Stephen M. Wu

Reversible electric control of exchange bias in a multiferroic field-effect device

Electric-field control of magnetization has many potential applications in magnetic memory storage, sensors and spintronics. One approach to obtain this control is through multiferroic materials. Instead of using direct coupling between ferroelectric and ferromagnetic order parameters in a single-phase multiferroic material, which only shows a weak magnetoelectric effect, a unique method using indirect coupling through an intermediate antiferromagnetic order parameter can be used. In this article, we demonstrate electrical control of exchange bias using a field-effect device employing multiferroic (ferroelectric/antiferromagnetic) BiFeO(3) as the dielectric and ferromagnetic La(0.7)Sr(0.3)MnO(3) as the conducting channel; we can reversibly switch between two distinct exchange-bias states by switching the ferroelectric polarization of BiFeO(3). This is an important step towards controlling magnetization with electric fields, which may enable a new class of electrically controllable spintronic devices and provide a new basis for producing electrically controllable spin-polarized currents.

Series array of incommensurate superconducting quantum interference devices from YBa2Cu3O7-δ ion damage Josephson junctions

We have fabricated a series array of 280 superconducting quantum interference devices (SQUIDs) using YBa2Cu3O7−δ thin film ion damage Josephson junctions. The SQUID loop areas were tapered exponentially so that the response of the current-biased array to magnetic field is a single voltage spike at zero field. We fitted the current-voltage characteristics of the array to a model in which we summed the voltages across the SQUIDs assuming a resistively shunted junction model with a normal distribution of SQUID critical currents. At 75 K the standard deviation of these critical currents was 12%.

Very Large Scale Integration of Nano-Patterned YBa2Cu3O7-delta Josephson Junctions in a Two-Dimensional Array

Very large scale integration of Josephson junctions in a two-dimensional series-parallel array has been achieved by ion irradiating a YBa(2)Cu(3)O(7-delta) film through slits in a nanofabricated mask created with electron beam lithography and reactive ion etching. The mask consisted of 15820 high aspect ratio (20:1), 35 nm wide slits that restricted the irradiation in the film below to form Josephson junctions. Characterizing each parallel segment k, containing 28 junctions, with a single critical current I(ck) we found a standard deviation in I(ck) of about 16%.

Spin waves in micro-structured yttrium iron garnet nanometer-thick films

We investigated the spin-wave propagation in a micro-structured yttrium iron garnet waveguide of 40 nm thickness. Utilizing spatially-resolved Brillouin light scattering microscopy, an exponential decay of the spin-wave amplitude of (10.06 ± 0.83) μm was observed. This leads to an estimated Gilbert damping constant of α=(8.79±0.73)×10−4, which is larger than damping values obtained through ferromagnetic resonance measurements in unstructured films. The theoretically calculated spatial interference of waveguide modes was compared to the spin-wave pattern observed experimentally by means of Brillouin light scattering spectroscopy.

Comparison of measurements and simulations of series-parallel incommensurate area superconducting quantum interference device arrays fabricated from YBa2Cu3O7−δ ion damage Josephson junctions

We have fabricated series-parallel (two-dimensional) arrays of incommensurate superconducting quantum interference devices (SQUIDs) using YBa2Cu3O7−δ thin film ion damage Josephson junctions. The arrays initially consisted of a grid of Josephson junctions with 28 junctions in parallel and 565 junctions in series, for a total of 15 255 SQUIDs. The 28 junctions in the parallel direction were sequentially decreased by removing them with photolithography and ion milling to allow comparisons of voltage–magnetic field (V–B) characteristics for different parallel dimensions and area distributions. Comparisons of measurements for these different configurations reveal that the maximum voltage modulation with magnetic field is significantly reduced by both the self inductances of the SQUIDs and the mutual inductances between them. Based on these results, we develop a computer simulation model from first principles which simultaneously solves the differential equations of the junctions in the array while considering...

Unambiguous separation of the inverse spin Hall and anomalous Nernst effects within a ferromagnetic metal using the spin Seebeck effect

The longitudinal spin Seebeck effect is measured on the ferromagnetic insulator Fe

Large voltage modulation in magnetic field sensors from two-dimensional arrays of Y-Ba-Cu-O nano Josephson junctions

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Simulation of Series Arrays of Superconducting Quantum Interference Devices

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Spin Seebeck devices using local on-chip heating

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Magnetic effects in sulfur-decorated graphene

with the ferromagnetic metal Co