We present experimental studies of high quality underdamped 0, pi, and 0-pi ferromagnetic Josephson tunnel junctions of intermediate length L (lambda_J < L < 5 lambda_J, where lambda_J is the Josephson penetration depth). The junctions are fabricated
as Nb/Al_2O_3/Cu_40Ni_60/Nb Superconductor-Insulator-Ferromagnet-Superconductor heterostructures. Using microwave spectroscopy, we have investigated the eigenfrequencies of 0, pi, and 0-pi Josephson junctions in the temperature range 1.9K...320mK. Harmonic, subharmonic and superharmonic pumping is observed in experiment, and the experimental data are compared with numerical simulations. Escape rate measurements without applied microwaves at temperatures T down to 20mK show that the width of the switching current histogram decreases with temperature and saturates below T=150mK. We analyze our data in the framework of the short junction model. The differences between experimental data and theoretical predictions are discussed.
The dependence of the critical current density j_c on the ferromagnetic interlayer thickness d_F was determined for Nb/Al_2O_3/Cu/Ni/Nb Josephson tunnel junctions with ferromagnetic Ni interlayer from very thin film thicknesses (sim 1 nm) upwards and
classified into F-layer thickness regimes showing a dead magnetic layer, exchange, exchange + anisotropy and total suppression of j_c. The Josephson coupling changes from 0 to pi as function of d_F, and -very close to the crossover thickness- as function of temperature. The strong suppression of the supercurrent in comparison to non-magnetic Nb/Al_2O_3/Cu/Nb junctions indicated that the insertion of a F-layer leads to additional interface scattering. The transport inside the dead magnetic layer was in dirty limit. For the magnetically active regime fitting with both the clean and the dirty limit theory were carried out, indicating dirty limit condition, too. The results were discussed in the framework of literature
We present experimental studies of static and dynamic properties of 0, pi and 0-pi superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson junctions of small and intermediate length. In the underdamped limit these junctions exhibit a ric
h dynamical behavior such as resonant steps on the current-voltage characteristics. Varying the experimental conditions, zero field steps, Fiske steps and Shapiro steps are observed with a high resolution. A strong signature of the 0-pi Josephson junction is demonstrated by measuring the critical current as a function of two components (B_x, B_y) of an in-plane magnetic field. The experimental observation of a half-integer zero field step in 0-pi SIFS junctions is presented.
