Weak magnetic anisotropy in GdRh_2Si_2 studied by magnetic resonance

摘要

The antiferromagnetically (AFM) ordered state of GdRh_2Si_2 which consists of AFM-stacked ferromagnetic layers is investigated by magnetic resonance spectroscopy. The almost isotropic Gd~(3+) paramagnetic resonance becomes anisotropic in the AFM ordered region below 107 K. The emerging internal anisotropic exchange fields are still small enough to allow an investigation of their magnetization dynamics using a standard microwave-frequency magnetic resonance technique. We could characterize this anisotropy of the excitation at 9 and 34 GHz and found that the material can serve as an interesting illustration of what happens with the dynamics of the order parameter as the anisotropy restrictions become very soft. We have worked out in detail how the magnetic resonance shifts due to a characteristic property of the system, namely, the retardation of the magnetization when the sample is rotated in an external field. To describe the weak in-plane anisotropic behavior, we derived an AFM resonance condition in closed analytical formulas.