J. A. Katine

HGST, A Western Digital Company, San José, California, United States

Are you J. A. Katine?

Claim your profile

Publications (241)684.42 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A method for making a current-perpendicular-to-the-plane magnetoresistive sensor structure produces a top electrode that is "self-aligned" on the top of the sensor and with a width less than the sensor trackwidth. A pair of walls of ion-milling resistant material are fabricated to a predetermined height above the biasing layers at the sensor side edges. A layer of electrode material is then deposited onto the top of the sensor between the two walls. The walls serve as a mask during angled ion milling to remove outer portions of the electrode layer. The height of the walls and the angle of ion milling determines the width of the resulting top electrode. This leaves the reduced-width top electrode located on the sensor. Because of the directional ion milling using walls that are aligned with the sensor side edges, the reduced-width top electrode is self-aligned in the center of the sensor.
    Full-text · Patent · Jan 2016

  • No preview · Article · Jan 2016 · Applied Physics Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A side-by-side magnetic multi-input multi-output (MIMO) read head is provided. The read head may include a pair of side-by-side MIMO read sensors disposed between a bottom shield, a top shield and between a pair of side shields. The read head may also include a pair of electrical leads, each of which is coupled with one of the MIMO read sensors. The electrical leads extend away from an air bearing surface.
    Full-text · Patent · Dec 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The prediction and realization of magnetic excitations driven by electrical currents via the spin transfer torque effect, enables novel magnetic nano-devices where spin-waves can be used to process and store information. The functional control of such devices relies on understanding the properties of non-linear spin-wave excitations. It has been demonstrated that spin waves can show both an itinerant character, but also appear as localized solitons. So far, it was assumed that localized solitons have essentially cylindrical, $s-$like symmetry. Using a newly developed high-sensitivity time-resolved magnetic x-ray microscopy, we instead observe the emergence of a novel localized soliton excitation with a nodal line, i.e. with $p-$like symmetry. Micromagnetic simulations identify the physical mechanism that controls the transition from $s-$ to $p-$like solitons. Our results suggest a potential new pathway to design artificial atoms with tunable dynamical states using nanoscale magnetic devices.
    Full-text · Article · Nov 2015 · Nature Communications
  • [Show abstract] [Hide abstract]
    ABSTRACT: We review the recent progress in the development of magnetoelectric RAM (MeRAM) based on electric-field-controlled writing in magnetic tunnel junctions (MTJs). MeRAM uses the tunneling magnetoresistance effect for readout in a two-terminal memory element, similar to other types of magnetic RAM. However, the writing of information is performed by voltage control of magnetic anisotropy (VCMA) at the interface of an MgO tunnel barrier and the CoFeB-based free layer, as opposed to current-controlled (e.g., spin-transfer torque or spin-orbit torque) mechanisms. We present results on voltage-induced switching of MTJs in both resonant (precessional) and thermally activated regimes, which demonstrate fast (<1 ns) and ultralow-power (<40 fJ/bit) write operations at voltages ∼1.5-2 V. We also discuss the implications of the VCMA-based write mechanism on memory array design, highlighting the possibility of crossbar implementation for high bit density. Results are presented from a 1 kbit MeRAM test array. Endurance and voltage scaling data are presented. The scaling behavior is analyzed, and material-level requirements are discussed for the translation of MeRAM into mainstream memory applications.
    No preview · Article · Nov 2015 · IEEE Transactions on Magnetics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In one embodiment, a device includes a reference layer, a free layer positioned above the reference layer, and a spacer layer positioned between the reference layer and the free layer, the spacer layer providing a gap between the reference layer and the free layer, wherein the reference layer extends beyond a rear extent of the free layer in an element height direction perpendicular to a media-facing surface of the device, and wherein a rear portion of the spacer layer that extends beyond the rear extent of the free layer has an increased resistivity in comparison with a resistivity of a rest of the spacer layer. In other embodiments, a method for forming the device is presented, along with other device structures having an extended pinned layer (EPL).
    Full-text · Patent · Sep 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An apparatus according to one embodiment includes a near field transducer comprising a conductive metal film having a main body, a notch extending from the main body, and a notch diffusion barrier layer interposed between the notch and the main body. An apparatus according to another embodiment includes a write pole, and a near field transducer adjacent the write pole. The near field transducer includes a conductive metal film having a main body, a notch extending from the main body, and a notch diffusion barrier layer interposed between the notch and the main body. The notch diffusion barrier layer includes a metal selected from a group consisting of Rh, W, Mo, Ru, Ir, Co, Ni, Pt, B, and alloys thereof. Additional systems and methods are also presented.
    Full-text · Patent · Aug 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have used a MHz lock-in x-ray spectro-microscopy technique to directly detect changes of magnetic moments in Cu due to spin injection from an adjacent Co layer. The elemental and chemical specificity of x-rays allows us to distinguish two spin current induced effects. We detect the creation of transient magnetic moments of $3\times 10^{-5}$ $\mu_\mathrm{B}$ on Cu atoms within the bulk of the 28 nm thick Cu film due to spin-accumulation. The moment value is compared to predictions by Mott's two current model. We also observe that the hybridization induced existing magnetic moments on Cu interface atoms are transiently increased by about 10% or $4\times 10^{-3}$ $\mu_\mathrm{B}$. This reveals the dominance of spin-torque alignment over Joule heat induced disorder of the interfacial Cu moments during current flow.
    Full-text · Article · Aug 2015 · Physical Review Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We examine the effect that bias current has on the spectral response of spin-torque oscillators designed to have large precessional orbits. These devices exhibit a nonmonotonic dependence of auto-oscillator frequencies and linewidths as a function of bias current, indicating that oscillator nonlinearity first decreases and then increases with increasing oscillator power. Macrospin simulations indicate that this behavior is characteristic of orbits with large precession angles, as oscillation frequency is a function of the deviation away from a 90° alignment of the free- and reference-layer moments. Using a recent nonlinear oscillator theory, we analyze these results by using two different techniques, both of which confirm that these theories predict the behavior of large-angle oscillations and that the linewidths of these oscillators have a different dependence on oscillator power than shown in previous studies of small-angle precession. From these results, we find that the details of the excited orbital motion can have a significant impact on a spin-torque oscillator’s properties, providing additional methods for optimizing device performance.
    Full-text · Article · Jul 2015 · Physical Review Applied
  • Source
    Patrick M. Braganca · yang li · jordan katine · neil robertson
    [Show abstract] [Hide abstract]
    ABSTRACT: The embodiments of the present invention relate to a method for forming a magnetic read head having one or more sensors disposed over one or more sensors. The method includes forming one or more first sensors on a shield, forming a spacer layer over the one or more first sensors and forming one or more second sensors over the spacer layer. A single photolithography process is performed on a resist that is disposed over a portion of the one or more second sensors, the spacer layer and the one or more first sensors, and portions of the one or more second sensors, the spacer layer and the one or more first sensors not covered by the resist are removed by multiple removal processes. The stripe heights of the free layers and the pinned layers of the one or more first sensors and the one or more second sensors are defined as a result of the multiple removal processes.
    Full-text · Patent · Jul 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: The high contrast in the electrical resistivity between amorphous and crystalline states of a phase change material can potentially enable multiple memory levels for efficient use of a data storage medium. We report on our investigation of the role of the current injection site geometry (circular and square) in stabilizing such intermediate states within a nanoscale single-phase change material system (Ge 2Sb2Te5). We have developed a three dimensional multiphysics model, which includes phase change kinetics, electrical, thermal, thermoelectric, and percolation effects, all as a function of temperature, using an iterative approach with coupled differential equations. Our model suggests that the physical origin of the formation of stable intermediate states in square top contact devices is mainly due to anisotropic heating during the application of a programming current pulse. Furthermore, the threshold current requirement and the width of the programming window are determined by crystallite nucleation and growth rates such that a higher crystallization rate leads to a narrower range of current pulses for switching to intermediate resistance level(s). The experimentally determined resistance maps, those that are indicative of the crystallinity, show good agreement with the simulated phase change behavior confirming the existence of stable intermediate states. Our model successfully predicts the required programming conditions for such mixed-phase levels, which can be used to optimize memory cells for future ultra-high density data storage applications.
    No preview · Article · Jun 2015 · Journal of Applied Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a comparative study of high frequency dynamics and low frequency noise in elliptical magnetic tunnel junctions with lateral dimensions under 100 nm presenting current-switching phenomena. The analysis of the high frequency oscillation modes with respect to the current reveals the onset of a steady-state precession regime for negative bias currents above $J=10^7 A/cm^2$, when the magnetic field is applied along the easy axis of magnetization. By the study of low frequency noise for the same samples, we demonstrate the direct link between changes in the oscillation modes with the applied current and the normalised low frequency (1/f) noise as a function of the bias current. These findings prove that low frequency noise studies could be a simple and powerful technique to investigate spin-torque based magnetization dynamics.
    Full-text · Article · Jun 2015 · Applied Physics Letters
  • Source

    Full-text · Dataset · May 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Vortex dynamics within arrays of square ferromagnetic nanoelements have been studied by time-resolved scanning Kerr microscopy (TRSKM), while x-ray photoemission electron microscopy has been used to investigate the equilibrium magnetic state of the arrays. An alternating field demagnetization process was found to initialize a distribution of equilibrium states within the individual elements of the array, including quasiuniform states and vortex states of different chirality and core polarization. Repeated initialization revealed some evidence of stochastic behavior during the formation of the equilibrium state. TRSKM with a spatial resolution of ∼300 nm was used to detect vortex gyration within arrays of square nanoelements of 250-nm lateral size. Two arrays were studied consisting of a 9×9 and 5×5 arrangement of nanoelements with 50- and 500-nm element edge-to-edge separation to encourage strong and negligible dipolar interactions, respectively. In the 5×5 element array, TRSKM images, acquired at a fixed phase of the driving microwave magnetic field, revealed differences in the gyrotropic phase within individual elements. While some phase variation is attributed to the dispersion in the size and shape of elements, the vortex chirality and core polarization are also shown to influence the phase. In the 9×9 array, strong magneto-optical response due to vortex gyration was observed across regions with length equal to either one or two elements. Micromagnetic simulations performed for 2×2 arrays of elements suggest that particular combinations of vortex chirality and polarization in neighboring elements are required to generate the observed magneto-optical contrast.
    Full-text · Article · May 2015 · Physical Review B
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study thin films and magnetic tunnel junction nanopillars based on Ta/Co20Fe60B20/MgO multilayers by electrical transport and magnetometry measurements. These measurements suggest that an ultrathin magnetic oxide layer forms at the Co20Fe60B20/MgO interface. At approximately 160 K, the oxide undergoes a phase transition from an insulating antiferromagnet at low temperatures to a conductive weak ferromagnet at high temperatures. This interfacial magnetic oxide is expected to have significant impact on the magnetic properties of CoFeB-based multilayers used in spin torque memories.
    Full-text · Article · May 2015 · Applied Physics Letters
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Picosecond magnetization dynamics in the free and pinned layers of a microscale magnetic tunnel valve have been studied using time-resolved scanning Kerr microscopy. A comparison of the observed dynamics with those of individual free and pinned layers allowed the effect of interlayer coupling to be identified. A weak interlayer coupling in the tunnel valve continuous film reference sample was detected in bulk magnetometry measurements, while focused Kerr magnetometry showed that the coupling was well maintained in the patterned structure. In the tunnel valve, the free layer precession was observed to have reduced amplitude and an enhanced relaxation. During magnetization reversal in the pinned layer, its frequency approached that of the low frequency mode associated with the free layer. At the pinned layer switching field, the linewidth of the free layer became similar to that of the pinned layer. The similarity in their frequencies promotes the formation of precessional modes that exhibit strong collective properties such as frequency shifting and enhanced linewidth, while inhomogeneous magnetization of the pinned layer during reversal may also play a role in these observations. The collective character of precessional dynamics associated with mixing of the free and pinned layer magnetization dynamics must be accounted for even in tunnel valves with a small interlayer coupling.
    Full-text · Article · May 2015 · Journal of Applied Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study thin films and magnetic tunnel junction nanopillars based on Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO multilayers by electrical transport and magnetometry measurements. These measurements suggest that an ultrathin magnetic oxide layer forms at the Co$_{20}$Fe$_{60}$B$_{20}$/MgO interface. At approximately 160 K, the oxide undergoes a phase transition from an insulating antiferromagnet at low temperatures to a conductive weak ferromagnet at high temperatures. This interfacial magnetic oxide is expected to have significant impact on the magnetic properties of CoFeB-based multilayers used in spin torque memories.
    Full-text · Article · Apr 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have used a MHz lock-in x-ray spectro-microscopy technique to detect the accumulation of transient spins flowing across a Co/Cu interface. The elemental and chemical specificity of x-rays allows us to distinguish spin accumulation on Cu atoms located at the interface from those within the 28 nm thick Cu film. Spin accumulation in the film gives rise to an average transient magnetic moment per Cu atom of $3\times 10^{-5}$ $\mu_\mathrm{B}$, which is explained by Mott's two current model. We find a greatly enhanced transient moment of $4\times 10^{-3}$ $\mu_\mathrm{B}$ on the Cu interface atoms which is attributed to enhanced spin dependent scattering via localized interface states.
    Full-text · Article · Mar 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A current-perpendicular-to-the plane magnetoresistive sensor has top and bottom electrodes narrower than the sensor trackwidth. The electrodes are formed of one of Cu, Au, Ag and AgSn, which have an ion milling etch rate much higher than the etch rates for the sensor's ferromagnetic materials. Ion milling is performed at a high angle relative to a line orthogonal to the plane of the electrode layers and the layers in the sensor stack. Because of the much higher etch rate of the material of the top and bottom electrode layers, the electrode layers will have side edges that are recessed from the side edges of the free layer. This reduces the surface areas for the top and bottom electrodes, which causes the sense current passing through the sensor's free layer to be confined in a narrower channel, which is equivalent to having a sensor with narrower physical trackwidth.
    Full-text · Patent · Mar 2015
  • Source

    Full-text · Dataset · Dec 2014

Publication Stats

7k Citations
684.42 Total Impact Points

Institutions

  • 2015
    • HGST, A Western Digital Company
      San José, California, United States
  • 2012
    • University of California, Irvine
      • Department of Physics and Astronomy
      Irvine, California, United States
  • 2011
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2006
    • San Jose State University
      San Jose, California, United States
  • 1999-2000
    • Cornell University
      • School of Applied and Engineering Physics
      Ithaca, New York, United States