromagnetic simulation. The good agreement between experiments and simulations allows us to deduce the evolution of the in-depth magnetic configuration as a function of the applied field orientation and amplitude. The chirality transition of the interfacial domain wall developing in the structure can also be determined with this technique.

  • ultrafast spin transfer switching in spin valve nanopillars with Perpendicular Anisotropy
    Applied Physics Letters, 2010
    Co-Authors: Daniel Bedau, Eric E Fullerton, H Liu, A D Kent, J Z Sun, J J Bouzaglou, S Mangin
    Abstract:

    Spin-transfer switching with short current pulses has been studied in spin-valve nanopillars with Perpendicularly magnetized free and reference layers. Magnetization switching with current pulses as short as 300 ps is demonstrated. The pulse amplitude needed to reverse the magnetization is shown to be inversely proportional to the pulse duration, consistent with a macrospin spin-transfer model. However, the pulse amplitude duration switching boundary depends on the applied field much more strongly than predicted by the zero temperature macrospin model. The results also demonstrate that there is an optimal pulse length that minimizes the energy required to reverse the magnetization.

  • suppression of the Perpendicular Anisotropy at the coo neel temperature in exchange biased coo co pt multilayers
    Applied Physics Letters, 2009
    Co-Authors: Erik Shipton, Keith Chan, Thomas Hauet, O Hellwig, Eric E Fullerton
    Abstract:

    We performed high field torque magnetometry measurements on CoO/[Co/Pt] magnetic multilayers that exhibit Perpendicular exchange bias. We find that the antiferromagnet CoO layers strongly modify the uniaxial Anisotropy of the multilayer structures. The strongest effects due to the CoO layers occur in the vicinity of the Neel temperature, where we observe a suppression of the first-order Anisotropy and a smaller enhancement of the second-order Anisotropy. This results in a nonmonotonic variation of the Anisotropy with temperature and for selected samples a transition from Perpendicular to in-plane and back to Perpendicular Anisotropy with increasing temperature.

  • reducing the critical current for spin transfer switching of Perpendicularly magnetized nanomagnets
    Applied Physics Letters, 2009
    Co-Authors: Stephane Mangin, Jordan A. Katine, Dafine Ravelosona, Y Henry, Eric E Fullerton
    Abstract:

    We describe nanopillar spin valves with Perpendicular Anisotropy designed to reduce the critical current needed for spin transfer magnetization reversal while maintaining thermal stability. By adjusting the Perpendicular Anisotropy and volume of the free element consisting of a [Co/Ni] multilayer, we observe that the critical current scales with the height of the Anisotropy energy barrier and we achieve critical currents as low as 120 μA in quasistatic room-temperature measurements of a 45 nm diameter device. The field-current phase diagram of such a device is presented.

  • domain structure and magnetization reversal of antiferromagnetically coupled Perpendicular Anisotropy films
    Journal of Magnetism and Magnetic Materials, 2007
    Co-Authors: Olav Hellwig, Eric E Fullerton, A Berger, Jeffrey B Kortright
    Abstract:

    We describe experimental and theoretical investigations of the magnetic domain formation and the field reversal behavior in antiferromagnetically coupled Perpendicular Anisotropy multilayers that mimic A-type antiferromagnet (AF) structures. The samples are sputter deposited Co/Pt multilayers with Perpendicular Anisotropy that are periodically interleaved with Ru to mediate an antiferromagnetic interlayer exchange. This structure allows precise tuning of the different magnetic energy terms involved. Using various magnetometry and magnetic imaging techniques as well as resonant soft X-ray scattering we provide a comprehensive study of the remanent and demagnetized configurations as well as the corresponding reversal mechanisms. We find that adding AF exchange to Perpendicular Anisotropy system alters the typical energy balance that controls magnetic stripe domain formation, thus resulting in two competing reversal modes for the composite system. In the AF-exchange dominated regime the magnetization is ferromagnetically ordered within the film plane with the magnetization of adjacent layers anti-parallel thus minimizing the interlayer AF exchange energy. In the dipolar dominated regime the magnetization pattern forms ferromagnetic (FM) stripe domains where adjacent layers are vertically correlated, but laterally anti-correlated thus minimizing the dipolar energy at the expense of the AF interlayer coupling. By tuning the layer thickness or applying a magnetic field, we observed the co-existence of AF domains and FM stripe domains. We find that a FM phase exists at AF domain boundaries, causing complex mesoscopic domain patterns with surprising reversibility during minor loop field cycling.

Bernard Rodmacq - One of the best experts on this subject based on the ideXlab platform.

  • periodic magnetic domain wall pinning in an ultrathin film with Perpendicular Anisotropy generated by the stray magnetic field of a ferromagnetic nanodot array
    Applied Physics Letters, 2009
    Co-Authors: Peter J Metaxas, J Ferre, J P Jamet, Bernard Rodmacq, Pierrejean Zermatten, Gilles Gaudin, A Schuhl, R L Stamps
    Abstract:

    The stray magnetic field of an array of hard ferromagnetic Perpendicularly magnetized [Co/Pt]4 nanodots is used to nondestructively generate a periodic pinning potential for domain walls in an underlying [Pt/Co]2/Pt layer with Perpendicular Anisotropy. Pinning is evidenced using magneto-optical microscopy. The magnetic field (H) dependence of the average wall velocity in the presence of the periodic pinning potential is consistent with thermally activated creep, modified only by the addition of a uniform retarding field Hret, whose magnitude depends on the relative alignment of H and the dots' magnetizations.

  • creep and flow regimes of magnetic domain wall motion in ultrathin pt co pt films with Perpendicular Anisotropy
    Physical Review Letters, 2007
    Co-Authors: J Ferre, Peter J Metaxas, J P Jamet, A Mougin, M Cormier, Vincent Baltz, Bernard Rodmacq, Bernard Dieny, R L Stamps
    Abstract:

    We report on magnetic domain-wall velocity measurements in ultrathin Pt=Co� 0:5–0: 8n m� =Pt films with Perpendicular Anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domainwall motion, analysis of which yields values for the damping parameter, � .

  • creep and flow regimes of magnetic domain wall motion in ultrathin pt co pt films with Perpendicular Anisotropy
    Physical Review Letters, 2007
    Co-Authors: J Ferre, Peter J Metaxas, J P Jamet, A Mougin, M Cormier, Vincent Baltz, Bernard Rodmacq, Bernard Dieny, R L Stamps
    Abstract:

    We report on magnetic domain-wall velocity measurements in ultrathin $\mathrm{Pt}/\mathrm{Co}(0.5--0.8\text{ }\text{ }\mathrm{nm})/\mathrm{Pt}$ films with Perpendicular Anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, $\ensuremath{\alpha}$.

  • pinned synthetic ferrimagnets with Perpendicular Anisotropy and tuneable exchange bias
    Applied Physics Letters, 2003
    Co-Authors: J Sort, Bernard Rodmacq, S Auffret, Bernard Dieny
    Abstract:

    Pinned synthetic ferrimagnets (syFerri) with Perpendicular-to-plane magnetic Anisotropy, of the form AP1/Ru/AP2/FeMn [where AP1 and AP2 are (Co/Pt) multilayers], have been prepared and characterized. The magnitudes of the exchange bias fields of both AP1 and AP2 can be tuned at room temperature by simply varying the relative number of (Co/Pt) repeats in each multilayer. This effect can be quantitatively interpreted by considering the different energy contributions involved during magnetization reversal. Moreover, from the values of these fields, the characteristic parameters of the system (i.e., coupling strength through the Ru and AP2/FeMn pinning energy), can be evaluated. Interestingly, an extended plateau with a virtually constant magnetization is observed around zero field when the number of Co/Pt repeats in AP1 is equal or larger than in AP2. This is very appealing for field sensor or memories applications using spin valves or tunnel junctions with Perpendicular Anisotropy, since it offers a large dynamic range over which the magnetic configuration of the syFerri remains stable.

  • crossovers from in plane to Perpendicular Anisotropy in magnetic tunnel junctions as a function of the barrier degree of oxidation
    Journal of Applied Physics, 2003
    Co-Authors: Bernard Rodmacq, Bernard Dieny, S Auffret, S Monso, P Boyer
    Abstract:

    Pt/Co/M sandwiches (M=Al, Ta, Cr) were prepared by sputtering. The M capping layer was oxidized either by natural oxidation in air or by exposure to an oxygen plasma. By measuring the extraordinary Hall effect in these systems, we observed that the magnetic Anisotropy of the Co electrode is extremely sensitive to the degree of oxidation of the capping layer. In particular, when M=Al, the magnetic Anisotropy is found in plane when the AlOx layer is under or overoxidized whereas it is out of plane when this oxide layer is stochiometric alumina. The conditions of oxidation which give the Perpendicular Anisotropy in Pt/Co/AlOx are found to be the same than those which lead to a maximum of specular reflection at Co/AlOx interface in Co/Ru/Co/Cu/Co/AlOx synthetic spin-valves. This crossover of Anisotropy therefore provides a very useful way for controlling the oxidation of tunnel barriers. Furthermore, this phenomenon can be used to study the aging of naturally oxidized tunnel junctions exposed to air, and it i...

Bernard Dieny - One of the best experts on this subject based on the ideXlab platform.

  • creep and flow regimes of magnetic domain wall motion in ultrathin pt co pt films with Perpendicular Anisotropy
    Physical Review Letters, 2007
    Co-Authors: J Ferre, Peter J Metaxas, J P Jamet, A Mougin, M Cormier, Vincent Baltz, Bernard Rodmacq, Bernard Dieny, R L Stamps
    Abstract:

    We report on magnetic domain-wall velocity measurements in ultrathin Pt=Co� 0:5–0: 8n m� =Pt films with Perpendicular Anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domainwall motion, analysis of which yields values for the damping parameter, � .

  • creep and flow regimes of magnetic domain wall motion in ultrathin pt co pt films with Perpendicular Anisotropy
    Physical Review Letters, 2007
    Co-Authors: J Ferre, Peter J Metaxas, J P Jamet, A Mougin, M Cormier, Vincent Baltz, Bernard Rodmacq, Bernard Dieny, R L Stamps
    Abstract:

    We report on magnetic domain-wall velocity measurements in ultrathin $\mathrm{Pt}/\mathrm{Co}(0.5--0.8\text{ }\text{ }\mathrm{nm})/\mathrm{Pt}$ films with Perpendicular Anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, $\ensuremath{\alpha}$.

  • pinned synthetic ferrimagnets with Perpendicular Anisotropy and tuneable exchange bias
    Applied Physics Letters, 2003
    Co-Authors: J Sort, Bernard Rodmacq, S Auffret, Bernard Dieny
    Abstract:

    Pinned synthetic ferrimagnets (syFerri) with Perpendicular-to-plane magnetic Anisotropy, of the form AP1/Ru/AP2/FeMn [where AP1 and AP2 are (Co/Pt) multilayers], have been prepared and characterized. The magnitudes of the exchange bias fields of both AP1 and AP2 can be tuned at room temperature by simply varying the relative number of (Co/Pt) repeats in each multilayer. This effect can be quantitatively interpreted by considering the different energy contributions involved during magnetization reversal. Moreover, from the values of these fields, the characteristic parameters of the system (i.e., coupling strength through the Ru and AP2/FeMn pinning energy), can be evaluated. Interestingly, an extended plateau with a virtually constant magnetization is observed around zero field when the number of Co/Pt repeats in AP1 is equal or larger than in AP2. This is very appealing for field sensor or memories applications using spin valves or tunnel junctions with Perpendicular Anisotropy, since it offers a large dynamic range over which the magnetic configuration of the syFerri remains stable.

  • crossovers from in plane to Perpendicular Anisotropy in magnetic tunnel junctions as a function of the barrier degree of oxidation
    Journal of Applied Physics, 2003
    Co-Authors: Bernard Rodmacq, Bernard Dieny, S Auffret, S Monso, P Boyer
    Abstract:

    Pt/Co/M sandwiches (M=Al, Ta, Cr) were prepared by sputtering. The M capping layer was oxidized either by natural oxidation in air or by exposure to an oxygen plasma. By measuring the extraordinary Hall effect in these systems, we observed that the magnetic Anisotropy of the Co electrode is extremely sensitive to the degree of oxidation of the capping layer. In particular, when M=Al, the magnetic Anisotropy is found in plane when the AlOx layer is under or overoxidized whereas it is out of plane when this oxide layer is stochiometric alumina. The conditions of oxidation which give the Perpendicular Anisotropy in Pt/Co/AlOx are found to be the same than those which lead to a maximum of specular reflection at Co/AlOx interface in Co/Ru/Co/Cu/Co/AlOx synthetic spin-valves. This crossover of Anisotropy therefore provides a very useful way for controlling the oxidation of tunnel barriers. Furthermore, this phenomenon can be used to study the aging of naturally oxidized tunnel junctions exposed to air, and it i...

  • exchange bias with Perpendicular Anisotropy in pt co sub n femn multilayers
    IEEE International Magnetics Conference, 2002
    Co-Authors: F. Garcia, Bernard Rodmacq, Bernard Dieny, S Auffret, J Moritz, F Ernult, J Carnarero, Yan Pennec, S Pizzini, Jan Vogel
    Abstract:

    Sputtered (Pt-Co)/sub n/-FeMn multilayers exhibit both Perpendicular magnetic Anisotropy and exchange bias at room temperature. Their magnetic properties after in-plane and Perpendicular-to-plane magnetic annealing have been studied by means of extraordinary Hall effect and magnetic force microscopy or polar Kerr microscopy. A crossover from in-plane to Perpendicular Anisotropy was observed as a function of number of repeats n. The dynamics of magnetization switching has been investigated on both sides of the hysteresis loops. A clear asymmetry exists in the dynamics depending whether the field is parallel or antiparallel to the exchange bias field. Similarly, strong differences in the domain patterns at the coercive field were observed. Exchange-biased (Pt-Co)-Pt-(Pt-Co)-FeMn spin-valves were also investigated. Well-separated hysteresis loops were associated with the "soft" and pinned components of the stack. These structures were used to study the interlayer coupling through the Pt spacer.

Peter J Metaxas - One of the best experts on this subject based on the ideXlab platform.

  • periodic magnetic domain wall pinning in an ultrathin film with Perpendicular Anisotropy generated by the stray magnetic field of a ferromagnetic nanodot array
    Applied Physics Letters, 2009
    Co-Authors: Peter J Metaxas, J Ferre, J P Jamet, Bernard Rodmacq, Pierrejean Zermatten, Gilles Gaudin, A Schuhl, R L Stamps
    Abstract:

    The stray magnetic field of an array of hard ferromagnetic Perpendicularly magnetized [Co/Pt]4 nanodots is used to nondestructively generate a periodic pinning potential for domain walls in an underlying [Pt/Co]2/Pt layer with Perpendicular Anisotropy. Pinning is evidenced using magneto-optical microscopy. The magnetic field (H) dependence of the average wall velocity in the presence of the periodic pinning potential is consistent with thermally activated creep, modified only by the addition of a uniform retarding field Hret, whose magnitude depends on the relative alignment of H and the dots' magnetizations.

  • creep and flow regimes of magnetic domain wall motion in ultrathin pt co pt films with Perpendicular Anisotropy
    Physical Review Letters, 2007
    Co-Authors: J Ferre, Peter J Metaxas, J P Jamet, A Mougin, M Cormier, Vincent Baltz, Bernard Rodmacq, Bernard Dieny, R L Stamps
    Abstract:

    We report on magnetic domain-wall velocity measurements in ultrathin Pt=Co� 0:5–0: 8n m� =Pt films with Perpendicular Anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domainwall motion, analysis of which yields values for the damping parameter, � .

  • creep and flow regimes of magnetic domain wall motion in ultrathin pt co pt films with Perpendicular Anisotropy
    Physical Review Letters, 2007
    Co-Authors: J Ferre, Peter J Metaxas, J P Jamet, A Mougin, M Cormier, Vincent Baltz, Bernard Rodmacq, Bernard Dieny, R L Stamps
    Abstract:

    We report on magnetic domain-wall velocity measurements in ultrathin $\mathrm{Pt}/\mathrm{Co}(0.5--0.8\text{ }\text{ }\mathrm{nm})/\mathrm{Pt}$ films with Perpendicular Anisotropy over a large range of applied magnetic fields. The complete velocity-field characteristics are obtained, enabling an examination of the transition between thermally activated creep and viscous flow: motion regimes predicted from general theories for driven elastic interfaces in weakly disordered media. The dissipation limited flow regime is found to be consistent with precessional domain-wall motion, analysis of which yields values for the damping parameter, $\ensuremath{\alpha}$.