Antiferromagnetic resonance and magnetic anisotropy in single crystals of the YFe3(BO3)4-GdFe3(BO3)4 system

The antiferromagnetic resonance in single crystals of the YFe3(BO3)4-GdFe3(BO3)4 system is studied in the frequency range 25–140 GHz and the temperature range 4.2–50.0 K. It is established that the YFe3(BO3)4 crystal containing only the magnetic subsystem of Fe3+ ions is an antiferromagnet with an easy anisotropy plane. The temperature dependences of the gaps in the antiferromagnetic resonance spectra of GdFe3(BO3)4 and YxGd1 − xFe3(BO3)4 are used to calculate the contributions of the Fe3+ and Gd3+ subsystems to the magnetic anisotropy of these crystals. The contributions are found to be close in magnitude and have opposite signs. This leads to a relatively weak uniaxial anisotropy field in the crystals under investigation. Since the exchange interaction between the Gd3+ and Fe3+ ions magnetizes the magnetic subsystem of gadolinium, both subsystems start to contribute simultaneously at the Néel temperature of the iron subsystem.