Dynamics of flux motion observed by esr in superconducting oxides

Dynamic esr measurements compare I:Nd(Nd.05Ba.95)2Cu3O7,Tc0=72K; II:(Y.2Ca.8)Sr2[Cu2Tl1 2P b1 2]O7, Tc0 = 108 K; III:NbO1.1, Tc-<10K and IV:La2NiO4.00, Tc-<70K. Proximity effects are observed for the first time in the esr absorption of I by the 5% dilute Nd3+,4I9 2 in the Ba layer, following the Curie-Weiss law above TC0, ga,b,c=2.06, 2.13, 2.24; below Tc proximity effects give rise to temperature dependent interference fringes with period τf(T)=1 to 10s, giving an activation energy for the flux motion Ea(I)/R=16K and Ea(III)/R=3K{reversed tilde equals}Tc/4. In the superconducting state a coherent flux expulsion response to a change in BZ from 1 2 tesla to 0 is observed in times τr=8 to 10 s; the inverse rate flux expulsion, when the samples are cooled through Tc in B>0, varies from τn=1 to 20s. Spectra identify 3 temperature regimes: i) T<Tc/4 obtains superconducting behavior in the energy loss near zero magnetic field and kinetics of flux expulsion, near g=2 esr absorption is observed for all materials; ii) Tc>T>Tc/4 obtains a broad absorption near 0.1T at 9.36 GHz (attributed to antiferromagnetic AF resonance), flux motion produces interference fringes in spectra; iii) T>Tc obtains AF resonance on warming. © 1994.