Microwave study of influence of trapped vortices on intergrain 
weak links in Eu-123 ceramics

M.K. Aliev, F.K. Aliev, G.R. Alimov, 
A.T. Muminov, I. Kholbaev, Kh.I. Turkmenov

Institute of Applied Physics of National University of Uzbekistan, Tashkent

The following sequence of actions on Eu-123 ceramic thin platelet was carried out in the experiment: zero-field cooling from T>TC=90K to T=79K; raising the field to H=HA (1OeHA80Oe); heating to T=TA (79KTA93K); returning backwards to T=79K, H=0; measuring the microwave absorption signal at T=79K, H=0 with switching on the field-modulating technique of an ESR-spectrometer; switching off the field modulation and heating to T>TC for making a new cycle with another TA, HA; and so on. The drastically different dependencies of the signal on HA, TA have been obtained for two orientations of the platelet’s plane, parallel (case 1) and perpendicular (case 2) to external field: in the case 1 a three dimensional picture of the dependence displays a well outlined zero-signal plateau corresponding to Meissner states of the grains and a line of the signal’s minima close to the TC-line; in the case 2 the plateau is distorted while the minima become very pronounced and are found at significantly lower values of HA, TA. It is shown that both the two pictures can be explained by competitive influences of the trapped Abrikosov and Josephson type vortices on the critical currents of intergrain weak links. The grains’ penetration fields also are discussed.