Resonant and nonresonant microwave absorption study of ferromagnetic transition in RuSr 2Gd 0.5Eu 0.5Cu 2O 8 superconductor

Abstract

Replacement of half of the Gd ions by Eu in the superconductor RuSr 2GdCu 2O 8 does not affect the ferromagnetic transition temperature detected by the emergence of the derivative of the low magnetic field nonresonant microwave absorption. This suggests that the Gd ions are not the source of the ferromagnetism at 136 K. A marked narrowing of the line width and the shift of the field position of the electron paramagnetic resonance of Gd 3+ is observed as the Curie temperature is approached from above. These latter effects are likely a result of precursor ferromagnetic fluctuations, which can occur well above the ferromagnetic transition in low dimensional systems probably arising from the fluctuations of the Ru moments in the Ru–O layers.