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Barrier interface condition is critical for spin-polarized tunneling and spin-transfer torque switching in CoFeB∣MgO∣CoFeB-based magnetic tunnel junctions. The differential tunnel conductance gV contains information on CoFeB’s magnetic properties at tunnel interfaces. Experimentally, we find gV to follow a “cross-normalization” relationship between the parallel and antiparallel alignments. This we show originates from the leading order spin-flip scatter terms related to CoFeB interface magnetic properties such as its exchange-stiffness. By connecting the observable gV slopes to electrode-specific spin-flip scatter rates, we obtain an efficient measurement for mass-screening of junctions for interface magnetic differences. This provides valuable information for device and fabrication process optimization.Barrier interface condition is critical for spin-polarized tunneling and spin-transfer torque switching in CoFeB∣MgO∣CoFeB-based magnetic tunnel junctions. The differential tunnel conductance gV contains information on CoFeB’s magnetic properties at tunnel interfaces. Experimentally, we find gV to follow a “cross-normalization” relationship between the parallel and antiparallel alignments. This we show originates from the leading order spin-flip scatter terms related to CoFeB interface magnetic properties such as its exchange-stiffness. By connecting the observable gV slopes to electrode-specific spin-flip scatter rates, we obtain an efficient measurement for mass-screening of junctions for interface magnetic differences. This provides valuable information for device and fabrication process optimization.

Exchange biased magnetic tunnel junction (MTJ) structures are shown to have useful properties for forming magnetic memory storage elements in a novel cross-point architecture. MTJ elements have been developed which exhibit very large magnetoresistive (MR) values exceeding 40% at room temperature, with specific resistance values ranging down to as little as ∼60 Ω(μm)2, and with MR values enhanced by moderate thermal treatments. Large MR values are observed in magnetic elements with areas as small as 0.17 (μm)2. The magnetic field dependent current–voltage characteristics of an MTJ element integrated with a silicon diode are analyzed to extract the MR properties of the MTJ element itself.

We have measured and simulated the dynamics of magnetization reversal in 5 nm by 0.8 by 1.6 $\ensuremath{\mu}\mathrm{m}$ ${\mathrm{Ni}}_{60}{\mathrm{Fe}}_{40}$ thin films. The films measured form the upper electrode of a spin-polarized tunnel junction so that the magnetization direction of the film can be probed by measuring the tunneling resistance of the junction. When a magnetic field pulse is applied, the time to switch the film magnetization changes from greater than 10 ns to less than 500 ps as the pulse amplitude is increased from the coercive field to 10 mT and beyond. We have simulated these transitions using micromagnetic modeling of the exact experimental conditions. The simulations agree well with the experimental measurements.

Using a wide-field Kerr microscope, we have studied the magnetic domain structures of epitaxial and polycrystalline La0.67Sr0.33MnO3 thin films as well as a film having thermally induced 〈110〉 microcracks. The epitaxial film on a (001) SrTiO3 substrate has different magnetic domain behaviors for in-plane fields applied along the 〈100〉 and 〈110〉 directions. Magnetic domain orientation and contrast suggest a biaxial magnetic anisotropy with 〈110〉 easy axes. Defects such as microcracks and grain boundaries have a strong perturbing effect on the local magnetization and can lead to an enhanced and controllable spin-dependent scattering.

We have studied the switching properties of micron-scale magnetic tunnel junctions in two-dimensional magnetic fields. We present data on interlayer magnetic coupling for multiple samples. We interpret these data as the sum of a magnetostatic and a Neel coupling contribution. The data are presented as functions of layer structure. In addition, we have extracted information about interface roughness. We have also studied the area of switching critical curves as a function of device geometry.

We have studied bias and magnetic field dependence of voltage noise in metallic magnetic tunnel junctions with areal dimensions on the order of 1 μm. We generally observe noise with Gaussian amplitude distribution and pure 1/f power spectra at low frequencies. The 1/f noise scales with bias voltage as V2. Two kinds of deviations from this low frequency behavior have been observed. One is at fixed magnetic field when the junction bias reaches above a critical value, the other occurs at a fixed bias when the external magnetic field brings the sample to certain magnetic configurations. In both cases the noise spectra become dominated by Lorentzian noise and in both cases we have observed two level fluctuators in the time domain. We attribute the bias dependent noise to charge traps in the tunnel barrier. The field dependent noise is associated with the switching of the magnetization direction of portions of the top electrode, which we believe to be reversible.

Although considerable work has been done investigating the properties of arrays of magnetic elements, there have been few investigations on the reverse geometry, i.e., an array of nonmagnetic regions defined within a magnetic thin film. The 10 Hz BH loops, 10–500 MHz permeability spectra, and domain patterns of homogeneous, single layer 100 nm radio frequency (rf) sputtered Ni81Fe19 thin films with arrays of 23-, 50-, and 100-μm-diam holes defined by laser ablation were measured. The holes were defined in a grid along the hard and easy axes of the sample. Letting (x,y) represent, respectively, the hole spacing parallel to the easy and hard axes, the point to point spacing of the ablated circular regions was varied from (5, 2 mm) to (0.1, 0.1 mm).

We have measured the rate of thermally assisted magnetization reversal of submicron-sized magnetic thin films. For fields H just less than the zero-temperature switching field H(C), the probability of reversal, P(exp)(s)(t), increases for short times t, achieves a maximum value, and then decreases exponentially. Micromagnetic simulations exhibit the same behavior and show that the reversal proceeds through the annihilation of two domain walls that move from opposite sides of the sample. The behavior of P(exp)(s)(t) can be understood through a simple "energy-ladder" model of thermal activation.

Ferrite MiG heads intended for narrow track (≲10 μm) digital recording were recently investigated in the critical pole‐tip region at the air‐bearing‐surface using micro‐ellipsometry, Kerr microscopy, and electron back‐scatter diffraction from individual grains,1 and using magnetic force microscopy to detect air‐gap remanent fields.2 Comparison of these direct observations with readback‐after‐write waveforms from written test tracks, and consideration of granularity influences on bulk permeability and domain size, indicate that waveform instability and asymmetry from polycrystalline ferrite (PCF) heads would be diminished by suitable size and orientation of the grains.1 The use of single‐crystal ferrite3 (SCF) for advanced laser enhanced etch definition3 of narrow pole MiGs can avoid this type of distortion. However, secondary signals4 often appear as weak pulses separated in time from the main gap pulse. We have associated this effect with a zig‐zag shaped wall seen nucleated and propagated from the pole ...

Laminated Permalloy, with edge‐curling walls replacing closure domains, has been proposed to increase permeability and reduce wall noise in recording. However, in structures meeting the criteria for Slonczewski’s ‘‘easy‐axis’’ state, normal walls often coexist with edge‐curling walls. We have used our laser magneto‐optic microscope to study inductive‐head‐yoke shaped elements of two and four Permalloy layers separated by nonmagnetic, metallic spacers. In the four‐magnetic‐layer sample a state with a single wall, terminating at the edge‐curling regions and lying along the easy‐axis direction, is often observed on the top and bottom layers. Some elements may be driven into an easy‐axis state with no observed domain walls. The two‐magnetic‐layer sample also exhibited simultaneous one‐wall structures on the top and bottom layers. The other stable configuration was a no‐wall state on the top layer and a two‐wall (three‐domain) state on the lower layer. These ‘‘coupled’’ states were exceptionally stable in both...

Understanding the magnetic switching behavior in micron and submicron scale specimens is important for a number of applications. In this study, magnetic-tunnel junctions of various sizes and shapes were fabricated and their switching behavior was studied in detail. Using exchange bias to offset the magnetic response of one electrode, the response of the other (free) electrode was determined from measurements of junction resistance. Switching threshold curves were measured by sweeping magnetic fields in both easy and hard direction. Single domain like switching was observed in some of our smallest submicron junctions. The observed behavior was compared with predictions from the Stoner–Wohlfarth rotational model and from numerical calculations.