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The magnetoquenched superconducting valve is a nonvolatile switch consisting of a ferromagnetic film that spans a superconducting strip. A device state is dictated by the magnetization orientation of the ferromagnetic element and the corresponding magnetic fringe fields at its edge which control the critical current in the underlying superconductor. A Pb-based device has been fabricated with a “write wire” inductively coupled to the ferromagnetic layer as an integrated control line. A current pulse through the control line produces a small local magnetic field that is larger than the coercivity Hc of the ferromagnet and which orients the magnetization, thus switching the device state. A comparison of device switching is made between use of a current pulse through the control line and use of an external magnetic field pulse. There is good agreement between the two methods, and device switching is demonstrated with fields as small as 20 Oe. In a further effort to develop a practical device, the quenchvalve ...

In a simple bilayer geometry, a thin, microstructured ferromagnetic film spans a superconducting strip. Locally strong magnetic fringe fields at the edge of the ferromagnet quench the superconductivity, creating a weak link. The strength of the weak link can be varied between on and off by controlling the orientation of the in-plane magnetization of the ferromagnet. The observation of Shapiro steps demonstrates the ac Josephson effect in the “quenched” state. In this switchable Josephson junction, energy is required only to change states, which are thereafter maintained in thermodynamic equilibrium.

In this paper, we study the magnetization reversal process of single-domain Stoner-Wohlfarth particles subject to circularly polarized fields and short pulses using analytical and numerical models. We investigate the effect of short unipolar, bipolar field, and circularly polarized field pulses, which are applied perpendicular to the uniaxial magnetocrystalline anisotropy axis, on the magnetization switching dynamics.

Using the micromagnetics package MAGPAR, we study the ground states of NiFe nanorings with sub-100-nm lateral dimensions, in zero external field. We solve the Landau-Lifschitz-Gilbert equation for three different initial magnetizations (in plane, out of plane, and vortex) to obtain the lowest energy state. Plotting the total energy as a function of thickness, along with its corresponding magnetostatic and exchange energies, we are able to identify various phase transitions and derive phase diagrams as a function of thickness and outer radius, normalized to the exchange length, for rings with different inner to outer radius ratios. We discuss the results in terms of shape anisotropy and its effect on the magnetostatic and exchange energies. We also compare the results of our numerical method to the phase diagram of a nanodot and the phase diagrams of rings obtained by analytical models. Finally, we present a new ground state configuration, the helix, found along the boundary between the vortex and out of plane phases, where the magnetization is vortex like, but with moments canted along the z direction

High-frequency characterization of perpendicular media is demonstrated on disk with a novel nondestructive local probe. The probe is micron-scale and has high bandwidth. We measure the permeability of the soft underlayer (SUL) and observe its ferromagnetic resonance (FMR). We extract physical parameters that cannot typically be measured on disk, such as FMR frequency, anisotropy field, HK, saturation magnetization, MS, and damping alpha in good agreement with independent measurements. Media of arbitrary form factor can be characterized and any location can be probed with spatial resolution that scales with the size of the probe "tip."

We have investigated the pinning and magnetic-field dependence of the mixed-state Hall conductivity ${\ensuremath{\sigma}}_{\mathrm{xy}}$ in thin films of two superconductors, amorphous ${\mathrm{Mo}}_{3}\mathrm{Si}$ and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}.$ The effects of pinning were varied by measuring at different current densities $j$. In both superconductors, ${\ensuremath{\sigma}}_{\mathrm{xy}}$ is independent of $j$ (and, therefore, pinning) in support of theory. The magnetic-field dependence of ${\ensuremath{\sigma}}_{\mathrm{xy}}$ at large and small magnetic fields strongly supports calculations based on time-dependent Ginzburg-Landau theory. In addition, we find sample inhomogeneities can cause a fictitious current dependence of ${\ensuremath{\sigma}}_{\mathrm{xy}}.$ We argue this explains the conflicting reports of the pinning and magnetic-field dependence of ${\ensuremath{\sigma}}_{\mathrm{xy}}$ found in the literature.

We measured the longitudinal and Hall resistive transitions of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ films in applied fields up to 9 T. The longitudinal fluctuation conductivities obey the scaling behavior of the three-dimensional Hartree fluctuation theory of Ullah and Dorsey. The fluctuation Hall conductivities do not scale. Our analysis shows that there are substantial contributions from the Maki-Thompson (MT) process as well as the Aslamazov-Larkin (AL) one. Using an ansatz suggested by the microscopic theory of Fukuyama et al., we separated the AL term from the total fluctuation conductivity. The AL Hall conductivity follows a scaling law, and the AL and MT terms have opposite sign. The sign of the AL term is consistent with the sign change in the flux-flow regime, as predicted by theory. At low fields and temperatures just above ${\mathrm{T}}_{\mathrm{c}}$(H), the AL term dominates the MT term, therefore causing the total Hall-conductivity sign change.

At 1 Tbit/in 2 areal density magnetic recording dimensions, reliable magnetic field metrology does not exist. One technique to map the spatial profile of the magnetic field of a write head is to use a contact read/write tester. A magnetic recording head is brought into contact with a Hall sensor, and is subsequently scanned with nm resolution. For a 300 nm track width longitudinal recording head, the magnetic field of the head was mapped. Measurements include the down track field gradient and cross-track field profile and the current-field transfer curve. These results suggest this technique offers a viable write field metrology.

We have studied the role of pinning in the mixed-state thermomagnetic transport properties of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. We demonstrate the pinning independence of the transport entropy ${S}_{\ensuremath{\varphi}}$, and its consequent scaling within an anisotropic mass model. Due to the anisotropy of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ the extrinsic pinning strength effectively decreases as we rotate the magnetic field into the $\mathrm{ab}$ plane. The Nernst ($\frac{{E}_{y}}{{\ensuremath{\nabla}}_{x}T}$) and Seebeck ($\frac{{E}_{x}}{{\ensuremath{\nabla}}_{x}T}$) effects are enhanced as we reduce the effective pinning, yet the transport entropy ${S}_{\ensuremath{\varphi}}\ensuremath{\propto}\frac{(\frac{{E}_{y}}{{\ensuremath{\nabla}}_{x}T})}{{\ensuremath{\rho}}_{\mathrm{xx}}}$, the ratio of the Nernst and Seebeck signals, and the ratio of Seebeck and longitudinal resistivity ${\ensuremath{\rho}}_{\mathrm{xx}}$ are unchanged, similar to the pinning independence observed for the Hall conductivity ${\ensuremath{\sigma}}_{\mathrm{xy}}$. These results can be explained within a simple phenomenological model of vortex dynamics.

A focused ion beam (FIB) is used to fabricate single-pole perpendicular writers by micro-machining longitudinal (ring) heads at the HGA. The heads are designed for media characterization, and a comparison is made between the performance of the FIBed and ring heads on perpendicular media. The FIBed heads write much more effectively, approximately 7 dB gain in the signal-to-noise ratio (SNR), and efficiently than their ring-head counterparts. In addition, the FIBed heads generate very reliable (small scatter) thermal decay rates for the evaluated disks whereas the unFIBed ring heads cannot, all of which make them more suitable for characterization of perpendicular media. Our results further demonstrate the value and versatility of FIB-machining as a research tool to design and fabricate novel recording heads with robust performance.

Ga implantation during focused-ion-beam (FIB) milling of metallic magnetic materials for magnetic recording heads was examined using Auger electron spectroscopy (AES). The Ga concentration profiles were characterized in two directions: in the depth direction (parallel to the incident beam) and in the lateral direction (perpendicular to the incident beam). The sample for AES analyses in the depth direction was prepared by FIB etching of a plated Ni78.5Fe21.5 film surface. The AES depth profile showed a maximum implanted Ga concentration of ∼20 at. % at a distance of ∼15 nm, and the tail of the implantation profile reached more than 100 nm. The sample for the lateral direction analyses was prepared by cutting a cross-sectional specimen out of the air-bearing surface of a working recording head. The lateral profile showed a maximum implanted Ga concentration of 47 at. % at the surface, with a lateral implantation depth of ∼10 nm. These results were compared with results predicted by a Monte Carlo implantatio...

The effect of magnetic transition curvature has been studied for a perpendicular recording system. The curvature of the medium transitions is varied in a controlled manner by altering the write poles using a focused ion beam. Tracks are written using these write heads and are characterized with a magnetic force microscope, which demonstrates the ability to manipulate transition shape and even correct the curvature. The effect of transition curvature on the perpendicular recording performance is characterized by spinstand measurements and bit error rate simulations. These results show a significant performance loss, demonstrating that transition curvature degrades perpendicular recording performance.

A novel focused-ion-beam (FIB) head trimming technique is described. As compared to the conventional approach of a symmetric trim, an asymmetric process, whereby only one side of a write pole is FIB milled to achieve the target width, is demonstrated to be robust and advantageous. We use this technique for both longitudinal and perpendicular HGA-level head trimming, demonstrating excellent recording performance out to areal densities of more than 100 Gb/in/sup 2/.

We report the angular magnetic-field dependence of the critical current density in epitaxial thin films of Nd 1.85 Ce 0.15 CuO 4-δ in the temperature range 1.4 K to 14 K. At low temperatures, the critical current anisotropy is well described by the 2D model of Josephson-coupled layers. Above 10 K we observe deviations from the 2D behavior which may be attributed to the temperature dependence of the coherence lenght and the influence of the anisotropy of the upper critical field. The field dependence of the critical current density for the field orientation parallel to the CuO 2 planes is consistent with the dimensionality indicated by the angular dependence.

Small angle neutron scattering has been used to investigate the vortex scattering in single crystal niobium. In the mixed state (${\mathit{H}}_{\mathit{c}1}$H${\mathit{H}}_{\mathit{c}2}$) a sixfold hexagonal pattern of peaks is observed at all temperatures. Below the irreversibility line these peaks are resolution limited, while above it the width in the transverse direction increases with temperature due to the vortex dynamics. Close to ${\mathit{H}}_{\mathit{c}2}$ the radial widths of the peaks also broaden. However, the basic hexagonal pattern of peaks is maintained throughout, indicating that a correlated flux fluid exists in the reversible regime.

We have performed longitudinal and perpendicular magnetic recording measurements using a contact write/read tester, which scans a magnetic recording head in contact with the recording media. Our tester has a demonstrated positioning resolution of

A magnetoquenched superconductor device or cell includes a superconductor element disposed on a substrate and a bilayer ferromagnetic film which provides uniaxial switching. The bilayer film is formed by a first ferromagnetic film disposed on and isolated from the superconductor element; and a second ferromagnetic film disposed on and separated from the first ferromagnetic film. The first and second films are magnetically coupled and have magnetizations which are switchable between a parallel relation wherein the films produce additive magnetic fringe fields that form a weak link in a portion of the superconductor element and an antiparallel relation wherein one of the films substantially absorbs the fringe field of the other film and the resultant fringe fields in the vicinity of the superconductor are such that a weak link is not formed in the superconductor. A number of two dimensional memory arrays are provided which use rows and columns of the devices. Switching of the devices is controlled by respective write (read/write) lines or bias lines.

Neutron scattering has been used to investigate the magnetic ordering of the rare-earth ions in the ErBa{sub 2}Cu{sub 4}O{sub 8} and DyBa{sub 2}Cu{sub 4}O{sub 8} materials. For the Er system a simple three-dimensional (3D) antiferromagnetic structure is observed, in which the magnetic unit cell is twice the chemical unit cell along the {ital a} axis, with a Neel temperature {ital T}{sub {ital N}}{approx}0.49 K. In the vicinity of the Neel temperature, however, scattering characteristic of two-dimensional behavior, indicative of the strong anisotropy of the magnetic interactions, is observed. The magnetic anisotropy arises naturally from the crystal structure, as the {ital c}-axis spacing of the magnetic ions is {similar to}3 times the {ital a}-{ital b} spacing. 2D behavior is also observed in the Dy material near its Neel temperature of {similar to}0.9 K. However, the scattering in the Dy system does not cross over to the expected 3D Bragg peaks at low temperatures, but rather the 2D line shape persists to the lowest temperatures measured. We explain this result as originating from a geometric cancellation of interactions between {ital c}-axis layers for the specific Dy {ital a}-{ital b} spin configuration, which together with the weak intrinsic {ital c}-axis interaction renders themore » {ital net} interaction along the {ital c} axis much smaller than all other known 2D magnets.'' Hence the 2D and 3D ordering temperatures appear to be quite different for the Dy material. We anticipate that a similar cancellation of interactions is likely to occur in other {ital R}Ba{sub 2}Cu{sub 4}O{sub 8} ({ital R} being a rare-earth element) systems.« less

A spin polarized current has been injected into high Tc superconductors resulting in a significant reduction in the superconductor’s critical current. Such injection may serve as the basis of a new class of superconducting devices for control, switching and amplification. Preliminary results using both Permalloy and CMR materials as injectors are presented.

A superconducting switch has been developed in a simple bilayer cross strip geometry using the magnetic fringe field of a ferromagnetic film to control the critical current in an underlying superconducting bridge. The magnetization of the ferromagnet is rotated in the plane of the film to vary the magnitude of the fringe field locally applied to the superconductor from negligible to substantial values. In the latter case, the magnetization is oriented such that the magnetic poles are along the edges of the cross strip directly above the superconductor. The large fringe field near the poles suppresses superconductivity over a length of order microns, giving rise to superconducting weak link behavior. A large modulation of the critical current is observed. The effect is demonstrated in the low Tc superconductors Pb (Tc=7.3 K) and Sn (Tc=3.9 K). Fabrication of the device involves minimal processing. Applications as a high speed switch, amplifier, nonvolatile storage cell, and controllable weak link are possible.

A superconducting switch has been developed using the magnetic fringe field of a ferromagnetic film to control the critical current in an underlying superconducting Sn film. The magnetization of the ferromagnet is rotated in the plane of the film to vary the magnitude of the fringe field applied locally to the superconductor from negligible to substantial values. A large suppression of the critical current is observed. Applications as an amplifier and a nonvolatile storage cell are possible, and a device based on high Tc materials has promise.

In this paper, we report a detailed experimental study on the effect of the transition curvature on the read-back signal and magnetic recording performance.

Neutron scattering and specific heat measurements have been carried out on a series of NdBa2Cu3O6+x powder samples with varying oxygen concentrations (x=0.94, 0.78, 0.45, 0.3, 0.13) in order to study the effects of oxygen on the magnetic order of Nd. For our highest oxygenated superconducting NdBa2Cu3O6.94 (Tc≂92 K), three‐dimensional (3D) long range order develops below TN≂0.53 K, with a spin configuration which is antiferromagnetic along all three crystallographic axes. For a small reduction of oxygen to x=0.78, we observe drastic effects on the Nd order; 3D order is inhibited and only short range 2D correlations are found at low temperature. However, the 2D correlations develop at a much higher temperature, near 1.5 K. At (nonsuperconducting) x=0.45, the 3D magnetic order is better developed at low temperature, yet long range order still does not occur. For x=0.3, 3D long range magnetic order of the Nd ions is reestablished, developing below TN≂1.5 K, three times that of the fully oxygenated material. ...

Neutron diffraction has been used to study the magnetic fluctuations and long range order of the Dy ions in single crystals of superconducting DyBa2Cu3O7. The temperature dependence of the rod of scattering, characteristic of 2D behavior, has been measured above and below the 3D Neel temperature (TN ≂ 0.9 K). This rod intensity is observed to increase as the temperature decreases until TN is reached, and then the intensity decreases rapidly below TN. The 2D magnetic correlation length, which is obtained from measurements of the width of the rod, grows continuously with decreasing temperature, then reaches a resolution‐limited maximum at the Neel temperature when long range magnetic order sets in. At low T, two separate types of simple 3D antiferromagnetic structures are found, one characterized by a wave vector of (1/2 1/2 0), and the other by (1/2 1/2 1/2). We believe the two types of order occur because the (dipolar) energies for these two configurations are nearly identical. This behavior is analogous ...

Neutron diffraction has been used to study the magnetic order of the Er ions in superconducting ErBa2Cu3O7. Above the three‐dimensional (3D) Neel temperature (TN=0.618 K) a rod of scattering characteristic of two‐dimensional (2D) behavior is unambiguously observed, showing that the magnetic interactions of the rare earth ions are highly anisotropic, while there are no significant correlations observed between the sheets of Er spins. The system orders two dimensionally, and as a necessary consequence 3D order also sets in at the same temperature. The order parameter is found to obey the exact Onsager solution for a S= (1)/(2) , 2D Ising antiferromagnet. At low T, two separate types of simple 3D antiferromagnetic structures are found, one characterized by a wave vector of ( (1)/(2) , 0,0), and the other by ( (1)/(2) ,0, (1)/(2) ).

Polarized and unpolarized neutron scattering techniques along with x‐ray diffraction have been used to study the magnetic and structural properties of a single crystal of Nd2CuO4. Long‐range magnetic order of the Cu moments develops at TN=245 K, with a simple antiferromagnetic configuration of spins as found in La2NiO4, while the spin directions may be either collinear or noncollinear. Additional abrupt transitions are observed at 75 and 30 K, in which spin reorientations take place. Bragg peaks associated with the crystal structure are found at the same positions as the magnetic Bragg peaks, and indicate that a small distortion of the basic tetragonal structure has occurred above 300 K. At low temperatures the Nd moments also order antiferromagnetically (TN=1.5 K), while an additional transition of a continuous nature is observed at 150 mK.

We calculate the mixed-state longitudinal and Hall resistivity of superconductors based on the perturbation approach of Schmid and Larkin with a frictional force of the form proposed by Vinen and Warren under the influence of randomly distributed weak point pinning centers. The longitudinal resistivity has the Bardeen-Stephen behavior in the flux-flow region. In the weak collective pinning case, for either sample thickness much smaller or much greater than the penetration depth, scaling {rho}{sub {ital x}{ital y}}{proportional_to}{rho}{sub {ital x}{ital x}}{sup 2} holds, but no sign reversal in {rho}{sub {ital x}{ital y}} is predicted. The Hall conductivity is {ital independent} of pinning to the first nonvanishing order of the perturbation calculation.

We have studied the mixed-state Hall effect of the high-{ital T}{sub {ital c}} superconductors Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4} (NCCO), Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} (Tl2212), and YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO), and the isotropic low-{ital T}{sub {ital c}} superconductor amorphous Mo{sub 3}Si ({ital a}-Mo{sub 3}Si). We demonstrate the pinning independence of the Hall conductivity {sigma}{sub {ital xy}} and its consequent scaling in terms of the anisotropy of NCCO, Tl2212, and YBCO. In YBCO and {ital a}-Mo{sub 3}Si the Hall angle is enhanced as we reduce the effective pinning, yet {sigma}{sub {ital xy}} is unchanged. For all of these materials there is a vortex contribution {sigma}{sub {ital xy}}{similar_to}1/{ital H} at low fields while at high fields {sigma}{sub {ital xy}}{similar_to}{ital H}. These results provide evidence that beneath the effects of pinning and anisotropy a relatively simple and universal behavior of the mixed-state Hall effect exists.

We observe a sign reversal in the Hall resistivity ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{y}}$ of the conventional superconductor amorphous (a) ${\mathrm{Mo}}_{3}$Si. In the Ohmic regime, ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{y}}$ is qualitatively similar to that observed in the high-${\mathit{T}}_{\mathit{c}}$ superconductors. It changes sign near ${\mathit{T}}_{\mathit{c}}$, and the sign change persists until both ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{y}}$ and ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{x}}$ become immeasurably small at T\ensuremath{\sim}0.8${\mathit{T}}_{\mathit{c}}$(H). At current densities above the depinning current density, the Hall anomaly persists at low temperatures T\ensuremath{\sim}0.2${\mathit{T}}_{\mathit{c}}$(H). This is contrary to a theory by Ferrell which attributes the anomaly to the backflow of thermally excited quasiparticles. In addition a model proposed by Harris, Ong, and Yan explains the anomaly as an effect arising from the layered nature of the high-${\mathit{T}}_{\mathit{c}}$ cuprates. This model, however, does not explain the anomaly in a-${\mathrm{Mo}}_{3}$Si which is an isotropic unlayered material.

We demonstrate electrical control of the ferromagnetic resonance (FMR) in multiferroic nanostructures. A series of heteroepitaxial BiFeO3–NiFe2O4 nanocomposites of varying thickness are characterized using a microwave probe with magnetic and electric sensitivity. We apply an electric field to a sample and observe voltage-driven shifts in the FMR frequency, reflecting a change in magnetic anisotropy. The voltage dependence of the FMR linewidths is even more pronounced, indicating the electric polarization can induce relatively large magnetic nonuniformity in the material. These characteristics may lead to a class of rf filters where both frequency and bandwidth are electrically tunable.

The effect of holmium (Ho) doping in films of Ni0.8Fe0.2 (NiFe) is investigated. The ferromagnetic resonance (FMR) is measured, and the linewidths (Δf) are fit to a model that incorporates broadening from inhomogeneities and intrinsic damping (αLLG). The data reveal a drastic increase in Δf for increasing Ho concentration in the NiFe films, while the fits of this data to the model indicate this is largely due to an increase in αLLG. At Ho concentrations of 10% and greater, the saturation magnetization is reduced by more than 60% while the FMR is no longer observable, which is likely due to the signal falling below the noise floor from further linewidth broadening and decreased magnetization. In general, the saturation magnetization decreases continuously with Ho concentration, presumably due to local ferrimagnetic order induced by the Ho moments. However, the coercivity is essentially unchanged by the doping, while the magnetic anisotropy HK is unchanged out to 2% Ho, beyond which there is an abrupt step-...

The electromagnetic eigenmodes of and light transmission through a C-aperture to the far field, and to a storage medium, have been studied based on the full vectorial finite difference method. It is found that the cutoff wavelength of C-aperture waveguides in a gold film is much longer than that in a perfect electric conductor, and the fundamental mode is confined in the gap and polarized with the electric field along the gap. The light transmission resonance through C-apertures to far field and to a storage medium occurs at wavelengths below the waveguide cutoff wavelength. Measurements on the fabricated C-apertures confirm the mode confinement and transmission resonance.

A new fabrication technique for a near-field microwave probe that greatly improves the sensitivity is presented. This design and fabrication has enabled quantitative measurements (with a probe as small as micron scale) that were not previously possible, such as ferromagnetic resonance in media with relatively small permeability, large damping, and high anisotropy (HK). The new method uses a focused ion beam to deposit and lithographically define a SiO2 or Pt buffer between the inner and outer conductors of a microcoax. A thin Cu film is then deposited, after which the Cu is etched in the field, preserving the Cu over the buffer to complete a microbridge. The buffer layer results in surface smoothness on the order of 10nm at the top and bottom (Cu∕buffer) surfaces of the Cu.

A near-field microwave technique is used to locally probe ferromagnetic resonance (FMR) in a series of CoCrPt alloys with varying perpendicular anisotropy (5kOe

A local ferromagnetic resonance (FMR) technique using a thin-film microwave probe fabricated on coaxial transmission line is presented. Some key features of this probe are its micron-scale size coupled with broadband FMR characterization and mobility: a small area of any location on a magnetic medium can be probed. Permeability of Permalloy (Py) films has been measured, where the authors extract physical parameters, such as FMR frequency, anisotropy field, damping, and spin wave exchange constant, in excellent agreement with independent measurements. Samples of arbitrary shape and size can be measured with a spatial resolution that scales with the size of the probe “tip.”

We report reliable, reversible trapping of live magnetotactic bacteria, Magnetospirillum magneticum AMB-1, using a commercial magnetic recording head. The magnetic recording head was modified to generate spatially localized magnetic fields of high magnitude and gradient, and effectively trapped AMB-1, which have a magnetic moment per cell one order of magnitude smaller than cells previously trapped using Amperian fields. We also describe selective trapping of magnetic wild-type AMB-1 with discrimination against a nonmagnetic mutant strain of the same bacteria. Finally, we discuss the prospects of using the built-in spin valve sensor on a recording head for integrated detection of trapped bacteria. Using the chip-based methods we describe, it may be possible to capture, sort, and count magnetic bacteria quickly from samples taken directly from their natural aquatic habitat. More generally, the method may be applicable to the manipulation, spatial control, and integrated detection of magnetically labeled ce...

A patterned InAs Hall cross was used to quantitatively image the magnetic field produced by magnetic recording write head as a function of current, obtaining field-current transfer functions for both poles. Using the same instrument, the magnetic field of current-carrying wires as small as 95 nm was measured using a magnetic recording read head in near-contact with the wire surface. The measured magnetic fields from the wire agree closely with the Biot–Savart law predictions for the field from a rectangular current carrying wire over a range of sub-500 nm wire widths. However, for narrow wires, a broadening of the wire field is observed. This broadening is likely due to the finite magnetic response width of the read head. These measurements demonstrate the potential of near-contact recording metrology for magnetic recording heads targeting 1Tbit∕in2 areal-density information storage.

We measured resistive transitions of YBCO films in applied fields up to 9T. The longitudinal fluctuation conductivities obey a scaling law. After separating the AL term from the total fluctuation Hall conductivity, the AL Hall conductivity follows the same scaling law, while the MT Hall conductivity does not scale. In addition, the AL and MT terms have opposite sign. At low fields and temperature close toT c (H), the AL term dominates the MT term, therefore causing the total Hall conductivity sign change.

A focused ion beam (FIB) has been used to trim write heads for perpendicular magnetic recording using untrimmed HGA-level longitudinal heads. The ion-beam imaging of the write head during FIB processing was minimized to limit exposure of the active magnetic material at the ABS to a 30 keV Ga+ ion dose of less than 1014 Ga+/cm2 (≈10−13 C/μm2) (the GMR reader was never exposed), which is significantly below levels where magnetic properties have been observed to degrade [W. M. Kaminsky et al., Appl. Phys. Lett. 78, 1589 (2001)]. The corresponding recording characteristics and spatial profiles of written tracks have been measured on a spin stand and a magnetic force microscope (MFM). Recording performance, such as SNR, and pulse shape of transitions, for example, as a function of head design and FIB processing is discussed, which compares very favorably to the performance of untrimmed heads. The MFM images reveal curvature in the magnetic transitions (transition smile) when writing with a single-pole writer w...

The effect of stray fields from the recording layer on the reading and writing process has been studied for a perpendicular recording system. The system consists of a single pole writer with a wide return pole, a conventional spin-valve reader and a double layer recording medium. A writer- and reader-induced asymmetry is observed in the recording process for a dc erased background. The asymmetry is interpreted as stray fields of the dc background giving rise to reader saturation and an offset in the current driven inductive write field.

We have observed two-dimensional magnetic behavior associated with the magnetic ordering of Dy in DyBa 2 Cu 3 O 7 , and have studied the 2D magnetic correlations of Dy in DyBa 2 Cu 3 O 7 as well as Er in ErBa 2 Cu 3 O 7 . The temperature dependence of the rod of scattering, characteristic of 2D behavior, has been measured above and below the Neel temperature ( T N ⋍0.9 K for Dy, T N ⋍0.62 K for Er). For both systems the rod intensity, which is proportional to the magnetic susceptibility, is observed to increase as the temperature is decreased until T N is reached. Below T N the intensity decreases rapidly. The 2D magnetic correlation length is seen to grow continuously with decreasing temperature and then peak at the respective Neel temperatures when long range magnetic order sets in.

Neutron and X-ray diffraction have been used to study the magnetic and structural properties of single crystal Nd2CuO4. Long range magnetic order of the Cu moments develops at TN=245 K, with a noncollinear antiferromagnetic arrangement of spins. Additional abrupt transitions are observed at 75 K and 30 K, in which a spin reorientation takes place. Bragg peaks associated with the crystal structure are found at the same positions as the magnetic Bragg peaks, and indicate that a distortion of the basic tetragonal structure has occurred above 300 K.

The magnetic order of Pr in nonsuperconducting PrBa{sub 2}Cu{sub 3}O{sub 7} has been studied by specific-heat, susceptibility, and neutron-diffraction measurements. The basic ordering consists of a simple antiferromagnetic arrangement, with a saturated moment of 0.24{mu}{sub {ital B}} and a Neel temperature {ital T}{sub {ital N}} of {similar to}17 K, which is two orders of magnitude higher than expected from either dipolar or Rudeman-Kittel-Kasuya-Yosida interactions alone. The small moment, along with the large value of the low-temperature electronic specific-heat coefficient {gamma} of 196 mJ/mol K{sup 2}, suggests that there is substantial {ital f}-electron character at the Fermi level.

Neutron scattering has been used to study the magnetic order of the Er ions in superconducting ${\mathrm{ErBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. Above the 3D N\'eel temperature (${\mathrm{T}}_{\mathrm{N}}$=0.618 K) a rod of scattering characteristic of 2D behavior is unambiguously observed, showing that the magnetic interactions of the rare-earth ions are highly anisotropic; below ${\mathrm{T}}_{\mathrm{N}}$ the order parameter follows the exact Onsager solution for a 2D Ising antiferromagnet. At low T, two separate types of simple 3D antiferromagnetic structures are found, one characterized by a wave vector of (1/2,0,0), and the other by (1/2,0,1/2).