Paramagnetic resonance in La2NiMnO6 probed by impedance and lock-in detection techniques

Abstract

We studied the frequency-dependent (f = 1 GHz to 5 GHz) microwave absorption in the double perovskite La2NiMnO6 at room temperature using two cavity-less methods: An indirect impedance method that uses a radio frequency impedance analyzer and a folded copper strip coil for the frequency range f = 1–2.2 GHz and a lock-in based broadband setup using a coplanar waveguide for microwave excitation in the frequency range f = 2–5 GHz. The high-frequency resistance of the strip coil exhibits a sharp peak and the reactance curve crosses zero at a critical value of dc magnetic field as a consequence of the paramagnetic resonance in the sample. The resonance fields (Hr) obtained from both the techniques increase linearly with frequency. Line shape analysis and analytical fitting were performed to characterize the material in terms of its initial susceptibility and damping parameters. From the fit, we obtain a large spectroscopic g-factor, equal to 2.1284, which supports the presence of Ni2+ cation with strong spin-orbit coupling.