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.

A bilayer ferromagnetic film, consisting of a soft- and hard-magnetic layer separated by a nonmagnetic layer, has been incorporated into a magnetoquenched superconducting valve, making it possible to control the valve with uniaxial magnetic fields. Device switching is demonstrated with fields as small as 20 Oe. The switch is inherently nonvolatile, has linear output characteristics, and requires a single inductively coupled “write wire” for integrated operation, all of which make it promising for application as a storage cell in a high-density superconducting random-access memory.

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.

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.

Effects of intermediate layers on magnetic properties and read/write performance in CoCrPt perpendicular recording media with an FeHfN soft magnetic underlayer J. Appl. Phys. 93, 7747 (2003); 10.1063/1.1540154Micromagnetic study of effect of media intergranular exchange interaction in perpendicular recording