Magnetic interactions and magnon gap in the ferromagnetic superconductor RuSr2GdCu2O8

A. FAINSTEIN, E. WINKLER, A. BUTERA, AND J. TALLON

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Año: 1999 vol. 60 p. 12597 - 12600

1098-0121

By means of X- and Q-band magnetic-resonance measurements we have investigated the magnetic interactions and derived the magnon gap in the ferromagnetic superconductor RuSr2GdCu2O8. Two microwave absorptions are observed: first, a paramagnetic resonance of the Gd3+ ions, and second, appearing below the Curie temperature (TCurie), a ferromagnetic resonance due to the ruthenium lattice. Located between the superconducting CuO2 planes, the Gd ions serve as intrinsic probes of the internal magnetic fields near the Cu sites. Below TCurie the Gd3+ signal shifts, evidencing the appearance of a homogeneous internal field, HRu-Gd∼600Oe. We show that HRu-Gd is due to a Ru-Gd ferromagnetic exchange interaction. The Ru ferromagnetic resonance indicates the existence of a magnon anisotropy gap ω/γ≳4600Oe. We estimate the out-of-plane and in-plane anisotropy fields to be, respectively, Hz∼110kOe and Hx∼200Oe.