Metastability and Transient Effects in Vortex Matter Near a Decoupling Transition

We examine metastable and transient effects both above and below the first-order decoupling line in a 3D simulation of magnetically interacting pancake vortices. We observe pronounced transient and history effects as well as supercooling and superheating between the 3D coupled, ordered and 2D decoupled, disordered phases. In the disordered supercooled state as a function of DC driving, reordering occurs through the formation of growing moving channels of the ordered phase. No channels form in the superheated region; instead the ordered state is homogeneously destroyed. When a sequence of current pulses is applied we observe memory effects. We find a ramp rate dependence of the V(I) curves on both sides of the decoupling transition. The critical current that we obtain depends on how the system is prepared.Comment: 10 pages, 15 postscript figures, version to appear in PR

SHIELDING THE a.c. MAGNETIC FIELDS IN BITTER-TYPE MAGNETS

Nous présentons les résultats des examens des coefficients d'efficacité pour plusieurs types d'écrans pour la composante alternative du champ magnétique engendré par des aimants du type de Bitter. Les meilleurs effets obtenus sont ceux pour l'écran en In avec RRR = 105 et pour un solenoïde à une seule couche de V3Ga court-circuité avec un fil de Cu. Dans les deux cas la composante alternative diminuait de 10 fois dans un champ de 14 T.We present the results of shielding efficiency investigations of various shields for a.c. component of magnetic field generated by Bitter magnets. The best effects were obtained for shields made of In with RRR ≃ 105 and for single-turn V3Ga solenoid shorted by Cu wire. In both cases the a.c. component was decreased about ten times in field of 14 T