Anomalies in the surface impedance penetration depth in ferromagnetic superconductors

The surface impedance penetration depth, Λ, of ErRh4B4 and Ersub(0.5)Hosub(0.5)Rh4B4 have been investigated both experimentally and theoretically. For ErRh4B4, owing to the critical spin fluctuations just above Tsub(s) (> Tsub(c2)), the critical temperature at which surface ferromagnetism appears, Λ-1 decreases smoothly as T decreases toward Tsub(s). For Ersub(0.5)Hosub(0.5)Rh4B4, the decrease in Λ-1 owing to spin fluctuations for T >approx. Tsub(c2) is very small, and Λ-1 decreases abruptly at Tsub(c2). Theoretical values of Λ-1 are in good agreement with the data. (author)