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 Y _x Gd_{1 ? x} Fe₃(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.