Microwave magnetoabsorption in R_0.6Sr_0.4MnO₃ (R = Pr and Nd)

We report microwave (MW) magnetoabsorption (ΔP) at room temperature in R_0.6Sr_0.4MnO₃ (R = Pr and Nd) samples. ΔP as a function of dc magnetic field (− 2.5 kOe ≤ H_dc ≤ 2.5 kOe) was measured for a broad frequency range ( f = 0.1–4 GHz) of an MW magnetic field using a vector network analyzer and a copper strip coil which encloses one of the above samples. As the external dc magnetic field decreased from the maximum value, ΔP initially increases and shows a maximum for a critical field and then decreases as the field approaches zero. The critical field value increases with increasing frequency of the MW signal. Line shape analysis of the obtained spectra suggests that the observed features in ΔP are caused by ferromagnetic resonance in R = Pr and electron paramagnetic resonance in R = Nd samples, which were later confirmed using a coplanar waveguide-based broadband magnetic resonance spectrometer. (paper)