Ac magnetoresistance and microwave absorption in Sr2FeMoO6

This work investigates the microwave absorption property of the ferrimagnetic double perovskite, Sr2FeMoO6 (SFMO) using two different methods: magnetoimpedance (MI) and lock-in based broadband magnetic resonance detection. In the MI method, radio frequency (rf) current (f = 0.001 to 2.8 GHz) is injected into the sample. When dc magnetic field is swept, rf resistance exhibits a single sharp peak centred at H = 0 for f < 0.1 MHz. As f increases, the peak at H = 0 transforms into a dip accompanied by symmetrical double peaks at H = ±HP, which we attribute to the ferromagnetic resonance within the grains. HP increases with increasing frequency of the current. In the lock-in based broadband method the sample, placed on top of a coplanar waveguide, experiences an intense microwave magnetic field from the waveguide, and the field derivative of microwave power absorption is measured as the dc magnetic field is swept. Correlation between MI and microwave power absorption is shown. Landé g factors obtained from both the measurements are close, equal to 2.085, which implies the presence of Fe3+ cations. Large ac magnetoresistance in SFMO compared to its dc value, dominated by the dynamics of transverse permeability and ferromagnetic resonance within grains could be exploited for high-frequency device applications.