Anomalous surface impedance in reentrant ferromagnetic superconductors
We report evidence which suggests surface ferromagnetism in a ferromagnetic superconductor arising from the competition between the Meissner current shielding effect and the fluctuations of the localized magnetic moments. We have measured the surface impedance penetration depth .λ. of ErRh 4 B 4 and Er 0.5 Ho 0.5 Rh 4 B 4 by employing a spectrometer operated at 9 GHz. For ErRh 4 B 4 , owing to the critical spin fluctuations just above T s ( > T c 2), the critical temperature at which surface ferromagnetism appears, .λ. -1 decreases smoothly as temperature decreases toward T s . For Er 0.5 Ho 0.5 Rh 4 B 4 , the decrease of .λ. -1 arising from spin fluctuations for T > T c 2 is very small, and .λ. -1 decreases abruptly at T c 2. We will discuss the theory and show how the predicted values of .λ.(T) compare well with the observed values
Article, 1985